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- Front Matter: Volume 9634
- Distributed Sensing
- Applications and Techniques
- Sensors for Smart Structures
- Biological and Enviromental Sensing
- New Sensing Concepts and Applications
- Multiplexed and Networked Sensors
- Brillouin and Acoustic Sensing
- Sensing of Physical Parameters
- Micro- and Nano-sensors
- Sensing with Interferometers
- Non-conventional Fibre Sensors
- Fiber Devices and Systems
- Sensors for the Living State
- Post-Deadline Papers and Closing
- Poster Session I
- Poster Session II
- Poster Session III
Front Matter: Volume 9634
Front Matter: Volume 9634
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This PDF file contains the front matter associated with SPIE Proceedings Volume 9634, including the Title Page, Copyright information, Table of Contents, Introduction, Authors, Sponsor Support and Conference Committee listing.
Distributed Sensing
Brillouin analysis with 8.8 km range and 2 cm resolution
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Brillouin analysis of a 8.8 km-long fiber with 2 cm resolution is reported. Pump and signal are jointly modulated by a binary phase Golomb code. Over 2,000 correlation peaks are simultaneously introduced and interrogated in a single trace. All 440,000 resolution points are covered in just 211 scans of peaks positions. The pump wave is amplitude modulated by a second, 10,000 bits long code. Post-processing of the output signal provides a measurement signal-tonoise ratio that is equivalent to that of 5,000 single-pulse acquisitions. A 7cm-long hot spot is identified. The uncertainty in Brillouin frequency measurements is ±3.5 MHz.
Enlargement of measurement range in Brillouin optical correlation domain analysis with high-speed random accessibility using temporal gating scheme for multiple-points dynamic strain measurement
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We propose and experimentally demonstrate a Brillouin optical correlation domain analysis system both with high-speed random accessibility and with temporal gating scheme to extend the measurement range. High-speed dynamic strain measurement at multiple points selected arbitrarily along an elongated measurement range is demonstrated. We successfully measured the dynamic strain at the selected two points along a fiber, with 200 m measurement range, 8 cm spatial resolution, and 1,000 points/s measurement speed of random accessibility.
Brillouin optical correlation domain analysis with more than 1 million effective sensing points
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Huge enlargement of the sensing range of Brillouin optical correlation domain analysis (BOCDA) is achieved by simultaneously applying double modulation and optical time gate on the basis of differential measurement scheme. The BOCDA system with a spatial resolution less than 1 cm and a sensing range over 10 km is experimentally demonstrated, which corresponds to distributed measurement with more than 1 million effective sensing points.
200 km fiber-loop Brillouin distributed fiber sensor using bipolar Golay codes and a three-tone probe
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Aiming at taking full advantage of bipolar codes, a method using a three-tone probe is proposed to alleviate the probe power limitation imposed by pump depletion in Golay-coded Brillouin distributed fiber sensors. Experimental results validate the technique, which reduces significantly the measurement distortions induced by the gain/loss unbalance resulting from pump depletion/amplification. The method supports a probe power increment of more than 12.5 dB, resulting in low-uncertainty measurements (< 0.9 MHz) at a real 100 km distance, using a 200 km-long fiber loop and 2 m spatial resolution. The method is evaluated with a record figure-of-merit of 380’000.
Applications and Techniques
Fiber optic sensing of magnetic fields utilizing femtosecond laser sculpted microslots and long period gratings coated with Terfenol-D
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Fiber optic sensors are fabricated for detecting static magnetic fields. The sensors consist of a UV inscribed long period grating with two 50 micron long microslots. The microslots are fabricated using the femtosecond laser based inscribe and etch technique. The microslots and the fiber surface are coated with a magnetostrictive material Terfenol-D. A spectral sensitivity of 1.15 pm/mT was measured in transmission with a working resolution of ±0.2 mT for a static magnetic field strength below 10 mT. These devices also present a different response when the spatial orientation of the fiber was adjusted relative to the magnetic field lines.
Multi-parameter sensing based on the stimulated Brillouin scattering of higher-order acoustic modes in OAM fiber
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We report for the first time a unique multi-parameter optical fiber sensor based on the stimulated scattering of higher order acoustic modes of Orbital Angular Momentum (OAM) guiding fiber. Both optical modes and acoustic modes guided within the core region of OAM fiber are characterized and demonstrated theoretically and experimentally. Simulation analysis shows that the multi-peak feature in the Brillouin gain spectrum (BGS) of OAM fiber is attributed to the couplings among the guided optical modes and higher-order acoustic modes. The frequency shifts of first two Brillouin peaks are successfully monitored to discriminate the temperature and strain with an accuracy of 0.21oC and 4.6με.
Adaptive interferometry for high sensitivity optical fiber sensing
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We report on the use of an adaptive holographic interferometer, based on a liquid crystal light valve, to achieve phase shift measurements in an optical fiber. Owing to the physical mechanisms involved, the interferometer adapts itself to slow phase variations. As a consequence, it is possible to use a multimode fiber for sensing, which improves the sensitivity. Moreover, a distributed architecture relying on phase-OTDR principle is presented and a localization experiment is performed.
Real time monitoring oxidation of transition metals with long period fiber gratings
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In this paper real time monitoring of oxidation of transition metals using long period fiber gratings (LPFG) is performed for nickel, copper, titanium, chromium and zinc. A thin layer is deposited over the LPFG with physical process deposition and is annealed up to 700 °C in air with a small oven. The whole oxidation process can be monitored by tracking the LPFG features of the attenuation band which results in an abrupt change when the oxidation occurs depending on the metal sample. A preliminary study to optimize optical fiber sensors sensitivity allowing choosing the correct oxide layer in a specific application is presented.
High resolution fiber Bragg grating interrogation using a random distributed feedback fiber laser
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In this study, a new sensing application for random distributed feedback fiber lasers is presented. Temperature measurements of a phase-shifted fiber Bragg grating with a resolution higher than 0.01 ºC have been attained. The resolution limitation of classical fiber lasers has been overcome due to the absence of longitudinal modes and high frequency stability of random fiber lasers. The frequency shift of the grating has been measured as 1.195 ºC/GHz and it is detected in the electrical domain by beating an external laser source with the random emission line generated.
Sensors for Smart Structures
Structural health monitoring of composite-based UAVs using simultaneous fiber optic interrogation by static Rayleigh-based distributed sensing and dynamic fiber Bragg grating point sensors
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Embedded fiber-optic strain sensing networks for airworthy assessment of operational Unmanned Aerial Vehicles (UAVs) are presented. Sensing is based on in-flight fiber Bragg grating technology, as well as on on-ground Rayleigh backscattering distributed strain sensing. While the in-flight instrumentation monitors loads, looking for excessive values, the Rayleigh-based technique is used for high spatial resolution strain distribution along the UAV wings, under prescribed loading. Consistency of measurements over time indicates structural integrity. Simultaneous strain measurements using both distributed Rayleigh and fiber Bragg gratings, on the same fiber, promises to combine high spatial resolution, though practically static measurements with dynamic, though discrete ones.
SS316 structure fabricated by selective laser melting and integrated with strain isolated optical fiber high temperature sensor
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Smart metal having integrated high temperature sensing capability is reported. The SS316 structure is made by additive layer manufacturing via selective laser melting (SLM). Sensor component is embedded in to the structure during the SLM build process. The strain isolated in-fiber Fabry-Perot cavity sensor measures temperature up to 1100 °C inside the metal.
Gas refractometer based on an S-taper fiber tailored fiber Bragg grating
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A fiber Bragg grating (FBG)-based gas refractometer is proposed and demonstrated experimentally. The configuration consists of a short section of S-type taper followed with a FBG. The S-taper is capable to couple the core mode to cladding modes into the downstream SMF, and the low-order cladding modes can be reflected back to the fiber core via the FBG, in which the recoupling efficiency is highly dependent on surrounding refractive index (RI) of liquid and gas. Experimental results show that some recoupled cladding modes show high sensitivities to surround RI. This power-referenced RI measurement and wavelength-referenced temperature measurement have been achieved via selective cladding modes monitoring.
Novel method of defect identification in bent structures through feature-guided wave detection using fiber Bragg grating sensors
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Feature-guided waves (FGW) have emerged as a promising technique for structural health monitoring as they are well confined in local features such as bends and welds. In this paper, we propose and demonstrate a novel method for identifying defects in 90 ̊ transverse bent structures through FGW detection using fiber Bragg gratings. Our experimental results are in excellent agreement with results predicted using 3D-Finite Element (FE) simulations of the bent structure.
Measuring residual stresses in metallic components manufactured with fibre Bragg gratings embedded by selective laser melting
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Metal clad single mode optical fibres containing Fibre Bragg Gratings are embedded in stainless steel components using bespoke laser based Selective Laser Melting technology (SLM). Significant residual stresses can be created in SLM manufactured components through the strong thermal gradients during the build process. We demonstrate the ability to monitor these internal stresses through embedded optical fibres with FBGs on a layer to layer basis, confirming estimates from models for residual stresses in additive manufactured components.
Biological and Enviromental Sensing
Dispersive Raman spectroscopy for the nondestructive and rapid assessment of honey quality
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Raman spectroscopy performed using optical fibers, with excitation at 1064 nm and a dispersive detection scheme, was utilized to measure a selection of unifloral honeys produced in the Italian region of Calabria. The honey samples had three different botanical origins: chestnut, citrus, and acacia, respectively. A multivariate processing of the spectroscopic data enabled us to distinguish their botanical origin, and to build predictive models for quantifying important nutraceutic indicators such as the main sugars and potassium. Furthermore, the Raman spectra of chestnut honeys were compared with the taste profile measured by an electronic tongue, and a good correlation to bitter/savory taste was obtained. This experiment indicates the excellent potentials of Raman spectroscopy as an analytical tool for the nondestructive and rapid assessment of food-quality indicators.
Surface-core fiber gratings
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In this paper, we report, to our knowledge, the first demonstration of the induction of long-period and Bragg gratings on surface-core optical fibers. Surface-core fibers described herein were fabricated from commercial silica tubes and germanium-doped silica rods by employing a very simple procedure. Being the core on the fiber surface, it can be sensitive to refractive index variations in the environment in which the fiber is immersed. Thus, results concerning the sensitivity of these gratings to environmental refractive index variations are presented. Besides, simulation data are presented for comparison to the experimental behavior and for projecting future steps in this research.
Photothermal effect in gas-filled hollow-core photonic bandgap fiber
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We exploit photothermal effect in gas-filled hollow-core photonic bandgap fibers, and demonstrate remarkably sensitive all-fiber (acetylene) gas sensors with noise equivalent concentration of 1-3 parts-per-billion and an unprecedented dynamic range of nearly six orders of magnitude. These results are two to three orders of magnitude better than previous direct absorption-based optical fiber gas sensors. The realization of photothermal spectroscopy in fiber-optic format will allow a new class of sensors with ultra-sensitivity and selectivity, compact size, remote and multiplexed multi-point detection capability.
DNA aptamer-based fiber optic biosensor for selective and label-free detection of dopamine
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Dopamine (DA) analysis is complicated by the interference from other electrochemically active endogenous compounds present in the brain, including DA precursors and metabolites and other neurotransmitters (NT). Here we report a simple, sensitive and selective optical fiber biosensor for the detection of DA in the presence of other NT. It is composed of a 57-mer dopamine-binding aptamer (DBA) as recognition element and nonadiabatic tapered optical fiber (NATOF) as probe. Upon the addition of DA, the conformation of DBA would change from a random coil structure to a rigid tertiary structure like a pocket. The conformational change of DBA lead to the refractive index (RI) change around the tapered fiber surface. Specific recognition of DA by the aptamer allowed a selective optical detection of DA within the physiologically relevant 500 nM to 10 μM range. Some common interferents such as epinephrine (EP) and ascorbic acid (AA) showed no or just a little interference in the determination of DA.
Photodecomposition of a target compound detected using an optical fibre long period grating coated with a molecularly imprinted titania thin film
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An optical fibre long period grating (LPG) coated with an inorganic molecularly imprinted thin film based on TiO2 was used to measure in real time the photodecomposition of an organic target compound. The TiO2 film was deposited onto the LPG using the aqueous liquid phase deposition method and its photo-catalytic properties were employed to decompose a porphyrin. The principle of operation is based on the measurements of the refractive index (RI) change of the TiO2 thin film at the binding and removal of the imprinted organic compound.
New Sensing Concepts and Applications
In-fiber modal interferometer for high sensitivity gas detection
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We demonstrate a gas sensor based on mode interference in a hollow-core photonic bandgap fiber. Gas absorption of a pump laser beam induces phase modulation of a propagating probe beam, which is detected by use of an in-fiber modal interferometer. An estimated detection limit of ~2 ppm acetylene (~7x10-5 in terms of noise equivalent absorbance or NEA) is achieved with 30-cm-long HC-PBF operating at the near infrared wavelength. This NEA is ~22 times better than state-of-the-art HC-PBF gas sensors based on direct absorption spectroscopy.
Portable smartphone optical fibre spectrometer
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A low cost, optical fibre based spectrometer has been developed on a smartphone platform for field-portable spectral analysis. Light of visible wavelength is collected using a multimode optical fibre and diffracted by a low cost nanoimprinted diffraction grating. A measurement range over 300 nm span (λ = 400 to 700 nm) is obtained using the smartphone CMOS chip. The spectral resolution is Δλ ~ 0.42 nm/screen pixel. A customized Android application processed the spectra on the same platform and shares with other devices. The results compare well with commercially available spectrometer.
Enhanced Terahertz transmission through 3D non-spherical terajets
Alice L. S. Cruz,
Cristiano M. B. Cordeiro,
Marcos A. R. Franco
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In this paper we demonstrate the capability of non-spherical dielectric objects to generate terajets ‒ similar to the photonic nanojets ‒ at Terahertz frequencies. We investigated numerically three geometries with non-usual shape and compared them with a common dielectric sphere. The focusing terajet performance was evaluated and one of the proposed geometry shown an enhancement power ~32 times with respect to the incident wave power. Using harmonic frequencies to excite the geometries, the power enhancement can achieve an intensity of ~64 times.
Silicon photonics-based laser system for high performance fiber sensing
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We present a compact four-laser source based on low-noise, high-bandwidth Pound-Drever-Hall method and optical phase-locked loops for sensing narrow spectral features. Four semiconductor external cavity lasers in butterfly packages are mounted on a shared electronics control board and all other optical functions are integrated on a single silicon photonics chip. This high performance source is compact, automated, robust, operates over a wide temperature range and remains locked for days. A laser to resonance frequency noise of 0.25 Hz/rt-Hz is demonstrated.
Multiplexed and Networked Sensors
Remote optical sensing network for gas monitoring based on laser spectroscopy over hybrid TDM/WDM-PONs
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We propose an optical gas sensing network directly overlaid onto optical access networks, hybrid TDM/WDM-PONs. Centralized remote gas monitoring is demonstrated using three different sensing technologies: Chirp Laser Dispersion Spectroscopy (CLaDS), Direct Laser Absorption Spectroscopy (DLAS) and tunable diode laser absorption spectroscopy (TDLS). DLAS performs fast threshold detection while CLaDS provides quantitative information about the gas. Additionally, TDLS utilizes a cost-effective solution for multiple gases detection. The results confirm that centralized remote gas sensing can be realized in optical communication networks using standard single-mode fiber (SMF), which provides a real time, low cost, and maintenance-free solution.
Time and wavelength division multiplexing scheme for ultra-long sensing based on a cavity-modulated random DFB fiber laser
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In this work, a new multiplexing scheme for ultra-long range measurements (up to 200 km) is presented. Time and wavelength sensor multiplexing is achieved by means of a modulated random distributed feedback laser (DFB). The direct modulation of the laser’s cavity allows the interrogation of sensors by measuring the reflected power for different wavelengths and distances. As a proof of concept, nine fiber Bragg gratings (FBGs) placed at different fiber locations and wavelengths have been interrogated.
All-fiber ultrasound sensor array implemented by swept frequency interferometry
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Fiber ultrasound (US) sensing is gaining popularity in recent years. Unique characteristics such as immunity to electromagnetic interference and embedding compatibility makes them advantageous in many applications. Multiplexing of US fiber sensors, however, remains a challenge. Here, a new multiplexing approach is introduced. Based on Swept Frequency Interferometry (SFI), it enables practical multiplexing of tens of US sensors. For demonstration, a 3-sensors setup was excited by ultrasound tone-bursts. While using low driving voltage (2.5-10V vs. ~100-400V in similar studies) and not implementing acoustic-impedance optimization or optical-resonance sensitivity enhancement, the sensors detected the excitation with high SNR (~25dB).
Vibration measurement of electrical machines using integrated fibre Bragg gratings
M. Fabian,
J. Borg Bartolo,
M. Ams,
et al.
Show abstract
In this paper a method to track the rotating force vector set up within the air-gap of radial flux rotating electrical machines using fibre Bragg gratings is reported. The proposed technique offers the potential for simultaneous rotor speed and position monitoring. This specific sensor design, together with other FBG-based multi-parameter measurements, is aimed to create an all-optical sensor solution for electrical machines, reducing the component count of existing systems and addressing noise issues traditionally associated with electrical sensors used. In this work, an optical fibre sensor system has been successfully integrated into an off-the-shelf four-pole 11kW induction motor.
Monitoring multiple interferometric sensors multiplexed in a single fiber loop mirror
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Three HiBi PCF sections have been multiplexed and monitored as strain sensors in a single fiber loop mirror (FLM) interferometer. The strain applied to each fiber has been measured without crosstalk by using the fast Fourier transform analysis. This study enhances the multiplexing capability in FLM and improves previous results, where a maximum of two fiber section were multiplexed in a single multi-section FLM. The HiBi fibers are spliced together with an angle offset given by the theoretical analysis of the interference. Consequently, just one polarization controller is needed in the system, which greatly simplifies the operation of the system.
Brillouin and Acoustic Sensing
Simultaneous gain and phase profile determination on an interferometric BOTDA
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Up to now, complex (phase and intensity) measurements in Brillouin Optical Time-Domain Analysis (BOTDA) systems required complex phase modulation methods and high-bandwidth (multi-GHz) detection. In this work, we propose a novel technique that is able to retrieve simultaneously both gain/loss and phase characteristics of the Brillouin interaction by just introducing a Sagnac Interferometer (SI) on a standard BOTDA sensing scheme. The technique is described analytically and demonstrated experimentally. With this technique, a reliability increase is produced since redundant measurements can be performed.
Brillouin optical correlation domain reflectometry with temporal gating scheme and apodization scheme
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We experimentally demonstrate a Brillouin optical correlation domain reflectometry system with temporal gating scheme and apodization scheme. Temporal gating onto the pump light is used for expanding the measurement range, and apodization onto the laser spectrum shape is used for reducing background noise to enhance spatial resolution and strain dynamic range. A section with 50 cm length and 7000 μepsilon strain was detected in 1100 m single mode fiber with 29 cm nominal spatial resolution.
Over 100km long ultra-sensitive dynamic sensing via Gated-OFDR
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Cumulative acoustically-induced phase modulation along the sensing fiber significantly degrades the performance of Optical Frequency Domain Reflectometry (OFDR) systems. Here we present a new method to mitigate this phenomenon using hybrid time-frequency interrogation and analysis. The method, which we term Gated-OFDR (G-OFDR), achieves remarkable results: ultra-sensitive dynamic sensing at z≈101km with 1.4m spatial resolution and acoustical sampling rate of 600Hz. As an example, the system detected and recorded, with high SNR, falls of two ~1g paperclips from height of ~20cm, on two fiber sections, 10m apart, at the end of the 101km fiber, without any crosstalk artifacts.
Distributed acoustic sensing: towards partial discharge monitoring
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We report on the successful application of distributed acoustic sensing (DAS) to the detection of partial discharge (PD). A detection limit of about 1 nC discharge magnitude was achieved for PD in a real-scale model of a high voltage termination. Dedicated ultrasonic fibre-optic transducers were interrogated using coherent optical time-domain Rayleigh backscatter reflectometry (C-OTDR). Random quadrature demodulation was employed for retrieving relevant acoustic information from the raw C-OTDR backscatter traces. To our knowledge, our results are a first-time demonstration that quasi-distributed fibre-optic acoustic sensing is a candidate technology for the acoustic partial discharge monitoring of power cable joints and terminations.
Differential chirped-pulse pair for sub-meter spatial resolution Brillouin distributed fiber sensing
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A distributed fiber sensor based on a differential chirped-pulse pair Brillouin optical time domain analysis (DCPBOTDA) is proposed for sub-meter spatial resolution sensing. The technique is based on the subtraction of two measurements made with the same pump pulse widths, but differing in the final short section of the pulse by a positive or negative frequency chirp, respectively. Experimental results are compared with a precise theoretical modeling, validating the sub-meter sensing capabilities of the technique.
Sensing of Physical Parameters
Two-dimensional optical fibre cantilever accelerometer
Jun Li,
J. N. Sun,
M. M. Miliar,
et al.
Show abstract
Focused Ion Beam (FIB) machining has been demonstrated to be capable of fabricating nano and micro scale elements
onto optical fibres. In this paper we exploit FIB to fabricate core aligned 45° mirrors at the end of multi-core fibres
(MCF). The resulting fibre is used as a component in a two dimensional optical fibre accelerometer. The mirror is
produced using a two step process: first a scanning process is used to make a rough cut to define the overall mirror
structure. This is followed by a polishing process to create an optical surface finish. The machined 45° mirror can be
accurately aligned with optical fibre core, which avoids issues associated with the alignment of external turning mirror
components. Proof-of-concept tests demonstrate the use of such a fibre as a two axis acceleration sensor that is
interrogated interferometrically. The sensor operated between 0.5g and 4.5g with a cross talk of -24.3dB between axes.
Optical frequency domain reflectometry based fiber Bragg grating vibration sensor array using sinusoidal current modulation of laser diodes
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We present multipoint vibration sensing using fiber Bragg gratings and optical frequency domain refrectometry (OFDR). In OFDR based method, the maximum number of arrayed sensor can be few thousands and the measurement time is determined by wavelength scanning rate of a light source. In our sensor system, a laser diode is used as a wavelength scanning light source. Lasing wavelength of a laser diode can be modulated by changing its injection current. The injection current can be precisely modulated at high frequency up to 1 MHz using a laser-diode controller and wavelength scanning can be then easily achieved with a laser diode.
Curvature sensing using an added-signal in a fiber optic cavity ring-down system
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This work presents a fiber-optic Cavity Ring-Down (CRD) configuration using an added-signal for curvature sensing. An Optical Time-Domain Reflectometer (OTDR) was used to send impulses down into the fiber loop cavity, inside of which a long period grating (LPG) was placed to act as sensing device. The added-signal was obtained by the sum of several conventional CRD impulses, thus providing an improvement on the curvature sensitivity when compared to the conventional CRD signal processing. Sensitivity to applied curvature of 15.3 μs/m-1 was obtained. This result was found to be 20-fold the one obtained for the conventional CRD signal processing.
Laboratory investigation of an intensiometric dual FBG-based hybrid voltage sensor
Grzegorz Fusiek,
Paweł Niewczas
Show abstract
In this paper, we investigate experimentally the performance of a prototype optical voltage sensor utilizing a piezoelectric component and a dual FBG sensor combined with an intesiometric detection scheme. The sensor construction allows for the sensor interrogation using a single photodetector, and by eliminating spectral scanning devices, the measurement system benefits from a significant cost reduction and potentially improved speed of operation. Preliminary voltage characterization reveals that the proposed sensor is capable of reliable ac voltage measurement.
Coherent pulse compression Brillouin dynamic gratings reflectometry for slope-assisted, fast and distributed fiber strain sensing
Show abstract
The performance of optical time-domain sensing technique, employing the slope of Brillouin dynamic gratings in polarization-maintaining fibers, is significantly enhanced using coherent pulse compression techniques. The strain sensitivity of the reflectivity of a coded probe, orthogonally polarized to the pumps which generated the grating, depends on both pumps and probe detuning. Employing a 64 bit Golay code, the system sensitivity was enhanced eightfold, while retaining the high sampling rate of 1MHz. We report the measurement of 750Hz strain vibrations (limited by the bandwidth of the vibration source) with a spatial resolution of 20cm (limited by the bandwidth of the balanced photoreceivers).
Micro- and Nano-sensors
All-fiber photoacoustic gas sensor with graphene nano-mechanical resonator as the acoustic detector
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We demonstrate an all-optical-fiber photoacoustic (PA) spectrometric gas sensor with a graphene nano-mechanical resonator as the acoustic detector. The acoustic detection is performed by a miniature ferrule-top nano-mechanical resonator with a ∼100-nm-thick, 2.5-mm-diameter multilayer graphene diaphragm. Experimental investigation showed that the performance of the PA gas sensor can be significantly enhanced by operating at the resonance of the grapheme diaphragm where a lower detection limit of 153 parts-per-billion (ppb) acetylene is achieved. The all-fiber PA sensor which is immune to electromagnetic interference and safe in explosive environments is ideally suited for real-world remote, space-limited applications and for multipoint detection in a multiplexed fiber optic sensor network.
Long high finesse fiber Fabry-Perot resonators
Konstantin Ott,
Sébastien Garcia,
Ralf Kohlhaas,
et al.
Show abstract
We present the realization of millimeter long fiber coupled open Fabry-Pérot resonators with a finesse of 46.000. Deterioration of the finesse with increasing resonator length observed in previous experiments could be suppressed by advances in the CO2 laser-based fabrication process of the fiber micro mirrors. In this way, resonator lengths up to 1.4 mm could be realized, corresponding to a free spectral range of 107 GHz and linewidths of 2.2 MHz.
Fiber optic anemometer based on metal infiltrated microstructured optical fiber inscribed with Bragg grating
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An all-fiber optical anemometer with high light-heat conversion efficiency by using an in-house microstructured optical fiber Bragg grating (MOFBG) is presented. Low-molten-temperature BiSnIn alloy was successfully infiltrated into 11- cm length of a six-hole microstructured optical fiber which was inscribed with a fibre Bragg grating (FBG) centered at ~848 nm. Light launched into the MOFBG was strongly absorbed by the metal to generate heat, while the FBG was utilized to monitor temperature change due to surrounding wind speed. The sensitivity of the laser-heated MOFBG anemometer was measured to be ~0.1 nm/(m/s) for wind speed ranged from 0.5 m/s to 2 m/s. The efficiency of the anemometer, defined as effective sensitivity per pump power, is 8.7 nm/(m/s*W).
Self-assembled periodic patterns on the optical fiber tip by microsphere arrays
Show abstract
In this work, we report a fabrication route for self-assembling periodic patterns on optical fiber tips. The technique is based on self-assembling polystyrene microspheres at the air/water interface and on successive transferring of the monolayer colloidal crystal on the fiber tip. By applying to the fiber further treatments like particle size reduction, metal coating and sphere removal, different periodic structures are conveniently realized. The results obtained indicate that self-assembly technique affords opportunity to create on the optical fiber tip dielectric and metallic-dielectric spheres’ arrays with a feature size down to a submicron scale or metallic patterns with a few hundred nanometers at low fabrication costs.
Sensing with Interferometers
Resonator fiber optic gyro with high backscatter-error suppression using two independent phase-locked lasers
Show abstract
A resonator fiber optic gyro was constructed using separate lasers for counter-rotating waves to overcome interference between optical backscatter and signal light that causes dead-zone behavior and scale factor nonlinearity. This approach enabled a 2 MHz frequency separation between waves in the resonator; eliminating the intended backscatter error. The two lasers were phase-locked to prevent increased gyro noise due to laser frequency noise. Dead-band-free operation near zero-rate, scale factor linearity of 25 ppm and stability of 11 ppm were demonstrated ─ the closest results to navigation-grade performance reported to date. The approach is also free of impractical frequency shifter technology.
Ultra-sensitive acoustic fiber sensors utilizing nano-membranes
Show abstract
A new, highly sensitive, compact fiber acoustic sensor is reported that implements a micro-fabricated silicon membrane with a π/2 phase step combined to a single-mode fiber to form a simple interferometric sensor head. Compared to high-sensitivity membrane-based fiber Fabry-Perot (FP) sensors, it has a similar pressure resolution, it operates over a much broad range of wavelengths (~±150 nm vs. ~±1 nm), and fabrication is simpler. A prototype is reported with an average minimum detectable pressure (MDP) as low as 5.4 μPa/√Hz (1-30 kHz), in agreement with a model. A state-of-the-art FP fiber sensor with an average MDP about twice as low is described for comparison.
Range-resolved signal processing for fibre segment interferometry applied to dynamic long-gauge length strain sensing
Show abstract
A range-resolved interferometric signal processing technique using sinusoidal optical frequency modulation is applied to fibre segment interferometry. Here, six optical fibre segments of gauge length 12.5 cm are used as interferometric strain sensors and are formed between seven weak, broadband fibre Bragg gratings, acting as in-fibre partial reflectors. In a very simple and cost-effective optical setup using injection current modulation of a laser diode source, interferometric measurement of acoustic wave propagation in a metal rod is used to demonstrate the capabilities of the technique.
Drastic sensitivity enhancement of temperature sensing based on modal interference in plastic optical fibers
Show abstract
It has been reported that temperature sensors based on modal interference in perfluorinated graded-index (GI) plastic optical fibers (POFs) show the world’s highest temperature sensitivity of +49.8 nm/°C/m at 1300 nm at room temperature, which is over 1800 times the value in silica multimode fibers (MMFs). In this work, we newly find that the temperature sensitivity (absolute value) is significantly enhanced with increasing temperature toward ~70°C, which is close to the glass-transition temperature of the core polymer. When the core diameter is 62.5 μm, the sensitivity at 72 °C at 1300 nm is +202 nm/°C/m, which is approximately 26 times the value obtained at room temperature and even over 7000 times the highest value previously reported using a silica MMF. As the glass-transition temperature of polymers can be generally set to an arbitrary value, this characteristic could be used to develop POF-based temperature sensors with ultra-high sensitivity not only at ~70°C but at arbitrary temperature in future.
A hybrid Michelson-FP interference fiber sensor
Show abstract
A novel hybrid Michelson-FP (M-FP) interference fiber sensor based on a twin-core fiber has been proposed. It consists
of an in-fiber integrated Michelson interferometer and an air FP cavities. The radial strain and axial strain sensing
properties are explored and analyzed. By using this novel structure, we can measure radial strain and axial strain
simultaneously.
Non-conventional Fibre Sensors
High power laser and explosive driven shock wave characterization in solids using fiber optic probes
Show abstract
Shock wave transmission and propagation in solid media is studied using fiber optic pressure and velocity probes. Shock waves are generated in two experiments using a high power laser facility as well as conventional explosives. Shock wave properties including peak overpressure, mass velocity, shock duration, impulse, arrival time and shock velocity are characterized using fiber tip interferometric displacement sensors and Fabry-Perot pressure sensors. Measurements are conducted in polymethyl methacrylate and limestone. The probes recorded shock pressures up to 0.1 GPa (1 kbar). Measurements from the fiber optic sensors are shown to be in close agreement with measurements from an electrical sensor based on a Dremin loop.
Cryogenic temperature monitoring in superconducting power transmission line at CERN with hybrid multi-point and distributed fiber optic sensors
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Distributed and multi-point fiber-optic based measurements of cryogenic temperature down to 30 K are presented. Measurements have been performed along the cryostat of a superconducting power transmission line, which is currently being tested at CERN over a length of about 20 m. Multi-point measurements were based on two kinds of FBG with different coatings (epoxy and PMMA). In addition, distributed measurements exploited optical frequency-domain reflectometry to analyze the Rayleigh scattering along two concatenated fibers with different coatings (acrylate and polyimmide). Results confirm the viability of these approaches to monitor cryogenic temperatures along a superconducting transmission line.
First field demonstration of end-reflection assisted Brillouin analysis for in-service loss monitoring of branched fibers in PONs
Show abstract
The in-service loss monitoring of branched fibers in passive optical networks (PONs) is demonstrated in the field for the first time. End-reflection assisted Brillouin analysis employing a frequency shift averaging technique compensated for the variation in the Brillouin gain profile of installed optical cables. Complete loss monitoring for individual branched fibers in deployed PONs was successfully achieved.
In-fiber Michelson interferometer inclinometer
Show abstract
This work describes an in-fiber Michelson interferometer inclinometer which is sensitive to curvature applied in the tapered region. The performance of this inclinometer is evaluated by calculating the variation of the fringe visibility near the 1550 nm spectral range as a function of the tilt angle. It is presented the results of four experimental measurements and calculated the average and standard deviation of those measurements. The results indicate a good response of the sensor within the angular range between 3° and 6°. The average of those four measurements is around -0.15/° and the greatest standard deviation is about 5.5%.
Design of a triangulation based fiber optical distance sensor for application in large rotating machines
Show abstract
Commercial distance sensors basing on the triangulation principle are highly accurate and reliable. However due to their contained electronics and optoelectronics they cannot be used in harsh environments such as high temperatures and strong electromagnetic fields. An all fiber optical triangulation sensor principle is presented here which can be used for tip clearance measurements of rotors of large engines such as power generators and turbines.
Fiber Devices and Systems
A method to gather/arrange particles based on thermal convection
Show abstract
We propose a novel method to gather or arrange multiple micro particles by using the thermal convection effect in the water. We fabricate the fiber tip to be a nonadiabatic-tapered shape and then plate a gold film on the fiber tip. The gold film coated on the fiber tip absorbs the light output from the fiber and then generate lots of heat in the water, which causes the thermal convection. The convection forces bring the micro particles moving towards the fiber tip where the temperature is much higher. By using this thermal convection effect, we can realize the multiple micro particles gathering or arranging quickly, easily and simply.
Highly birefringent polymer fibers for hydrostatic pressure sensing
Show abstract
We present two polymer birefringent fibers with enhanced polarimetric sensitivity to hydrostatic pressure. In the first fiber, with birefringence induced by the arrangement of holes in the microstructured cladding, an increased sensitivity to pressure was obtained by enlarging selected holes in the cladding. The second is a side-hole fiber with an elliptical core made of polymethyl metacrylate–polystyrene (PMMA/PS) copolymer and pure PMMA cladding. The fiber core is located in a narrow PMMA bridge separating the holes. The transmission and sensing characteristics of both fibers are compared, including spectral losses, birefringence, polarization cross-talk and polarimetric sensitivity to hydrostatic pressure.
All-fiber laser mode-locked by the acousto-optic modulation of a fiber Bragg grating in suspended core fiber
Show abstract
An ytterbium-doped fiber laser mode-locked by the interaction of a fiber Bragg grating and longitudinal acoustic waves in a suspended core fiber is experimentally investigated. An optimized design of an acousto-optic modulator is also proposed. The results indicate output pulses with a width of less than 550 ps at a repetition rate of 10 MHz. The reduction of the power consumed by the transducer and the grating length points out to more efficient, compact and fast acousto-optic modulators for mode-locked all-fiber lasers.
Mach-Zehnder interferometric based on a 5-core fiber
Show abstract
A linear 5-core fiber was sandwiched in between two single mode fibers (SMF) to construct an all fiber Mach-Zehnder interferometer (MZI). The interferences between the fundamental supermodes, between the fundamental supermodes and the high order core modes, and between the fundamental supermodes and the low order cladding mode are investigated. The experimental results show both the interference between the core modes and the interference between the core modes and the cladding modes have approximately equal temperature sensitivity. The interference between the core modes is insensitive to the axial strain.
Fast interrogation of fiber Bragg grating sensors using electro-optic dual optical frequency combs
Show abstract
In this document, a FBG interrogation system based on a multimode optical source and a direct read-out is proposed for measuring fast phenomena such as vibrations and ultrasounds. The system is based on an electro-optic dual optical frequency-comb. This architecture allows the configuration of the multimode optical source parameters such as the number of modes that are within the reflected spectrum (FWHM) of the FBG. Results are presented for the dual-comb operating under optimized control when mapping these optical modes onto detectable tones of multiples of 100 kHz around a centre radiofrequency tone (40 MHz). Dynamic strain is induced onto the fiber through an actuator, which generates changes in the reflected wavelength of the FBG and in turn the modes within the reflected spectrum. The electrical signals are analyzed using fast Fourier transform algorithms allowing identification of the vibrations.
Sensors for the Living State
Lab-on-Fiber biosensing for cancer biomarker detection
Show abstract
This work deals with a novel Lab-on-Fiber biosensor able to detect in real time thyroid carcinomas biomarkers. The device is based on a gold nanostructure supporting localized surface plasmon resonances (LSPR) directly fabricated on the fiber tip by means of electron beam lithography and lift-off process. Following a suitable chemical and biological functionalization of the sensing area, human Thyroglobulin has been detected at nanomolar concentrations. Also, compatibility with full baseline restoration, achieved through biomarkers/bioreceptors dissociation, has been demonstrated.
Central arterial pressure assessment with intensity POF sensor
Show abstract
The central pressure monitoring is considered a new key factor in hypertension assessment and cardiovascular prevention. In this work, it is presented the central arterial systolic pressure assessment with an intensity based POF sensor. The device was tested in four subjects, and stable pulse waves were obtained, allowing the calculation of the central pressure for all the subjects. The results shown that the sensor performs reliably, being a simple and low-cost solution to the intended application.
The force magnitude of a human bite precisely measured at the molar intercuspidation using FBG: part II
Show abstract
This study describes the evolution of a punctual method to determine the bite force. Now the fiber Bragg grating sensor is encapsulated in minimal material between uppers and lowers first molars, at the moment of occlusion, avoiding precontacts between the other teeth in a dentition model. The gypsum dentition castings were performed in semi-adjustable articulator in the occluded situation to maintain angulations of the occlusal plane of a volunteer. The sensor was characterized using loads from 0 to 90 N. Forces of about 0.0112 nm/N were found between right uppers and lowers first molars.
Detection specificity studies of bacteriophage adhesin-coated long-period grating-based biosensor
Show abstract
In this work, we present a label-free detection specificity study of an optical fiber long-period grating (LPG) biosensor working near the dispersion turning point of higher order cladding modes. The LPG sensor functionalized with bacteriophage adhesin is tested with specific and non-specific bacteria dry weight. We show that such biosensor is able to selectively bind, thus recognize different bacteria. We use bacteria dry weights of E. coli B as positive test and E. coli K12 and Salmonella enterica as negative tests. The resonance wavelength shift induced by E. coli B reaches over 90 nm, while for E. coli K12 and Salmonella enterica approximately 40 and 20 nm, respectively.
In-vivo determination of chewing patterns using FBG and artificial neural networks
Show abstract
This paper reports the process of pattern classification of the chewing process of ruminants. We propose a simplified signal processing scheme for optical fiber Bragg grating (FBG) sensors based on machine learning techniques. The FBG sensors measure the biomechanical forces during jaw movements and an artificial neural network is responsible for the classification of the associated chewing pattern. In this study, three patterns associated to dietary supplement, hay and ryegrass were considered. Additionally, two other important events for ingestive behavior studies were monitored, rumination and idle period. Experimental results show that the proposed approach for pattern classification has been capable of differentiating the materials involved in the chewing process with a small classification error.
Optical fiber biocompatible sensors for monitoring selective treatment of tumors via thermal ablation
Show abstract
Thermal ablation (TA) is an interventional procedure for selective treatment of tumors, that results in low-invasive outpatient care. The lack of real-time control of TA is one of its main weaknesses. Miniature and biocompatible optical fiber sensors are applied to achieve a dense, multi-parameter monitoring, that can substantially improve the control of TA. Ex vivo measurements are reported performed on porcine liver tissue, to reproduce radiofrequency ablation of hepatocellular carcinoma. Our measurement campaign has a two-fold focus: (1) dual pressure-temperature measurement with a single probe; (2) distributed thermal measurement to estimate point-by-point cells mortality.
Glucose optical fibre sensor based on a luminescent molecularly imprinted polymer
Show abstract
An optrode able to detect glucose dissolved in water has been implemented. The device is based on the luminescence emission of a Molecularly Imprinted Polymer synthesized specifically for glucose detection, therefore its intensity changes in presence of glucose. This sensing material is attached onto a cleaved ended polymer-clad optical fibre and it is excited by light via 1x2 fibre coupler. The reflected fluorescence signal increases when it is immersed into glucose solutions and recovers to the baseline when it is dipped in ultrapure water. This reversible behaviour indicates the measurement repeatability of using such a glucose sensor.
Post-Deadline Papers and Closing
All Fiber Grating (AFG): a new platform for fiber optic sensing technologies
Show abstract
A versatile all fiber grating sensor network based on ultra-weak fiber Bragg gratings (FBGs) was firstly proposed and demonstrated. On-line writing identically weak fiber Bragg grating array by the phase mask technique was developed. The sensing network is interrogated with time- and wavelength-division multiplexing method. The proposed ultra-weak FBG system was very promising for the large-scale sensing network.
Very high sensor-density multiplexing using a wavelength-to-time domain reflectometry approach based on a rapidly swept akinetic laser
Show abstract
We demonstrate a scheme for the interrogation of arrays of FBG sensors based on a Swept Laser Distributed Sensing
system which can achieve 1000 sensors or more in a single fiber, while retaining the sensitivity and repeatability
expected with FBG sensors of better than 0.5 μepsilon and 0.05 C. The system utilizes an ‘akinetic’ wavelength swept source
and an arrival time-dependent detection approach to allow potentially 1000s of very low reflectivity FBGs to be
monitored via a form of Wavelength-to-Time Domain Reflectometry. We demonstrate the interrogation of 250 gratings
in a system architecture designed to support 1000 gratings.
A distributed acoustic and temperature sensor using a commercial off-the-shelf DFB laser
Show abstract
In this paper, we experimentally demonstrate a hybrid distributed acoustic and temperature sensor (DATS) based on
Raman and coherent Rayleigh scattering processes in a standard singlemode fiber. A single commercial off-the-shelf
DFB laser and a common receiver block are used to implement a highly integrated hybrid sensor system with key
industrial applications. Distributed acoustic sensing and Raman temperature measurement are simultaneously performed
by exploiting cyclic Simplex pulse coding in a phase-sensitive OTDR and in Raman DTS using direct detection. Suitable
control and modulation of the DFB laser ensures inter-pulse incoherence and intra-pulse coherence, enabling accurate
long-distance measurement of vibrations and temperature with minimal post-processing.
Intensifying Brillouin distributed fibre sensors using image processing
Show abstract
Image processing is proposed to enhance the performance of Brillouin distributed fibre sensors. The technique exploits the two-dimensional nature of the measurements, so that each frequency-position pair is assimilated to a pixel of a noisy image. Based on the level of redundancy existing in the two-dimensional information, the method offers unmatched denoising capabilities when compared to classic unidimensional denoising methods, even if those ones are consecutively used in distance and frequency domains. With no modification of the basic configuration, up to ~14 dB SNR improvement is experimentally demonstrated with unobservable loss of spatial resolution. A figure-of-merit of 115’000 is verified.
Reaching the ultimate performance limit given by non-local effects in BOTDA sensors
Show abstract
Non-local effects have been traditionally identified as one of the most limiting factors of the performance of Brillouin
optical time-domain analyzers. These phenomena, directly linked with the energy gained/lost by the pump pulse, limit
the probe power and ultimately the SNR of the system. Several solutions have been proposed, although none offers the
possibility to increase the probe power until its limit, the onset of amplified spontaneous Brillouin scattering. In this
work, we propose a technique that avoids non-local effects and permits to set the probe power at its maximum, reaching
a 100 km sensing distance with 2 meter resolution.
Demonstration of an advanced fibre laser hydrophone array in Gulf St Vincent
Show abstract
We have developed an 8-element fibre laser seabed array demonstrating state-of-the art performance characteristics for a
fibre laser sensing system. The system employs sea-state-zero sensitivity hydrophones with a flat acoustic response over
a bandwidth exceeding 5kHz and very low inertial sensitivity. The system contains no outboard electronics and few metal
components making it extremely light, compact, and low complexity. The array may be deployed up to 4 km from a land
or sea based platform to a depth of up to 80m. Power delivery and telemetry for all 8 sensors is achieved via a single 2mm
diameter optical fibre cable weighing less than 5kg per km. We report here results of the first field trials of this system.
Poster Session I
High sensitive reflection type long period fiber grating biosensor for real time detection of thyroglobulin, a differentiated thyroid cancer biomarker: the Smart Health project
Show abstract
We report the development of a reflection-type long period fiber grating (LPG) biosensor able to perform the real time detection of thyroid cancer markers in the needle washout of fine-needle aspiration biopsy. A standard LPG is first transformed in a practical probe working in reflection mode, then it is coated by an atactic-polystyrene overlay in order to increase its surrounding refractive index sensitivity and to provide, at the same time, the desired interfacial properties for a stable bioreceptor immobilization. The results provide a clear demonstration of the effectiveness and sensitivity of the developed biosensing platform, allowing the in vitro detection of human Thyroglobulin at sub-nanomolar concentrations.
Nanowire humidity optical sensor system based on fast Fourier transform technique
Show abstract
In this paper, a new sensor system for relative humidity measurements based on its interaction with the evanescent field of a nanowire is presented. The interrogation of the sensing head is carried out by monitoring the fast Fourier transform phase variations of one of the nanowire interference frequencies. This method is independent of the signal amplitude and also avoids the necessity of tracking the wavelength evolution in the spectrum, which can be a handicap when there are multiple interference frequency components with different sensitivities. The sensor is operated within a wide humidity range (20%–70% relative humidity) with a maximum sensitivity achieved of 0.14rad/% relative humidity. Finally, due to the system uses an optical interrogator as unique active element, the system presents a cost-effective feature.
Plastic optical fibre sensor for in-vivo radiation monitoring during brachytherapy
Show abstract
An optical fibre sensor is presented for applications in real-time in-vivo monitoring of the radiation dose a cancer patient receives during seed implantation in Brachytherapy. The sensor is based on radioluminescence whereby radiation sensitive scintillation material is embedded in the core of a 1mm plastic optical fibre. Three scintillation materials are investigated: thallium-doped caesium iodide (CsI:Tl), terbium-doped gadolinium oxysulphide (Gd2O2S:Tb) and europium-doped lanthanum oxysulphide (La2O2S:Eu). Terbium-doped gadolinium oxysulphide was identified as being the most suitable scintillator and further testing demonstrates its measureable response to different activities of Iodine-125, the radio-active source commonly used in Brachytherapy for treating prostate cancer.
Fiber optic evaporation analysis of environmental parameters and of synthetic urine samples
Eyal Preter,
Moshe Katzman,
Ziv Oren,
et al.
Show abstract
The evaporation rate of water droplets is evaluated as a function of temperature and relative humidity using a fiber-optic sensor. Either parameter may be monitored when the other is known, with uncertainties of 0.5 deg. C or 1.5% relative humidity. Further, the sensor is used in the analysis of negative control synthetic solutions, made to mimic human urine. Samples of binary mixtures of the solution with water at different volume ratios are categorized using correlation analysis of the recorded evaporation dynamics, with 87% success. The results represent an important first step towards potential use of the sensor in point-of-care diagnostics.
Polymeric optical fiber tweezers as a tool for single cell micro manipulation and sensing
Show abstract
In this paper a new type of polymeric fiber optic tweezers for single cell manipulation is reported. The optical trapping of a yeast cell using a polymeric micro lens fabricated by guided photo polymerization at the fiber tip is demonstrated. The 2D trapping of the yeast cells is analyzed and maximum optical forces on the pN range are calculated. The experimental results are supported by computational simulations using a FDTD method. Moreover, new insights on the potential for simultaneous sensing and optical trapping, are presented.
Humidity insensitive step-index polymer optical fibre Bragg grating sensors
Show abstract
We have fabricated and characterised a humidity insensitive step index(SI) polymer optical fibre(POF) Bragg grating sensors. The fibre was made based on the injection molding technique, which is an efficient method for fast, flexible and cost effective preparation of the fibre preform. The fabricated SIPOF has a core made from TOPAS with a glass transition temperature of 134°C and a cladding from ZEONEX with a glass transition temperature of 138°C. The main advantages of the proposed SIPOF are the low water absorption and good chemical resistance compared to the conventional poly-methyl-methacrylate (PMMA) based SIPOFs. The fibre has a minimum loss of ~6dB/m at 770nm.
Immunobiosensor for fast detection of bacteria in water using plastic optical fiber (POF) bended
Show abstract
This paper presents an immunobiosensor of fast response time to detection of bacteria, made by Plastic Optical Fiber. Probes were tested in U-shaped and Meander-shaped to investigate the best sensitivity, accuracy and repeatability. During calibration was used for sucrose solutions refractive index (RI) from 1.33 to 1.39. This is equivalent to IR range of the water and the highest concentration of bacteria, respectively. Immunobiosensor was able to detecting the presence of enteropathogenic Escherichia coli in water from suspensions of different concentrations of 106 and 104 colonies forming units per millilitre (CFU/mL) in twenty minutes.
Multi FBG femtosecond laser inscription in FPI based pressure sensors for temperature distribution
Show abstract
We present in this paper an optical fiber pressure and temperature sensor (OFPTS) with multi Fibre Bragg Grating (FBG) array. The sensor based on an extrinsic Fabry Perot interferometer and is fabricated from silica glass. A femtosecond laser (FSL) was used to inscribe multiple FBGs proximately close to the diaphragm, parallel to each other. This concepts allows a chain of FBGs with miniature active length which can be a significant important tool for medical application, like radio frequency ablation (RFA) cancer treatment.
Rapid detection of methanol in artisanal alcoholic beverages
R. E. de Goes,
M. Muller,
J. Luís Fabris
Show abstract
In the industry of artisanal beverages, uncontrolled production processes may result in contaminated products with methanol, leading to risks for consumers. Owing to the similar odor of methanol and ethanol, as well as their common transparency, the distinction between them is a difficult task. Contamination may also occur deliberately due to the lower price of methanol when compared to ethanol. This paper describes a spectroscopic method for methanol detection in beverages based on Raman scattering and Principal Component Analysis. Associated with a refractometric assessment of the alcohol content, the method may be applied in field for a rapid detection of methanol presence.
Fiber optic thermo-hygrometers for soil moisture and temperature measurements: the SFORI project
Show abstract
This work deals with the development of fiber optic sensors for the measurement of soil moisture and temperature over large areas. It has been carried out within the Regional Project "Sensoristica in Fibra Ottica per il Risparmio Idrico - SFORI". The sensor system is based on the fiber Bragg gratings (FBGs) technology and is aimed at optimizing the irrigation practice in order to guarantee a sustainable water resources management. Two sensors networks, each one based on FBG thermo-hygrometers, have been realized and installed in two experimental sites. Preliminary results envisages good perspectives for a massive usage of the proposed technology.
A fiber optic buckle transducer for measurement of in vitro tendon strain
Show abstract
The purpose of the present study is to present a prototype of a fiber optic based buckle transducer suitable for measuring strain caused by stretching of a tendon. The device has an E-shape and its central arm is instrumented with a fiber Bragg grating (FBG) sensor. The tendon adjusts to the E-form in a fashion that when it is stretched the central arm bends causing a shift of the Bragg’s wavelength (λB) that is proportional to the amount of strain. This prototype is presented as an alternative to conventional strain gauge (SG) buckle transducers.
Acetone evaporation monitoring using a caterpillar-like microstructured fiber
Show abstract
A new microstructured optical fiber is demonstrated to detect acetone evaporation by observing the time response of the reflected signal at 1550nm. The sensor consists on a caterpillar-like fiber, with a transversal microfluidic channel created with a Focused Ion Beam technique, spliced to a single-mode fiber. Different stages were visible between the dipping and the evaporation of acetone and of a mixture of water and acetone. It was also possible to detect the presence of water vapor.
Dissolved oxygen sensing using an optical fibre long period grating coated with hemoglobin
Show abstract
A method for the preparation of a sensor consisting of an optical fibre long period grating coated with human hemoglobin is described. The utility of this sensor in detecting dissolved oxygen in phosphate buffered saline solution, by the conversion of the coated hemoglobin from deoxyhemoglobin to oxyhemoglobin, is described. The sensor shows good repeatability with a %CV of less than 1% for oxygenated and deoxygenated states and no drift or hysteresis with repeated cycling.
PAMAM dendrimer/gold nanoparticle nanocomposites for a reflection LSPR optical fiber sensor
Show abstract
The viability of a fiber optic reflection-based Localized Surface Plasmon Resonance (LSPR) sensor using layer-by-layer technique composed by PAMAM-AuNP with and without AuNP-citrate was investigated. The PAMAM-AuNPs and PAMAM-AuNPs/AuNP-citrate layers were deposited on the endface of an optical fiber and the reflected signal was acquired. Deposition time and number of layers were optimized viewing LSPR sensing applications. Results with and without AuNP-citrate were compared. The sensor is being characterized as a refractive index sensor.
Novel approach for simultaneous sediment classification and concentration determination of water turbidity
Show abstract
A new approach for data analysis and classification for datasets obtained by a multiparameter optical turbidity sensor is proposed. This approach is based on the combination of statistical or machine learning methods such as linear regressions and clustering analysis. A case study is presented using a 6 dimensional fiber optic sensor to simultaneously classify types of sediments and concentration. Results show a 79% of success for the used training data sets. The methodology proposed is flexible because can be easily adapted to other physical scenarios.
High-performance Brillouin optical correlation-domain reflectometry
Show abstract
We develop a new configuration of Brillouin optical correlation-domain reflectometry by sophisticated electrical signal processing. Through a variety of demonstrations, we experimentally show that this system can satisfy many advantages simultaneously, such as (1) high sampling/repetition rate, (2) intrinsically one-end-access interrogation, (3) high spatial resolution, (4) wide strain dynamic range, (5) high signal-to-noise ratio, and (6) system simplicity and cost efficiency.
Distributed fiber vibration measurement based on phase extraction from time-gated digital OFDR
Show abstract
We demonstrate a novel distributed fiber vibration sensor based on the phase extraction from time-gated digital optical frequency domain reflectometry (TGD-OFDR), which have an advantage of wide dynamic range. With the much improved signal to noise ratio (SNR) compared to conventional phase-sensitive optical time domain reflectometry (OTDR), the phase of optical signals is extracted over a long distance up to 29 km with 2.2 m spatial resolution.
Spontaneous anti-Stokes backscattering in Brillouin dynamic gratings
Show abstract
Spontaneous Brillouin backscattering, which accompanies the operation of Brillouin Dynamic Gratings (BDG) sensors, is experimentally investigated for the anti-stokes configuration, where the probe wave propagates against the orthogonally polarized high frequency writing pump. Even in the absence of the low frequency writing pump but for a strong enough high frequency writing pump, the observed anti-Stokes reflection of the probe becomes much stronger than its corresponding value under classical anti-Stokes backscattering. It is also shown that, eventually, as the probe reaches a critical value, the anti-Stokes reflection sharply decreases to its classical value.
Compensation of optical source phase noise in long-range OFDR by using an optical fiber delay loop
Show abstract
We demonstrate a novel method to compensate the optical source phase noise in long-range OFDR by using an optical fiber delay loop (OFDL). In this method, a 10 km OFDL is incorporated in the reference interferometer of the reflectometry. A frequency shifter is used to count the circulation rounds of the light traveling in OFDL. The preliminary “proof-of-concept” experiment shows a successful compensation effect and an 11 cm spatial resolution over 20 km measurement range is realized by this method.
Influence of polarization scrambling on Brillouin optical correlation-domain reflectometry using plastic fibers
Show abstract
We evaluate whether the measurement stability of Brillouin optical correlation-domain reflectometry (BOCDR) using plastic optical fibers (POFs) can be enhanced by polarization scrambling. Two major factors that affect the signal-to-noise ratio in BOCDR, i.e., the spatial resolution and the incident power are varied, and their influences on the distributed measurements with polarization scrambling are experimentally investigated. We thus clarify that in POF-based BOCDR, unlike BOCDR using standard silica glass fibers, polarization scrambling is effective in enhancing the measurement stability only when the spatial resolution is sufficiently low or when the incident power is sufficiently high.
Unexpected non-local effects in dual-probe-sideband BOTDA
Show abstract
Until now, non-local effects in dual-probe-sideband Brillouin Optical Time Domain Analysis (BOTDA) systems have been considered negligible if the probe power is below the Stimulated Brillouin Scattering (SBS) threshold. In this paper, we show the appearance of non-local effects even below the SBS threshold. The pump pulse experiences a frequency dependent spectral deformation that affects the readout process differently in the gain and loss configurations. The main conclusion of our study is that the measurements in gain configuration are more robust to this non-local effect than the loss configuration. These results are of particular interest for manufacturers of long-range BOTDA systems.
Colour cyclic code for Brillouin distributed sensors
Show abstract
For the first time, a colour cyclic coding (CCC) is theoretically and experimentally demonstrated for Brillouin optical time-domain analysis (BOTDA) distributed sensors. Compared to traditional intensity-modulated cyclic codes, the code presents an additional gain of √2 while keeping the same number of sequences as for a colour coding. A comparison with a standard BOTDA sensor is realized and validates the theoretical coding gain.
Study of the hydrogen influence on the acoustic velocity of single-mode fibers by Rayleigh and Brillouin backscattering measurements
Show abstract
We study the effect of hydrogen gas diffusion in silica optical fibers on Brillouin and Rayleigh scatterings. By modeling hydrogen diffusion kinetics as a function of temperature and pressure and by measuring simultaneously Rayleigh and Brillouin scattering on G652 single-mode fiber samples during H2 desorption (previously exposed to 175 bars H2 at 80°C), we have demonstrated experimentally that acoustic velocity increases linearly with H2 concentration with a ratio of about (4.8 m/s) / (%mol H2).
Mitigation of modulation instability in Brillouin distributed fiber sensors by using orthogonal polarization pulses
Show abstract
A technique based on the use of orthogonally-polarized pulses is proposed to mitigate the detrimental impact of modulation instability on Brillouin distributed fiber sensors. While the theoretical underpinnings of the method are described by introducing a detailed model for the vector modulation instability, the technique is experimentally validated in a 25-km sensing link. Numerical and experimental results demonstrate that the use of orthogonally-polarized pulses not only mitigates the impact of modulation instability, but also the four-wave mixing occurring in systems using pumps with parallel polarization; thus, providing an important sensing range enhancement with a reduced pump depletion.
Sources of noise in Brillouin optical time-domain analyzers
Show abstract
This paper presents a thorough study of the different sources of noise affecting Brillouin optical time-domain analyzers (BOTDA), providing a deep insight into the understanding of the fundamental limitations of this kind of sensors. Analytical and experimental results indicate that the noise source ultimately fixing the sensor performance depends basically on the fiber length and the input pump-probe powers. Thus, while the phase-to-intensity noise conversion induced by stimulated Brillouin scattering can have a dominating effect at short distances, a combination of sources determines the noise in longrange sensing, basically dominated by probe double Rayleigh scattering.
Measurements of endotracheal tube cuff contact pressure using fibre Bragg gratings
Show abstract
An optical fibre Bragg grating (FBG) was used to measure local strain (due to contact pressure) at the interface of a cuffed endotracheal tube (ETT) tested in a tracheal model. The tracheal model consisted of a corrugated tube. Two FBG sensors written in a single optical fibre were attached to the outside wall of the cuff of the ETT. Intracuff endotracheal pressure was measured using a digital manometer, while the contact pressure between the model trachea and the ETT was measured using Flexiforce sensors. Changes in the Bragg wavelengths in response to the inflation of the cuff of the ETT, and concomitant pressure increase, were observed to be dependent on the location of the FBGs at the corrugations, i.e., the annular peaks and troughs of the corrugated tube. The performance of both contact pressure sensors FBG and Flexiforce suggests that FBG technology is better suited to this application as it allows the measurement of contact pressures on non-uniform surfaces such as in the tracheal model.
Simultaneous demodulation of polarization mode coupling and fiber Bragg grating within a polarization maintaining fiber
Show abstract
We propose a simultaneous demodulation scheme of polarization mode coupling and fiber Bragg grating in a polarization maintaining fiber based on a white light interferometer. A polarization maintaining fiber with two inscribed fiber Bragg gratings is used to demonstrate the feasibility.
Simple refractometer based on in-line fiber interferometers
Show abstract
A very simple but accurate optical fiber refractometer based on the Fresnel reflection in the fiber tip and two in-line low-reflective mirrors for light intensity referencing is reported. Each mirror was generated by connecting together 2 fiber sections with FC/PC and FC/APC connectors using the standard FC/PC mating sleeve. For the sensor interrogation, a standard DFB diode laser pumped with a sawtooth-wave current was used. A resolution of 6 x 10-4 was experimentally demonstrated using different liquids. A simple sensor construction and the use of low cost components make the reported system interesting for many applications.
Magnetic field sensing with an in-line Fabry-Perot interferometer based on capillary optical fiber and Terfenol-D
Show abstract
In this paper we discuss results obtained with an in-line Fabry-Perot interferometer (FPI) built by splicing a small section of capillary fiber between two pieces of standard single mode fiber, resulting in a rectangular air cavity. The FPIs were characterized regarding sensitivity to temperature and longitudinal strain. The FPIs were bonded to pieces of Terfenol-D, a magnetostrictive alloy, to be used as magnetic field sensors. Fiber Bragg Gratings were also bonded to Terfenol-D for comparison. The FPI based on capillary optical fiber and Terfenol-D showed a higher sensitivity to an applied magnetic field when compared to an FBG.
Expanding the dynamic range of an open loop IFOG
Show abstract
We propose and implement a new modulation and demodulation scheme which allows an open loop Interferometric Fiber Optic Gyroscope (IFOG) to expand its dynamic range, extending the maximum Sagnac phase measurement from the typical π/6 rad to values limited only by the increase of signal to noise ratio when interference approaches the coherence length of the light source. Here we achieve a Sagnac phase measumerent of 116.8 rad keeping the measurement error below 0.1 rad for the whole range. Theoretically, there is no reason the error could not go as low as the typical error of a closed loop IFOG.
Fourier transform-based absolute phase interrogation algorithm for Sagnac interferometer-based PMF sensors
Show abstract
A high resolution and absolute phase interrogation algorithm for Sagnac interferometer based polarization maintaining fiber (PMF) sensor is proposed. Taking wavenumber instead of wavelength as the function variable, the output spectrum will be a standard cosine spectrum function. After Fourier transform, the frequency and relative phase of this spectrum function can be obtained and the precise absolute phase due to optical path difference between the two polarization modes in sensing PMF can be determined. A typical Sagnac interferometer based PMF temperature sensor was built and the absolute phase was determined by use of the proposed algorithm. Experiments show that 0.1°C temperature resolution and up to 900°C temperature can be measured with good linearity.
Hydrostatic pressure sensing with surface-core fibers
Show abstract
In this paper, we report the employment of surface-core fibers for hydrostatic pressure sensing. To our knowledge, this is the first demonstration of the use of these fibers for the referenced purpose. Theoretical simulations of the fiber structure were performed in order to estimate fiber phase and group birefringence values and its pressure sensitivity coefficient. In order to test fiber performance when acting as a pressure sensor, the same was placed in an polarimetric setup and its spectral response was measured. A sensitivity of 4.8 nm/MPa was achieved, showing good resemblance to the expected sensitivity value (4.6 nm/MPa).
Fiber Bragg grating inscription in optical multicore fibers
Show abstract
Fiber Bragg gratings as key components in telecommunication, fiber lasers, and sensing systems usually rely on the Bragg condition for single mode fibers. In special applications, such as in biophotonics and astrophysics, high light coupling efficiency is of great importance and therefore, multimode fibers are often preferred. The wavelength filtering effect of Bragg gratings in multimode fibers, however is spectrally blurred over a wide modal spectrum of the fiber. With a well-designed all solid multicore microstructured fiber a good light guiding efficiency in combination with narrow spectral filtering effect by Bragg gratings becomes possible.
Component and setup for insertion of gases in a hollow-core optical fiber sensor
Show abstract
An optical fiber component and setup were developed to insert and remove gases from hollow-core optical fibers, allowing gas/light mixing over the length of the fiber for gas sensing applications. Transmitted signals acquired at the output of the fiber contain information regarding absorption occurring inside the fiber, providing a spectroscopic signature of the gas or gases in the fiber. Spectra for 1 atm of acetylene (C2H2) around 1525 nm and 1 atm of carbon dioxide (CO2) around 1432 nm were obtained and compared to HITRAN data, showing good agreement. The setup can also be used to prepare gas cells.
Air-structured optical fibre drawn from a 3D-printed preform
Show abstract
We report the first optical fibre drawn from a 3D-printed preform. An air-structured polymer preform is printed using a modified butadiene plastic called Bendlay as opposed to the more-common Acrylonitrile Butadiene Styrene (ABS). The preform is subsequently drawn to fibre form at a relatively low temperature of 160 ⁰C and maintains its air-structured cladding holes. Such ability to freely-design and 3D-print complex preform structures, such as photonic bandgap and photonic crystal structures, opens up an exciting new front in optical fibre fabrication.
Submicron accuracy fiber taper profiling using whispering gallery modes in a cylindrical fiber micro-resonator
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This paper experimentally demonstrates a method for geometrical profiling of thin microfiber tapers with small waist diameters ranging from 10 to 40 μm with submicron accuracy. The method is based on analysis of whispering gallery mode resonances excited in cylindrical fiber resonators as a result of evanescent coupling of light propagating through the fiber taper under test. Measurement results have been verified by optical and SEM microscopic studies. The proposed method can be applied in the fabrication of fiber micro tapers for accurate control of the taper profile and in sensing of biochemical species on the surface of the microfiber.
Thermally tunable bandgaps in a hybrid As2S3/silica photonic crystal fiber
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We report the fabrication and characterization of a hybrid silica photonic crystal fiber (PCF) with integrated chalcogenide glass layers and we show how the bandgaps of the fiber can be thermally tuned. The formation of the high index chalcogenide films on the inner surface of the PCF holes revealed resonances as strong as ~35 dB both in the visible and infrared regime. Temperature measurements indicate that the transmission windows can be tuned with a sensitivity as high as ~3.5 nm/°C. The proposed fiber has potential for all-fiber filtering and temperature sensing.
Lab-on-fiber platforms for ultrasound detection: a comparative study
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Sub-wavelength metallo-dielectric gratings integrated on optical fibers tip and supporting plasmonic resonances were numerically investigated in their behavior as acousto-optical transducers. Different configurations have been analyzed and compared among them in terms of sensitivity, defined as reflectivity intensity variation (at fixed wavelength) with respect to dielectric layer thickness changes. Our results demonstrate that the maximum sensitivity is obtained when an interaction between different plasmonic modes occurs. Sensitivity enhancement up to a factor of 3 with respect to Fabry- Perot cavity like transducer with same materials and sizes can be achieved.
Bragg grating fabrication on tapered fiber tips based on focused ion beam milling
Show abstract
Focused ion beam milling is used on chemically etched tapered fiber tips to create fiber Bragg gratings. These fiber Bragg gratings are based on a modulation of silica and external medium. This leads to a wide and structured spectrum obtained due to imperfections and the inherent structure of the tip. The fiber Bragg gratings presented are very short and have a length of 27 μm and 43 μm and are milled on the tapered fiber tip. They are characterized in the high temperature range 350-850ºC and a sensitivity of 14.4 pm/K is determined.
Asymmetrically and symmetrically coated tapered optical fiber for sensing applications
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The deposition of a non-metallic thin-film in a symmetrically coated tapered optical fiber leads to the generation of resonances due to guidance of a mode in the thin-film. At certain conditions, the resonances overlap each other, which can be avoided with an asymmetric coated tapered optical fiber, which permits to obtain resonances for TM and TE polarization separately. Numerical results showing the sensitivity to coating thickness and surrounding medium refractive index are also presented for both polarizations.
Improved response time of laser etched polymer optical fiber Bragg grating humidity sensor
Show abstract
The humidity sensor made of polymer optical fiber Bragg grating (POFBG) responds to the water content change in fiber induced by the change of environmental condition. The response time strongly depends on fiber size as the water change is a diffusion process. The ultrashort laser pulses have been providing an effective microfabrication method to achieve spatial localized modification in materials. In this work we used the excimer laser to create different microstructures (slot, D-shape) in POFBG to improve its performance. A significant improvement in the response time has been achieved in a laser etched D-shaped POFBG humidity sensor.
Fabrication of in-line modal couplers based on multicore fibers and their applications to fiber optic sensors
Show abstract
We propose an in-line modal coupler based on a multicore fiber (MCF) which can be readily fabricated by using the adiabatic tapering method. The intermodal coupling of the in-line modal coupler apparently generated the transmission oscillation of the center core and the multiple side core modes depending on the waist diameter. The reduction of the waist diameter of the adiabatically tapered MCF could dramatically change its sensitivities to strain, temperature, and ambient index. We believe that experimental results are very useful to fabricate the in-line modal coupler based on the MCF and to improve the performance of the fiber-optic sensors by controlling the waist diameter of the adiabatically tapered MCF.
Study of few-mode fiber based SMS sensor for simultaneous measurement of temperature and strain
Kazuhide Nakajima,
Taiji Sakamoto,
Yukihiro Goto,
et al.
Show abstract
The applicability of few-mode fiber (FMF) as a single-multi-single (SMS) sensor is investigated. We examine experimentally the wavelength shift and/or visibility characteristics in an FMF based SMS sensor by changing the external temperature and longitudinal strain individually. We investigate numerically the temperature sensitivity of the fabricated sensor by considering the temperature dependence of the effective refractive index difference. Our results show that an FMF based SMS sensor can be used to measure the relative variation in temperature and strain simultaneously, and whose sensitivity can be tailored easily by designing two LP modes in an FMF.
Femtosecond laser inscription of Bragg and complex gratings in coated and encapsulated silica and low-loss polymer optical fibers
Show abstract
The development of wavelength filters, such as Bragg and superstructure gratings in glass and polymer optical fibers, using a femtosecond laser is reported. By using a femtosecond laser operating in the green, which offers greater inscription efficiency, we demonstrate the reliable inscription of Bragg and superstructure gratings in coated silica and low-loss CYTOP polymer optical fibers. We employ line by line and point by point inscription methods, allowing for multiple and overlapping gratings in the fiber core. Moreover, we demonstrate a novel fibre Bragg grating inscription technique to modify and add versatility to an existing, encapsulated optical fiber pressure sensor.
Optical fiber sensor for simultaneous measurement of hydrostatic pressure and temperature in soil embankments
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An optical fiber sensor for the simultaneous measurement of hydrostatic pressure and temperature in soil embankments is presented. The sensor exploits a dual chambers transduction mechanism and is based on the optical measurement of the differential strain induced in the fiber by temperature and pressure in the two chambers. A prototype has been built and interrogated by means of optical coherent frequency domain reflectometry and the results of a preliminary experimental characterization are presented and discussed. Temperature and pressure sensitivities are approximately -7.1 GHz/°C and -4.4 GHz/kPa, respectively.
Measuring strain at extreme temperatures with a Fabry-Perot optical fiber sensor
Show abstract
In this work, a Fabry-Perot optical fiber sensor for the measurement of strain at extreme temperatures is proposed. The cavity is formed by splicing a short section of a silica tube between two sections of single mode fiber. The tube, with a cladding ~14 μm thick and a hollow core, presents four small rods, of ~20 μm in diameter each, positioned in in diametrically opposite positions. This design ensures higher mechanical stability of the tube. Strain measurements are performed over a wide range of temperatures, until 900 °C. Some of the annealing effects are addressed in this study.
Simultaneous multipoint strain measurement using cascaded long period fiber gratings
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A fiber-optic strain sensor array using long period fiber gratings (LPGs) is proposed and demonstrated, in which cascaded LPGs (C-LPGs) are employed as the sensing elements and a Fourier transform technique is applied to their periodic channeled spectra for the interrogation scheme. In this technique, strain-induced shift of the channeled spectrum of C-LPG can be determined precisely from the cross-spectrum (i.e. Fourier transform of cross-correlation) between the original and shifted channeled spectra and multiplexing operation of C-LPG sensor array can be achieved by using the different C-LPGs having the channeled spectra with various periods. In the experiment, several kinds of CLPGs are fabricated by UV-irradiation technique and simultaneous multipoint strain measurements are successfully demonstrated.
Common frequency suppression method for fiber specklegram perimeter sensors
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In this work, a frequency based processing scheme has been employed to improve the sensitivity of Fiber Specklegram Sensors (FSSs) applied to perimeter fences. Based on 1.8 km of multimode fiber, two laser sources with different spectral properties have been employed to feed the optical fiber. These two laser sources provoke sensing systems with very different SNRs to which the common frequency suppression method has been applied. The final results suggest enough improvement on SNR to reduce the quality of the laser source on perimeter sensors, also decreasing the final cost.
Stretching the limits for the decoupling of strain and temperature with FBG based sensors
Show abstract
The ability to decouple strain from temperature is being explored using Bragg gratings written in highly birefringent fiber in combination with a high accuracy interrogator. Both the birefringent preform as well as the interrogator have been optimized in order to reach maximum measurement accuracy. The results from calibration measurements will be presented together with the estimated stability.
0.1-nano-strain resolution fiber optic sensor for quasi-static strain measurement with 1 kS/s sampling rate
Show abstract
We present a newly developed high performance fiber optics sensor for quasi-static strain measurement. The sensor consists of a piece of π-phase shifted FBG for static strain sensing, and fiber Fabry-Perot interferometer for reference, interrogated by an improved sideband interrogation method with real-time feedback loops. Strain resolution of 0.12 nano-strain was achieved with sampling rate up to 1 kS/s in laboratory experiments. Compared with previous sensor systems, the proposed method shows great improvement in the sensing rate as well as the resolution.
Simultaneous regeneration of seed FBGs during the HFCVD diamond-grating coating process and its thermal monitoring
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In this work, the simultaneous regeneration of seed fibre Bragg gratings (FBGs) during the diamond-grating coating and the thermal monitoring of that process is presented. The diamond was deposited through the hot filament chemical vapour deposition (HFCVD) process, and due to the high temperatures characteristics of this method (above 800 ºC), regenerated FBGs are suitable samples to be coated. The advantages of this study are the possibility to regenerate the seed gratings during the coating process, becoming the fibre more resistant and the procedure less time consuming, and to control the temperature, a critical parameter for the morphology of the deposited layers.
Effective refractive index modulation based optical fiber humidity sensor employing etched fiber Bragg grating
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Relative humidity (RH) sensor employing etched fiber Bragg grating (FBG) is reported where RH variations are captured using effective-index-modulation, rather than traditional strain-modulation. Additionly, linear sensor response over wide dynamic range with optimum characteristics is focused. Comprehensive experimental investigation is carried out for the sensor that comprises uniformly etched cladding in the FBG region. Obtained results are observed to be in agreement with the theoretical analysis. Sensor response is observed to be linear over dynamic range 3–94%RH with ~ 0.082 pm/%RH sensitivity, ~0.6%RH resolution, ~ ±2.5%RH accuracy, ~ ±0.2 pm average discrepancy and ~ 0.2s response time during humidification/desiccation.
Elastomeric fluorescent POF for partial discharge detection: recent progress
Daniel Siebler,
Michaela Hohberg,
Philipp Rohwetter,
et al.
Show abstract
We present recent progress in our development of fibre-optic sensors for the detection of partial discharge (PD) in silicone cable accessories, based on detecting related low-level optical emission. We experimentally show that the sensitive optical detection of PD can dramatically enhance the performance of conventional electrical PD measurement in electromagnetically noisy environments, and that it can yield high sensitivity and specificity even when no synchronous electrical PD measurement is conducted. This is demonstrated using a real-scale model of a high voltage cable accessory with a surface-attached conventional thermoplastic fluorescent polymer optical fibre (F-POF) sensor. In order to increase light collection efficiency, as a prerequisite for a commercially competitive implementation using cost-efficient detectors, sensing fibres will have to be integrated into the silicone rubber insulation, close to the potential origin of PD-induced damage. This is the rationale for our efforts to develop elastomeric fluorescent sensing fibres, tailored to the requirements of the application. We discuss specific challenges to be tackled and report on the successful implementation of all-silicone rubber fluorescent POF, to our best knowledge for the first time.
Entrained-flow gasifier and fluidized-bed combustor temperature monitoring using arrays of fs-IR written fiber Bragg gratings
Robert B. Walker,
Huimin Ding,
David Coulas,
et al.
Show abstract
Femtosecond written fiber Bragg gratings, have shown great potential for sensing in extreme environments. This paper discusses the fabrication and deployment of several fs-IR written FBG arrays, for monitoring main-spool skin temperatures of an entrained-flow gasifier, as well as the internal temperature gradient of a fluidized bed combustor.
Fiber optic sensing system for temperature and gas monitoring in coal waste pile combustion environments
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It is presented an optical fiber sensing system projected to operate in the demanding conditions associated with coal waste piles in combustion. Distributed temperature measurement and spot gas sensing are requirements for such a system. A field prototype has been installed and is continuously gathering data, which will input a geological model of the coal waste piles in combustion aiming to understand their dynamics and evolution. Results are presented on distributed temperature and ammonia measurement, being noticed any significant methane emission in the short time period considered. Carbon dioxide is also a targeted gas for measurement, with validated results available soon. The assessment of this technology as an effective and reliable tool to address the problem of monitoring coal waste piles in combustion opens the possibility of its widespread application in view of the worldwide presence of coal related fires.
Identification of hand postures by force myography using an optical fiber specklegram sensor
Show abstract
The identification of hand postures based on force myography (FMG) measurements using a fiber specklegram sensor is reported. The microbending transducers were attached to the user forearm in order to detect the radial forces due to hand movements, and the normalized intensity inner products of output specklegrams were computed with reference to calibration positions. The correlation between measured specklegrams and postures was carried out by artificial neural networks, resulting in an overall accuracy of 91.3% on the retrieval of hand configuration.
Partial regeneration of Aluminum coated FBG along 450 days
Valmir de Oliveira,
Camila Carvalho de Moura,
Maria Aurora Vincenti,
et al.
Show abstract
An Aluminum coated FBG was heated to 650 °C in order to study the regeneration process at low temperature. When compared to the standard regeneration process (at 800 °C -1000 °C) the regeneration occurred at longer times, the onset of the process took around 150 days to appear. The reflected signal after regeneration also is weaker than that obtained in the usual process, although it presents a good stability after the recovery phase – measured for a time span of ~200 days.
Analysis of mechanical and thermal response of rock due to laser drilling using optical fiber Bragg grating sensors
Sully M. M. Quintero,
Guilherme B. Patusco,
Hugo G. da Silva,
et al.
Show abstract
Optical fiber Bragg grating sensors (FBGs) were used to measure strain and the temperature field that develop during laser drilling of carbonate rock samples. The shear deformation and high temperature gradient measured are clearly correlated with traces of fractures observed. Beyond the volume directly evaporated by laser exposure, a greater volume around the drilling area was fractured. From the perforation process point of view, it results in an increase of efficiency.
200 MW hydroelectric generator stator surface temperature monitoring using a DTS system
Show abstract
A distributed temperature sensing (DTS) system is used to monitor the surface temperature of a high power hydroelectric generator. Two sensing fibers were installed; one is bare fiber whilst the other is jacketed with a Teflon® protection, in two distinct configurations: first, they were fixed parallel to the stator bars; secondly, they were wrapped around the stator surface. The fibers were embedded on the stator surface by using an electrically insulating resin which does not interfere with the generator operation. This technique can be used as a predictive maintenance tool.
Thermal and vibration dynamic analysis of an induction motor using optical fiber Bragg gratings
Kleiton de Morais Sousa,
Uilian José Dreyer,
Cicero Martelli,
et al.
Show abstract
In this paper it is presented the results of temperature and vibration measurements in a Three-phase Induction Motor (TIM) running at no-load condition. Vibration and temperature analysis are the most successful techniques used for condition monitoring of induction motors. The vibration is measured using two FBGs installed inside of the motor between two subsequent stator teeth. The motor spectrum of vibration when power is at 60 Hz presents the frequencies 60 Hz, 120 Hz, 180 Hz, and 240 Hz as theoretically expected. For the temperature measurement two FBGs are encapsulated in an alumina tube fixed along the stator. The results show 0.9°C difference between the two FBG caused by the motor ventilation nearer of one FBG. These measurements can be used to determine TIM parameters and still be predictive maintenance tool.
A Bragg grating tunable filter based on temperature control system to demodulate a voltage sensor
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This work presents an innovative automated Fiber Bragg Grating (FBG) based tunable optical filter (TOF) controlled by temperature to be used in temperature compensating schemes in FBG sensing set-ups. Mechanical and electronic aspects are discussed, and the implemented FBG-TOF viability and reliability in sensing systems are showed. The system was employed to demodulate a high voltage AC signal applied to a FBG-PZT sensor, showing good linearity and sensitivity.
An efficient and fast detection algorithm for multimode FBG sensing
D. Ganziy,
O. Jespersen,
B. Rose,
et al.
Show abstract
We propose a novel dynamic gate algorithm (DGA) for fast and accurate peak detection. The algorithm uses threshold determined detection window and Center of gravity algorithm with bias compensation. We analyze the wavelength fit resolution of the DGA for different values of signal to noise ratio and different typical peak shapes. Our simulations and experiments demonstrate that the DGA method is fast and robust with higher stability and accuracy compared to conventional algorithms. This makes it very attractive for future implementation in sensing systems especially based on multimode fiber Bragg gratings.
Raman distributed temperature measurement at CERN high energy accelerator mixed field radiation test facility (CHARM)
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In this paper we present a validation of distributed Raman temperature sensing (RDTS) at the CERN high energy accelerator mixed field radiation test facility (CHARM), newly developed in order to qualify electronics for the challenging radiation environment of accelerators and connected high energy physics experiments. By investigating the effect of wavelength dependent radiation induced absorption (RIA) on the Raman Stokes and anti-Stokes light components in radiation tolerant Ge-doped multi-mode (MM) graded-index optical fibers, we demonstrate that Raman DTS used in loop configuration is robust to harsh environments in which the fiber is exposed to a mixed radiation field. The temperature profiles measured on commercial Ge-doped optical fibers is fully reliable and therefore, can be used to correct the RIA temperature dependence in distributed radiation sensing systems based on P-doped optical fibers.
Bridge SHM system based on fiber optical sensing technology
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The latest progress of our lab in recent 10 years on the area of bridge structural health monitoring (SHM) based on optical fiber sensing technology is introduced. Firstly, in the part of sensing technology, optical fiber force test-ring, optical fiber vibration sensor, optical fiber smart cable, optical fiber prestressing loss monitoring method and optical fiber continuous curve mode inspection system are developed, which not only rich the sensor types, but also provides new monitoring means that are needed for the bridge health monitoring system. Secondly, in the optical fiber sensing network and computer system platform, the monitoring system architecture model is designed to effectively meet the integration scale and effect requirement of engineering application, especially the bridge expert system proposed integration of sensing information and informatization manual inspection to realize the mode of multi index intelligence and practical monitoring, diagnosis and evaluation. Finally, the Jingyue bridge monitoring system as the representative, the research on the technology of engineering applications are given.
Thermo-optic coefficient dependent temperature sensitivity of FBG-in-SMS based sensor
Show abstract
Fiber Bragg grating in single-multi-single mode fiber structure (FBG-in-SMS) is proposed to be used as a sensor. It could realize temperature and strain measurement simultaneously because of the different responses of the different parts of the FBG-in-SMS transmission spectrum. The temperature response is decided by the thermo-optic coefficient of the multimode fiber mainly, which is focused on especially in order to optimize its performance.
Fiber Bragg grating strain sensor for hard rocks
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Strain is an important property to be measured in rock structures such as tunnels, slopes, dams, and mining. However, commercial surface mountable fiber Bragg grating (FBG) strain sensors are packaged in planar configuration, which is not appropriate for the irregular surface of the rocks since an unacceptable bonding layer fails to transfer the strain from the rock to the FBG. As a first approach to this problem, in this work we analyze packaged FBG sensors for cylindrical samples of hard rocks. A calibration process was carried out to evaluate the performance of the packaging and bonding layer as compared to electrical resistance strain gage methods. We show the importance of both packaging and bonding layer in FBG sensor technology for measuring strain in hard rocks.
Fiber laser sensor system based on a random mirror and a compound ring resonator for displacement measurements
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In this work, we present a random laser sensor system for increasing simultaneously the sensitivity and interrogation stability of a fiber-optic displacement sensor. The system is based on a random distributed fiber laser modulated by a double-coupler ring resonator within which is placed the sensor. This allows to increase the sensitivity of the sensor and also its interrogation stability. The experimental results show a dynamic range increment (and consequently its sensitivity) of 10dB. Moreover, by using this laser-based interrogation system, the instability is reduced to 0.04 dB. In addition, wavelength filtering elements are not required, simplifying the system.
Poster Session II
Cantilevers orthodontics forces measured by fiber sensors
Neblyssa Schneider,
Maura Scandelari Milczewski,
Valmir de Oliveira,
et al.
Show abstract
Fibers Bragg Gratings were used to evaluate the transmission of the forces generates by
orthodontic mechanic based one and two cantilevers used to move molars to the upright position. The
results showed levels forces of approximately 0,14N near to the root of the molar with one and two
cantilevers.
A label free aptamer-based LPG sensor for detection of mercury in aquatic solutions
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We demonstrate a label free fiber optic sensor for detection of mercury ions in aquatic solutions. This sensor utilizes aptamers as bio-recognition element which traps mercury ions and cause a refractive index change in the vicinity of the sensor. Refractive index variations lead to a change in the transmission spectrum that can be used to calculate the concentration of mercury ions in that solution. The concentration of 1 nM mercury ions was detected which is below the specific amount determined by the US environmental protection agency as the maximum authorized contaminant level of Hg2+ ions in drinking water.
Concentration measurements in silica and quartz nanofluids by optical fiber sensor
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The measurement of concentration in colloidal silica nanoparticles and quartz nanocrystals dispersions by using an optical fiber reflectometer is reported. The reflected light intensities assessed by the fiber sensor were applied on the computation of autocorrelation functions, and the decay rates were associated to the colloids concentrations. The sensor provided reliable results, with sensitivities of 0.45 wt% ms and 0.23 wt% ms on the analysis of quartz and silica dispersions, respectively, for concentrations <1wt%. The differences on decay rate profiles are probably due to the differences on particles morphology and average dimension, as observed in the scanning electron microscopy images.
Real time monitoring of Pb2+-induced formation of G-quadruplex DNA with LPFG sensor
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In this paper the potential of real time monitoring of AS1411 Guanine-quadruplex folding by using long period fiber grating (LPFG) biosensor was described. AS1411 ss-DNA folds into parallel bimolecular quadruplex in solution containing metal ions. While immobilized AS1411 folds, molecular crowding of sensing area will increase and cause change the refractive index (RI) around the sensor. In addition RI change is absolutely dependent on G-quadruplex factor concentration.
High temperature assessment of an Er3+/Yb3+ co-doped phosphosilicate optical fibre for lasers, amplifiers and sensors
Show abstract
The excited state lifetime of Er3+ and gain coefficient of an Er3+/Yb3+ co-doped phosphosilicate optical fibre with and without hydrogen loading can be recovered and even improved by high temperature annealing. Consequently processes optimizing room temperature component fabrication such as hypersensitisation are found to offer no added value for high temperature operation. The implications for harsh environmental laser performance are discussed.
Real-time multi-monitoring interrogation based on Fourier domain mode-locked fiber laser for measurement of radiation dose and multipoint strain
Show abstract
We propose a real-time multi-monitoring interrogation technique based on Fourier domain mode-locked fiber laser for simultaneous measurement of radiation dose and multi-point strain. Radiation dose and multipoint strain can be monitored in real-time by measuring the variation of output power and detection time interval of the sensing signals. Since the operating wavelength of the FDML is continuously controlled as a function of time, it is possible to simultaneously measure the variation of radiation dose and multipoint strain in real time.
Stability aspects of a fiber optic sensor for CO2 phase monitoring
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In this paper we discuss the stability and effectiveness of an optical fiber sensor for CO2 phase monitoring that could be used inside pipelines, rock caverns and steel tanks for Carbon Capture and Storage (CCS) systems; in Enhanced Oil Recovery (EOR) processes; and in mapping of natural reservoirs. The sensor is an optical fiber refractometer and is shown to be capable of identifying phase changes and when two-phase systems co-exist, even near the phase transition line. When properly calibrated, the sensor can be used to obtain the refractive index and density (calculated with the Lorentz-Lorentz formula) of CO2.
Reflective refractometer based on strong optical coupling between a tilted fiber Bragg grating and a parallel D-shaped fiber
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A novel fiber-to-fiber tip-reflection sensing configuration for power-referenced refractometry with the capability to measure surrounding refractive index (SRI) as low as 1.33 is proposed and demonstrated. A short D-shaped fiber stub is parallel adjacent to another unshaped fiber containing a weakly tilted Bragg grating (TFBG). Light from the unshaped fiber can be effectively coupled into the adjacent D-shaped fiber through the TFBG which functions as a "bridge" between the core and cladding. Strong "comb" like cladding modes over a broad wavelength range have been recaptured in D-shaped fiber in reflection. These re-coupled cladding modes show different amounts of power as the SRI changes and the sensitivity is much higher than reported in-fiber sensing schemes, especially for low SRI measurement.
An optical fibre sensor for combined point pressure measurement and spatially resolved temperature measurement
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In this paper, two optical fibre sensors are presented: 1) based on extrinsic Fabry-Perot Interferometer (EFPI) with Fibre Bragg Grating array and 2) and EFPI sensor with a chirped Fibre Bragg grating (CFBG). The CFBG with EFPI sensor fabrication technique is described and temperature response of both sensors is presented. Such sensors have many potential applications including applications in the aerospace industry and medical industry (e.g. radio frequency thermal ablation of tumors).
Detection of the volatile organic compounds emitted from paints using optical fibre long period grating modified with the mesoporous nano-scale coating
Show abstract
An optical fibre long period grating (LPG) modified with a mesoporous film infused with a calixarene as a functional compound was employed for the detection of a mixture of volatile organic compounds (VOCs). The sensing mechanism is based on the transduction of the refractive index change induced by the complexion of the VOCs with calixarene into a change in the form of the transmission spectrum of the LPG. An LPG, modified with a calixarene-infused coating comprising 5 cycles of silica nanoparticles/poly(allylamine hydrochloride) polycation (SiO2/PAH), was exposed to mixture of VOCs emitted from paint at conditions simulating ISO standards test (16000-10).
Temperature and strain insensitive long period gratings (LPGs) in W fibre with post-annealing
Show abstract
LPGs with ultra-low strain and temperature sensitivities are reported in germanosilicate fibre with a W-shaped index profile. Through low temperature annealing, the temperature and strain coefficients are dramatically reduced to dλ/dT ~ - (8.75×10-2) pm/K and dλ/d epsilon ~ (2.21×10-2) pm/μepsilon respectively. As a control reference, LPGs in standard SMF-28 fibre were inscribed but were not found to exhibit similar reductions in sensitivity; this illustrates that the design of the W-shaped, with its inner cladding, plays a key role in altering the LPG performance.
Application of a fluorescence intensity ratio technique for the intrinsic determination of pH using an optical fiber sensor
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An intensity ratio technique has been used for characterizing fluorescence spectra from novel coumarin dyes for pH sensing, in the range of 0.5 – 6, providing results that are independent of possible fluctuations in the intensity of the excitation source, deterioration of the indicator and changes in optical coupling. The arrangement was determined to have a sensitivity of 25% per unit pH change (at a pH of 4).
Detection of volatile organic compounds using optical fibre long period grating modified with metal organic framework thin films
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An optical fibre long period grating (LPG) modified with a thin film of ZIF-8, a zeolitic immidazol framework (ZIF) material, a subgroup of the metal organic framework (MOF) family, was employed for the detection of organic vapours. ZIF-8 film was deposited onto the surface of the LPG using an in-situ crystallization technique. The sensing mechanism is based on the measurement of the refractive index (RI) change induced by the penetration of the chemical molecules into the ZIF-8 pores. An LPG modified with 5 growth cycles of ZIF-8 responded to exposure to methanol and ethanol vapours.
Chitosan-hydrogel-based fiber optic sensor for heavy metal ion detection
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A no-core fiber (NCF) based intermodal sensor for nickel ion (Ni2+) detection is proposed. Bilayers of chitosan and Poly Acrylic acid (PAA) functionalized on the sensor surface serve as adsorption sites for nickel ions thereby causing change in refractive index (RI) along the cladding bilayer boundary. Nickel adsorption at different concentrations was monitored continuously through measurement of wavelength shifts. As observed, the proposed sensor exhibits Ni2+ detection sensitivity of 0.0237 nm/μM.
Fiber optic gas sensor for on-line CO2 monitoring
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An optical fiber CO2 gas sensor is reported in this work. Sensor is based on the change of absorption of a selected dye dissolved in an organically modified silica coating of an optical fiber. CO2 in the atmosphere decreases the pH of the deposited active layer, which eventually leads to the change of the fiber transmittance. Elaborated sensor exhibits high sensitivity, short response time and good stability, which makes it suitable for potential industrial, agricultural and household use. Described method can also be used for sensing other gases in sensor matrices.
Novel multi-point disturbance detection method for polarization-sensitive optical time domain reflectometry
Show abstract
Multi-point disturbance detection is always challenging in polarization-sensitive optical time domain reflectometry (POTDR). In this paper, we propose a novel method to solve such a challenging problem by accumulating the temporally differentiated OTDR traces and building up a two-dimensional temporally-spatially evolving graph, and then using edge detection and automatic-clustering, adopted from imaging processing techniques, to discriminate different disturbance points and find out their locations. Many multi-point disturbance cases are tested and the results show that the method proposed has better performance than the conventional direct differentiation method and the Fast Fourier Transform (FFT) spectrum analysis. In particular, the location accuracy has been improved significantly.
Temperature calibration of optical fiber attenuation differences induced measurement error of Raman distributed temperature sensor
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The effect of optical fiber attenuation differences (AD) induced temperature error of Raman distributed temperature sensor (RDTS) is analyzed using the temperature demodulation algorithm. First of all, a novel method to address the effects caused by the AD between Stokes and anti-Stokes light is proposed. Furthermore, the temperature measurement error caused by additional AD of fiber temperature is also reduced by using a formula obtained by experimental data. The experimental results demonstrate that the RDTS system can measure different temperature zones more accurately.
Interrogation of a cascaded FBG sensor using a wavelength-to-delay mapping technique
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An optical fiber sensor composed of six standard FBGs in cascade is interrogated by use of a technique based on wavelength to delay mapping. A microwave-modulated optical signal enters the FBG cascade and, after being sliced and reflected, experiences dispersion in standard single-mode fiber. The Bragg wavelengths of the FBGs are mapped into the delays that determine the peaks in the system’s electrical impulse response. The Bragg wavelength shifts are calculated from the difference of the delays undergone by FBGs samples. A resolution of 9.2 pm in Bragg wavelength shift is demonstrated.
Dynamic distributed Brillouin optical fiber sensing based on multi-slope analysis
Show abstract
We propose and demonstrate a dynamic Brillouin optical fiber sensing based on the multi-slope analysis, which features a large measurement range of strain and the capability of real-time data processing. The multi-slope analysis is realized by using the frequency-agility modulation and it can significantly increase the measurement range compared with the single-slope analysis, while maintaining the advantage of fast data processing time and suitable for real-time monitoring. In experiment, we performed a measurement of strain up to 5000 με with the frequency of 13 Hz by using a six-slope analysis.
Brilloun optical time domain analysis sensor assisted by a Brillouin distributed amplifier
Javier Urricelqui,
Mikel Sagues,
Alayn Loayssa
Show abstract
We demonstrate the extension of the measurement range of Brillouin optical time-domain analysis (BOTDA) sensors using a distributed Brillouin amplifier (DBA). The technique is based on injecting a DBA pump wave in the fiber to generate an additional Brillouin interaction that amplifies the BOTDA pump pulses. Furthermore, the differential pulse-width pair method is used to counteract the detrimental effects of the DBA amplification on the temporal shape of the pulses. Experimental proof-of-concept results in a 50-km fiber link demonstrate full compensation of the fiber’s attenuation with no penalty on the signal-to-noise ratio of the detected probe wave.
Steady state gamma ray radiation effects on Brillouin fiber sensors
Show abstract
Brillouin optical time-domain analysis (BOTDA) sensors offer remarkable advantages for the surveillance of the planned French deep geological radioactive wastes repository, called Cigéo1,2. In this work we study the performances of Brillouin distributed sensors in harsh environment. We evaluate the radiation tolerance of different sensor classes and their responses evolution during γ-ray exposition with 1kGy/h dose rate (to reach ~0.2MGy) and after 1, 3, 6 and 10 MGy accumulated doses. Measurements on strained Ge-doped SMF are reported to highlight the variation on Brillouin scattering proprieties, both intrinsic frequency position of Brillouin shift and its dependence on temperature and strain.
Deformation of Brillouin gain spectrum shape caused by strain varying linearly with respect to time
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The shape of the Brillouin gain spectrum (BGS) that is produced in an optical fiber undergoing strain varying linearly with respect to time, which is a typical example of temporally non-uniform strain, is theoretically derived through an analysis similar to that by which the BGS under spatially non-uniform strain would be derived. The BGS shape that is theoretically derived agrees well with the shape experimentally observed. The characteristics of the BGS deformation and strain measurement error under the temporally linear strain are discussed based on their similarity to the BGS shape derived under spatially linear strain.
Fast inscription of Bragg grating arrays in undoped PMMA mPOF
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In this work, the inscription in few seconds of a Bragg grating array in undoped PMMA mPOF using the phase mask technique is reported. The fast growth was possible through the use of a 248 nm UV laser, with suited laser parameters, allowing the creation of a core refractive index modulation without damaging the fiber surface. The Bragg gratings were written in the IR region presenting good spectral properties, achieving for the best case 30 dB reflectivity and 0.2 nm bandwidth. The Bragg grating array was characterized to strain and results are in agreement with the values reported in literature.
Bend-insensitive distributed sensing in singlemode-multimode-singlemode optical fiber structure by using Brillouin optical time-domain analysis
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We propose a bend-insensitive distributed Brillouin optical fiber sensing by using a singlemode-multimode-singlemode optical fiber structure for the first time to the best of our knowledge. The sensing fiber is a graded-index multimode fiber (GI-MMF) sandwiched by two standard single-mode fibers (SMFs) with centrally alignment splicing at the interface between GI-MMF and SMF to excite the fundamental mode only in GI-MMF. The sensing system can resist a minimal bend radius of 1.25mm while maintaining the measurement performance, with which the measured coefficient of strain is 421.6MHz/%. We also demonstrate that the higher-order modes exciting in GI-MMF can be easily influenced by bending, so that the fundamental mode exciting is essential for bend-insensitive distributed sensing.
Enhanced tolerance to pulse extinction ratio in Brillouin optical time domain analysis sensors by dithering of the optical source
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We demonstrate the relaxation of the stringent requirements placed on the pulse extinction ratio in long-range Brillouin optical time-domain analysis sensors (BOTDA) by modulating the wavelength of the laser source that is used to generate both pump and probe waves. This modulation makes the counter-propagating pulse pedestal and probe waves to become correlated only at certain locations in the fiber, thus reducing the gain experienced by the probe wave, which is precisely the process that limits the performance in long-range BOTDAs. Proof-of-concept experimental results in a 20-km sensing link demonstrate a 6-dB reduction of the required modulator extinction ratio.
Some refractometric features of dual-core chirped microstructured optical fibers
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Refractometric features of dual-core transversally chirped microstructured optical fibers (MOF) are evaluated. It is shown from numerical results that the chirped MOF could act as a structure with decoupled cores, forming a Mach– Zehnder interferometer in which the analyte directly modulates the device transmittance by its differential influence on the effective refractive index of each core mode. We investigate the influence of the MOF parameters and the analyte refractive index on sensor performance. This novel structure is suitable for measuring refractive indices in the 1.33–1.44 range.
Low voltage integrated optics electro-optical modulator applied to optical voltage transformer based on WLI technique
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The use of two electro-optical modulators linked in series, one for sensing and one for recovering signals, was formerly presented by some of the authors as a solution for interrogation of optical fiber sensor systems based on WLI method. A key feature required from such systems is that half-wave voltage (Vπ) of recovering modulator must be as small as possible. Aiming at meeting this requirement, in this paper it is presented the use of an unbalanced Michelson Interferometer implemented using an integrated optics component as recover interferometer in an optical voltage transformer intended for high voltage measurements.
Measurement for polarization mode dispersion of LiNbO3 integrated waveguide modulator used white light interferometry
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We present a method to measure the polarization mode dispersion (PMD) of the LiNbO3 multifunctional integrated waveguide modulator (MFIWM) which is consist of a Y-waveguide, two extended polarization maintaining (PM) fibers, lead-in PM pigtail and lead-out PM pigtail. This method is based on an all-fiber time-domain scanning white light interferometer and utilizes fast Fourier transform (FFT) technology to obtain interferometric phase. The PMD of each part of MFIWM was measured and distinguished accurately. It’s demonstrated that, the PMD of Y-waveguide is 13.5 ps/nm/km@1555nm which is approximately 40~160 times of the PMD of PM fibers in the MFIWM under test.
Ultrahigh sensitive twist sensor employing Sagnac interferometer based on PM-elliptical core fibers
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An ultrasensitive optical fiber twist sensor is proposed by employing a Sagnac interferometer based on polarization-maintaining elliptical core fibers (PM-ECFs). The twist effects are theoretically analyzed and experimentally demonstrated. Based on the photoelastic effect, the wavelength shift in response to twist rate turns out linear tendency and is torsion-direction-dependent. The maximum torsion sensitivity reaches 18.59593nm/(rad/m) (or 0.67582nm/°) for clockwise (CW) torsion direction and 15.83073nm/(rad/m) for anticlockwise (ACW) torsion direction, respectively. Furthermore, it is further improved up to 1.675 nm/° by rotating two ends of PM-ECF simultaneously. The prominent advantage of ultrasensitivity keep it meritorious in the applications of spaceflight and constructional engineering.
Integrated liquid-filled directional coupler for temperature sensing
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A silicon nitride directional coupler filled with toluene is proposed as temperature sensor. This liquid material has a high thermo-optic coefficient, which allows large variations on its refractive index in function of temperature variations. Simulations were performed to obtain the sensor's sensitivities, which measured on the output ports (P2, P3) of the structure are 0:11392= °C and 0:11499= °C, respectively.
Negative curvature fibres: exploiting the potential for novel optical sensors
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One of the main challenges for fibre optic based sensing is robust operation in the mid-infrared (mid-IR) region. This is of major interest because this wavelength region is where the characteristic absorption spectra for a wide range of molecules lie. However, due to the high absorption of silica (above 2 μm), mid-IR sensors based on solid core silica fibres are not practical. Of the many alternatives to solid silica fibres, hollow core microstrutured optical fibres are being explored and show great promise. One relatively new fibre, the hollow core negative curvature fibre (NCF) is promising for novel optical devices due to the simple structure (in comparison to other microstructured fibres) in combination with a hollow core which enables low loss mid-IR infrared guidance in a silica based fibre. In this paper, an all silica NCF that is post-processed with a fs laser, in order to increase access to the hollow core, is presented with acceptable loss and significant potential for mid-IR gas sensing.
Enhancing sensitivity of long-period gratings by combined fiber etching and diamond-like carbon nano-overlay deposition
Show abstract
This work presents an application of reactive ion etching (RIE) followed by diamond-like carbon (DLC) nano-overlay deposition using radio frequency plasma enhanced chemical vapor deposition (RF PECVD) method for effective tuning of the refractive-index (RI) sensitivity of long-period gratings (LPGs). Both etching and deposition take place within one process. Combination of both plasma-based processes allows for well controlled tuning of the LPG sensorial response up to its operation at both dispersion turning point (DTP) of higher order cladding modes and mode transition regime. As a result of processing, RI sensitivity can be enhanced up to over 12,000 nm/RIU per single resonance in narrow RI range (1.3344-1.3355) and over 2000 nm/RIU in broader RI range (1.34-1.356).
A novel three-core fiber optic spanner
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We present a numerical modeling of a novel three-core fiber optic spanner. The spanner is realized by properly shaping the three-core fiber facet into a truncated triangular pyramid whose slope surfaces are not symmetric to the fiber cores. Three dimensional trapping forces and rotating torques are calculated and optimized as function of different parameters of the structure in ray optics regime. Simulation results show specific rotors can be trapped and rotated efficiently and stably by the spanner.
Laser structured fibre Bragg gratings as enhanced force sensors
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The production and characterisation of a micro-structured FBG force sensor is described. Employing femtosecond laser micro machinery a circumferential ditch of about 30 μm depth and 40 μm width is engraved in the clad of an optical fibre at the centre of a 3 mm long type I fibre Bragg grating (FBG). The purpose of the structure is the enhancement of the force sensitivity characteristics for the measurement of sub-mN forces. Phase-shift spectra occur when axial stress is applied to the fibre. Exploiting this phenomenon experimental tests show a 10% improvement in the sensitivity performance when compared to an unstructured FBG.
Combined regenerated fibre Bragg gratings and Fabry-Perot etalons for dual strain and temperature sensing
Show abstract
A highly integrated fibre-optic sensor with regenerated fibre Bragg grating (RFBG) and a micro Fabry-Pérot (MFP) is proposed and demonstrated for simultaneous measurement of temperature and strain under high temperature (> 600 °C). The MFP is fabricated by using a 157 nm fluorine gas (F2) laser to micromachine the core of a standard optical fibre. The RFBG is fabricated by regenerating a seed grating written over the Fabry-Pérot. Since the MFP and RFBG have different sensitivity coefficients, their combination can be used to realise simultaneous measurement of temperature and strain. It is believed that such a high-temperature strain sensor could find important applications in many areas where simultaneous measurement of temperature and strain under high temperature is required.
Nanoporous nanocrystalline monoclinic zirconia for luminescent oxygen sensors
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In this work we present a nanocrystalline monoclinic ZrO2 with large free volumen open towards the nanocrystals surface dedicated for optical oxygen sensors. Nanoporous zirconia nanopowder was fabricated in hydrothermal microwave-driven process followed by annealing at 800°C. Metal-coated optical fibers are proposed as a light carrier when the working temperature exceeds 500°C. The obtained results may also find application in luminescent fiber optic oxygen sensors.
High-pressure sensor based on fiber in-line Mach-Zehnder interferometer
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A fiber in-line Mach-Zehnder interferometer based on an inner air-cavity is presented for high-pressure measurement.
The inner air-cavity is fabricated by use of femtosecond laser micromachining together with fusion splicing technique.
A micro-channel is created on the top of the inner air-cavity to allow the high pressure gas to flow in. The fiber in-line
device is featured with miniature size, good robustness and excellent operation stability while exhibiting a high pressure
sensitivity of 8,239 pm/MPa.
Scanning-free characterization of temperature dependence of forward stimulated Brillouin scattering resonances
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Forward stimulated Brillouin scattering (FSBS) between two co-propagating optical waves is observed in 220 meterslong sections of standard single-mode fibers. The interaction is mediated by high-order, radial acoustic modes that are supported by the fiber. The acoustic resonance frequency and the gain spectrum of an individual mode are characterized using a single-frequency stimulation procedure, with no need for frequency scanning. The measurement protocol is employed in the characterization of the temperature dependence of the resonance frequency. Good agreement with previous literature is achieved. The temperature sensitivity of the measurements is ±0.65 °C.
Ultra-long and high-stability random laser based on EDF gain-media and Rayleigh scattering distributed mirror
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An ultra-long, low-threshold and high-stability Random distributed feedback fiber laser (RDF-FL) based on Erbium-doped fiber (EDF) to provide the gain medium, and single mode fiber (SMF) as a distributed mirror in combination with fiber-brag grating (FBG) to form the cavity is proposed in this paper. Typical random laser radiation for a SMF length of 50 km with a low-threshold of 10 dBm and high-stability (~0.1 dB) is achieved, thanks to the design of the cavity and the high-gain from the pumped erbium-doped fiber. Besides, 200 km quasi-losses random laser due to the distributed mirror and the FBG reflector is demonstrated.
Modified Brillouin ring laser technology for Brillouin-based sensing
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We present a tunable narrow-linewidth dual pump-probe optical source based on modified Brillouin ring laser technology aimed at Brillouin-based sensing. The developed source exhibits a narrow linewidth and allows for a large tuning range, attaining <2.5 MHz bandwidth, ~200 MHz tuning range and ~0.5 mW power, thus constituting an efficient and cost-effective solution for sensing interrogators.
Photonic liquid crystal fibers tuning by four electrode system produced with 3D printing technology
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Photonic liquid crystal fiber has been intensively investigated in last few years. It has been proved that guiding properties of such fibers could be tuned with an electric field. In particular efficient tuning could be obtained if multi-electrode system allowing for dynamic change of not only intensity of the electric field, but also its direction. In this work we report a simple to build four electrode system, which is based on a precisely aligned four cylindrical microelectrodes. As an electrodes we use enameled copper wire with diameter adequate to the diameter of the fiber to be tuned. To ensure uniform and parallel alignment of the wires a special micro-profiles has been designed and then produced with filament 3D printer. The possibility of the dynamic change of the electric field direction in such scalable and cost effective electrode assembly has been experimentally confirmed.
Magneto-optic properties of Pb/Al codoped silica fiber via atomic layer deposition
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A Pb/Al codoped silica fibers were fabricated using atomic layer deposition (ALD) technique in combination with modified chemical vapor deposition (MCVD). PbO and Al2O3 were induced into fiber core area by ALD. Faraday Effect of Pb/Al codoped silica fiber (PADF) was investigated for current sensor. Its Verdet Constant with 1 mm pitch was larger than 12% that of single mode fiber (SMF). It is very important for fiber-optic gyroscope and fiber-optic current sensors to optimize fabrication and design optical fibers, and to obtain relatively good magneto-optic sensitivity of optical fiber. This can be improved by Pb/Al codoped materials.
A MHz speed wavelength sweeping for ultra-high speed FBG interrogation
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We demonstrated a MHz speed wavelength-swept fiber laser based on the active mode locking (AML) technique and applied to interrogation system of an array of fiber Bragg grating (FBG) sensors. MHz speed wavelength sweeping of wavelength-swept fiber laser can be obtained by programmable frequency modulation of the semiconductor optical amplifier (SOA) without any wavelength tunable filter. Both static and dynamic strain measurement of FBG sensors were successfully characterized with high linearity of an R-square value of 0.9999 at sweeping speed of 50 kHz.
In-situ temperature calibration procedure for temperature and strain fibre Bragg grating sensors for monitoring pre-stressing strands
I. Mckeeman,
G. Fusiek,
M. Perry,
et al.
Show abstract
In this work, we demonstrate active and passive methods for in-situ temperature calibration of fibre Bragg grating strain and temperature sensors. The method is suitable for characterising sensors which are already attached to the steel reinforcements of civil structures. The proposed method, which involves the use of active induction heating or passive room temperature fluctuations, can be implemented using portable equipment, is time efficient, and can be used to calibrate attached sensors on-site, rather than in lab conditions. Preliminary results of the induction heating calibration show good agreement with pre-calibrated temperature sensors. In-situ calibration of fibre strain sensors, attached to a prestressing strand is also successfully carried out.
Enhancement of temperature sensitivity of a Mach-Zehnder interferometer based on a polymer-overlaid microfiber
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A simple technique to effectively enhance the temperature sensitivity of the Mach-Zehnder interferometer (MZI) by using a microfiber with low index polymer coating is theoretically and experimentally investigated. We successfully improve the temperature sensitivity of the polymer-overlaid microfiber MZI to be -6.68 nm/°C around a temperature of 25°C, which is 13 times higher than that of the microfiber MZI without polymer coating. A linear temperature sensitivity of 10.44 pm-1/°C was achieved in the spatial frequency domain after Fourier transform.
Fiber Bragg grating regeneration temperature in standard fibers
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In this work, the regeneration process of FBGs written into both standard and bend-insensitive fiber has been studied. Several dopants present in these fibers lead to different regeneration properties which, based on previous experiments, have been tested, paying special attention to the regeneration temperature. The achieved results suggest a reduction on the regeneration temperature for FBGs written into bend-insensitive fiber that favors mechanical properties of silica.
Oscillatory behaviour in Type IA FBG: ruling out chemical complexity
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Type IA FBG are regenerated gratings that appear in hydrogenated germanosilicate fibre of all types during prolonged UV exposure. The gratings are characterised by a large Bragg wavelength shift and a concomitant increase in the mean fibre core index. Modulated index changes are complex by comparison and significantly weaker, often characterised by oscillatory growth behaviour. Low thermal stability of Type IA gratings suggests a possible chemical role similar to thermally processed optical fibres where autocatalysis has been observed. We show that GeOH and SiOH formation are not out-of-phase and follow each other, with no evidence of autocatalysis, ruling out a chemical origin.
Hydrostatic pressure sensor based on micro-cavities developed by the catastrophic fuse effect
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In this work, an optical fiber hydrostatic pressure sensor based in Fabry-Perot micro-cavities is presented. These micro structures were generated by the recycling of optical fiber previously damaged by the fiber fuse effect, resulting in a cost effective solution when compared with the traditional methods used to produce similar micro-cavities. The developed sensor was tested for pressures ranging from 20.0 to 190.0 cmH2O and a sensitivity of 53.7 ± 2.6 pm/cmH2O for hydrostatic pressures below to 100 cmH2O was achieved.
Vector magnetic measurement based on directional scattering between polarized plasmon wave and arrayed nanoparticles
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A vector magnetic field sensor based on surface plasmon resonance (SPR) of a 15° tilted fiber Bragg grating (TFBG) and magnetic fluid is proposed and experimentally demonstrated. Both the orientation and the amplitude of the magnetic fields can be determined unambiguously via the wavelength and intensity monitoring of the SPR, which is essentially dominated by the arrayed Fe3O4 nanoparticles over the nanometric-film of fiber surface.
Alkanes-filled photonic crystal fibers as sensor transducers
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In this paper we propose alkanes-filled PCFs as the new class of transducers for optical fiber sensors. We investigated experimentally thermo-optic properties of a commercially available LMA8 partially filled with different alkanes with a higher number of carbon atoms. A partially filled PCF spliced with standard SMFs constitutes one of the newest type transducer. We have selected a group of eight alkanes which have melting points in different temperatures. An analysis of temperature spectral characteristics of these samples will allow to design an optical fiber sensor with different temperature thresholds at specific wavelengths.
In-line Sagnac interferometer-type optical voltage sensor for DC voltage measurement
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In-line Sagnac Interferometer-type optical voltage sensor for DC voltage measurement was proposed. The high input resistance of pockel’s cell contributes to the miniaturization of a sensor size and realizes highly precise measurement. The problem of DC voltage measurement was offset drift of signal processor. To solve the problem, in-line Sagnac interferometer which used in DC current sensor has been applied. Input-output characteristics and long term stability within 3 days has been confirmed. These results show that the stabilities of the optical voltage sensor are within ±0.5%.
Birefringence properties of a polarization maintaining Panda fibre during Bragg grating regeneration
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Regeneration of fibre Bragg gratings under application of a high temperature annealing process in a high birefringent polarisation maintaining fibre of type Panda was investigated. During the annealing process, a distinct nonlinearity and hysteresis of the birefringence with temperature was observed. After the temperature process, the birefringence between slow and fast axis at room temperature was nearly doubled, which is in agreement with observations of other researchers. The hysteresis in birefringence might be explained by the crossing of the transition temperature of the stress applying parts and the relief of in-frozen mechanical and thermal stresses.
Diamond-like carbon thin film for tuned high sensitivity etched fiber Bragg grating refractometer
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Deposition of thin diamond-like carbon films in etched fiber Bragg gratings as substrate was used to increase the sensitivity of a fiber Bragg grating refractometer. The nanometric film was also used for tuning the sensitivity to a maximum for a desired application of liquid refractive index measurement. Simulation and experiments were performed in order to understand the light propagation inside the modified optical fiber and its effects in the refractometry measurements.
Electric field sensor based on cholesteric liquid crystal Fabry-Perot etalon
Myeong Ock Ko,
Sung-Jo Kim,
Jong-Hyun Kim,
et al.
Show abstract
We propose an electric field sensor using a cholesteric liquid crystal (CLC) Fabry-Perot etalon and a broadband optical source. The CLC cell consists of glass substrates, polyimide layers, electrodes, and CLC layer. There is a threshold behavior for CLC cell and no change in the transmitted wavelength occurs until a threshold value. The threshold value is 0.8 V/μm for fabricated CLC cell in this experiment. The transmitted or reflected wavelength from the CLC Fabry-Perot etalon depends on the applied electric field. The valley wavelengths of the transmitted light from the CLC device are linearly increased from 1303 nm to 1317 nm as the applied electric field to the CLC device is increased from 0.8 V/μm to 1.9 V/μm.
Erbium doped optical fiber lasers for magnetic field sensing
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In this work two erbium doped optical fiber laser configurations for magnetic field measurement are implemented and compared. The first laser is set-up in a loop configuration and requires only a single FBG (Fiber Bragg Grating), acting as mirror. A second laser employs a simpler linear cavity configuration but requires two FBGs with spectral overlap to form the laser cavity. A bulk magnetostrictive material made of Terfenol-D is attached to the laser FBGs enabling modulation of its operation wavelength by the magnetic field. Moreover, a passive interferometer was developed to demodulate the AC magnetic field information where the corresponding demodulation algorithms were software based. Both configurations are tested and compared with the results showing different sensitivities and resolutions. Better performance was accomplished with the double FBGs linear cavity configuration with a resolution of 0.05 mTRMS in the range of 8 to 16 mTRMS. For the same range the loop configuration attained a resolution of 0.48 mTRMS.
A mechanical method to tuning a FBG-PZT voltage sensor
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When using a Fiber Bragg Grating (FBG) for strain measurements it is always necessary to compensate the FBG against temperature fluctuations. In this paper it is shown an innovative method for mechanically compensating an FBG in a high voltage measurement application using an FBG-PZT sensor. The system takes advantage of a mechanical assembly that, as the PZT displaces, the screw where the FBG is bonded on displace in the opposite direction, keeping the FBG length constant. A theoretical analysis is done and experimental results are shown.
Fiber optic liquid level monitoring system using microstructured polymer fiber Bragg grating array sensors: performance analysis
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A highly sensitive liquid level monitoring system based on microstructured polymer optical fiber Bragg grating (mPOFBG) array sensors is reported for the first time. The configuration is based on five mPOFBGs inscribed in the same fiber in the 850 nm spectral region, showing the potential to interrogate liquid level by measuring the strain induced in each mPOFBG embedded in a silicone rubber (SR) diaphragm, which deforms due to hydrostatic pressure variations. The sensor exhibits a highly linear response over the sensing range, a good repeatability, and a high resolution. The sensitivity of the sensor is found to be 98 pm/cm of water, enhanced by more than a factor of 9 when compared to an equivalent sensor based on a silica fiber around 1550 nm. The temperature sensitivity is studied and a multi-sensor arrangement proposed, which has the potential to provide level readings independent of temperature and the liquid density.
Optical fibre sensors based on multi-mode fibres and MIMO signal processing: an experimental approach
Andreas Ahrens,
Andre Sandmann,
Kort Bremer,
et al.
Show abstract
In this paper multiple-input multiple-output (MIMO) signal processing is investigated for fibre optic sensor applications. A (2 × 2) MIMO implementation is realized by using lower-order and higher-order mode groups of a graded-index (GI) multi-mode fibre (MMF) as separate transmission channels. A micro-bending pressure sensor changes these separate transmission characteristics and introduces additional crosstalk. By observing the weight-factors of the MIMO system the amount of load applied was determined. Experiments verified a good correlation between the change of the MIMO weight coefficients and the load applied to the sensor and thus verified that MIMO signal processing can beneficially be used for fibre optic sensor applications.
Customizing CO2 laser inscription of LPG sensors to enhance the sensitivity to refractive index
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The manufacturing process of long period fiber gratings (LPG) is investigated in order to enhance the sensitivity of the sensors to the surrounding refractive index, considering a specific mode and wavelength range. The LPG is inscribed in a standard single-mode fiber with a CO2 laser beam. It is found that the environment refractive index sensitivity is increased mainly due to the duty cycle of the grating. Results show an increase of 89% on the resonant wavelength shift for samples with refractive index varying from 1 to 1.42.
An improved PGC demodulation method to extend dynamic range and compensate low-frequency drift of modulation depth
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In this paper, we propose an improved method of phase generated carrier (PGC) combined with 3×3 coupler to extend dynamic range and compensate low-frequency drift of modulation depth. The small amplitude signal(≤10-2 rad) is figured out by the PGC method to keep the minimum phase resolution and the large amplitude signal(≥10rad) can be calculated by the 3×3 fixed phase difference algorithm to extend the maximum amplitude of the dynamic range. We can get the same result to the signal with the normal amplitude(10-2 rad≤D≤10rad) by any two kinds of methods. Furthermore, the modulation carrier wave amplitude and frequency information can be monitored by the 3×3 auxiliary algorithm to compensate low-frequency drift of modulation depth and keep the system stability as a feedback. According to the result, the interferometer is able to resolve 2.0 ×10-5 rad/√Hz with a dynamic range of 182.2dB@10Hz frequency and 2Mbps sample rates.
BOTDA-based DTS robustness demonstration for subsea structure monitoring applications
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We demonstrate that BOTDA is the equipment of choice for Distributed Temperature Sensing (DTS) when challenging components such as Wet Mate Connectors (WMC) and Fiber Optic Rotary Joints (FORJ) are inserted in the sensing line. The parameter of Temperature Measurement Dead Zone (TMDZ) is introduced to support the discussion and quantify possible impairments. A laboratory qualification test with real FORJ and WMC is conducted confirming the theoretical expectations. The system is then implemented offshore demonstrating that FORJ and WMC do not affect the sensing operation in field environment.
Femtosecond laser inscribed Bragg gratings in gold-coated fiber for space application
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We reported a Bragg grating inscribed in gold-coated fiber (FBG) by NIR femtosecond laser (fs) for space application. Gold coating can shield the FBG from ultraviolet radiation and oxygen atom erosion. Cryogenic test, high temperature test, and gamma irradiation test were carried out. The reflectivity of the H2-free FBG remained stable at ± 120 °C for 100 h or with 50.4 krad γ irradiation, and the central wavelength shifted within 5 pm and 1.6 pm respectively. Regeneration of the fs-FBG was observed in case the FBG was annealed at 800 °C for 5 h, and the remained 5% in reflectivity after 19 h. Such fs-FBGs inscribed in gold-coated fiber could be employed as high performance fiber sensors for space application.
Long-term monitoring of local stress changes in 67km installed OPGW cable using BOTDA
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The initial results from continuing long-term monitoring of a 67 km of an aerial fiber optic cable installed on a 500 kV power line cable (total fiber length of 134km) using BOTDA are presented. The effects of thunderstorms and rime ice on the cable were identified by monitoring strain on OPGW fibers. Variations of strain between day and night on the OPGW cable were observed and can potentially be exploited.
Characterization of a polyimide-coated humidity sensor in a hybrid fibre grating configuration
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A Relative Humidity (RH) sensor incorporating a Long Period Grating (LPG) and a Fibre Bragg Grating (FBG) in a series configuration was developed and evaluated. The LPG was coated with polyimide allowing it to respond to humidity changes while the FBG is used for temperature compensation. The hybrid sensor was then tested over the change in RH from 20-95 % and temperature of 20-80 °C. The sensitivity of the hybrid sensor to temperature and RH were determined to be 9 pm/°C and 0.23 nm/%RH, with negligible hysteresis (<1% RH), showing the value of the dual LPG/FBG approach to optimize sensitivity.
Fiber Bragg grating inscriptions in multimode fiber using 800 nm femtosecond laser
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A short fiber Bragg grating (FBG) was successfully written in a multimode fiber (MMF) tube with core and cladding diameters of 105 μm and 125 μm using 800 nm femtosecond laser. A side-illumination technique was utilized to ensure the grating inscriptions regain over the core of MMF. Both fundamental mode and high-order modes of MMF are coupled at the core-mismatch junction and appear as two well-defined resonances in transmission. Femtosecond laserwritten three FBG-types present good thermostability up to 900 °C.
Numerical analysis of stress distribution in embedded highly birefringent PANDA fibers
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The paper presents numerical analysis compared with experimental data of influence of polymerization shrinkage on highly birefringent (HB) PANDA optical fibers embedded in a composite material. Since polymerization is a chemical process consisting in combining single molecules in a macromolecular compound [1], principal directions of the polymerization shrinkage depend on a number of the composite layers associated with this process. In this paper a detailed analysis of the piezo-optic effects occurring in HB optical fibers before and after the lamination process answers the question to what extent a degree of the material degradation can be properly estimated.
Identification of cavitation signatures using both optical and PZT acoustic sensors
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This paper presents the results obtained from monitoring a simulated material cavitation process using both a fibre Bragg grating (FBG)-based acoustic sensor system developed at City University London and a commercial PZT (Piezoelectric Transducer) acoustic sensor, with an aim to identify the cavitation signatures. In the experiment, a sample metal plate with its back surface being instrumented with both sensors is positioned very close to an excitation sonotrode with a standard frequency of 19.5kHz. The data obtained from both sensors are recorded and analyzed, showing a very good agreement.
Metal-packaged fibre Bragg grating strain sensors for surface-mounting onto spalled concrete wind turbine foundations
M. Perry,
G. Fusiek,
I. McKeeman,
et al.
Show abstract
In this work, we demonstrate preliminary results for a hermetically sealed, metal-packaged fibre Bragg grating strain sensor for monitoring existing concrete wind turbine foundations. As the sensor is bolted to the sub-surface of the concrete, it is suitable for mounting onto uneven, wet and degraded surfaces, which may be found in buried foundations. The sensor was able to provide reliable measurements of concrete beam strain during cyclic three- and four- point bend tests. The strain sensitivity of the prototype sensor is currently 10 % of that of commercial, epoxied fibre strain sensors.
Poster Session III
Optical fiber Fabry-Perot interferometer with pH sensitive hydrogel film for hazardous gases sensing
Show abstract
An optical fiber Fabry-Perot interferometer (FPI) coated with polyvinyl alcohol/poly-acrylic acid (PVA/PAA) hydrogel film for toxic gases measurement has been developed. Splicing a short section of hollow core fiber between two single mode fibers forms the FPI. Dip-coated pH-sensitive PVA/PAA hydrogel film on the fiber end performs as a receptor for binding of volatile acids or ammonia, which makes the sensing film swelling or shrinking and results in the dip wavelength shift of the FPI. By demodulating the evolution of reflection spectrum for various concentrations of volatile acids, a sensitivity of 20.8 nm/ppm is achieved with uniform linearity.
Unobtrusive heart rate monitor based on a fiber specklegram sensor and a single-board computer
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This paper proposes a portable and unobtrusive heart rate monitor based on fiber specklegram sensors. The proposed module uses the Raspberry Pi module to perform the image acquisition and the fiber specklegram sensor, which is based on multimode plastic optical fibers. The heart rate is obtained by welch power spectral density estimate and the heart beats are identified by means of a threshold analysis.
Novel gas sensor combined fiber cavity ring-down and frequency-shifted interferometry
Show abstract
A novel gas senor combined fiber cavity ring-down (CRD) with frequency-shifted interferometry (FSI) is proposed and demonstrated. Compared to the conventional fiber CRD techniques, the CRD decay transient was originated from continuous-wave light as a function of the distance transmitted in the cavity, therefore this method needs neither pulsed light nor fast detection. As a proof-of-concept experiment, we employed a micro-optical gas cell as the sensing element and measured different concentrations of acetylene samples. The experimental results show that the FSI-CRD system has a resolution of 0.15798%/dB, and it provides a simple and cost-effective scheme for gas sensing.
Long period grating inscribed in multimode fibre interferometer and its application in refractive index sensing
Show abstract
A long period grating (LPG) is inscribed by a femtosecond laser in the multimode region of a singlemode-multimode-singlemode fibre device to provide a compact refractive index sensor. An average sensitivity of 39 nm/RIU and a resolvable index change of 2.56×10-4 are obtained experimentally with a 44.4 mm long multimode fibre over a measured refractive index range of 1.33-1.35. Because of its compactness, ease of fabrication, linear response, high sensitivity, easy connectivity to other fiberized optical components and low cost, this refractometer could find various applications in chemical and biological sensing.
Phase interrogated plasmonic optical fiber optrode with bimetallic layers
Show abstract
Optical fiber optrodes are attractive sensing devices due to their ability to perform point measurement in remote locations. Mostly, they are oriented to biochemical sensing, quite often relying on fluorescent and spectroscopic techniques, but with the refractometric approach being also considered when the objective is high measurement performance, particularly when focusing on measurand resolution. In this work, we address this subject proposing and theoretically analyzing the characteristics of a fiber optic optrode relying on plasmonic interaction. The optrode structure is a fiber optic tapered tip layout incorporating a lateral bimetallic layer (silver + gold) and operating in reflection.
A fluorescent optical fibre chemosensor for mercury detection
Show abstract
A proof-of-concept mercury probe was developed based on covalent attachment of a chemical coating to optical fibre. The sensing element comprised a dansyl derivative and crown ether moiety, acting as fluorophore and metal ion chelator respectively. An ON-OFF type fluorescence (quench) occurred upon binding of mercury ions, via an intramolecular charge transfer mechanism, in aqueous solution in the 909nM-90.9μM (247 ppb -24.7 ppm) concentration range. A washing protocol was identified for sensor regeneration allowing the probe to be re-used.
Fluorescence excitation on tapered polymer optical fibers through microfiber evanescent field
E. Rodríguez-Schwendtner,
M. C. Navarrete,
Ó. Esteban,
et al.
Show abstract
In this work, we show the feasibility of using the evanescent field of a microfiber to excite the fluorescence of a fluorophore deposited on the surface of a polymer optical fiber. The fluorescence intensity gathered by the polymer optical fiber from the emitted on its surface has been measured for several gaps with the excitation fiber, showing a remarkable influence of the evanescent field at distances as high as 2.5mm. A further development of a device based on wrapping the microfiber around the polymer one has been measured, proving a more efficient fluorescence excitation.
Construction aspects of a plastic optical fiber-based surface plasmon resonance biochip
M. F. S. Santiago,
T. B. Silva,
M. H. Mozzini,
et al.
Show abstract
The design of a plastic optical fiber-based surface plasmon resonance biochip has been developed and their theoretical and experimental aspects are presented here. Multilayer Fresnel equations combined with an available experimental database are used to verify the SPR effect over different metal thin film and substrate materials, considering the sensor immersed in an aqueous solution. Also, the optical substrate preparation with the cladding removing and experimental aspects are presented and discussed. Only angular interrogation mode has been observed and finally an experimental setup has been proposed.
Intensity-modulated refractometer with long period fiber grating cascaded by chirped fiber grating
Show abstract
An intensity-modulated refractometer is proposed and experimentally demonstrated by using a long period fiber grating
(LPG) cascaded with a chirped-fiber Bragg grating (CFBG). The reflection wavelength band of the CFBG was properly
selected to contain the most sensitive spectral part of the LPG. As a result, intensity of the reflected signal was
modulated linearly by refractive index (RI) of surrounding liquid outside the LPG. RI measurement in a range from 1.33
to ~1.45 was realized with enhanced sensitivity up to 48.93 μW/R.I.U.
Ultra-thin silver-coated tilted fiber grating for surface and bulk refractive index measurement
Show abstract
An ultra-thin silver-coated tilted fiber Bragg grating (TFBG) sensor with clear surface plasmon resonance (SPR) together with strong evanescent wave in transmission for "surface" and "bulk" surrounding refractive index (SRI) measurement is proposed and experimentally demonstrated. The thickness of the silver coating over the fiber surface is precisely controlled at 12~16 nm (much thinner than 40~50 nm for traditional SPR excitation). The transmission spectrum of the sensor provides a fine comb of narrowband resonances that overlap with the broader absorption of the surface plasmon and thus provide a unique tool to measure small shifts of the plasmon and identify the "surface" SRI changes with high accuracy. Meanwhile, the ultra-thin nanometric-coating permits part of high-order cladding modes to become leaky modes which have a large sensitivity to variations in the background solution for "bulk" SRI measurement. Experimental results show that above two resonances have an inverse amplitude responses to the SRI changing. Biological solutions (urine of rats with different concentration of Aquaporin) with different RI ranging from 1.3400 to 1.3408 were clearly discriminated in-situ by using the differential amplitude monitoring between “cut-off” cladding resonance and plasmonic resonance, with an amplitude variation sensitivity of ~8100 dB/RIU and a limit of detection of ~10-5 RIU.
Acetone vapor fiber sensor based on side polished fiber coated with cholesteric liquid crystal
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The organic acetone vapor sensing characteristics of side-polished fiber coating with cholesteric liquid crystal film were investigated. The cholesteric liquid crystal used in our experiments is a mixture compound, which contains 30% cholesteryl oleyl carbonate, 60% cholesteryl pelargonat, and 25% cholesteryl chloride. When cholesteric liquid crystal film was coated on the surface of side-polished fiber, an interference transmission spectrum of fiber could be observed. When the fiber is exposing in acetone vapor, a blue shift of the interference spectrum was found. The higher concentration of acetone vapor is, the larger blue shift of spectrum is found. The shift of transmission spectrum is linear to the concentration of acetone vapor. The sensitivity is 1.356nm/vol% when the concentration of acetone vapor ranges from 3vol% to 16vol%. This study demonstrates a new all-fiber low-cost and portable acetone vapor sensor. It can be also used to investigate the helical structure and molecular orientation of cholesteric liquid crystal.
Compound parabolic concentrator optical fiber tip for FRET-based fluorescent sensors
Show abstract
The Compound Parabolic Concentrator (CPC) optical fiber tip shape has been proposed for intensity based fluorescent sensors working on the principle of FRET (Förster Resonance Energy Transfer). A simple numerical Zemax model has been used to optimize the CPC tip geometry for a step-index multimode polymer optical fiber for an excitation and emission wavelength of 550 nm and 650nm, respectively. The model suggests an increase of a factor of 1.6 to 4 in the collected fluorescent power for an ideal CPC tip, as compared to the plane-cut fiber tip for fiber lengths between 5 and 45mm.
Optic fiber hydrogen sensor based on high-low reflectivity Bragg gratings and WO3-Pd-Pt multilayer films
Show abstract
A novel optic fiber hydrogen sensor is proposed in this paper. Two Bragg gratings with different reflectivity were written in single mode fiber with phase mask method by 248 nm excimer laser. The end-face of singe mode fiber was deposited with WO3-Pd-Pt multilayer films as sensing element. The peak intensity of low reflectivity FBG is employed for hydrogen characterization, while that of high reflectivity FBG is used as reference. The experimental results show the hydrogen sensor still has good repeatability when the optic intensity in the fiber is only 1/3 of its initial value. The hydrogen sensor has great potential in measurement of hydrogen concentration.
Arc-induced gratings in the turning points
Show abstract
We demonstrated the inscription of arc-induced long-period fiber gratings (LPFGs) in the B/Ge co-doped fiber and in the SMF28 fiber by using grating periods shorter than 150 μm and 200 μm, respectively. This achievement was a result of the development of a high voltage power supply that allows for a constant and stable electric current ranging from 10.5 mA up to 21 mA. The fabricated LPFGs were characterized as a function of the external refractive index from 1.333 up to 1.420 and a refractive index sensitivity of the order of 1000 nm/RIU was obtained without further optimization.
Simple BOTDA temperature sensor based on distributed Brillouin phase-shift measurements within a Sagnac interferometer
Show abstract
In this work we demonstrate an extremely simple BOTDA scheme capable of delivering distributed Brillouin Phase Shift measurements along an optical fiber. It is based on exploiting the non-reciprocity of the Stimulated Brillouin Scattering effect. This non-reciprocity is easily characterized by means of a suitably tuned Sagnac Interferometer. The technique is advantageous as, in comparison with previous methods, no complex modulation, no sharp filtering and no highbandwidth detection is needed. Theoretical and experimental proofs of the concept are given.
High-sensitive distributed transverse load sensing based on Brillouin dynamic gratings
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We report on a high-sensitive distributed transverse load sensing based on Brillouin dynamic gratings (BDGs) for the first time to the best of our knowledge. The sensing mechanism is to measure the transverse-load induced birefringence through exciting and probing a BDG in an elliptical-core polarization-maintaining fiber. A distributed measurement of transverse load is experimentally demonstrated with a 20-cm spatial resolution, and the measurement accuracy is as high as 4.8x10-4N/mm, which improves by three orders of magnitude compared with the prior techniques.
High-resolution Brillouin analysis of composite materials beams
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High-resolution Brillouin optical correlation domain analysis of fibers embedded within beams of composite materials is performed with 4 cm resolution and 0.5 MHz sensitivity. Two new contributions are presented. First, analysis was carried out continuously over 30 hours following the production of a beam, observing heating during exothermal curing and buildup of residual strains. Second, the bending stiffness and Young's modulus of the composite beam were extracted based on distributed strain measurements, taken during a static three-point bending experiment. The calculated parameters were used to forecast the beam deflections. The latter were favorably compared against external displacement measurements.
Simplified Brillouin sensor for structural health monitoring applications based on passive optical filtering
Show abstract
We present a simplified configuration for distributed Brillouin optical time domain analysis sensors. The technique is based on passive optical filtering of the spectral components generated in an RF-pulse-modulated optical source. The aim of this configuration is to reduce the cost of the sensor by simplifying the generation of the optical waves involved in the sensing process. Proof-of-concept experiments demonstrate distributed temperature measurement with 1 m resolution over a 20 km sensing fiber.
Raman-based distributed temperature sensor using simplex code and gain controlled EDFA
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In this work we present a comparison between simplex coded and optical amplified simplex coded Raman based Distributed Temperature Sensing (DTS). An increase in performance is demonstrated using erbium doped fiber amplifier (EDFA) with proper gain control scheme that allows a DTS operates with simplex code. Using 63-bit simplex code and gain controlled EDFA we demonstrated the temperature resolution and dynamic range improvement in 16 °C @ 10 km and 4 dB, respectively.
The effect of the gain dependency of the linewidth of Brillouin amplification on double slope-assisted dynamic sensing techniques
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The effect of the gain dependency of the Brillouin linewidth on double-slope-assisted Brillouin optical domain, dynamic sensing techniques is studied. These double-slope methods are immune to pump-power related peak Brillouin gain variations, however, they are not immune to gain-dependent variations of the shape of the Brillouin gain spectrum. For a 15ns pump pulse, this gain-dependent shape of the normalized Brillouin gain is shown to lead to a 5.5 [%/dB] strain error when the double-slope sum-difference approach is used, compared with a 7 [%/dB] error when the double-slope ratio approach is used. Ways to compensate for these issues are discussed.
Rating the limitations and effectiveness of BOTDA range extension techniques
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Brillouin Optical Time Domain Analysis (BOTDA) is becoming a consolidated technique in applications requiring high-resolution
monitoring over extremely long distances. Extension of the measuring range has therefore become one of the
main areas of research around BOTDA technology. To increase the sensing range, it is necessary to increase the Signal
to Noise Ratio (SNR) of the retrieved signal. This has been achieved so far by applying techniques like pre-amplification
before detection, pulse coding or Raman amplification. Here, we analyze these techniques in terms of their performance
limits and provide guidelines that determine which is the best configuration to overcome current range limitations.
A calibration scheme of optical path correlator scan speed and position based 3×3 coupler and dual Mach-Zehnder interferometer
Show abstract
This paper proposed a calibration scheme of optical path correlator(OPC) for optical coherence domain polarimeter (OCDP), the calibration scheme employs a dual Mach-Zehnder interferometers multiplexing one OPC by dual wavelength wave division multiplexer, one interferometer as target interferometer is used to sensing measurement, another interferometer with 3×3 coupler as reference interferometer is used for OPC scan speed and positon calibration to improve the target interferometer signal-to-noise ratio(SNR) and interference envelope positioning accuracy, this calibration scheme is used OCDP to measure polarization crosstalk, the experimental results show that SNR is achieved 95dB and the polarization crosstalk position accuracy is achieved submicron.
Fiber optic distributed chemical sensor for the real time detection of hydrocarbon fuel leaks
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With the increase worldwide demand for hydrocarbon fuels and the vast development of new fuel production and delivery infrastructure installations around the world, there is a growing need for reliable hydrocarbon fuel leak detection technologies to provide safety and reduce environmental risks. Hydrocarbon leaks (gas or liquid) pose an extreme danger and need to be detected very quickly to avoid potential disasters. Gas leaks have the greatest potential for causing damage due to the explosion risk from the dispersion of gas clouds. This paper describes progress towards the development of a fast response, high sensitivity, distributed fiber optic fuel leak detection (HySense™) system based on the use of an optical fiber that uses a hydrocarbon sensitive fluorescent coating to detect the presence of fuel leaks present in close proximity along the length of the sensor fiber. The HySense™ system operates in two modes, leak detection and leak localization, and will trigger an alarm within seconds of exposure contact. The fast and accurate response of the sensor provides reliable fluid leak detection for pipelines, storage tanks, airports, pumps, and valves to detect and minimize any potential catastrophic damage.
Coating impact and radiation effects on optical frequency domain reflectometry fiber-based temperature sensors
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Temperature response of radiation-tolerant OFDR-based sensors is here investigated, with particular attention on the impact of coating on OFS. By performing consecutive thermal treatments we developed a controlled system to evaluate the performances of our distributed temperature sensor and to estimate the radiation impact. We show an important evolution of the temperature coefficient measurements with thermal treatments for non-irradiated fiber and that the amplitude of this change decreases increasing radiation dose. As final results, we demonstrate that sensor performances are improved if we performed a pre-thermal treatment on the fiber-based system permitting to monitor temperature with an error of 0.05°C.
Narrow-linewidth laser source with precision frequency tunability for distributed optical sensing applications
Show abstract
We demonstrate a narrow-linewidth laser source for high spatial resolution distributed optical sensing by utilizing the high-order modulation sidebands injection locking. A pair of phase-locked lasers with arbitrary frequency offset from 5 GHz to 50 GHz is generated. Meanwhile, a linearized frequency sweep covering range of 15 GHz in 6 ms with frequency errors of 240 kHz from linearity is also achieved using the same scheme, the instantaneous linewidth of the frequency-swept laser is measured to be ~2.5 kHz.
Magnetic-field sensor based on tapered all-solid waveguide-array fiber and magnetic fluids
Show abstract
A compact fiber-optic magnetic-field sensor based on tapered all-solid waveguide-array fiber (WAF) and magnetic fluid (MF) has been proposed and experimentally demonstrated. The transmission spectra of the fiber-optic magnetic field sensor have been measured and analyzed under different magnetic field intensities. Experimental results show that the acquired magnetic field sensitivity is 44.57 pm/Oe for a linear magnetic field intensity range from 50 Oe to 200 Oe. It also indicates that the magnetic field sensor based on tapered all-solid WAF and MF is helpful to reduce temperature cross-sensitivity for the measurement of magnetic field.
Relative humidity sensor based on an optical microfiber knot resonator with a polyvinyl alcohol overlay
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A highly sensitive RH sensor based on the MKR with the PVA overlay is investigated. After making a tie using the microfiber with a diameter of 2 μm, the MRK with a loop diameter of 90 μm is fabricated and coated by using a PVA which can absorb humidity. The optical spectra of the MRK with the PVA overlay are converted to the spatial frequency spectra by using the FFT for precise measurement. The absorption of humidity in the proposed MKR-based sensing probe effectively changes the spatial frequency of the MKR. The RH sensitivities of the proposed MKR-based RH sensing prober with higher order modes can be dramatically improved.
Fabrication and sensing characteristics of helical long-period fiber gratings written in the rotated fiber by CO2 laser
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A helical long-period grating (HLPG) was fabricated by twisting a conventional single-mode fiber when CO2 laser beam was sweeping along the fiber axis. A grating with a contrast of 20 dB can be written in the fiber with a length of 1 cm. The spectral and sensing characteristics were investigated experimentally. The maximum sensitivity to surrounding refractive index and temperature measurement was measured to be 995 nm/RIU and 53 pm/°C, respectively.
New SPR PCF D-type optical fiber sensor configuration for refractive index measurement
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This paper presents the performance analysis of a new geometry sensing configuration for refractive index, based on surface plasmon resonance (SPR) in photonic crystal fiber (PCF) D-type optical fiber with a thin gold layer, using the finite element method (FEM). The configuration is analyzed in terms of the loss. The results are compared with a conventional SPR D-type and with a PCF D-type optical fiber sensor for refractive index measurement. The simulation results show an improvement of the sensitivity and resolution (3.70×103nm/RIU and 2.72×10-5RIU, respectively, when considering an accurately spectral variation detection of 0.1nm).
Single-polarization single-mode hollow core photonic bandgap fiber for gyroscope applications
Valdir A. Serrão,
Marcos A. R. Franco
Show abstract
This paper presents a design of hollow-core bandgap fiber operating as single-polarization single-mode device. The hollow-core fiber has a cladding with high air filling fraction consisted of hexagonal air-holes in a triangular lattice. The design consists of changing the diameter of one radial line of air-holes. The asymmetric cladding leads to obtain single-mode operation with high birefringence, and fundamental modes with bandgaps in different spectral ranges. The single-polarization single-mode condition is demonstrated over 11 nm with polarization dispersion loss (PDL) of 800 dB/m at 1550 nm. The birefringent and polarizing hollow-core fiber is proposed to fiber optic gyroscope (FOG) applications.
Femtosecond laser micromachining of Fabry-Perot cavity in fibre Bragg grating
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A 10 μm (length) × 75 μm (depth) open channel is fabricated in fibre Bragg gratings (FBG) by femtosecond laser micromachining. The FBG Fabry-Perot (FP) cavity formed by this complex structure has a length of 4 mm; value estimated from interference spectrum for the air open channel. Reflection spectra of FBG FP cavity as a function of the temperature shows the cavity phase change. The sensor is thermally characterized by filling polymer in the channel and subsequent UV curing; the results show a period shift of approximately 12 x10-3, value obtained of interferometer pattern for 30°C temperature range.
Simultaneous measurement of refractive index and temperature with micro silica sphere cavity hybrid Fabry Perot optical fiber sensor
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In this article, a novel Micro Silica Sphere Cavity Hybrid Fabry Perot optical fiber sensor is reported where refractive index (RI) and temperature can be simultaneously measured. The sensor is based on Micro Silica Sphere that was fabricated using a capillary tube. The micro silica sphere and optical fiber form a Hybrid Fabry Perot cavity. The temperature cross sensitivity of this sensor is small enough to be used for accurate RI measurement. The temperature sensitivity and RI sensitivity are -0.0028 dBm/ºC, -0.0044 dBm/ºC , -24.09 dBm/RIU and -20.6 dBm/RIU respectively, using two selected resonances.
Interrogation of fiber Bragg grating sensors using a VCSEL and correlation techniques
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We describe a demodulation technique for optical fiber Bragg grating (FBG) sensors based in the utilization of a long wavelength Vertical Cavity Surface Emitting Laser (VCSEL). The identification of the FBG wavelength is performed by sweeping the VCSEL wavelength over the operation range of the sensors and correlating its raising and falling periods in order to automatically determine the initial and final points of the wavelength to time mapping readout. The process is carried out by a simple computational routine, which allows the identification of the FBGs’ spectral position leading to a cost-effective scheme.
Temperature sensor based on a tapered optical fiber with ALD nanofilm
Show abstract
A temperature sensor with high sensitivity based on a tapered optical fiber with Al2O3 nanofilm by atomic layer deposition (ALD) technology is presented. Attributed to the high refractive index Al2O3 nanofilm overlay, an asymmetry Fabry-Perot interferometer is formed along the tapered fiber. Based on the ray-optic analysis, the resonant dip in the interference transmission spectrum depends on the phase delay variation induced by the Goos-Hänchen shift at the nanofilm-coating interface. As a result, the interference transmission spectrum shows good sensitivity to the change of surrounding refractive index. In this work, a temperature-sensitive silicone gel is coated around the fiber taper with Al2O3 nanofilm to realize a high sensitivity temperature sensor. The high sensitivity of 2.44 nm/°C is obtained.
Reliable spectrometric fiber Bragg grating peak detection
Filipe Magalhães,
Paulo Martins,
Luís A. Ferreira,
et al.
Show abstract
A method for reliable fiber Bragg grating peak detection compatible with spectrometric demodulation schemes is presented. High immunity to differential losses and independency on the threshold settings was achieved. The effectiveness of the demonstrated method was corroborated by a 3σ accuracy of 2pm determined over 109 samples of 100 resonant peaks multiplexed in [1500; 1600] nm spectral range acquired throughout a year.
Stable dual-wavelength erbium fiber laser for temperature measurements
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In this work, a new stable dual-wavelength erbium fiber ring laser is proposed and experimentally demonstrated. This configuration is made by creating two symmetrical laser cavities with similar optical power. This topology allows the performance of two laser emission lines in single-longitudinal mode and with a power instability lower than 0.23 dB, and an optical signal-to-noise ratio higher than 40 dB for all the emitted wavelengths. The sensing capability of the FBGs enables this source to be also used as sensor-network multiplexing scheme. The system offers a better stability and higher optical signal to noise ratios than similar configurations.
Temperature monitoring system using correlated FBGs
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This paper presents a novel, simple, low-cost and repeatable quasi-distributed optical sensor system using specially designed fibre Bragg gratings (FBGs). The main idea consists in modulation of optical power by inscribed FBGs. The optical power changes with regard to outer parameters which have an influence on dedicated FBGs. The unique configuration is provided by proper characteristics of FBGs spectra. Instead of advanced and high-cost systems we demonstrate a concept of a low-cost sensor network using specially correlated FBGs.
Optical code division multiplexed fiber Bragg grating sensing networks
Show abstract
We present the application of Optical Code Division Multiplexing (OCDM) techniques in order to enhance the spectral operation and detection capability of fiber Bragg grating (FBG) sensors networks even under overlapping conditions. In this paper, Optical Orthogonal Codes (OOC) are used to design FBG sensors composed of more than one reflection band. Simulation of the interaction between the encoded Gaussian-shaped sensors is presented. Signal decoding is performed in the electrical domain without requiring additional optical components by means of the autocorrelation product between the reflected spectrum and each sensor-codeword. Results illustrate the accuracy and distinction capability of the method.
Nonlinear acousto-optics coupling in fiber optics: model based on local bending for LP cladding modes
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In this paper, we present a procedure to compute analytically the acousto-optic coupling coefficient between the fundamental core mode and lower LP cladding modes in fiber optics. Based on the effect of the local bending, the variations in the refractive index are modelled. A set of equations and parameters are presented in order to compute and analyze the influence of acousto-optic effect in nonlinear pulse propagation.
Study of supercontinuum generation in photonic crystal fiber infiltrated with carbon disulfide using super-mode theory
Show abstract
The supercontinuum (SC) generation has found numerous applications in spectroscopy, pulse compression and design of tunable ultrafast femtosecond laser sources, some improvement has been done in many fields. Since carbon disulfide (CS2) has highly nonlinear characteristics, this makes it a good candidate for achieving an infrared broadband source. In this work, we implemented numerical simulations of propagating ultra-fast optical pulses through a photonic crystal fiber (PCF) with two infiltrated holes using CS2. Based on supermodes theory, we calculate dispersion and nonlinear parameters in order to study the SC generation characteristic of the infiltrated PCF.
Generation of optical super-Gaussian pulses using tapered fibers
Show abstract
Using a model for the shape of tapered fiber optics, we numerically study the effect of the taper shape profile on nonlinear optical pulse propagation. We show that super-Gaussian pulses can be generated and controlled and they are independent of higher-order nonlinearities, which makes them a good candidate for optical communications. We see that it is possible to compensate for the z variation of the dispersion with the nonlinear parameter and obtain the solutions of the homogeneous nonlinear Schroedinger equation.
Single mode fiber and twin-core fiber connection technique for in-fiber integrated interferometer
Show abstract
A novel twin-core fiber connector has been made by two side-polished fibers. By using side polishing technique, we present a connector based on the twin-core fiber (TCF) and two D-shaped single-core fibers. After simple alignment and splicing, all fiber miniaturizing connector can be obtained. Two cores can operate independently and are non-interfering. The coupling loss of this connector is low and the fabrication technologies are mature. The connector device could be used for sensors or particle trapping.
Spider silk: a novel optical fibre for biochemical sensing
Show abstract
Whilst being thoroughly used in the textile industry and biomedical sector, silk has not yet been exploited for fibre optics-based sensing although silk fibres directly obtained from spiders can guide light and have shown early promises to being sensitive to some solvents. In this communication, a pioneering optical fibre sensor based on spider silk is reported, demonstrating for the first time the use of spider silk as an optical fibre sensor to detect polar solvents such as water, ammonia and acetic acid.
Hydrogen sensing array based on weak fiber Bragg grating
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Optical fiber hydrogen sensing system based on weak fiber Bragg grating (WFBG) array deposited with palladium (Pd) film is proposed and experimentally demonstrated. For multi-point measurement, three hydrogen WFBG sensors array are weld in a single optical fiber. A time-division multiplexing (TDM) interrogation system is employed to demodulate the sensing array. Sensing experiments to different hydrogen concentrations ranging from 0 to 3.6% are conducted, and the results show good agreement with standard FBG technology. Due to its strong multiplexing capability of weak FBG, the system is possible to integrate thousands of WFBG hydrogen sensors in a single optical fiber.
Quasi-distributed fiber sensor based on Fresnel-reflection-enhanced Incomplete-POTDR system
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A novel scheme of quasi-distributed vibration disturbances detection system based on incomplete Polarization optical time domain reflectometry was proposed. The system was enhanced by employing Fresnel-reflection caused by FC/PC connector, which can improve the signal’s SNR significantly, while the temporal depolarization effect can be almost completely suppressed. Without performing any data averaging, the intrusion event can be detected and located precisely/instantaneously with good stability. Also the frequency components of vibration events applying on sensing fiber can be obtained with large dynamic range. It shows a very good potential in intrusion detection, vibration frequency measuring, etc.
A novel method to generate a self-accelerating Bessel-like beam based on graded index multimode optical fiber
Show abstract
We propose and demonstrate a transverse self-accelerating Bessel-like beam generator based on a graded index multimode optical fiber(GIF). The single-mode fiber and the graded-index multimode fiber are spliced with a defined offset. The offset Δx and the GIF length L affect the final properties of the Bessel-like beam, here we choose the offset Δx=20μm and the GIF length L=430μm to be optimal. The beam accelerates along the designed parabolic path up to 250μm in z direction and 40μm in x direction, the curvature of bending is 16% (40μm/250μm, x/z). This transverse self-accelerating Bessel-like beam generator based on the graded index multimode optical fiber constitutes a new development for high-precision micro particles experiments and manipulations because of its simple structure, high integration and small size.
Centre of mass determination based on an optical weighing machine using fiber Bragg gratings
Show abstract
The purpose of the present work was to construct a weighing machine based on fiber Bragg gratings (FBGs) for the location of the 2D coordinates of the center of gravity (COG) of objects with complex geometry and density distribution. The apparatus consisted of a rigid equilateral triangular platform mounted on three supports at its vertices, two of them having cantilevers instrumented with FBGs. As an example, two femur bone models, one with and one without a hip stem prosthesis, are used to discuss the changing of the COM caused by the implementation of the prosthesis.
Lamb wave detection with a fiber optic angular displacement sensor
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In this work we show that the fiber optic angular displacement sensor is capable of Lamb wave detection, with results
comparable to a piezoelectric transducer. Therefore, the fiber optic sensor has a great potential to be used as the Lamb
wave ultrasonic receiver and to perform non-destructive and non-contact testing.
Fiber specklegram sensors sensitivities at high temperatures
Show abstract
In this work, the sensitivity of Fiber Specklegram Sensors to high temperatures (up to 800ºC) have been studied. Two multimode silica fibers have been introduced into a tubular furnace while a HeNe laser source was launched into a fiber edge, projecting speckle patterns to a commercial webcam. A computer generated different heating and cooling sweeps while the specklegram evolution was recorded. The achieved results exhibit a remarkably linearity in FSS’s sensitivity for temperatures under 800ºC, following the thermal expansion of fused silica.
Torsion sensing characteristics of a highly birefringent photonic crystal fiber with two asymmetric cores in the Sagnac loop
Show abstract
We experimentally demonstrated torsion sensing characteristics of a highly-birefringent asymmetric two-core photonic crystal fiber (HB-ATCPCF) in the Sagnac loop configuration. Two cores in the HB-ATCPCF exhibit distinct birefringence properties and light launched into them propagate with negligible coupling. The transmission interference spectrum of the device shows six frequency peaks in the spatial domain, which corresponds to the two Sagnac and four Mach-Zehnder interference spectra characterized by the four-beam interference model. Torsion response of the device was investigated by measuring the shift of the peak wavelength and the fringe visibility of the fiber interferences using fast Fourier transform-based spectrum-demodulation method.
FBG feedback's effects on distributed Bragg reflector fiber laser's polarization modes’ beat
Show abstract
Distributed Bragg reflector (DBR) fiber optic laser has recently been extensively explored as a powerful sensor for various measurands, thanks to its high sensitivity, excellent signal-to-noise ratio, and inherent electronic magnetic immunity. The phase noise and linewidth of the laser’s beat note limits this sensor’s performances. We report in this letter, our recent experiments on noise reduction employing optical feedback from an external FBG. We also investigated the sensitivity reduction of the DBR sensor after feedback is introduced.
Indium-Tin-Oxide coated optical fibers for temperature-viscosity sensing applications in synthetic lubricant oils
Show abstract
In this work, is presented the fabrication and characterization of optical fiber refractometer based on lossy mode resonances (LMR). Indium-Tin-Oxide (ITO) thin films deposited on optical fibers are used as the LMR supporting coatings. These resonances shift to the red as a function of the external refractive index. The refractometer has been used to characterize temperature variations related to the viscosity of synthetic industrial gear lubricant.
Liquid damped fiber laser accelerometer
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Liquid damped fiber laser accelerometer (LD-FLA) was proposed and a kind of LD-FLA structure, of which damping liquid could be easily change, was designed to study its damping characteristic. The principles of a LD-FLA were analyzed comparing with a common FLA, which found that liquid damper could produce additional liquid pressures in vibration so that not only damping responses but sensitivities and frequency responses could be changed at the same time. Four double diaphragm-based LD-FLAs were manufactured and experiments under several kinds of damping liquids were carried out. The experimental results are close to the calculated values and verify the theoretical analysis on LDFLA. The theoretical model provides guidance for further research on damping characteristic.
Interferometric fiber Bragg grating shift demodulation
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In this paper we present a fiber Bragg grating shift demodulator with changeable resolution based on an unbalanced fiber Mach–Zehnder interferometer. Preliminary research proves phase sensitivity to Bragg wavelength changes of 6,83 rad/mε. Phase sensitivity can be modified by changing the optical path difference witch is only limited by the coherence length of light reflected by the fiber Bragg grating. This solution can be used as a single sensor or as a part of a more complex system.
A SPR sensor based on twin-core fiber
Show abstract
We propose and demonstrate a novel fiber surface plasmon resonance (SPR) sensor based on a twin-core fiber (TCF). We grind the TCF tip into a frustum wedge shape, and plate a 50nm sensing gold film on the end face, two 500nm reflected gold films on the side faces of the wedge. We launch light source into the core of the TCF by using the high accuracy three-dimensional adjusting mount and microscope objective system. This SPR probe can be combined with microfluidic chip, and realize the real-time monitoring of the refractive index (RI) sensing of flow liquid in the microfluidic channel. The probe successfully monitors the refractive index of liquid ranged from 1.33 to 1.37 and the average sensitivity reaches to 5213nm/RIU in the solution.
High-speed FBG interrogation system insensitive to fiber link attenuation for magnetic field sensing
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A high-speed FBG interrogation method for magnetic field sensing is proposed. A FBG attached to a magnetostrictive material (Terfenol-D) was used to show the output invariance when increasing the attenuation on the optical link. This was achieved by computing the ratio between the sensing and the reference signals, both generated using different DFB lasers properly tuned. The output remained invariant to attenuations up to 12 dB. Also, the system’s interrogation speed was tested and compared to a commercial solution. While the commercial model was limited by its 6 kHz sampling frequency, this method provided responses up to 60 kHz.
Evaluation of shrinkage polymerization and temperature of different acrylic resins used to splinting transfer copings in indirect impression technique
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The aim of the present study was evaluate the shrinkage polymerization and temperature of different acrylic resins used to splinting transfer copings in indirect impression technique. Two implants were placed in an artificial bone, with the two transfer copings joined with dental floss and acrylic resins; two dental resins are used. Measurements of deformation and temperature were performed with Fiber Braggs grating sensor for 17 minutes. The results revealed that one type of resin shows greater values of polymerization shrinkage than the other. Pattern resins did not present lower values of shrinkage, as usually reported by the manufacturer.
Smartphone-based portable intensity modulated force sensor
Lucas Hermann Negri,
Elberth Manfron Schiefer,
Aleksander Sade Paterno,
et al.
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This work proposes a low-cost force sensor, based on intensity modulation in an optical fibre. The transducer element is composed of a knot in a single mode fibre embedded to a silicone adhesive cuboid, and can be easily fabricated. A simple sensing scheme is devised by using a visible light source and a CCD camera of a smartphone, allowing implementation costs to be reduced. Experimental results have shown that the sensor presents a linear response and a standard uncertainty of 1:07N within the dynamical range from 0 to 30 N.
Fabry-Perot cavity based on sapphire-derived fiber for high temperature sensor
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An optical fiber high temperature sensor is demonstrated by using a special sapphire-derived fiber. An air cavity is easily created through splicing the sapphire-derived fiber with standard single mode fiber (SMF). Utilizing the air cavity as one reflecting face, a Fabry-Perot (F-P) interferometer is fabricated in the special fiber. Attributed to the high ratio alumina component, the F-P interferometer exhibits high sensitivity response to temperature variation within the range up to 1000 °C. The sensitivity is 15.7 pm/°C.
Magnetic field sensor based on fiber taper coupler coated with magnetic fluid
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In this paper, we have demonstrated a magnetic field sensor based on the fiber taper coupler coated with Magnetic fluid. The proposed sensor is fabricated by immersing a fiber taper coupler into the Magnetic fluid and then sealing it with the paraffin. The sensor exhibits high response as a function of the magnetic field with sensitivities of 0.154 nm/Oe with measurement range from 50 Oe to 200 Oe and -0.06301 dB/ Oe from 75 Oe to 200 Oe. Owing to the advantages of high sensitivity, small footprint, and ease of fabrication, the proposed sensor would find potential applications in magnetic field sensing field.
Lithium batteries temperature and strain fiber monitoring
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Fiber Bragg grating sensors were attached to the surface of a rechargeable lithium battery in order to monitor its thermal and strain fluctuations through charge and different discharge C rates. During the discharge process above 1C, it were observed, a temperature and strain fluctuations of a 4.12 ± 0.67 °C and 24.64 ± 6.02 με, respectively. In the regular charge process, a temperature and strain variation of 1.03 ± 0.67 °C and 15.86 ± 6.02 με, were detected.
A new optical pressure sensor interrogated by speckles pattern for oil industry
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A new optical pressure control concept in petroleum industry based on laser speckle analysis, with inherent safety light, is investigated in this work. A plastic optical fiber (POF) utilized to instrument a conventional manometer enabled pressure monitoring of a system that is interrogated by speckle photography technique. Specklegrams were imaged on a CCD camera and then analyzed, after Mathematical Morphology Filter, regarding its movement. Tests demonstrated that the speckle pattern movement is radial towards the center of pressure and accordingly reverse during depressurization within 5% maximum error.
Early detection of pipeline integrity threats using a smart fiber optic surveillance system: the PIT-STOP project
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The preliminary results of a surveillance system set up for real time monitoring activities along a pipeline and analyzing for possible threats are presented. The system consists of a phi-OTDR based sensor used to monitor vibrations along an optical fiber combined with a pattern recognition system that classifies the recorded signals. The acoustic traces generated by the activities of different machines at various locations along a pipeline were recorded in the field. The signals, corresponding to machinery activities, were clearly distinguished from background noise. A threat classification rate of 68.11% with 55.55% false alarms was obtained.
Long term strain behavior of PMMA-based polymer optical fibers
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We are reporting on the viscoelasticity of PMMA based Fiber Bragg Grating (FBG) strain sensors when exposed to repeated sequences of long term strain and relaxation with various duty-cycles. In terms of the FBG wavelength and how it follows the strain cycle, we have shown that in the small strain regime (up to 1%) an elastic-dominated fast relaxing range, which is followed by a mainly viscous relaxation, depends both on the strain level and on the strain duration. For a small ratio of the strain-relax durations, this fast relaxation range stays almost the same. However, with increasing strain duration, for the same relaxation time, this range will be shortened, which might influence the sensing capabilities of the fiber sensor.
HOBAN project: towards the development of radiation-tolerant fiber-based temperature sensors for nuclear industry
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HOBAN (Development of Hard Optical Fiber BrAgg GratiNgs Sensors) is an European H2020 project granted by Kic InnoEnergy and aiming the development of fiber-based temperature and strain monitoring systems that can withstand harsh nuclear environment (350°C temperature and MGy dose levels). The objective will be achieved by employing ‘ad hoc’ fiber Bragg grating (FBG) sensors and their associated instrumentation system which will bring to the market new tools for optimizing the running and the services in current and future nuclear power plants. We’ll present the challenges associated with this project and recent advances at the OFS conference.
Simultaneous strain and temperature measurement with enhanced intrinsic sensitivity using etched polymer fibre Bragg gratings
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A PMMA based single-mode polymer optical fibre is etched to different diameter and it is observed that etching can lead to change in the material properties of the fibre such as Young’s modulus and thermal expansion coefficient. This can play a vital role in improving the intrinsic sensing capabilities based on etched polymer optical fibre. Thus, exploiting the different strain and temperature sensitivities exhibited by the etched and un-etched polymer FBGs and by using an FBG array, strain and temperature can be measured simultaneously and also with very high sensitivity.
High-order polarization mode crosstalk effect: a calibration scheme of white light-based optical coherence domain polarimetry
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We propose a calibration scheme of the white light interferometer based optical coherence domain polarimetry (OCDP), which could be used to measure the ultra-weak polarization mode crosstalk (PMC) or the ultra-high polarization extinction ratio (PER) of different polarization optical devices. The calibration depends on the first and second order PMC effect of different polarization devices in series. The first and second PMCs between 0 and -90dB, established by five pieces of polarization maintaining fiber (PMF) and a Y-waveguide, is used to prove its feasibility.
Feasibility of crack monitoring in a road tunnel based on a low cost plastic optical fiber sensor
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In this work, a low cost optical fiber sensing system for cracks growth monitoring in the concrete lining of a road tunnel is presented. A plastic optical fiber (POF), with large dynamic strain range, is used for sensing by means of phase measurement of a RF modulated optical signal. Preliminary results suggest that the system represents a viable solution to the aim of crack monitoring.
New properties of a fiber optic sensor in application of a composite fence for critical infrastructure protection
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This paper presents a new solution of using the composite fence with a novel fiber optic modalmetric sensor integrated within its structure. The modalmetric sensor is based on changes in a transverse modal field which is generated at the output of a multimode fiber. By a spatial limitation of the transverse modal field observation to its fragment thereof, changes’ transformation in the modal distribution into changes of the output signal amplitude is made. Due to a constant analysis of the structure output signal, detection of an external disorder is possible. Integration of optical fibers with the fence structure allows for an accurate reproduction of the fence movement onto the optical fiber by significantly improving sensitivity of the modalmetric fiber sensor structure.
Optical fiber Fabry-Perot refractive index sensor based on porous Al2O3 film
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A fiber refractive index sensor based on porous alumina is fabricated by pasting porous alumina film with 42.36μm on single mode fiber tip using the UV-cured adhesive. Experimental results show that the proposed sensor has a very high correlation with glycerine concentration (0.0%~80.0%) with correlation coefficient of 99.771%. Its sensitivity and resolution was measure to be 99.771%, 154 nm/RIU and 1×10-4 respectively when the refractive index changes from 1.333 to 1.443.
1200°C high-temperature distributed Brillouin optical fiber sensing based on photonics crystal fiber
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We demonstrate an up to 1200°C high-temperature distributed Brillouin sensing based on a pure-silica photonics crystal
fiber. A Brillouin frequency shift (BFS) hopping is observed between 800°C-900°C for the first annealing process and
after that the BFS exhibits the stability and repeatability with a measurement accuracy as high as ±2 °C . The BFS
dependence on temperature in the range of room temperature to 1200°C agrees well with an exponential function instead
of a linear function, which is mainly attributed by the change of the acoustic velocity in a silica fiber.
Microgel photonics: a breathing cavity onto optical fiber tip
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We experimentally demonstrate a novel multifunctional optical fiber probe resulting from the integration between two
rapidly emerging technologies such as Lab-on-Fiber and Microgel Photonics. The device consists of a microgel based
cavity formed by metallic slabs supporting plasmonic resonances, directly integrated on the optical fiber tip. By
exploiting the multiresponsivity of microgel systems, variations of temperature, PH, ionic strength, as well as molecular
binding events, make the cavity to ‘breath’, thus modulating the interference pattern in the reflection spectrum. The
microgel layer can be synthetized in such a way to obtain different thicknesses, corresponding to different operating
regimes, opening new avenues for the realization of advanced multifunctional nanoprobes.
Overcoming non-local effects and Brillouin threshold limitations in Brillouin distributed sensors
Javier Urricelqui,
Rubén Ruiz-Lombera,
Mikel Sagues,
et al.
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We demonstrate, for the first time to our knowledge, a Brillouin optical time domain analysis sensor that is able to operate with a probe power larger than the Brillouin threshold of the deployed sensing fiber and that is free from detrimental non-local effects. The technique is based on a dual-probe-sideband setup in which a frequency modulation of the probes waves along the fiber is introduced. This makes the frequency of maximum interaction between pump and probes to vary along the fiber, thus mitigating the pump pulse depletion and making it possible to use very large probe power, which brings an improved signal-to-noise ratio in detection.