Proceedings Volume 7004

19th International Conference on Optical Fibre Sensors

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Proceedings Volume 7004

19th International Conference on Optical Fibre Sensors

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Volume Details

Date Published: 4 June 2008
Contents: 16 Sessions, 223 Papers, 0 Presentations
Conference: 19th International Conference on Optical Fibre Sensors 2008
Volume Number: 7004

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7004
  • Opening Session
  • Microstructured Fibres I
  • Fibre Bragg Grating Sensors
  • Physical, Mechanical, and Electromagnetic Sensors I
  • Poster Session I
  • Chemical, Environmental, Biological, and Medical Sensors I
  • Special Session on Oil and Gas: Current Practice and Future Opportunity
  • Chemical, Environmental, Biological, and Medical Sensors II
  • Physical, Mechanical, and Electromagnetic Sensors II
  • Distributed Sensing
  • Passive and Active Devices for Photonic Sensing
  • Poster Sesion II
  • Polymer/Structured Fibers
  • Sensor Systems
  • Postdeadline Papers
Front Matter: Volume 7004
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Front Matter: Volume 7004
This PDF file contains the front matter associated with SPIE Proceedings Volume 7004, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
Opening Session
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Fiber-top micromachined devices
D. Iannuzzi, S. de Man, C. J. Alberts, et al.
After a general review on fiber-top technology, we will present our recent achievements in the utilization of fiber-top double-clamped cantilevers as refractometers and in the development of alternative techniques for the fabrication of fiber-top devices.
Microstructured Fibres I
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Recent developments in microstructured optical fibers and optical fiber glasses
J. M. Blondy, F. Gerome, J. L. Auguste, et al.
In the last ten years, the development of air-silica microstructured fibers has opened an exciting route to study new type of optical waveguides, leading to a wide range of applications. Now, the possibility offer by this photonic technology to incorporate original materials and mix different fabrication processes give a promising way to adapt the optical designs and extend the applications in a large area from UV to mid IR.
Photonic-crystal-diaphragm-based fiber-tip hydrophone optimized for ocean acoustics
We report a miniature fiber hydrophone that consists of a Fabry-Perot interferometer made of a photonic-crystal reflector embedded on a compliant silicon diaphragm placed at the tip of a single-mode fiber. A model was developed to show that after proper optimization to ocean acoustics, this sensor has a minimum detectable pressure that follows the minimum ambient noise of the ocean (reaching a minimum of ~10 μPa/Hz1/2 at ~30 kHz) in the bandwidth of 1 Hz-100 kHz. By placing several such sensors with different acoustic power ranges within a single hydrophone head, the hydrophone is able of exhibiting a dynamic range in the excess of 200 dB. A prototype was fabricated, assembled, and tested that confirmed this high sensitivity and bandwidth.
Merging porphyrins and structured optical fibres: future technology for chemical sensors
Cicero Martelli, John Canning, Maxwell J. Crossley, et al.
Spectroscopic characterisation of water soluble porphyrins using a structured optical fibre are presented and discussed. Porphyrin thin-films were also fabricated inside the holes of structured fibres. The thin-films self-assemble inside the fibres leading to energy coupling between the molecules. These are the first steps towards future chemically tailored optical fibre sensors for molecular detection.
High temperature sensor based on a photonic crystal fiber interferometer
We demonstrate a high temperature sensor by using an intrinsic photonic crystal fiber (PCF) based Mach-Zehnder interferometer. Air hole collapsed regions inside the PCF act as coupler between the core and cladding modes which form the two arms of the interferometer. The temperature measurements are obtained by measuring the shift in the peaks of the interference signal. The experiments confirm the reliability, repeatability and hysteresis. The small amount of hysteresis and deviation in the repeated experiments are within the experimental errors.
Compact in-fiber polarizer based on the hollow-core photonic bandgap fiber
A broadband, compact in-fiber polarizer was fabricated by using a pulsed CO2 laser to modify the air-holes along oneside of a hollow-core photonic bandgap fiber. The polarizer has a length of 3 to 6mm and exhibits a polarization extinction ratio of better than 20 dB over a wavelength range of 100nm around 1550nm.
Fibre Bragg Grating Sensors
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Progress in photosensitivity for writing Bragg gratings
Although mainstream grating writing, more often than not using single photon excitation of germanosilicate based defects with CW 244nm light, remains the key technology for complex devices it is now being complemented by a whole host of processes which can enhance and tailor the properties of both conventional and not-so-conventional fibre Bragg gratings. Further, processes for writing in non-germanosilicate based gratings have also continued to develop and include multi-photon excitation directly into the band edge of the glass. It is now possible to custom tailor a gratings property based on the application and the nature of production as well as custom tailor the grating writing process to suit the type of fibre and application.
Ratiometric interrogation of dynamically strained fiber Bragg gratings
Robert R. J. Maier, James S. Barton, Mathias Kuhn
We demonstrate a new and highly flexible technique for high speed dynamic interrogation of fiber Bragg gratings [FBG]. The technique is based on a ratiometric measurement employing a pulsed broad band light source, a single detector and 2 filter FBGs. The filter FBGs are mounted on a temperature controlled cantilever where the strain of the filter FBGs can be adjusted to requirement. The technique can be used on multiplexed FBGs and has been demonstrated here at a frequency of 20kHz although much higher frequencies are possible with a light source of higher power. Sub micro-strain resolution of 0.6 με at 23 kHz is demonstrated and the noise for strain ε(=ΔL/L) is 5•10-9ε√Hz-1.
Soldering fiber Bragg grating sensors for strain measurement
Mathias S. Müller, Lars Hoffmann, Tobias Lautenschlager, et al.
When measuring strain with a FBG sensor fixed to a structure by an adhesive, one will notice, that only axial strain is monitored. This is due to the low Young's modulus of both standard coating materials and adhesives. Metal coated fibers with high Young's modulus have become available recently, which may be surface bonded by soldering. Motivated by this, finite element simulations with different coating materials and adhesives were carried out. Increasing the Young's modulus of coating and adhesive in the simulation shows a difference in transverse strain of around 20 % for the two cross sectional fiber axes. On this basis a process to substitute standard fiber coatings with a copper coating is described. Satisfying results were obtained using a copper electroplating process. Especially its simple experimental access is noticeable. A sensor modified in the electroplating process is soldered to a cantilever beam and a quasi-static strain measurement is performed. Soldering the modified fiber sensors changes the spectral response of the FBG. Towards shorter wavelength which is a result of the strains induced by cooling.
High-sensitivity temperature-independent strain sensor based on a long-period fiber grating with a CO2-laser engraved rotary structure
T. Zhu, Y. J. Rao, Y. Song, et al.
We present a highly sensitive strain sensor based on the use of a long-period fiber grating with rotary grooves carved by high-frequency CO2-laser pulses. We observe that, when the rotation rate of the grooves is sufficiently large, the resonance peak of the grating split into two with a wavelength separation that changes sensitively with the strain applied along the grating and remains practically constant with a change in the ambient temperature. By measuring the wavelength separation of the two resonance peaks, we obtain a strain sensitivity of ~0.1 nm/με without any temperature compensation, which is larger than that of a conventional long-period fiber grating by almost two orders of magnitude.
The spectral characteristics of femtosecond laser inscribed long period grating bend sensors written into a photonic crystal fibre
A series of LPGs was inscribed in photonic crystal fibre by a low repetition femtosecond laser system. When subjected to bending they were found to be spectrally sensitive to bend orientation and displayed a strong polarisation dependence.
Physical, Mechanical, and Electromagnetic Sensors I
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Nonlinearities in the high-current response of interferometric fiber-optic current sensors
Klaus Bohnert, Philippe Gabus, Jürgen Nehring, et al.
The nonlinearities in the response of an interferometric fiber-optic current sensor associated with deviations of the light waves from perfect circular polarization are theoretically and experimentally investigated. The consequences for inherent temperature compensation of the Faraday effect by means of a non-90°-retarder are investigated for currents up to several 100 kA and temperatures between -40°C and 80°C. The results are of particular interest to sensors for high direct currents in the electro-winning industry where measurement accuracy to within ±0.1% is required up to 500 kA.
Triple wavelength SOA-based fiber ring laser for use in wavelength-division multiplexed FBG vibration sensor array
S. Tanaka, H. Somatomo, K. Inamoto, et al.
A multi-wavelength tunable fiber laser is constructed for a wavelength-division multiplexed (WDM) fiber Bragg grating (FBG) sensor array in which simultaneous detection of multipoint vibrations and temperature stabilization of the sensor outputs are achieved. The laser consists of a semiconductor optical amplifier (SOA) as a gain medium and of FBGs as wavelength selection components. Since the SOA is an inhomogeneous broadening gain medium, stable multi-wavelength oscillation at the Bragg wavelengths of the FBGs can be realized. In addition, the oscillation wavelengths of the laser can be tuned by applying strain to the FBGs used. In the sensor scheme, triple wavelength fiber laser is fabricated, in which the three wavelength components provide narrowband light sources for arrayed WDM FBG sensors and the wavelength tuning enables temperature compensation for the vibration detection. In the experiment, simultaneous three-point vibration detection with temperature stabilization has been successfully demonstrated.
Radial deformation measurement of a cylinder under compression using multicore fibre
Amanda Fender, William N. MacPherson, Robert R. J. Maier, et al.
A multicore fibre (MCF) sensor to measure the radial deformation of a compliant cylinder under compression is presented. The sensor is connectorised and need not be permanently bonded to the test object. A differential measurement technique using FBGs written into the MCF makes the sensor temperature insensitive. FBG measurement of axial strain of a cylinder under compression is also reported.
Optical temperature point-sensor array for oil and gas down-hole applications
D. Taverner, E. Dowd, J. Grunbeck, et al.
An armored, 1/4" cabled, temperature sensor array was developed for oil and gas down-hole applications using Bragg gratings written into large diameter, single-mode cane waveguides to provide strain-isolated temperature sensor elements. The temperature sensor array was deployed and evaluated in a test-well. A measured temperature 1-σ deviation of better than 0.002°C and an overnight stability range of 0.02°C were demonstrated.
3D planar velocity measurements using Mach-Zehnder interferometric-filter-based planar Doppler velocimetry (MZI-PDV) and imaging fibre bundles
Z. H. Lu, T. O. H. Charrett, H. D. Ford, et al.
Three component planar flow-field measurements are made using imaging fibre bundles to port different views of the measurement plane, defined by a laser light sheet, to a single imaging head. The Doppler frequency shifts of light scattered by particles entrained in the flow are transduced to intensity variations using a Mach-Zehnder interferometric filter. The free spectral range of the filter can be selected by adjusting the optical path difference of the interferometer. This allows the velocity measurement range, sensitivity and resolution to be varied. Any laser wavelength may be used. A phase locking system has been designed to stabilise the interferometric filter.
High-accuracy discriminative sensing of strain and temperature by use of birefringence and Brillouin scattering in a polarization-maintaining fiber
Weiwen Zou, Zuyuan He, Kazuo Hotate
We propose and demonstrate a novel method to discriminate strain and temperature by simultaneous measurements of birefringence and Brillouin frequency shift in a PANDA-type polarization-maintaining fiber. A high-accuracy discrimination of 3~4 με and 0.02~0.03 °C is realized.
Poster Session I
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Self-referenced Fizeau strain sensors based on an electronic scanning mirror
Jiang Yu, Jianzhong Zhang, Jun Yang, et al.
A self-referenced fiber optic Fizeau strain sensor based on Michelson interferometry with a electronic scanning mirror is proposed and demonstrated. The limitation of Fizeau cavity length is eliminated and it is possible to multiplex Fizeau strain sensors with the same cavity length. The returning-error caused by the scanning mirror is reduced dramatically by introducing the reference signal.
Crosstalk analysis of a smart sensor unit based on FBG and FOWLI
Jiang Yu, Jianzhong Zhang, Weimin Sun, et al.
The effective optical path method is proposed to analyze the measurement crosstalk of a smart fiber optic sensor unit based on multiplexing fiber Bragg gratings (FBG) and fiber optical white light interferometry (FOWLI). According the analysis, the crosstalk between FBG and FOWLI can be estimated. The experimental system with a sensor unit is given to show the feasibility of the multiplexing scheme.
A passive way to extend DTSS system distance
Yandong Gong, Jianzhong Hao, Michael Ong Ling Chuen, et al.
Brillouin or Raman-based Distributed Temperature and Strain Sensor (DTSS) provide a chance to distributed measure the temperature and strain over tens of kilometer with higher resolution. Lots of efforts, for example, Raman amplifier, Signal processing methods et al, have been used to extend their sensing distance and increase their sensitivity and signal noise ratio. A sensing fiber, which has a gradually increasing Brillouin gain-coefficient gB/Aeff or Raman gain coefficient gR/Aeff along its length and which can keep the received Brillouin or Raman Stoke's power constant in a Brillouin or Raman DTSS, is proposed in this paper. This novel fiber and practical fiber link with such nonlinear coefficient profile can further double or triple extend the sensing distance of the distributed Brillouin or Raman Fiber-optic Sensor system.
Revolutionizing the design of an evanescent-wave-based fiber-optic fluorometer
A typical evanescent-wave fiber-optic fluorometer (EWFOF) has an excitation (Ex) light source attached at one end, causing a significant level of stray Ex light mixed with a much weaker signal at the detection end. A high-performance filter / detector assembly is hence a common requirement for signal recovery. We have proposed a side-excited EWFOF featuring significant suppression of this stray light level and enhancement of the fluorescent emission signal. In particular, this EWFOF limits its sensing volume within a single droplet approximately the diameter of a fiber core. The paper compares the performance of this fluorometer with that of a conventional EWFOF based on several identical conditions such as fiber type, filter and Ex source power level as well as the detection system.
Fusion of a FBG-based health monitoring system for wind turbines with a fiber-optic lightning detection system
Wind turbine blades are made of composite materials and reach a length of more than 42 meters. Developments for modern offshore turbines are working on about 60 meters long blades. Hence, with the increasing height of the turbines and the remote locations of the structures, health monitoring systems are becoming more and more important. Therefore, fiber-optic sensor systems are well-suited, as they are lightweight, immune against electromagnetic interference (EMI), and as they can be multiplexed. Based on two separately existing concepts for strain measurements and lightning detection on wind turbines, a fused system is presented. The strain measurement system is based on a reflective fiber-Bragg-grating (FBG) network embedded in the composite structure of the blade. For lightning detection, transmissive &fiber-optic magnetic field sensors based on the Faraday effect are used to register the lightning parameters and estimate the impact point. Hence, an existing lightning detection system will be augmented, due to the fusion, by the capability to measure strain, temperature and vibration. Load, strain, temperature and impact detection information can be incorporated into the turbine's monitoring or SCADA system and remote controlled by operators. Data analysis techniques allow dynamic maintenance scheduling to become a reality, what is of special interest for the cost-effective maintenance of large offshore or badly attainable onshore wind parks. To prove the feasibility of this sensor fusion on one optical fiber, interferences between both sensor systems are investigated and evaluated.
Fiber-optic carbon dioxide sensor based on fluorinated xerogels doped with HPTS
This paper presents a high-performance fiber-optic carbon dioxide (CO2) sensor based on hybrid xerogels composed of alkyl and perfluoroalkyl ORMOSILs (organically modified silicates) doped with pH-sensitive fluorescent dye. The sensor film consists of 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt (HPTS, PTS-), tetraoctylammonium cation (TOA+), and a tetraoctylammonium hydroxide (TOAOH) phase transfer agent (i.e. the base) immobilized within the hybrid xerogels. The sensor has a sensitivity of approximately 18 and exhibits a linear response for CO2 concentrations in the range 0 ~ 30 %. The response time of the sensor is 1.7 s when switching from a pure nitrogen atmosphere to a pure CO2 atmosphere and 38.5 s when switching from CO2 to nitrogen.
A plastic optical fiber sensor for the dual sensing of temperature and oxygen
This study presents a low-cost plastic optical fiber sensor for the dual sensing of temperature and oxygen. The sensor features a commercially available epoxy glue coated on the side-polished fiber surface for temperature sensing and a fluorinated xerogel doped with platinum tetrakis pentrafluoropheny porphine (PtTFPP) coated on the fiber end for oxygen sensing. The temperature and oxygen indicators are both excited using a UV LED light source with a wavelength of 380 nm. The luminescence emission spectra of the two indicators are well resolved and exhibit no cross-talk effects. Overall, the results indicate that the dual sensor presented in this study provides an ideal solution for the non-contact, simultaneous sensing of temperature and oxygen in general biological and medical applications.
Two-beam optical tweezers built by a two-core fiber
Libo Yuan, Zhihai Liu, Jun Yang, et al.
We present an abruptly tapered twin-core fiber optical tweezers, which is fabricated by fusing and drawing the twin-core fiber (TCF). The two beams guided by the TCF, and a larger converge angle between the two beams are made due to the abrupt tapered shape. The two beams converged at the micro-lensed tip, then forming a fast divergent optical field. The microscopic particle trapping performance of this special designed tapered TCF tip is investigated. The distribution of the optical field emerging from the tapered fiber tip is simulated based on the beam propagation method (BPM). By using this two-beam combined technique, a strong enough gradient forces well is obtained for microscopic particles trapping in three-dimensional. The abruptly tapered TCF optical tweezers is rigid and easy to handle, especially useful for build-up a multi-tweezers system for trapping and manipulating micro-scale particles.
Three-core fiber far field structured light pattern generator and its shape sensing application
Libo Yuan, Jun Yang, Zhihai Liu, et al.
By using spherical designed three-core fiber, a micro structured light pattern generator for sensing of 3-D object shapes has been demonstrated. The square or hexagon grid interferometric fringe pattern formed by the fiber optic interferometric grid generator is projected on an object's surface. The deformed grid pattern containing information of the object's surface topography is captured by a CCD camera and is analyzed using a 2-D Fourier transforming profilometry. The use of fiber optic grid interferogram technique greatly simplifies the holographic interferometry system and the carrier grid interferogram can be conveniently generated without the use of excessive auxiliary components or sophisticated experimental devices, and moreover, the three-core fiber can be used in very narrow places due to its small size. Finally, the square or hexagon grid interferometric fringe pattern provides a data fusion ability, which could further improve the accuracy of the 3-D shape sensing results.
High temperature sensors exploiting low coherence signal recovery
High temperature probes are described, one with an operating temperature ≥1000°C based on a sapphire etalon interrogated by low coherence interferometry, the second a miniature Fabry-Perot maximum operational temperature 700°C interrogated by a tuneable laser capable of linear and sinusoidal scan rates of 2 kHz and 20kHz repectively.
Antiresonant guiding photonic crystal fibers for measuring refractive index
Refractometric sensor utilizing spectral properties of antiresonant guiding photonic crystal fibers is proposed. The sensor operation is based on the wavelength shift of the transmission spectrum with respect to the change of refractive index inside the air holes of the photonic crystal fibers. Both numerical and experimental analyses are carried out to investigate the spectral characteristics.
Maximum-intensity-projection images for dynamic analysis of mental sweating by optical coherence tomography
Hiroyuki Saigusa, Yoshihiro Ueda, Akihiro Yamada, et al.
We demonstrate a novel 3-D image construction method with maximum intensity projection (MIP) of B-mode images obtained by the swept-source OCT. The time-sequential MIP images with a frame spacing of only 0.7 sec are obtained to make dynamic analysis of mental sweating on human fingertips.
Characteristics of a cavity ring-up gas amplified fiber loop
N. Ni, C. C. Chan, J. Sun, et al.
A novel concept of cavity ring-up (CRU) spectroscopy is proposed for trace gas detection in an amplified fiber loop. Based on a rate equation approach, the time-evolving CRU signals in the fiber gas sensing loop are studied. The features of CRU output signals are numerically simulated and discussed. Those systemical studies and theoretical analyses will guide the future design of the fiber cavity ring-up gas sensing system.
DFB laser injection locking on Brillouin radiation for probe Stokes generation in distributed fiber optical sensing
Vasily Spirin, Marcial Castro
We report two novel optical injection-locking configurations of DFB laser without high-frequency modulator for probe Stokes signal generation in distributed fiber optical Brillouin sensing. The first one based on injection locking on ring Brillouin laser radiation and second one on self-injection locking on Brillouin amplified radiation. Locking on Brillouin amplified radiation exhibits properties inherent in two phenomena, self-injection locking and injection locking in master-slave configuration at the same time and provides significantly more intensity-stable Stokes signal.
Twin-core fiber white light interferometric bending sensor
Jun Yang, Libo Yuan, Xiaoliang Zu, et al.
A fiber optic bending sensing system that uses twin-core fiber as the sensing element has been proposed and demonstrated. The twin-core fiber act as a two-beam interferometer in which phase differences is a function of the curvature, and it can be demodulated by the shift of the unique identification spectrum. By way of FFT analysis of the white light interferometric spectrum, the variation of bending can be measured. The relationship between the bending curvature and the shift of the unique identification spectrum has been given and the experimental results were also confirmed this.
Multiple wavelength Raman fibre laser with asymmetric cavities
Swook Hann, Young-Eun Im, Dong-Hwan Kim, et al.
A low-cost Raman fibre laser for multiple wavelengths at 14xx nm has been proposed and demonstrated. Using asymmetric cavities, the Raman fibre laser provides flexible and easy complete solution of the desired multiple wavelengths output.
A wavelength swept laser with the sweep rate of 150 kHz using vibrations of optical fiber
In this report, we propose a high-speed wavelength swept light source using vibrations of an optical fiber and an external cavity laser. The end of an optical fiber coupling a semiconductor laser chip to a Littrow-mounted grating spectroscope is vibrated in the cantilever bending mode using a piezoelectric transducer. The incident angle to the grating is scanned at ultrasonic frequency, and the output wavelength is swept according to the vibration displacement amplitude. First, the relationship between the sweep span of wavelength and the linewidth is studied for different diameters of collimating lens. Second, the sweep characteristics of the output wavelength are observed in time domain. The maximum sweep rate of 167 kHz was achieved for the sweep span of 70 nm, the center wavelength of 1530 nm and the linewidth of 1.1 nm.
A high reading rate FBG sensor system using a high-speed swept light source based on fiber vibrations
We propose a fiber Bragg grating (FBG) sensor array system using a high-speed swept light source. The light source is an external cavity semiconductor laser using an optical fiber coupling with a Littrow-mounted grating spectroscope, where the fiber end is vibrated in the cantilever bending mode using a piezoelectric transducer. The incident angle to the grating is scanned at ultrasonic frequency, and the output wavelength is swept according to the vibration displacement amplitude. The maximum sweep rate of 167 kHz was achieved for the sweep range of 70 nm. In this report, the light source is used for high speed and high sensitivity FBG sensor interrogation. First, to test the operation of the proposed FBG sensor, the center wavelength variation due to temperature shift is measured in water. Second, we experimentally demonstrate the measurements of dynamic strain oscillating at 10 kHz. The observation of high frequency vibration is achieved with a sufficient sampling rate.
Detection of sub-millimeter faults with a time domain distributed Brillouin sensor
Fabien Ravet, Fabien Briffod, Branko Glisic, et al.
Sub-millimeter crack is detected with a dedicated fiber optic strain cable, a 1 m spatial resolution (w) distributed Brillouin sensor (DBS) and an advanced signal processing technique.
Effect of temperature on Brillouin gain spectrum and aging behavior in carbon/polyimide coated fiber
The effects of temperature on the Brillouin spectrum in novel carbon/polyimide coated fibers have been firstly studied. We also firstly investigated the aging behavior for these fibers by comparing the changing of the relationship between Brillouin frequency shift and temperature.
Optimization design of the pressure phase sensitivity of the fiber-optic air-backed mandrel hydrophone
Kai Yin, Hongpu Zhou, Min Zhang, et al.
Pressure phase sensitivity is one of the most important performance indexes of the fiber-optic hydrophone. Maximizing the pressure phase sensitivity is a basic principle in the fiber-optic hydrophone design. In this work, the orthogonal experimental method has been used to optimize the design of the pressure phase sensitivity of the fiber-optic air-backed mandrel hydrophone. A general three-dimensional theoretical model is carried out, and nine fiber-optic hydrophones are fabricated for orthogonal experiment. Several factors which affect the sensitivity are analyzed in the experiments, and the results validate the theory. The optimized designs are also gained by the analysis of the results to maximize the pressure phase sensitivity.
Optically powered DFB fiber laser magnetometer
G. A. Cranch, G. M. H. Flockhart, C. K. Kirkendall
An optically powered DFB fiber laser based magnetometer free from hysteresis, incorporating drift compensation is demonstrated. Optical power is delivered through a dedicated fiber to provide the required dither current yielding an electrically passive sensor.
Amplified CWDM self-referencing sensor network based on phase-shifted FBGs in transmissive configuration
A new amplified CWDM (Coarse Wavelength Division Multiplexing) self-referencing sensor network using phase-shifted fiber Bragg gratings (PS-FBGs) is experimentally demonstrated in this work. The network uses the PS-FBGs to address intensity sensors in a transmissive configuration, obtaining simultaneously in reflection a wavelength encoded reference signal. In order to enable the remote operation of the sensors, we have introduced optical amplification at the interrogation header of the network, using highly doped erbium fiber.
Highly accurate micro-displacement measurement based on Gaussian-chirped tilted fiber Bragg grating
Intensity-referenced and temperature-independent high accuracy displacement measurement is demonstrated by using a Gaussian-chirped tilted fiber Bragg grating (TFBG). A specially designed bending cantilever beam is used to provide a displacement-induced Gaussian-strain-gradient and internal tilt angle modulation along the sensing TFBG. Compared with a straight FBG, the peak intensity of the Bragg resonance in the TFBG shows an improved sensitivity to the displacement but is immune from the spatially uniform temperature changes. A displacement resolution up to 1×10-3 mm and thermal fluctuation less than 2% full-scale for a temperature range of 0~80°C are experimentally achieved.
Radiation mode resonances of tilted fiber Bragg gratings for high index media measurement
Chengkun Chen, Tuan Guo, Albane Laronche, et al.
We propose and experimentally demonstrate the feasibility high refractive indices measurement (larger than the fiber cladding index) by using individual radiation mode resonances of tilted fiber Bragg gratings. By tracking a single cladding mode relative to the Bragg resonance, improved sensitivity for refractive index measurement has been achieved and the temperature fluctuations could be eliminated. The maximum index sensitivity is 5×10-4 with a detected power resolution of 0.1dB.
Detection of micrometer crack by Brillouin-scattering-based distributed strain and temperature sensor
A Brillouin-scattering-based distributed strain and temperature sensor (DSTS) has been employed to detect cracks on ceramic by measuring the strain distributions along the surface of the ceramic for the first time. The existence of cracks and their locations are identified by measuring the strain distribution on a sensing fiber bonded on the ceramic surface. Due to innovated design and signal processing, the distributed Brillouin sensor developed for this study achieves a uniquely high resolution and accuracy. Experimental study on ceramic tile specimens demonstrated the efficacy of the distributed Brillouin fiber optic sensor in detecting and locating fine cracks.
Fibre Bragg grating use in fluid dynamic studies
S. A. Wade, M. Nazarinia, S. B. Wong, et al.
The application of fibre Bragg grating sensors for strain and force measurements in fluid dynamic experimental studies is presented. In the first example, a fibre Bragg grating is used as both a tether and a strain gauge for studies of neutrally buoyant spheres. The measured strains on the tether were found to agree well with the theory for the flow rates tested (0.14 to 0.33 m/s). In the second example a Bragg grating sensor has been used to monitor the forces acting on a cylinder as a function of flow rate and when the cylinder is translated in a stationary fluid. Excellent agreement was found between the vibration frequencies of the cylinder as measured by the Bragg grating and with a camera use to record the motion of the cylinder.
Wavelength domain interrogation of polarimetric temperature sensor based on polarization maintaining fiber
Yuanhong Yang, Tong Shen, Jinjin Guo, et al.
A wavelength domain technique based on the detection of peak wavelength in the interference pattern was proposed and applied to a reflection type polarimetric temperature sensor made of polarization maintaining fibers. The measurement equation that relates the temperature variation linearly to the shift of the peak wavelength in the interference pattern was derived. An experimental sensor was setup to verify the effectiveness and the accuracy of the detection technique over an applied temperature range from -40°C to 80°C. Experimental results agree well with theoretical prediction.
Shot noise limited fiber laser source for sensing applications
Jong H. Chow, Timothy T. Y. Lam, Ian C. M. Littler, et al.
We propose active feedback frequency locking of a single longitudinal mode fiber laser to passive, high Q fiber ring cavities, for filtering excess relative intensity noise, thereby producing shot-noise limited light source for sensing applications.
Optical fiber temperature sensor using a thin film band pass filter and dual wavelength push-pull reflectometry
Yasutoshi Komatsu, Keiichi Inoue, Masayuki Nakano, et al.
This experimental temperature sensing system uses dual wavelength push-pull reflectometry and a thin-film band pass filter deposited on an optical fiber end face. The system presents advantages over fiber Bragg grating sensors: it can use the mature optical time domain reflectometry (OTDR) technology instead of expensive wavelength-selective technology; it can probe the temperature in a small spot area; and it can be free from influences of disturbances along the optical fiber or within the measuring system. Moreover, it preserves merits of optical fibers such as low transmission loss and immunity to electromagnetic noise. The presented system has measurement accuracy of better than ±0.5°C.
Miniature in-line photonic-crystal-fiber etalon fabricated by 157nm laser micromachining
Zeng-ling Ran, Yun-jiang Rao, Hong-you Deng, et al.
A miniature in-line fiber-optic Fabry-Perot etalon sensor is fabricated on a photonic-crystal-fiber (PCF) by using 157nm laser micromachining for the first time to our knowledge. Experimental results show that such a PCF-based etalon sensor has an excellent fringe visibility of up to ~26dB due to the mirror-finish quality of the two cavity surfaces inside the PCF. This etalon sensor can be used as an ideal one for precise strain measurement under high temperature of up to 800°C. It can offer other outstanding advantages, such as fast and easy fabrication, high reproducibility, capacity of mass-production, low-cost, low temperature-strain cross-sensitivity, and high signal-to-noise ratio, etc.
Fiber Bragg grating based on nanostructure core fiber
In this paper, we report a fiber Bragg grating (FBG) using a novel nanostructure core fiber (NCF). The NCF is an all-solid silica based structure with a 2D periodic lattice of high index rods in the core. The FBG is written by a phase mask technique in an UV laser system. The temperature and strain sensitivities of the grating device have been obtained experimentally.
Pressure and temperature characterization of Bragg gratings in grapefruit microstructured optical fibers
Bai-Ou Guan, Da Chen, Yang Zhang, et al.
We report on the pressure characterization of Bragg gratings in grapefruit microstructured fibers. The air holes enhance the pressure response. The effect of air expansion in the holes on temperature response was also investigated.
Laser-micromachined Fabry-Perot fiber-optic tip sensor for temperature-independent measurement of refractive index
Zeng-Ling Ran, Yun-Jiang Rao, Wei-Jun Liu, et al.
We propose and demonstrate a Fabry-Perot fiber-optic tip sensor for high-resolution refractive-index measurement. The sensor head consists of a short air cavity produced near the tip of a single-mode fiber by 157-nm laser micromachining. The external refractive index is determined from the maximum visibility of the interference fringes in the reflection spectrum of the fiber. This sensor provides temperature-independent measurement of practically any refractive index larger than that of air and offers a refractive-index resolution of ~4×10-5 in its linear operating range. The experimental data agree well with the theoretical results.
Technique for estimating the tuning speed of fiber Bragg gratings
Alexandre A. P. Pohl, Paulo T. Neves Jr., Roberson A. Oliveira, et al.
The measurement of the tuning speed in fiber Bragg gratings is an increasingly important parameter for characterizing the dynamics of tunable devices. Optical spectrum analyzers and wavelength meters are not suitable due to their slow response for measuring the wavelength shift in time. In this paper we report on a technique for estimating the tuning speed of a fiber Bragg grating which is based on accessing the wavelength shift through a calibration curve and measuring the time in which the shift occurs with the help of a fast photo-detector.
Rotational dependence of laser light accessing photonic crystal fibre cores from the side
John L. Holdsworth, John Canning, Chris Dewhurst
We investigate the fluorescence of an Er-doped aluminosilicate stepped index core with surrounding structured lattice when pumped transversely with the collimated output of a 980nm diode. A small rotational dependence is observed indicating the importance of cladding structure alignment during experiments that involve processing the core from the side, including Bragg grating writing.
Generation of ultra-narrow sensing filters using cross polarisation in a linear SOI photonic crystal waveguide
John Canning, Martin Kristensen, Nina Skivesan, et al.
A narrow band (3dB bandwidth <2nm) transmission notch filter based on polarisation conversion within a photonic crystal waveguide is demonstrated. Signal contrast between quasi- TE and TM eigenstates reaching 40dB is achieved. Further, multiple resonant wavelength coupling between the two eigenstates is also observed. These offer a novel alternative approach to sensing and biodiagnostics compared to previous use of the band edge of a photonic crystal waveguide.
Strain sensor using phase measurement techniques in polymer optical fibers
A. Bachmann, M. Luber, H. Poisel, et al.
POF elongation sensors have been proposed e.g. by [1] as a low-cost alternative to FBG (single mode fiber Bragg gratings) sensors targeting the lower sensitivity range. A recently recovered detection system known from laser distance meters turned out to be very sensitive while staying simple. The approach is based on measuring the phase shift of a sinusoidally modulated light signal guided in a POF under different tensions resulting in different transit times and thus different phase shifts.
Highly sensitive optical refractometer based on edge-written ultra-long period fiber grating formed by periodic grooves
Y. Song, Y. J. Rao, T. Zhu, et al.
An ultra-long-period fiber grating with periodic grooves structure (G-ULPFG) fabricated by using an edge-writing method with high frequency CO2 laser pulses is reported, for the first time to our knowledge. The experimental results show that the different resonant peaks of the G-ULPFG have different temperature and refractive index sensitivities, and in particular, the refractive index sensitivity is much larger than that of conventional ULPFG due to the edge-groove structure. Such a G-ULPFG could be used as a highly sensitive optical refractometer with temperature self-compensation.
Development of borehole multiple deformation sensor system
Yoshio Kashiwai, Shuji Daimaru, Hiroyuki Sanada, et al.
The multiple deformation sensor system for small diameter borehole is required for the long term monitoring of deformation of rock mass of high-level radioactive waste disposal site. The conventional electric monitoring systems are difficult to apply for a long term monitoring in many cases because of the sensor failure caused by lowering of insulation or other problems and only available for the large borehole and for 6 or less measurement sections. The Borehole Multiple Deformation Sensor System was developed based on the FBG (Fiber Bragg Grating) sensor technology that is expected to have longer life time than electric systems. The developed system can be set in a 66 mm diameter borehole and available for 9 or more measurement sections that can be hardly achieved by electric systems. The sensor system is applying for the monitoring of ground deformation in the Horonobe Underground Research Laboratory in Japan.
Bi2O3-based erbium doped fiber laser with over 110 nm tunable range for fiber sensor sources
The advantage of optical fiber grating sensors are easily implemented multiplexing by using broadband light source. Erbium doped fiber (EDF) are important as a gain media, because it affects the performance of light sources. We demonstrated tunable fiber ring laser using Bi2O3-based Erbium doped fiber (BIEDF) and a tunable filter with bandwidth of 1 nm. We show the BIEDF fiber length dependence, pump power dependence and also show the its spectra. By increasing fiber lengths of BIEDF, the tunable range changes toward longer wavelengths with varying tunable range. By using 0.7 m of BIEDF as a gain media, the tunable range reached over 110 nm with just pump power of 100 mW at 1480 nm. Tunable range was insensitive to pump power in this experiment. Also we show the laser spectra. BIEDF laser shows high optical signal-to-noise ratio (OSNR) higher than 55 dB at over 110 nm tunable range, and 70 dB for 99 nm (1530 - 1629 nm) tunable range. This means that BIEDF has potential for broad band fiber sensor sources, especially for fiber grating sensors.
Polarimetric implementation of a low loss interferometric sensor array
A. Eyal, A. Isseroff, A. Oni, et al.
A low-loss polarimetric sensor array, comprising a cascade of five polarization maintaining fibers and a novel peeling algorithm, is experimentally demonstrated. With one segment buried in a sand box, the array successfully detected pressure variations.
Sensing and splicing applications of small core Ge-doped photonic crystal fibers
Yiping Wang, Sven Brueckner, Jens Kobelke, et al.
Sensor related properties of a small core (4.1μm) Ge-doped photonic crystal fiber (PCF) are being reported. Fiber Bragg gratings with 35% and almost 100 % reflectivity were written in the Ge-doped PCF before and after hydrogen loading, respectively, by use of a UV laser. A 5.6pm/°C temperature sensitivity of the FBG was observed. Additionally, a novel method is demonstrated to splice such PCF by use of a commercial fusion splicer with default splice parameters for standard single mode fibers (SMF). No parameter adjustments are required to splice the PCF to various SMFs and a low splice loss of 1.0 ~ 1.4dB can be achieved. No splice interface emerges at the splice joint, which is of advantage for the sensing applications of such a PCF.
Crack detection in reinforced concrete beam by use of distributed Brillouin fiber sensor
We conducted a strain characterization experiment to detect concrete beam cracks using distributed Brillouin sensor system. An accurate Brillouin multiple-peak fitting method is used to enhance the spatial and strain resolution. This allows us to exactly extract the distributed strain section that is smaller than the spatial resolution of the Brillouin sensor system.
Concrete pavement vibration monitoring due to the car passing using optical fiber sensor
Ziyi Zhang, Samuel LeBlanc, Xiaoyi Bao
An optical fiber vibration/acoustic sensor based on polarization diversity scheme has been developed to study the vibration of the highway pavement slabs with vehicles passing. This process induced the birefringence change in a 50m sensing fiber embedded along the FRP bars. The damping of the impact in time domain and a 2Hz vibration frequency are observed.
Performance improvement of a cascaded tapered long period grating refractometer by using nano-sized high refractive index coatings
P. Pilla, P. Foglia Manzillo, M. Giordano, et al.
In this work, nano-sized polymeric coatings with higher refractive index than the cladding one were used to induce the modal transition in tapered long period gratings in a cascaded configuration. The aim of this experimental investigation was to increase the sensitivity of the bare device to surrounding refractive index changes while preserving a good fringes visibility. An original configuration of the device in terms of coated/not coated area was identified that best achieve the aforementioned target.
Highly efficient fluorescence sensing using microstructured optical fibres: side-access and thin-layer configurations
A model is presented for calculating the performance of fluorescence-based optical-fibre sensors that considers the full vectorial nature of optical-fibre electromagnetic-field solutions making it suitable for modeling microstructured optical fibres with wavelength and sub-wavelength-scale features. By applying the model to a specific fibre geometry it is shown that high-index, small core (subwavelength) fibres allow for enhanced fluorescence capturing due to the formation of a thin, high-intensity layer at the core-cladding boundary. The model is evaluated in this regime for two sensing configurations of particular interest for future sensing systems, a side-access sensor for liquid-based sensing and a thin-layer (surface) sensor. Both configurations can offer improvements for fluorescence-based sensing.
Simultaneous measurement for temperature and strain by use of Sagnac interferometer with controlled sensitivity
We propose a novel approach for resolving temperature and strain variations by use of Sagnac interferometer incorporating two types of high birefringence fibers (HBFs) and a polarization controller. The two types of HBFs are spliced together to act as the sensing head for temperature and strain discrimination. The detected parameters are two wavelength dips over a broad wavelength range in the transmission spectrum of the Sagnac interferometer, whose sensitivity responses to temperature and strain both depend on those of the two HBFs. As a result, the sensitivity responses can be controlled by adjusting the polarization controller adjacent to the sensing head to shift the wavelength dips and then change their degrees of dependence on the two HBFs.
Structure optimization of air-hole fibers for high-sensitivity fiber Bragg grating pressure sensors
Charles Jewart, Di Xu, Kevin P. Chen, et al.
This paper presents sensitivity enhancement of fiber Bragg grating sensors written in two hole fibers to external hydrostatic pressure. Finite element analysis was used to optimize the size, diameter, and configuration of air holes. The fiber core was then fabricated in the region with the maximum birefringence induced by external pressure. Resonant peak splitting of fiber Bragg gratings were used to gauge the external hydrostatic pressures. By using 220-μm diameter two hole fibers with 90-μm air holes, the optimized fiber structure with a fiber core fabricated on the edge of the air hole registered 0.102 pm/psi hydrostatic pressure response, yielding 6.5 times enhancement than previously reported in two hole fibers. The sensitivity enhancement of fiber sensors is further demonstrated by controlling the size of air holes.
Self-referenced fiber microbend displacement sensor based on dual-wavelength fiber-Bragg gratings interposed with a multimode fiber micro bender
Xiufeng Yang, Varghese Paulose, Lie Yong Teo, et al.
A self-referenced multimode fiber (MMF) micro bend displacement sensor is presented in this paper. In this sensor, two single mode fiber Bragg gratings (FBGs) with different wavelengths are employed for the self-reference of the micro bend displacement measurement. A short piece of MMF with a mechanical micro bender, inserted between the two FBGs, acts as the sensing part. The sensor output is very stable (variation in the intensity difference was ~ 0.07dB) within the 8dB dynamic range of the transmission loss. And the maximum variation of the intensity difference with temperature is about 0.55dB from 20°C to 75°C. The sensor system offers many advantages, including higher stability, single end access, and high sensitivity.
Suppression of polarization sensitivity in BOTDA fiber distributed sensing system
We propose and demonstrate a novel method to suppress the polarization induced signal fluctuation in Brillouin Optical Time Domain Analysis (BOTDA) fiber distributed sensing system. The polarization diversity scheme contains two polarization beam splitters (PBSs) and a piece of single mode fiber (SMF). The pulsed pump wave is split into two beams with orthogonal polarization states and one of the beams is delayed by a time related to the pulse width. Then, the two beams are recombined. Theoretically, the Degree-of-Polarization (DOP) of the recombined wave is zero and the distributed sensing system is insensitive to the polarization state of the probe. Stable distributed temperature measurement is demonstrated along a 1.2 km SMF.
Fast four step digital demodulation for multiplexed fibre laser sensors
M. Milnes, A. Tikhomirov, S. Foster, et al.
We demonstrate an electro-optic phase modulator based demodulation system for acoustic frequency modulated optical signals. The system is free from polarisation fading and is capable of retrieving high frequency signals, ultimately limited by the time of flight of the interferometer itself. Digital interrogation method is based on the Carré algorithm and does not require fine tuning of the introduced phase and is suitable for simultaneous phase retrieval at multiple wavelengths without the need for correction transfer filters.
FBG sensor interrogation based on RF signal measurement
A novel interrogation method for optical fiber Bragg grating (FBG) sensors has been proposed by converting the change of the FBG wavelength into the phase difference between two radio frequency (RF) signals. As a result, the beating-induced RF signal power changes with the FBG wavelength shift. This technique could be used for high speed FBG interrogation and, due to the use of a second FBG to produce the reference RF signal, temperature cross-sensitivity effect is compensated automatically. Theoretical analysis and experimental demonstration have been carried out. Performances of the FBG sensor interrogation scheme have been studied.
Monitoring surface crystal growth using an intrinsic exposed-core optical fiber sensor (IECOFS)
David W. Lamb, Martijn Boerkamp, Peter Lye
An unclad section of silica optical fiber has been used to detect, and measure heterogeneous (surface) crystal growth in a solution of calcium carbonate. Surface crystal growth is found to attenuate radiation transmitted along the fiber core via the refraction of guided modes out of the core. Optical power output was found to be linearly correlated with crystal size (R2 = 0.97, n = 9) and the optical signal was found to be restored following chemical removal of deposited crystals (without physical intervention). Sensitivity to crystal growth was found to be proportional to the length of the unclad (exposed) core and inversely-proportional to fiber diameter. These results suggest a simple skip-length ray model, coupled with refraction of guided modes out of the fiber core can be invoked to explain the mechanism of optical power attenuation.
Fail-safe sensor for structural health monitoring
This paper introduces the concept of a fail-safe sensor to monitor the structural health of a composite repair. The low-cost fiber Bragg grating (FBG) sensor system consists of a light source, two specially designed fiber Bragg gratings and a photodiode detector. This system is applied to a typical bonded composite scarf joint often employed in aerospace structures. A finite element model is developed to assess the change in strain distribution as the result of a structural debond. The proposed monitoring system will be validated through an experimental investigation.
Pressure compensated distributed feedback fibre laser hydrophone
A pressure compensated distributed feedback fibre laser hydrophone is described. Pressure compensation is achieved by incorporating an air-filled bladder and acoustic filter into the hydrophone making it insensitive to hydrostatic pressures to depths of up to 50m.
Slotted microstructured optical fibers
Felicity M. Cox, Maryanne C. J. Large, Cristiano M. B. Cordeiro, et al.
A new type of microstructured optical fiber, with a transverse slot running along its length, has been fabricated from polymethylmethacrylate. The slot exposes the fiber core over long lengths, allowing for materials to be directly introduced into the vicinity of the evanescent waves of the core modes. The use of this fiber as an evanescent wave chemical sensor has been demonstrated.
Backscatter immune Mach-Zehnder-Sagnac hybrid interferometric sensor
We propose and demonstrate a Mach-Zehnder-Sagnac hybrid interferometer for precision sensing. This configuration facilitates immunity from Rayleigh backscatter, polarization wander and scale factor drift in high performance fiber gyroscopes.
Quasi-static fiber strain sensing with absolute frequency referencing
We present a highly sensitive detection system for quasi-static strain, employing radio-frequency modulation interferometry and absolute frequency referencing, demonstrating a few tens of pε/√Hz sensitivity between 1 - 6 Hz.
Biaxial measurement of optical frequency domain reflectometry using polarization maintaining fiber Bragg grating
Koji Omichi, Akira Sakamoto, Shunichiro Hirafune, et al.
We demonstrated the optical frequency domain reflectometry (OFDR) measurement system with all polarization maintaining fiber including fiber Bragg grating (FBG). We succeeded to obtain the slow and fast axial Bragg reflection spectra individually. We proposed the novel method to compensate the measured position miss matching between slow and fast axial Bragg reflection spectra, and confirmed the validity of the method.
U-shaped plastic optical fiber dissolved oxygen sensor
Haiwen Cai, Fenghong Chu, Ronghui Qu, et al.
A dissolved oxygen sensor based on U-shape plastic optical fiber (POF) was described. Analyte-sensitive fluorophore are entrapped into ormosil film by using Sol-gel method. Phase modulation technique is used to measure fluorescence lifetime. The influence of oxygen indictor concentration, annealing time and U-shaped POF curve radius on the systems sensitivity is studied.
Fabrication and characterization of long period gratings in air-core photonic bandgap fibers
W. Jin, Y. P. Wang, J. Ju, et al.
Long period gratings in hollow-core photonic-bandgap fibers were fabricated by use of a pulsed CO2 laser. The resonant wavelengths of these gratings are sensitive to strain but insensitive to temperature, bend and external refractive index.
Design and clinical results from a fibre optic manometry catheter for oesophageal motility studies
J. W. Arkwright, S. N. Doe, M. C. Smith, et al.
We report the design and operation of an optical fibre manometry catheter for measuring variation in pressure in the oesophagus during peristalsis. Catheters of this kind are used to help diagnose oesophageal disorders by recording the muscular contractions of the oesophageal wall in patients having difficulty swallowing. Traditional oesophageal catheters consist of an array of recording sites enabling pressure measurement from multiple locations along the the oesophagus. However, these catheters tend to be bulky or complex to operate whereas our optical equivalent uses a series of Fibre Bragg Grating (FBG) pressure sensors on a single fibre; significantly reducing complexity and allowing the catheter diameter to be minimised. The data from each FBG was recorded using a solid state spectrometer in which the reflected peaks each covered a number of pixels of the spectrometer. This has enabled the FBG peaks to be tracked in wavelength with sub-nanometre precision resulting in pressure sensitivities of less than 1mmHg. Results from a clinical trial carried out on 10 healthy subjects will be presented. For the trial, each subject was simultaneously intubated with the optical catheter and a commercially available solid-state catheter. Back-to-back readings were taken from both devices during a series of controlled water swallows. Ten swallows were recorded with the catheters sensors positioned in proximal, mid, and distal regions of the oesophagus and the data analysed statistically. The fibre optic device accurately picked up the dynamic variations in pressure, and can react at least as fast as the solid state device.
Characteristics of gas breakdown in hollow-core fibers
We succeeded in obtaining gas discharge in 250, 150, and 50μm bore-diameter hollow-core fibers by using longitudinal DC excitation. Stable glow discharges of at least several minutes were observed for these hollow-core fibers, and a flash glow was also observed for a hollow-core capillary with a diameter of ~20μm. Breakdown of helium and argon gases in a 26.2cm-length 250μm-inner-diameter hollow-core fiber was achieved with a voltage of less than 30kV. Breakdown voltages of helium and argon gases were measured for various bore-sizes, fiber-lengths, and a pressure range of from below 1 to 50 Torr. Experimental results deviated from previous theoretical models and further theoretical and experimental investigations are needed to understand the unique characteristics of gas-discharge in miniature capillaries with bore-diameter below 250μm.
Multiplexed fiber optic sensor array for geophysical survey
We present the latest results from our multiplexed fiber optic Fabry-Perot acoustic sensor array using modulated lasers. It offers the possibility of a robust, reliable and easy to deploy system, meeting the demands of geophysical survey.
Time-resolved all fiber fluorescence spectroscopy system
A. Y. H. Chen, F. Vanholsbeeck, D. C. S. Tai, et al.
We describe a simple fiber optic fluorescence spectrometry system with a wide variety of biomedical applications. This low-cost, all-fiber system is portable, robust and has the capacity to acquire fluorescence spectra at rates up to 1 kHz. We demonstrate the capabilities of the system by presenting experimental measurements of action potentials in the di-4-ANEPPS stained heart and the concentration of GFP tagged bacteria.
Nanoimprinting on optical fiber end faces for chemical sensing
Optical fiber surface-enhanced Raman scattering (SERS) sensors offer a potential solution to monitoring low chemical concentrations in-situ or in remote sensing scenarios. We demonstrate the use of nanoimprint lithography to fabricate SERS-compatible nanoarrays on the end faces of standard silica optical fibers. The antireflective nanostructure found on cicada wings was used as a convenient template for the nanoarray, as high sensitivity SERS substrates have previously been demonstrated on these surfaces. Coating the high fidelity replicas with silver creates a dense array of regular nanoscale plasmonic resonators. A monolayer of thiophenol was used as a low concentration analyte, from which strong Raman spectra were collected using both direct endface illumination and through-fiber interrogation. This unique combination of nanoscale replication with optical fibers demonstrates a high-resolution, low-cost approach to fabricating high-performance optical fiber chemical sensors.
10 kHz linewidth distributed feedback photonic crystal fibre (DFB-PCF) laser
Jason D. De Iuliis, Nathaniel Groothoff, John L. Holdsworth, et al.
A distributed feedback laser was fabricated in Er3+-doped photonic crystal fibre. Single mode lasing is obtained with <10kHz linewidth. The output was amplified to 12mW using a commercial erbium doped fibre amplifier (EDFA).
Vibration sensing of solid using long-period fiber grating
Long-period fiber gratings (LPG) are fabricated by illuminating 248 nm KrF excimer laser light to a single-mode optical fiber that is photosensitized with boron doping. By applying the intensity-modulation scheme, which is known to be effective as an interrogation method for fiber Bragg grating (FBG) vibration and underwater acoustic sensors, we construct an optical vibration sensor of a solid that uses a LPG as a sensing element. It is confirmed that the LPG vibration sensor yields a clear and stable signal waveform and shows good linearity when the amplitude of the vibration strain is varied. The dynamic range of the sensor would be more than 100 dB, which is larger than that with a FBG as a sensing element. Since a LPG is known to show higher sensitivity to static strain when one uses a higher-order cladding mode, it is expected that with proper choice of the cladding mode a LPG vibration sensor will show much higher sensitivity than a FBG vibration sensor.
Azimuthally symmetric long period fibre grating fabrication with a TEM01*-mode CO2 laser
We present a manufacturing method that produces azimuthally symmetric long period fibre gratings using a TEM01*-mode CO2 laser. The outlay and optimization of the optical system are introduced, and the long period fibre grating fabrication method is outlined. We also investigated the polarization properties of the fabricated long period fibre gratings to determine the quality of the grating structures.
A digital passive phase demodulation scheme using 3×3 coupler for fiber-optic interferometric sensors
M. Pang, M. Zhang, L. W. Wang, et al.
A real-time digital phase demodulation scheme is developed. This scheme, based on cos-1 and channel-choosing techniques, uses the two optical outputs from a 3×3 coupler to overcome the signal fading problem of fiber interferometer.
Cladding mode resonance of special optical fiber for bending sensor with temperature insensitivity
Tingyun Wang, Fufei Pang, Xianglong Zeng, et al.
In this paper, we fabricated and demonstrated a temperature-insensitive fiber bending sensor based on a special optical fiber with cladding mode resonance. The special fiber, with pure silica core and a fluorine-codoped inner cladding, fabricated by using conventional MCVD technique exhibited strong cladding mode resonance. The bend curvature dependence of resonant spectrum was investigated with high sensitivity to be -10.15nm•m-1 and was found to possess an insensitivity to temperature. The proposed special fiber bending sensor is simple and low cost.
Blind source separation techniques for percolation type leakage detection in dikes using fiber optic DTS signals
Amir A. Khan, Valeriu Vrabie, Guy D'Urso, et al.
Distributed temperature sensors (DTS) based on fiber optics present an efficient means for temperature data acquisition. The use of DTS data to detect leakages in dikes necessitates some processing of this data. Formulating leakage detection as a source separation problem, the goal of this paper is to compare various blind source separation techniques for percolation type leakage detection using a real data set. Singular value decomposition can be used as the first step to separate out the ground response where acquisitions are made. Two independent component analysis algorithms, JADE and FastICA, assuming independence of sources, are tested to find the best solution for leakage detection.
Wavelength-tuneable add/drop multiplexer using broadband transmission filters and a narrowband reflection filter
Ronnie Kritzinger, André Booysen
We present an optical add/drop multiplexing device utilising a pair of broadband transmission filters and a narrowband reflection filter, designed for operation in a dense wavelength-division multiplexing network. Evanescent field coupling in an optical fibre-based cladding-mode coupler allow broadband light to be transferred between two fibres containing non-uniform long-period fibre gratings. An erbium-doped fibre amplifier was used to restore the power level of the output signal obtained from the cladding-mode coupler, to its original level. A tuneable Bragg grating is used to select a specific wavelength channel from the broadband light routed through the cladding-mode coupler, and is able to work over a linear tuning range of 5.3 nm, covering ~13% of the C-band.
Vulnerability of fiber-optic links for high-speed diagnostics to pulsed-power facilities
Sylvain Girard, Jacques Baggio, Jean-Luc Bourgade, et al.
The vulnerability of fiber-optic links for high-speed diagnostics to the harsh environments (short pulse of 14 MeV neutrons, x- and γ-rays) associated with the future Megajoule class lasers (LMJ, NIF) is investigated through experiments at both ASTERIX and OMEGA facilities. Radiation responses of a Mach Zehnder modulator and single-mode fiber optics have been characterized with high dose rate x-ray pulses to simulate the conditions expected for the next generation of pulsed-power facilities. The tolerance of a fiber-optic link to the mixed environment to the present worldwide most powerful laser neutron source facility (OMEGA, Rochester) is also presented.
Highly efficient fluorescence sensing using microstructured optical fibres: general model and experiment
A general model of excitation and fluorescence recapturing by the forward and backward modes of filled microstructured optical fibres (MOFs) is developed for fluorecence-based fibre optic sensors. It is demonstrated that the light-matter overlap alone does not determine the optimal fibre choice for maximum sensing efficiency. Fibre designs with sub-wavelength features and high-index glasses exhibit localised regions of high intensity, and we show that these regions can lead to approximately two orders of magnitude enhancement of fluorescence recapturing. We demonstrate higher efficiency of fluorescence recapturing into backward modes in comparison with that of forward modes. We present experimental results for both backward and forward flourescence recapturing and demostrate a good qualitative agreement between the numerical model and experimental results.
Microstructured index-guiding fibers with large cladding holes for evanescent field chemical sensing
Hartmut Lehmann, Jens Kobelke, Kay Schuster, et al.
Design, fabrication and application of small solid-core microstructured optical fibers with large cladding holes for evanescent field chemical sensing of gases and liquids will be presented. Such steering-wheel fiber structures give a high mode-field overlap in the holey region, they show low losses over a broad spectral range and they are easier to fabricate than hollow-core bandgap-guiding photonic crystal fibers.
Fiber Bragg grating based accelerometer
H. Y. Au, S. K. Khijwania, H. Y. Tam
A novel design of fiber Bragg grating (FBG) based accelerometer is proposed in this paper. The chirp-free mechanism on the FBG sensing element is the methodology employed in this design. The sensor has the flexibility to apply different mechanical parameters, and it shows excellent performance to different applied signals. The performance is then optimized by varying different configuration of the sensor. Good sensitivity (18με/g) and signal-to-noise ratio (20.68dB re nm/g) is easily achieved. Maximum input signal frequency up to 150Hz is able to be caught up by the specific configuration of the accelerometer. The accelerometer also has the capability of capturing a full sine wave input signal with the maximum peak-to-peak amplitude up to 3.9nm.
Research on high-resolution distributed fiber optic stress sensor for landslide monitoring
In this paper, an early warning monitoring system for landslides, based on high spatial resolution distributed fiber optic stress sensing and monitoring the intra-stress distribution and changes in landslide bodies, was first presented. The principle of distributed fiber optic stress sensing and the monitoring method for landslides were described in detail. Through measuring the distributed polarization mode coupling in the polarization-maintaining fiber, the distributed fiber stress sensor with stress measuring range 0-15Mpa, 10cm spatial resolutions and measuring range 0.5km, was designed. The warning system was investigated in detail through the field test also.
10 keV x-ray radiation effects on Yb- and Er/Yb-doped optical fibers: a micro-luminescence study
Sylvain Girard, Youcef Ouerdane, Claude Marcandella, et al.
The use of rare-earth doped optical fibers in space implies to develop waveguides tolerant to the radiation levels associated with a space mission. Erbium (Er)- or Ytterbium/Erbium (Yb/Er)-doped fibers have been shown to be very vulnerable to ionizing radiations especially through the strong increase of their attenuation around the pump and amplified signal wavelengths. In this paper, we investigate by confocal luminescence microscopy the radiation-induced spectroscopic changes on prototype Yb or Yb/Er -doped optical fibers. The tested fibers allow us to provide new insights into the relative influence of the P, Al doping on the radiation responses of their silica-based host matrix and on the transitions between the energy states of rare-earth ions.
Novel fiber optic polarimetric torsion sensor based on polarization-maintaining photonic crystal fiber
H. Y. Fu, S. K. Khijwania, H. Y. Au, et al.
We proposed and demonstrated the application of a polarization-maintaining photonic crystal fiber for torsion sensing. The sensor has high twist angle resolution and exhibits reduced temperature sensitivity, making it an ideal candidate for torsion sensing.
Self aligning fibre for a fibre optic voltage sensor
P. Hambley, A. Michie, I. Bassett, et al.
The ongoing development of a fibre optic voltage sensor requires a self-aligning fibre. We experimentally demonstrate fibre designs with preferential bending directions which self-align when coiled as part of a voltage sensor device. Such a fibre has much wider applications.
Progress toward low-cost mass-produced polymer fibre tapers for liquid level monitors
Tapers suitable for a range of sensing applications have been produced using a heat and pull method. The standard heat and pull method is much faster than chemical tapering and also allows multiple tapers to be formed on to a single fibre for distributed sensing. A refinement of the heat and pull method is able to produce tapers extremely quickly, opening up the possibility of cheap, mass produced sensing tapers in polymer optical fibres. A single and multiple liquid level sensor is demonstrated.
Optical fiber sensor toward pyridine vapors detection
Cesar Elosua, Candido Bariain, Ignacio R. Matias, et al.
A novel vapochromic complex has been used to develop an optical fiber device sensitive to pyridine vapors. In solid state, this material is blue, and in the presence of pyridine vapors, its color changes to pink-white. The vapochromic material is solved in tetrahydrofuran (THF) and immobilized in a plasticized polymeric, fixing it onto a cleaved ended optical fiber pigtail by dip coating. The fabrication process was optimized in terms of number of dips and dipping speed, evaluating the final devices by dynamic range. Employing a reflection set up, the response of the sensors was registered in terms of absorbance spectrum and changes in reflected optical power. Devices showing a linear response with different vapors concentrations were obtained, with a detection limit of 1 PPM (v/v).
Hybrid optical fiber sensor and artificial neural network system for bioethanol quality control and productivity enhancement
Edmilton Gusken, Ricardo M. Salgado, Carlos E. V. Rossell, et al.
Bioethanol is produced by bio-chemical process that converts sugar or biomass feedstock into ethanol. After bio-chemical process, the solution is distilled under controlled conditions of pressure and temperature, in order to obtain an ethanol-water solution. However, the ethanol concentration analysis is generally performed off-line and, sometimes, a re-distillation process becomes necessary. In this research, an optical apparatus based on Fresnel reflection has been used in combination with artificial neural networks for determination of bioethanol concentration in hydro-alcoholic solution at any temperature. The volumetric concentration and temperature effect was investigated. This intelligent system can effectively detect and update in real-time the correction of distillation parameters to reduce losses of bioethanol and also to improve the quality in a production plant.
Chemical, Environmental, Biological, and Medical Sensors I
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Fiber Bragg grating applications in biomechanics
Fibre Bragg gratings are promising sensors for medical and bioengineering applications, mainly because of their small dimensions and chemical inertness. Although few examples of such applications are published up to date, we present results that show the expected potential for FBG sensor applications in biomechanical engineering.
Fiber-optic evanescent-field sensor device for CO2 and explosive detection
W. Schade, R. Orghici, U. Willer, et al.
A fiber optic sensor for monitoring CO2 during sequestration as well as for sensing the explosive TNT is described. The sensor is based on evanescent-field spectroscopy, functionality and sensitivity are characterized.
Novel FBG-based sensor configuration for H2 leak detection in air
C. Caucheteur, M. Debliquy, D. Lahem, et al.
The explosion risk linked to the use of hydrogen (H2) as combustible requires low-cost and efficient sensors. We present a multipoint in-fiber sensor capable of H2 leak detection as low as 1% concentration in air with a response time smaller than a few seconds. Our solution utilizes uniform fiber Bragg gratings (FBGs) surrounded by a catalytic sensitive layer made of a ceramic doped with a noble metal. In the presence of H2 in air, the sensitive layer undergoes an exothermic reaction and elevates the temperature around the FBGs. The sensor interrogation technique is based on the monitoring of the resonant wavelength shift. In this paper, the performances of the sensor are also discussed.
Comparison of palladium thin films used in a transmission based optical fibre hydrogen sensor
Results are presented of a comparison between two palladium films of different thicknesses used as the sensing element in a transmission based optical fiber hydrogen sensor. The palladium films, 16nm and 26nm thick, were deposited onto glass substrates using thermal vacuum evaporation. The absorption and desorption of hydrogen causes the optical properties of palladium to change depending on the concentration of hydrogen gas it is exposed to. Using a deuterium/halogen light source in conjunction with a UV/VIS spectrometer the changes in the optical transmittance in the visible spectrum of the Pd films was monitored for different concentrations of hydrogen from 0 to 5% in a nitrogen atmosphere. A comparison of the changes in the optical transmission intensity is presented for palladium films as they were exposed to varying concentrations of hydrogen gas. The 26nm palladium film was capable of measuring changes in transmission intensity of up to 46% while the range for the thinner palladium film was 20% when exposed to 5% hydrogen concentration in nitrogen.
All-fiber optical coherence tomography system incorporating a dual fiber stretcher dispersion compensator
Sairam Iyer, Stéphane Coen, Frédérique Vanholsbeeck
We report on the design and experimental demonstration of an all-fiber optical coherence tomography system in which residual chromatic dispersion is compensated for by a pair of fiber stretchers made with different fiber types. Both the dispersion variations resulting from fiber inhomogeneities and from a fiber length mismatch can be compensated for. Additionally, we anticipate that our system could be used to compensate for sample dispersion.
Special Session on Oil and Gas: Current Practice and Future Opportunity
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Active plug and play distributed Raman temperature sensing
Kwang Suh, Chung Lee, Michael Sanders, et al.
Raman-based Distributed Temperature Sensing (DTS) utilizing fiber probes is an effective method to determine temperature over distances up to 20km. Active Plug & Play is based on a full DTS solution (DTS system with PerfectVisionTM, Calibration Module, SensorTran DTS Commander software) using a dual laser approach with light sources operating at different wavelengths to determine and compensate for the wavelength dependent local variations in fiber attenuation. The wavelength values for the anti-Stokes Raman return of the primary light source is approximately the same value as the Stokes Raman return of the secondary source. This solution enables the first auto-correcting calibration for DTS.
Realisation of a full-scale fibre optic ocean bottom seismic system
Hilde Nakstad, Jon Thomas Kringlebotn
Optoplan has developed a novel, high-performance large-scale fibre optic Ocean Bottom seismic Cable (OBC) system, which has successfully been qualified through field installations. This OBC system is based on combined wavelength- and time-multiplexing of fibre Bragg grating (FBG) based interferometric sensors. A large-scale manufacturing system has been developed to handle the manufacturing of several system per year - each system having at least 2000 sensor stations. The first full scale OBC system will be ready for installation early 2009.
Fiber optic sensors for the exploration of oil and gas
Fiber optic sensors for the exploration of oil and gas will be reviewed. Technical superiority with high reliability and cost effectiveness is the key to success for expanding oil field applications.
Chemical, Environmental, Biological, and Medical Sensors II
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Recognition of Japanese devoiced vowels using array of plastic optical fiber moisture sensors
Masayuki Morisawa, Tomohito Taki, Yoichi Natori, et al.
A novel plastic-optical-fiber (POF) microphone for discerning devoiced breath, which is based on the detection of moisture pattern depending on the shape of mouth, have been studied. In the experiment coupled with this microphone and Dynamic Programming (DP) matching method, recognition rate over 90% was obtained against five devoiced vowels in Japanese. Therefore, using this system, verbally handicapped people will create sounds with a small effort.
Application of Mach-Zehnder interferometer based on long period grating structure for salinity measurement in water environment
Gustavo R. C. Possetti, Ricardo C. Kamikawachi, Celso L. Prevedello, et al.
In this work we studied the behavior of an in fiber Mach-Zehnder interferometer for salinity measurements. The salt species used are KCl, NaCl e NaCOOH (organic salt) within the concentration range from 3 g.L-1 to 150 g.L-1. The results are compared with traditional salinity measurement methods (conductivity and refractive index) and show that the device can distinguish and identify the concentration of each species saline.
Tissue ablation via optical fibre delivery of UV laser radiation
Joseph Miller, Xiaobo Yu, Paula K. Yu, et al.
We report the use of an ultraviolet (UV) laser and optical fibre arrangement capable of precise and controllable tissue ablation. The 5th (213nm) and 4th (266nm) harmonics of a Nd:YAG laser were launched into optical fibres using a hollow glass taper to concentrate the beam. Standard and modified silica/silica optical fibres were used, all commercially available. The available energy and fluence, as a function of optical fibre length, were evaluated and maximised. Single 5ns pulses were used to ablate both fresh porcine retina and in vivo rat trabecular meshwork. Fluences of 0.4 to 4.0 J/cm2 of 266nm and 0.2 to 1.0 J/cm2 of 213nm were used respectively. Thus demonstrating the potential use of this system for intraocular surgical applications.
Physical, Mechanical, and Electromagnetic Sensors II
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Fiber optic flow velocity sensor based on an in-fiber integrated Michelson interferometer
Libo Yuan, Jun Yang, Zhihai Liu
A novel fiber optic flow velocity sensor based on a twin-core fiber Michelson interferometer has been proposed and demonstrated. The sensor only is a segment of twin-core fiber acting as cylinder cantilever beam. The force exerted on the cylinder by the flow of a fluid with unknown velocity bends the fiber, which corresponding to the shift of the phase of the twin-core in-fiber integrated Michelson interferometer. This twin-core fiber sensing technique could automatically compensate the variation of environmental temperature and pressure due to both arms of the interferometer would be affected equally by such changes.
Optical fiber sensor cable for pipe thinning detection in high temperature environment conditions
Shimei Tanaka, Kazunaga Kobayashi, Tsuyoshi Shimomichi, et al.
The paper presents a newly developed, heat-resistant optical fiber sensor cable, exhibiting excellent sensitivity to local strain variations. The strain measurements acquired by means of the cable was used in 3D structural analysis, allowing us to detect pipeline wall thinning with high accuracy.
Passive and active optical sensing system for monitoring partial discharge on hydrogenerators
J. B. Rosolem, C. Floridia, M. R. F. Hurtado, et al.
We present a hydrogenerator partial discharge sensing system based in RF/Optical technology developed to obtain non-intrusive and large bandwidth characteristics. It was tested using hydrogenerator stator bars and showed a very good performance.
Hybrid LPFG/MEFPI sensor for simultaneous measurement of high-temperature and strain
Yun-Jiang Rao, Zeng-Ling Ran, Xian Liao, et al.
A hybrid fiber-optic sensor consisting of a long-period fiber grating (LPFG) and a micro extrinsic Fabry-Perot (F-P) interferometric (MEFPI) sensor is proposed and demonstrated for simultaneous measurement of high-temperature and strain. The LPFG written by using high-frequency CO2 laser pulses is used for high-temperature measurement while the MEFPI sensor fabricated by using 157nm F2 laser pulses is used for strain measurement under high temperature. The distinguishing feature of such a hybrid fiber-optic sensor is that it can stand for high temperature of up to 650°C and achieve precise measurement of strain under high temperature conditions simultaneously.
Lab tests of an all fibre voltage sensor system
A. Michie, J. Ingram, I. M. Bassett, et al.
All fibre voltage sensing using helically coiled lengths of thermally poled twin-hole silica optical fibre is presented. The thermally poled optical fibre possesses a small electro-optic response and forms the basis of an intrinsic sensor for electric fields. The helical arrangement of the poled silica fibre, from the ground to the high voltage conductor, allows an approximation to a tangential line integral of the electric field i.e. the voltage, to be calculated. The interferometric interrogation system combined with the high speed digital signal processing system allowed voltage measurements at an effective sampling rate of approximately 5000 samples per second. Preliminary lab system test results are presented.
How sensitive is the fibre laser strain sensor?
It is known that the strain resolution of fibre laser sensors is determined by frequency noise of the laser sensor element. We compare the frequency noise of a number of distributed feedback fibre laser sensors and find that all exhibit similar dominant 1/f noise below 10kHz. Examination of current theories of thermodynamic noise and 1/f noise in fibre lasers suggests that these lasers may be close to the theoretical limits of strain sensitivity.
Distributed Sensing
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Using dispersion decreasing fiber to generate pulse delay and compensate the pulse distortion
Xiaoyi Bao, Wenhai Li, Liang Chen
Dispersion effect in stimulated Brillouin scattering (SBS) slow light is studied to compensate the pulse distortion using SBS - dispersion decreasing fiber (SBS-DDF). SBS-DDF has the feature of the dispersion increasing and effective area decreasing, hence intensity increasing along the fiber. This increased intensity is used to balance the intensity decreasing of the pump beam from pump and probe interaction in Brillouin medium at the Brillouin frequency and fiber attenuation. The same principle is applied to the counter propagating Stokes wave, that decreased intensity due to the effective core area increasing is used to eliminate Stokes beam saturation through Brillouin loss interaction. A minimum pulse distortion with high delay of 1.8ns over 2ns pulse is achieved.
Highly sensitive reflectometry over 20 km with sub-meter spatial resolution based on phase-noise-compensated optical frequency domain reflectometry and concatenative reference method
Xinyu Fan, Yusuke Koshikiya, Fumihiko Ito
Highly sensitive reflectometry over 20 km with a sub-meter spatial resolution based on phase noise compensated optical frequency domain reflectometry and the concatenative reference method is proposed and demonstrated experimentally. A fiber laser is used as a light source to extend the measurement range although the distance remains limited to the laser coherence length because of the existence of laser phase noise. To reduce the influence of laser phase noise, the measurement signal is compensated using reference signals generated from a single auxiliary interferometer supported by a newly developed compensation process. By using the proposed technique, the measurement range is extended to 20 km with a sub-meter resolution and a sensitivity (relative to the Rayleigh backscattering level) of about -30 dB, which is nearly impossible to realize with the OTDR technique. The entire measurement time is 20 ms and the processing time is 20 s for each section.
Proposal and experiment of BOCDR: Brillouin optical correlation-domain reflectometry
We propose Brillouin optical correlation-domain reflectometry (BOCDR), which can measure the strain and/or temperature distribution along an optical fiber by controlling the interference of continuous lightwaves. In pulse-based conventional Brillouin optical time-domain reflectometry (BOTDR), it is difficult to achieve a spatial resolution less than 1 m in principle, and the measurement time is as long as 5-10 minutes. On the contrary, the continuous-wave-based BOCDR can exceed the limit of 1-m resolution, and realize much faster measurement and random access to measuring position. A 40-cm spatial resolution was experimentally demonstrated with 50-Hz sampling rate.
Distributed fiber sensing using Brillouin echoes
A simple physical description of the nonlinear optical interaction based on Brillouin echoes is presented. This technique makes potentially possible distributed Brillouin sensing down to centimeter spatial resolution while preserving the narrowband feature of the natural Brillouin gain spectrum. Experimental conditions for the generation of Brillouin echoes are described and demonstrations of distributed measurements using a 1 ns (10 cm) pulse are presented.
Wavelength sensitive time-domain interrogating system for a quasi-distributed temperature sensor
C. Crunelle, M. Wuilpart, C. Caucheteur, et al.
A quasi-distributed temperature monitoring system based on the concatenation of identical low reflective Fibre Bragg Gratings and interrogated by means of an Optical Time Domain Reflectometer is presented. A wavelength sensitive system placed before the OTDR detector is used to analyse the reflected signal. This system allows the height of the FBG reflection peaks in the OTDR trace to depend on their resonance wavelength, and therefore to temperature. Simulations and experimental results are exposed.
Multipoint fiber-optic-based corrosion sensor
Joaquim F. Martins-Filho, Eduardo Fontana, J. Guimarães, et al.
We present an optical fiber sensor for the corrosion process in metal (Aluminum) using the optical time domain reflectometry (OTDR) technique. Our proposed sensor system consists of several sensor heads connected to a commercial OTDR by a single-mode optical fiber and fiber couplers. Each sensor head consists of an optical fiber having the cleaved end coated with an aluminum film. For laboratory measurements the corrosion action was simulated by controlled etching of the Al film on the sensor head. The OTDR detects the light reflected by each sensor head. As the aluminum is etched the reflection decreases and the etch rate can be obtained from the OTDR traces. We present experimental results for the measurement of the corrosion rate of aluminum films in controlled laboratory conditions and also for the evaluation of the maximum number of sensor heads the system supports. Our proposed sensor system is multipoint, self-referenced, has no moving parts and can detect the corrosion rate for each head several kilometers away from the OTDR. This system may have applications in harsh environments such as in deepwater oil wells, for the evaluation of the corrosion process in the inner wall of the casing pipes.
Passive and Active Devices for Photonic Sensing
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Two wave mixing-based optical fiber sensor
A new concept of optical fiber dynamic strain sensor has been theoretically studied and its proof-of-the-principle experimentally demonstrated. It is based on two wave mixing by gain saturation in an optically pumped erbium doped optical fiber. The main feature of this sensor is insensitivity to slow varying perturbations, which is of major interest for underwater acoustic applications for instance.
Wide and fast wavelength-swept mode-locked fiber laser based on dispersion tuning and its application to dynamic FBG sensing
A fiber Bragg grating (FBG) sensor using wide and fast mode-locked wavelength-swept laser is demonstrated. The key device is the optical source, wide and fast wavelength-tunable mode-locked fiber laser based on dispersion tuning. This laser has wide tuning range (over 100nm) and a fast tunable speed (up to 20 kHz). Hence, it is suited for the dynamic FBG sensor system. Our sensor system enables dynamic measurement of strain in real-time at a high measurement rate. In this system,the signals of the sensor are obtained by analyzing temporal waveforms of refleceted light from the FBG without observing the spectrum. A measurement speed as high as 1 kHz is achieved when the wavelength-tunable source is swept at 1 kHz rate. The stability (indicated by the standard deviations of the results) is 30-60 pm in optical spectrum.
Measurement of Bragg wavelength distribution in a long-length fiber Bragg grating by synthesis of optical coherence function
Kazuo Hotate, Koji Kajiwara
A sensor system for measuring continuous Bragg wavelength distribution in a long-length fiber Bragg grating is newly proposed and implemented, based on the technique of synthesis of optical coherence function. Experimental results and simulations are comparatively examined.
All-optical dynamic grating generation based on Brillouin scattering in polarization maintaining fiber
Kwang-Yong Song, Kazuo Hotate
We report a novel kind of all-optical dynamic grating based on Brillouin scattering in polarization maintaining fiber (PMF). A moving acoustic grating is generated by stimulated Brillouin scattering between optical waves in one polarization, and used to reflect orthogonally polarized waves at different wavelength. A 3-dB bandwidth of ~ 100 MHz is observed with the tunable reflectivity of up to 2% in a 30 m PMF.
Surface strain measurement of rotating objects using shearography instrumentation based on fibre-optic imaging bundles
Quantitative, full-field surface strain measurement is achievable using shearography instrumentation that employs at least three measurement channels. The system presented here possesses four measurement channels consisting of four views of the object. Images from the four views are ported to the shearing interferometer using fibre-optic imaging bundles. The use of fibre-optic imaging bundles simplifies the experimental arrangement considerably, allowing full-field surface strain measurements to be made using just one CCD camera and one shearing interferometer. Simultaneous capture of data from the four measurement channels using a pulsed laser source allows the measurement of surface strain on dynamic objects. In this paper the use of the instrument to make measurements of the surface strain profile of a PTFE plate rotating at 600 rpm is described. The use of the spatial carrier technique allows the deformation induced phase variation to be calculated across the field of view from just two images recorded from the object on subsequent rotations.
Poster Sesion II
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Photonic liquid crystal fibers for electric field and hydrostatic pressure sensing
Photonic Crystal Fibers, optical fibers with regular structure of micro-holes running along the axial direction, have ability to change their optical properties through inserting different materials into their holes. The paper presents our latest experimental results of the influence of external electric field and hydrostatic pressure on propagation properties of the photonic crystal fibers infiltrated with liquid crystals clearly indicating great potential for electric field and hydrostatic pressure sensing applications. Operating range of both electric field and hydrostatic pressure sensors can be tailored by different combination of a host photonic crystal fiber and a liquid crystal used for infiltration. Moreover, by changing the operating wavelength different sensor responses can be obtained.
Tilted fibre Bragg gratings for the specific detection of biological species
We present a study aimed at developing fibre-optic-based biosensors for the specific detection of biological species. These sensors rely on the combined use of a Tilted short period Fibre Bragg Grating that detects changes in the refractive index of the surrounding solution and of an electrostatic self-assembly technique: self-assembled polyelectrolyte layers and immobilization of the sensor protein on the fibre surface were used for sensor fabrication. We observed changes in the sensor's spectrum induced by specific binding and we imaged fibre surface with atomic force microscopy (AFM). The results show the feasibility of the sensor for various biological or chemical applications.
Optical fiber-coupled flow cells and their application in in-situ water analysis
Günter Schwotzer, Hartmut Lehmann, Lars Kröckel, et al.
Liquid core wave guides (LCW) are particularly suited as flow-through cells for highly sensitive spectral analysis of small liquid sample volumes as the light propagation is constrained to the liquid core. We report on LCW formed by inside coating of glass capillaries with Teflon(R) AF 1600 (n ≈ 1.31). The wave guiding losses are between 0.2 and 0.3 dB/cm. On the base of fiber-coupled LCW flow-through cells both, a spectrophotometer and a fluorescence detector have been developed and tested for in-situ water analysis, especially for nitrate and phosphate detection in sea water.
Measurement of spontaneous Brillouin scattering in optical fiber with a fiber Bragg grating Sagnac loop
A novel method for direct optical detection of spontaneous Brillouin scattering in optical fiber by using a fiber Bragg grating (FBG) Sagnac loop is introduced. The transmission character as an optical filter of FBG Sagnac loop is investigated theoretically. The filter which is based on an asymmetric grating Sagnac loop is manufactured and used in the measurement of spontaneous Brillouin scattering sensing system, and the separation of backscattered spontaneous Brillouin from Rayleigh is achieved effectively. It is demonstrated that the fiber grating Sagnac loop filter can be applied in the distributed sensing system based on spontaneous Brillouin scattering.
PMMA optical fibers as intrinsic sensors of surface crystal growth
Martijn Boerkamp, David W. Lamb, Peter G. Lye
Polymethylmethacrylate (PMMA) optical fibers are evaluated for their potential as intrinsic sensors of surface crystal growth. Superior mechanical flexibility means they can be configured to maximize sensitivity, primarily via coiling to promote higher-order modes of radiation propagation in their core. The effects of coiling and exposing the fiber to elevated temperatures (greater than the glass transition temperature) are found to increase sensitivity of the PMMA fibers to surface crystallization while pre-bending is found to reduce sensitivity.
Fibre Fabry-Perot sensor for acoustic detection
Incipient fault diagnosis is closely related to isolation condition assessment. There are a great number of methods available for condition monitoring and diagnosis of power transformer isolation systems, but only few of them can take direct measurements inside the transformer. Fibre optic sensors can be applied to incipient fault diagnosis. In special, acoustic sensors are being developed for the detection and location of partial discharges in oil-filled power transformers. Towards such objective, this work reports investigation on the applicability of fibre Fabry-Pérot interferometers for acoustic detection both in air and in liquids.
Experimental results of antigliadin antibodies detection using long period fiber grating
J. M. Corres, I. R. Matias, J. Goicoechea, et al.
In this work a new nano-biofilm is proposed for the detection of celiac disease (CD). A long-period fiber grating (LPFG) is used as a transducer and the surface of the fiber is coated with a precursor layer of SiO2-nanospheres using the electrostatic self-assembly technique (ESA). This layer has been designed in order to create a substrate of high porosity where the gliadins could be deposited. Under the presence of specific antibodies antigliadin antibodies (AGA) the refractive index of the overlay changes giving a detectable shift in the resonance wavelength of the LPFG. Concentrations as low as 5 ppm were detected.
Polarisation mode coupling of excessively tilted fibre Bragg gratings with directional transverse loading
We report a distinctive polarisation mode coupling behaviour of tilted fibre Bragg gratings (TFBGs) with tilted angle exceeding 45°. The ex-45° TFBGs exhibit pronounced polarisation mode splitting resulted from grating structure asymmetry induced birefringence. We have studied and analysed the property of ex-45° TFBGs under transverse load applied to their equivalent fast- and slow-axis. The results show that the coupling between the orthogonally polarised modes takes place only when the load is applied to its fast-axis, giving a prominent directional loading response. This transverse load related polarisation property may be exploitable for implementation of optical fibre vector sensors capable of measuring the magnitude and orientation of the applied transverse load.
Fiber Bragg gratings for measuring pH and strain in concrete structures
D. Barrera, S. Sales, M. Cruz-Yusta, et al.
We show the basic mechanism of optical pH sensors using hydrogels and FBGs. We show the experimental results obtained and the importance of a precise formulation of the hydrogel an appropriated design of our transducer.
Using fiber Bragg gratings to measure Lamb waves in an anisotropic composite plate
The potential for using fiber Bragg grating rosettes for the location of ultrasound sources in anisotropic structures is discussed. Anisotropic propagation of Lamb waves in a carbon fiber composite plate has been investigated using two approaches. Firstly, a finite element model of the displacements/strains produced by the wave was developed and, secondly, in-plane ultrasonic strain mapping was carried out, utilizing the directional properties of FBG sensors. The possibility of designing FBG rosette configurations for use on anisotropic structures is discussed in light of these results.
Fibre refractometer based on a Fabry-Pérot interferometer
It is described a fibre optic sensor for liquid refractive index measurement based on the visibility variations of a Fabry-Perot interferometer with interfering waves generated in a short Bragg grating and in the fibre tip (Fresnel reflection) in contact with the liquid. The sensor was characterized emerging the fibre tip in distilled water with different concentrations of ethylene glycol. A linear relation was obtained, with a readout resolution of ≈ 10-3. It was also observed that the temperature direct cross sensitivity is residual.
Curvature sensor based on a fibre loop mirror using a highly birefringent photonic crystal fibre with two asymmetric hole regions
In this work, a curvature sensor based on a highly birefringent (Hi-Bi) photonic crystal fibre loop mirror is presented. For this purpose, a novel Hi-Bi photonic crystal fibre was designed and fabricated. Half of the microstructured region of the photonic crystal fibre was composed by holes with large diameter, while the other half contained holes with small diameter. Due to this geometry, the fibre core was shifted from the centre and high birefringence appears in the optical fibre. The Hi-Bi photonic crystal fibre loop mirror was demonstrated as a curvature sensor. The curvature was applied for three different fibre directions for the range of 0.6 - 5 metres-1. The configuration was also characterized for temperature and longitudinal strain, showing insensitivity for these two physical parameters.
Modal LPG-based Mach-Zehnder interferometer with controlled sensitivity for refractive index measurement
In this work, an LPG-based Mach-Zehnder interferometer was evaluated as a sensing structure for environmental refractive index measurement. To interrogate this sensing device, coherence addressing and pseudo-heterodyne processing were used. The impact of stretching, bending and twisting the interferometer on the sensitivity to refractive index changes r was studied. It is shown that, due to the antisymmetric nature of cladding modes in arc-induced LPGs, it is possible to tune the system sensitivity by simple mechanical action.
Combined fiber optic network for communication and measurement using a hetero-core spliced fiber optic sensor
H. Sasaki, M. Nishiyama, E. Kondo, et al.
We have developed a fiber optic network combining communication and measurement using a hetero-core spliced fiber optic sensor inserted into an existing communication line with a wavelength-division multiplexing (WDM) analogy. Switch modules using the proposed sensor were inserted into an actual communication line and the influence on the communication of the switch modules was examined. The communication link broke when approximately 21 dB is inflicted a loss on the communication light of 1.31-μm wavelength by the switch modules, the WDM filters and a fiber-optic coupler in the communication line. Because the amount of loss is the maximum allowable for a communication instrument, the proposed sensor has been clarified to have only the loss characteristic. If the loss is controlled to within tolerance for the communication wavelength, a measurement function can be added to a communication line by a comparatively simple method. It was also shown that a combined optical fiber network can be achieved, where the intensity of the communication light is measured. The combined method is highly cost effective, because it is not necessary to have a separate light source for measurement, WDM filters, and other elements in the communication line.
Embedded fibre Bragg grating array sensors in aluminium alloy matrix by ultrasonic consolidation
Chengbo Mou, Pouneh Saffari, Dezhi Li, et al.
Fibre Bragg Grating (FBG) array sensors have been successfully embedded in aluminium alloy matrix by ultrasonic consolidation (UC) technique. The temperature and loading responses of the embedded FBG arrays have been systematically characterised. The embedded grating sensors exhibit an average temperature sensitivity of ~36pm/°C, which is three times higher than that of normal FBGs, and a loading responsivity of ~0.1nm/kg within the dynamic range from 0kg to 3kg. This initial experiment clearly demonstrates that FBG array sensors can be embedded in metal matrix together with other passive and active fibres to fabricate smart materials to monitor the operation and health of engineering structures.
Multiplexed sensor of dynamic strains using photorefractive wave mixing in reflection geometry
S. Di Girolamo, A. A. Kamshilin, R. V. Romashko, et al.
We propose a novel multiplexing system for sensing of dynamic strains in which several multimode optical fibers are used as sensitive elements. In the proposed configuration several object beams emerged from different multimode fibers are mixed in one crystal altogether with a common reference beam, which is directed from the opposite face of the sample. The geometry of the light-beam interaction inside the crystal assures low cross-talk between the measuring channels in spite of the fact that all the object beams are mutually coherent since they originate from one and the same laser. We have found that the crosstalk is much smaller than the noise level of any channel, which relates to instability of the polarization state of the speckle field emerged from the fibers.
Simultaneous measurement of strain and temperature using a Lyot fiber filter and a fiber Bragg grating in linear configuration
Linh Viet Nguyen, Dusun Hwang, Dae Seung Moon, et al.
We report a fiber sensor capable of simultaneously measuring temperature and strain. A fiber Bragg grating (FBG) was incorporated in a Lyot fiber filter (LFF) by fusion splicing a section of high birefringence fiber (PM fiber) with an FBG and then placing them between 2 polarizers. Measured in the transmission mode, the fringe resulted from the LFF and the resonance wavelength dip of the FBG has different responses when a variation of temperature or strain is applied. The proposed device can therefore measure both strain and temperature simultaneously.
Intensity based optical fiber strain sensor using long period grating and core mode blocker
Du-sun Hwang, Linh Viet Nguyen, Dae Seung Moon, et al.
We report an intensity based fiber strain sensor using a long period grating (LPG) pair along with an in-line core mode blocker. By sandwiching the core mode blocker fabricated by arc method between a LPG pair, an band-pass filter was formed. Measured by optical power meter at one specific wavelength, the transmitted power was found to decrease as a variation of axial strain is applied on one single LPFG, therefore we can measure the applied strain by measuring the transmitted power. The measured response of voltage for change of strain was 6.37pV/ με.
Flexfuel vehicle alcohol-gasoline blend ratio determination by optical fiber sensoring
Rafael T. Takeishi, Edmilton Gusken, Klaus Raizer, et al.
The high efficiency combustion of flexfuel engine depends on the precise determination of the alcohol-gasoline ratios. Presently, commercial technique available uses the Lambda probe, a post-combustion sensor to analyze the exhaust gases (after combustion). This ratio can be measured in real-time using an optical fiber sensor. In the present research, different ratios of alcohol-gasoline blends were measured at temperatures in the range 0 to 50°C, by a Fresnel reflectometer. The sensoring principle is based on the phenomenon of light reflectivity in the interface fiber-fuel. The reflected intensity is proportional to the refractive index difference between the fiber sensor and the fuel, while the refractive index of the mixture is a function of the volumetric ratio of the substances. The real time determination of the mixture ratio of alcohol-gasoline concentrations by the reflected intensity can be used to optimize the combustion efficiency of the flexfuel engine. It can be expected that this technology can reduce both, the pollutant emissions and the fuel consumption.
Recent progress in polymer optical fibre gratings
C. Zhang, K. Carroll, D. J. Webb, et al.
We describe our recent progress in polymer fibre Bragg grating technology, including the writing of the first FBGs in TOPAS cyclic olefin copolymer, enhancements to photosensitivity brought about by dopants and studies on grating annealing.
Annealing and spectral characteristics of femtosecond laser inscribed long period gratings written into a photonic crystal fibre
A series of LPGs with the same period was inscribed by femtosecond laser into photonic crystal fibre with various powers. All suffered post-fabrication spectral evolution at low temperatures, apparently related to inscription power.
A surface plasmon resonance fibre device for environmental sensing
T. Allsop, R. Neal, P. Brown, et al.
We demonstrate a surface plasmon resonance sensor that operates in air and has index resolution ~10-4 in the 1 to 1.3 index range. The sensor comprises a multi-layered thin film on a D-shaped fibre.
Effect of pulse chirp on distributed Brillouin fiber sensing
The influence of the frequency chirp inherent to the generation of a pump pulse by a Mach-Zehnder intensity modulator is presented in the context of a distributed Brillouin sensor configuration. This frequency chirp depends on the pulse shape and its impact is related to the relative importance of the rising and falling edges with respect to the total pulse width. This results in a biased evaluation of the Brillouin frequency in regions where an abrupt change of this Brillouin frequency is observed.
Long-period grating fabricated using resistive filament heating
We fabricate and demonstrate a long-period grating (LPG) by periodically tapering a section of standard single-mode fiber using resistive filament heating. The obtained LPG has a large peak transmission attenuation of -30.31 dB with only 22 periods in a 1.0-cm long optical fiber. Such a LPG exhibits unique characteristics for sensing applications. The bending and strain sensitivities are 1.74 nm•m and 1.11 pm/με, respectively. The polarization dependent loss is large, up to 11.65dB, caused by asymmetric index profile in the cross section of the tapered LPG.
A high-speed sinusoidally frequency-modulated optical reflectometry with continuous modulation-frequency sweeping
Zuyuan He, Masatoshi Konishi, Kazuo Hotate
A high-speed sinusoidally-frequency-modulated optical reflectometry with continuous modulation-frequency sweeping is proposed and demonstrated. In preliminary experiment, we succeed in measuring reflectivity distributions in 5-10 seconds, compared to several hundred seconds in conventional method.
Gamma ray effects on double pass backward superfluorescent fiber sources for gyroscope applications
Zhi-Chiang Hsu, Zhi-Sheng Peng, Lon A. Wang, et al.
Mean-wavelength stable superfluorescent fiber sources composed of three kinds of EDFs were irradiated by a 60Co source up to 2000Gy to compare their mean-wavelength drifts and output power losses.
B-OTDR and OFDR distributed optical fiber strain sensing for sinkhole detection
Sylvie Delepine-Lesoille, Vincent Lanticq, Pierre Magnien, et al.
Optical fiber sensor is evaluated for sinkhole detection under railway tunnels. Tests performed on a decametric structure equipped with embedded 110 m-cable interrogated by Brillouin-OTDR and OFDR showed great performances in accordance with finite-element calculations.
Humidity sensor based on a long-period fiber grating coated with a SiO2-nanosphere film
D. Viegas, J. Goicoechea, J. M. Corres, et al.
This work addresses a humidity sensor using long-period fiber gratings (LPG) coated with silica nanospheres film. SiO2-nanospheres coating is deposited onto the LPG using the electrostatic self-assembly technique (ESA). The polymeric overlay changes its optical properties when exposed to different humidity levels, resulting in a shift of the resonance wavelength of the LPG. The obtained results are accordant with the theoretical simulations. Wavelength shifts up to 12nm in a humidity range from 20% to 80% are reported, maintaining the same dependence at different temperatures.
Frequency modulated continuous wave technique for referencing and multiplexing intensity based fibre optic sensors
We report on the use of a frequency-reflectometry domain technique for referencing optical intensity sensors located between two fibre Bragg gratings. The experiment combines the concept of frequency modulated continuous wave with the spectrally selective mirror properties of fibre Bragg gratings to interrogate with referencing properties intensity based sensors. Multiplexing two of these sensors using this technique in a parallel topology system was also experimentally demonstrated. Due to the use of different fibre lengths (delay lines), signals from the fibre Bragg gratings located at different positions in an array are separated in the frequency-domain.
Fiber optic sensor for determination of thickness of transparent plates
A fiber optic sensor for measuring thickness of transparent plates (1 to 2.5 mm) is proposed based on reflective type displacement fiber optic sensor. The peak position in the output of the receiving fiber, which various linearly, is related to the thickness of the transparent plate. Theoretical model is proposed and compared with the experimental results. The output characteristics of the sensor are studied in terms of fiber optic parameters such as numerical aperture and diameter.
Gas sensor based on PBG fiber: possibilities and limitations
Joanna Pawat, Takahiro Matsuo, Xuefeng Li, et al.
The Photonic Pandgap fiber was proposed as a new alternative for traditional glass-made gas cell used in spectroscopic measurements. Several PBG fibers were specially designed and produced for performed experiments. Gas flow within fiber was simulated and measured and ppm concentrations of ammonia gas were detected with short lengths of fiber. Final goal of the project is to produce portable and compact device for fast, ppb range measurement. Additionally, several fiber cutting methods were tested.
Hollow-core rib waveguide sensor
We propose a new hollow-core fiber that employs a rib-waveguide geometry for improved gas or liquid sensing. This waveguide supports a true guided mode that is connected laterally to the external environment through a hollow slab. Such designs eliminate the requirement of small transverse holes and open up new opportunities for sensing.
Fiber optic acoustic sensors for crack growth diagnostics
Dae-Cheol Seo, Il-Bum Kwon, Chi-Yeop Kim, et al.
There are to be some cracks on the material degradation part or the stress concentration parts of the main members, which carry on over-loads, of structures. Because these cracks can be used to evaluate the structural health status, it is important to monitor the crack growth for maintaining the structural safety. In this study, the fiber Bragg grating sensor with a drop ball was developed as a sensor for crack growth detection of an existing crack. The crack growth detection sensor was constructed with three parts: a probe part, a wavelength control light source and receiver part, and an impact part. The probe part was just formed with a fiber Bragg grating optical fiber. The wavelength control light source part was composed of a current supplying circuit, a DFB laser diode, and a TEC control circuit for wavelength control. Also, the impact part was just implemented by dropping a steel ball. The performance of this sensor was confirmed by the experiments of the crack detection with an aluminum plate having one existing crack. According to these experiments, the difference of the sensor signal outputs was correlated with the crack length. So, it was confirmed that this sensor could be applied to monitor the crack growth.
Methane sensing using multiple-coupling gaps in hollow-core photonic bandgap fibers
J. M. Lazaro, A. M. Cubillas, M. Silva-Lopez, et al.
Gas detection and gas sensing based on hollow core photonic bandgap fiber (HC-PBF) is a very promising technique due to the long interaction light-gas lengths that are achievable. However, long path-lengths also imply higher gas filling times of the hollow fiber and higher response times of the detection systems what can constitute a serious practical inconvenience. In this paper, the high sensitivity is maintained but the sensor response time is reduced by using multiple-coupling fiber gaps. The results and conclusions extracted from a systematic experimental study (comparing the spectra and filling time of different HC-PBF lengths and different number of coupling gaps) are presented and discussed. Finally, the maximum number of gaps allowed in the system is modelled.
Effect of humidity on optical fiber distributed sensor based on Brillouin scattering
In real sensors, the crosstalk or undesirable crossed sensitivities must be minimized. Distributed Brillouin sensing is a very useful technique to measure fluctuations of temperature along an optical fiber. However, the later measurement can be influenced by the humidity on the fiber; therefore its effect must be minimized. Because the aforementioned, the Brillouin frequency changes with the humidity. Thus, for a given temperature on a distributed fiber sensor such variations have been investigated. The experimental results obtained using three different types of single mode fibers with 1000m length, at 25°C are reported in this paper.
Fiber-optic gyroscope operated with a frequency-modulated laser
We propose using a frequency-modulated laser in a fiber-optic gyroscope (FOG) in a minimum configuration. Compared to the traditional broadband source, a narrow-band laser offers two significant advantages, namely the elimination of excess noise and thus improved sensitivity to rotation, and a more stable mean wavelength, hence a greater scale-factor stability. We show that the strong back-reflection and coherent backscattering noise introduced by the use of a laser is greatly reduced by modulating the laser frequency. In both a conventional FOG and in a FOG using an air-core fiber, we demonstrate experimentally that this technique reduces these two sources of noise by at least a factor of 4 compared to the same gyros operated with an unmodulated laser.
Laser-driven fiber optic gyroscope with reduced noise
We demonstrate experimentally that a fiber optic gyroscope (FOG) using an air-core fiber coil can be operated with a laser and still exhibit a fairly low phase noise. This noise is measured to be 1000 μrad/√Hz with a single-frequency laser, and 150 μrad/√Hz when the frequency is swept. When the fiber is replaced with SMF-28 fiber, these figures drop to 100 and 14 μrad/√Hz, respectively. This last value is 35 times lower than the previous record. Comparison to a new model shows that this noise is limited by coherent backscattering, and that the backscattering coefficient inferred for the air-core fiber is ~11 times higher than for the SMF-28 fiber. By reducing the air-core fiber loss from its current high value (24 dB/km) to its theoretical limit (~0.15 dB/km), we predict that this laser-driven air-core FOG will have a noise of only ~0.3 μrad/√Hz, and thus outperform commercial FOGs in terms of not only noise, but also improved thermal and mean-wavelength stability.
Reduction of crosstalk in inline sensor arrays using inverse scattering
Ole Henrik Waagaard, Erlend Rønnekleiv, Stig Forbord, et al.
Suppression of crosstalk in an FBG-based serially multiplexed interferometric sensor array is demonstrated by employing the layer peeling inverse scattering algorithm. A polarization resolved impulse response (array reflection Jones matrix versus time) is measured using dual pulse heterodyne interrogation with varying combinations of polarization states in the interrogating pulse pair, and used as input to the layer peeling algorithm. < -40 dB crosstalk is achieved with > 97% confidence in a sensor array with 5 % FBG reflectivity. This is a 15-20 dB improvement compared to interrogation without inverse scattering.
Improvement of accuracy of angular velocity detection in semiconductor fiber-optic ring laser gyroscope
Tomoki Ishida, Shuichi Tamura, Satoshi Sunada, et al.
A semiconductor fiber-optic ring laser gyroscope (S-FOG) consists of a semiconductor optical amplifier (SOA) and optical fiber to form a ring cavity. The fiber ring cavity enables larger sizes and smaller scattering, while the SOA gain is shared by the clockwise (CW) and counterclockwise (CCW) propagating modes. When the S-FOG is rotated, a new beat signal called the Sagnac beat frequency is observed. We investigated the effect of the fiber ring cavity's length on detection characteristics. Detection sensitivity was not dependent on the number of laps of fiber ring cavity. However, when the cavity length became longer, the linewidth of Sagnac beat became narrower, and then accuracy of angular velocity detection improved. The relation between the linewidth Δ ν of the Sagnac beat and cavity length P was proved to be Δ ν ≈ P-1.86.
Distributed strain measurement of welded tubular joint with long gauge FBG
H. Murayama, K. Kageyama, K. Ohara, et al.
Strain along a welded joint submitted to a load can fluctuate because of inhomogeneity in thickness or residual stress distributions and defects. Inversely, strain fluctuation may represent such inhomogeneities or defects. We applied the distributed strain sensing technique with a long gauge FBG to monitoring strain distributions along a welded tubular joint of a steel pipe. By using this sensing technique, we can measure a strain distribution at an arbitrary position along a FBG with the high spatial resolution less than 1 mm. In the tensile test of the steel pipe, we could successfully measure the strain distribution along the weld line of about 100 mm in length. We also observed the strain fluctuating sharply in some areas and acoustic emissions were simultaneously detected by the other sensors. In some areas where sharp fluctuations occurred, defects were observed by also computer tomography carried out after the tensile test. Applications for the sensing technique include health monitoring for other joint configurations, such as fastening and bonding.
Tunable fiber laser using concatenated non-adiabatic single-mode fiber tapers
M. A. Quintela, A. Quintela, N. Becue, et al.
An erbium doped fiber ring laser (EDFRL) that incorporates four non-adiabatic concatenated single-mode fiber tapers (acting as tunable filter in the laser cavity) is presented. These concatenated fiber tapers integrates a filter with a narrower band-pass and a higher modulation depth than a single taper. The tuning of this filter was implemented applying a controlled perturbation in the fiber taper. The proposed laser architecture was successfully demonstrated in the laboratory in which a tuning range of 20.8nm (1544.5nm-1565.3nm) were measured.
Hollow-core photonic crystal fiber high-pressure gas cell
Qing Sun, Qinghe Mao D.D.S., Erming Liu, et al.
Based on the investigation of the high-pressure nitrogen-filling and leaking characteristics of the HC-PCF, a new making technique for the all-fiber high-pressure HC-PCF gas cell is present. An HC-PCF nitrogen-filled cell with a pressure of 17.1 atm and an insertion loss of 9.3 dB is manufactured with the technique.
A portable multi-function weight-in-motion (WIM) sensor system based on fiber Bragg grating (FBG) technology
Hongtao Zhang, Zhanxiong Wei, Qiming Zhao, et al.
A portable, multi-function WIM sensing system based on Fiber Bragg Grating (FBG) technology is developed to measure the total weight, the distribution of weight of vehicle in motion (the weights of left front, right front, left rear and right rear wheels respectively), the distance of wheels axles and distance between left and right wheels. Currently the speed of vehicle to be tested can be up to 15 mph, the full scope of measurement for this system is 4000 lbs, and the static sensitivity of sensor head is 20 lbs. This system has been tested respectively at Stevens' campus and Army base. Compared to other schemes, our method has a number of advantages such as immune to electromagnetic interference, high repeatability, lightweight, low power consumption, high sensitivity to dynamic strain caused by load of vehicles in high-speed. The accuracy of whole system can be improved by simulating the mathematical model of sensor heads and improving the quality of manufacture as well as the calibration condition in the future.
Low noise planar external cavity laser for interferometric fiber optic sensors
Lew Stolpner, Sanggeon Lee, Steve Li, et al.
A 1550 nm DWDM planar external cavity laser is demonstrated to provide low phase / frequency noise and narrow linewidth. The cavity includes a semiconductor gain chip and a planar lightwave circuit waveguide with Bragg grating, packaged in a 14-pin butterfly package. The laser shows linewidth < 30 kHz and phase/frequency noise comparable with that of long cavity fiber lasers. Performance is suitable for various fiber optic sensing systems, including interferometric sensing in Oil and Gas, military/security and other applications, currently served mostly by costly and less reliable laser sources.
A tracking and stabilization oriented fiber optic gyroscope
Behzad Moslehi, Richard J. Black, Levy Oblea, et al.
We demonstrate for an unpolarized Fiber Optic Gyroscope (FOG) with open-loop electronics, that, by applying more source power and conserving optical power in the optical path, we can achieve improved Angle Random Walk (ARW) performance without enlarging loop or put in multiple turns of fiber. The predicted trends are demonstrated by the experiment in terms of bandwidth. Power-law dependency is shown within the accuracy of the instrumentation.
Simultaneous measurement of bending and temperature incorporating a sampled chirped fiber Bragg grating
We propose and experimentally demonstrate a simple and practical scheme for simultaneous measurement of bending and temperature with a single sampled chirped fiber Bragg grating embedded on a flexible cantilever beam.
Process/health monitoring for wind turbine blade by using FBG sensors with multiplexing techniques
In this study, we applied fiber Bragg grating sensors to conduct process/health monitoring of wind turbine blade manufactured by VaRTM. In this study, we used a long gauge FBG (about 100mm) based optical frequency domain reflectometory (OFDR) and 8 FBGs on a single fiber based wavelength division multiplexing (WDM). Resin flow front and resin cure were detected during VaRTM. After manufacturing, structural health monitoring was conducted with the blades. These sensors with multiplexing techniques were able to monitor VaRTM process and wind turbine blade successfully.
Validation of Bragg grating measurements of acoustic plate waves
Claire Davis, Nik Rajic, Cedric Rosalie
This paper reports on aspects of the design and validation of a Bragg grating sensor for acoustic plate wave detection. Advanced numerical modelling and an alternative experimental approach using Laser Vibrometry is used to validate the response of the Bragg measurements across a range of acoustic frequencies in a metal plate.
Magnetic field sensors and visualizers using magnetic photonic crystals
Mikhail Vasiliev, Kamal E. Alameh, Viatcheslav Kotov
Magneto-optical imaging is widely used to observe the domain patterns in magnetic materials, visualize defects in ferromagnetic objects, and measure the spatial distribution of stray magnetic fields. Optimized 1D magneto-photonic crystals enable a significant increase in the sensitivity of magneto-optical sensors. The properties of such devices based on the optimized reflection (doubled Faraday rotation) mode and the use of 1D magnetic photonic crystals as sensors are discussed. Experimental results of the fabrication and characterization of ferrite-garnet layers possessing uniaxial magnetic anisotropy are shown, and an optimized film structure suitable for magneto-optical imaging is proposed.
Photonic nano-structures for water quality monitoring
We propose a new type of sensors suitable for water quality testing and for monitoring water contamination levels in domestic, industrial and environmental applications. The proposed sensing scheme uses Fourier transform cavity-enhanced absorption spectroscopy and novel compact sensing elements based on nanostructured photonic crystal-type optical coatings enabling the sensitive Fourier-domain processing methodology and maximising the absorption path length within the measurement system. The measurement scheme is shown to be suitable for the determination of small changes in the water absorption coefficients at a discrete set of wavelengths in the visible spectral region in response to small concentrations of pollutants with high sensitivity. The proposed sensors are expected to provide real-time information on the water contamination levels, as well as potentially the types of substances dissolved.
Earth's rotation rate detection using an extremely large semiconductor fiber optic gyroscope extending over 10,000 m2
Keizo Inagaki, Shuichi Tamura, Tomoko Tanaka, et al.
We detect the Earth's rotation rate using a semiconductor fiber optic gyroscope (S-FOG), which is an active ring laser gyroscope that consists of a semiconductor optical amplifier (SOA) and a fiber optic ring resonator. Four different optical fiber layouts with different scale factors in rotation rate measurement are configured and measured. Expected Sagnac beat signals proportional to the scale factors are observed. The maximum layout of S-FOG is extended over 10,898 m2, which, to our knowledge, is the largest active ring laser gyroscope ever built.
Fiber optical temperature and strain measurements for monitoring and quench detection of superconducting coils
M. Willsch, H. Hertsch, T. Bosselmann, et al.
It has been demonstrated that Fiber Bragg Grating Sensors can measure at very low temperatures in Helium cryostats. The intrinsic temperature sensitivity is very low but can be significantly enhance by the thermal expansion of polymer carriers. Temperature and mechanical strain changes can be measured quite accurately.
Refractometric sensor based on induced losses in the region of transition from a curved side-polished POF fiber
M. Lomer, C. A. Galindez, M. A. Quintela, et al.
A refractometric sensor that uses the transition region of a U-bent Plastic Optical Fiber (POF) when it is polished laterally is presented. By polishing a lateral segment of the fiber, a part of the plastic optical fiber core is removed and an elliptical surface is formed on the bend. It is found that that the polishing with an angle equals to the critical angle of a straight optical fiber the sensitivity of this transducer structure is enhanced. Then, the incident light is totally reflected and the transition losses decrease locally. In addition, the sensitivity increases compared to the polishing in the region of bending losses. The proposed transducer is successfully checked with experimental measurements and different kinds of liquids. Potential applications are suggested.
FBG sensor interrogation on rotating parts of large machines in power generation plants
Large power engines are permanently increasing efficiency. Knowledge of thermal and mechanical loads is getting important. A novel coupling technique allows to interrogate FBG temperature and strain sensors on rotating parts which are normally not accessible.
Train axle counters by Bragg and chirped grating techniques
Weilai Li, Ning Jiang, Jinshan Liu, et al.
Both sensing techniques, FBG wavelength shift and FCG intensity, were applied in a train axle counting system. Their structure and the process of changing strain data into accurate axle numbers are discussed.
Photonic-based spectral reflectance sensor for ground-based plant detection and weed discrimination
Arie Paap, Sreten Askraba, Kamal Alameh, et al.
A bench prototype photonic-based spectral reflectance sensor architecture for use in selective herbicide spraying systems performing non-contact spectral reflectance measurements of plants and soil is described and experimental data obtained with simulated farming vehicle traveling speed of 7 and 22 km/h is presented. The sensor uses a three-wavelength laser diode module that sequentially emits identically-polarized laser light beams through a common aperture, along one optical path. Each laser beam enters a multi-spot beam generator which produces up to 14 parallel laser beams over a 210mm span. The intensity of the reflected light from each spot is detected by a high-speed line scan image sensor. Plant discrimination is based on calculating the slope of the spectral response between the 635nm to 670nm and 670nm to 785nm laser wavelengths. The use of finely spaced and collimated laser beam array, instead of an un-collimated light source, allows detection of narrow leaved plants with a width as small as 12mm.
Response of the transmission spectrum of tapered optical fibres to the deposition of a nanostructured coating
R. Jarzebinska, C. S. Cheung, S. W. James, et al.
Nanostructured coatings have been deposited onto tapered optical fibres using the Langmuir Blodgett technique. The response of the transmission spectrum of the tapered fibres to changes in thickness of the coating has been analysed. The effects observed are shown to be dependent on the diameter of the tapered region.
Long period grating-based refractive index sensor for chloride concentration measurement
C. Chung Chun Lam, M. Rajesh, T. Sun, et al.
Effective devices for the monitoring of chloride ions are required in industry this work reports on the development of a reflective long period grating-based senor for the measurement of chloride ions in solution. The device is based around a long period fibre grating (LPG)-based Michelson interferometer where the sensor was calibrated and evaluated in the laboratory using sodium chloride solutions, over a wide range of concentrations, from 0.01 M to 4.00 M. The grating response yields shifts in the spectral characteristic of the interferometer, due to the change of refractive index of the solution surrounding it. The work was stimulated by the need for the more effective measurement of the ingress water-borne ions in structural concrete. It was found that the sensitivity of the device could be enhanced over that obtained from a bare LPG by coating the LPG-based interferometer with gold nanoparticles. Devices using this approach were also evaluated and their performance cross-compared.
Structural concrete condition monitoring using a long period grating-based humidity sensor
T. Venugopalan, T. Sun, K. T. V. Grattan
An optically based sensor has been designed, fabricated and characterized in research to determine moisture ingress in a range of structural concrete samples subjected to a variety of changing environmental conditions. The approach taken to the creation of these novel humidity sensors is using long period grating (LPG) technology in an optical fibre. The sensor is configured by coating LPGs with a thin layer of polymer, following which it was characterized and its performance cross-compared with that of other sensors. The thin layer of polyvinyl alcohol (PVA), whose refractive index varies as a function of humidity level, provides a means to change the optical propagation in the fibre and thus to induce the a wavelength shift in the attenuation bands of its transmission spectrum.
Development of a microsphere laser-based sensor system
T. L. Yeo, S. Y. Chen, T. Sun, et al.
Some preliminary results obtained from research into the development of a fibre-coupled microsphere laser-based system, with potential for sensor use, are discussed in this paper. Based on a theoretical analysis of micro-cavity laser configurations and of the design of the laser components used, an experimental setup has been created to optimize the coupling efficiency between the microsphere and the wave-guiding tapered fibre and thus to show the potential for a low threshold compact laser system as a source for a compact gas sensing device.
A long period grating based directional flow sensor
A chirped long period grating (LPG) is used as a directional flow sensor by monitoring the change in the transmission spectrum upon immersion in an oil of refractive index higher than that of the fibre cladding. The change in profile of an attenuation band is shown to depend on the direction of immersion, indicating the possibility of using such devices in applications such as resin flow sensing in the manufacture of fibre reinforced plastic composite structures.
A transverse loading technique to enhance the pressure measurement capability of fibre Bragg gratings
R. Correia, E. Chehura, S. W. James, et al.
A fibre optic pressure sensor based on the application of a transverse load onto an epoxy-resin material embedded over a sub-section of a fibre Bragg grating (FBG) is presented. When a transverse load is applied to the epoxy material it deforms and transfers the load onto the optical fibre in the form of an axial strain that changes the period of the FBG over the embedded region. This introduces a phase shift between the two resulting identical gratings that lie either side of the loaded section, creating a spectral drop-out within the bandwidth of the FBG. A 2 mm section at the centre of FBGs of length 6 mm, recorded in both single mode and highly linearly birefringent optical fibres, was embedded in resin, and were subsequently subjected to a transverse load. The loading technique, while offering protection to the optical fibre from mechanical damage, enhances transverse load sensitivity, without introducing birefringence.
Optical fiber spectroscopy for measuring quality indicators of lubricant oils
A. G. Mignani, L. Ciaccheri, N. Díaz-Herrera, et al.
A collection of lubricant oils from different types of turbines, which were characterized by different degrees of degradation, were analyzed by means of UV-VIS-NIR absorption spectroscopy, fluorescence spectroscopy and scattering measurements. All these measurements were performed by means of optical fiber-based instrumentation that made use of LEDs or compact lamps for illumination and miniaturized spectrometers for detection. Multivariate data analysis was used to successfully correlate the wide optical spectral signature of lubricant oils to some of the most important parameters for indicating the degree of degradation of the oil, such as TAN, JOAP-index, water content, and phosphorus.
Optical fiber fluorescence spectroscopy for detecting AFM1 in milk
A. G. Mignani, C. Cucci, L. Ciaccheri, et al.
Fluorescence spectroscopy carried out by means of optical fibers was used for the rapid screening of M1 aflatoxin in milk, enabling the detection of concentrations up to the legal limit, which is 50 ppt. A compact fluorometric device equipped with a LED source, a miniaturized spectrometer, and optical fibers for illumination/detection of the measuring micro-cell was tested for measuring threshold values of AFM1 in pre-treated milk samples. Multivariate processing of the spectral data made it possible to obtain a preliminary screening at the earlier stages of the industrial process, as well as to discard contaminated milk stocks before their inclusion in the production chain.
Fiber-optic level indicator for liquid hydrogen
Sergei Khotiaintsev, Volodymyr Svyryd
This paper describes a fiber-optic level indicator designed to detect the liquid interface in the liquid-hydrogen storage tanks. The considerations which led to the choice of the particular fiber-optic sensor and the construction of the measurement system are discussed. A fiber-optic refractometric transducer with the detection element of ellipsoidal form was developed which features a step-like response to the external refractive index in the narrow interval of this quantity between unity (gas) and 1.0974 (liquid hydrogen). The fiber-optic inputs to the storage system secure the reduced heat ingress in the liquid-hydrogen in comparison to sensors with electrical wires. The fiber-optic transducer features small dimensions, is strong mechanically, and supports multiple cycles of cooling to 20 K and heating to the ambient temperature. The device successfully indicated the level of liquid interface in a liquid-hydrogen storage tank under the maximum excess pressure in the tank of 4 MPa. The paper discusses a number of prospective applications of the developed fiber-optic transducer in the liquid-hydrogen storage systems.
Polarization mode beating intracavity technique for fiber laser sensing
We propose a novel technique for measuring small changes of two independent polarization mode signals from within a single-frequency fiber laser cavity. Polarization mode beating measurement techniques eliminate intracavity common noise yielding highly sensitive detection.
Respiratory gating of endoscopic OCT images of the upper airway
Robert A. McLaughlin, Julian J. Armstrong, Sven Becker, et al.
Anatomical optical coherence tomography (aOCT) is an endoscopic imaging modality that can be used to quantify size and shape of the upper airway. We report the application of respiratory gating to aOCT images. Our results show that respiratory gating can reduce motion artefact in upper airway images. Using an error metric based on distance to the dominant reflection in each A-scan, we found notable improvements when the breath cycle was partitioned into approximately four gates, but only minor improvements as the number of gates was further increased.
Smart sensors for the petroleum sector based on long period gratings supervised by artificial neural networks
Gustavo R. C. Possetti, Francelli K. Coradin, Lílian C. Côcco, et al.
This work shows the use of long period gratings in the petroleum sector, in two specific applications. The proposed sensors are employed both to identify substances in a simulated flow inside a pipeline, and to assess the gasoline conformity commercialized in gas stations. The gratings responses for each specific case were employed to train and to validate two different topologies of artificial neural networks: perceptron multilayer and radial base function. The obtained results show that fiber optic sensors supervised by artificial neural networks can constitute systems for smart measurement with high applicability in the petrochemical field.
Investigation of embedded near infrared fibre Bragg grating (FBG) sensors (830 nm) in structural health monitoring of glass fibre composite structures
The transmitted spectrums of conventional FBG sensors operating in near infrared region (Bragg wavelength ~ 830nm) embedded in E-Glass/Vinylester composite sample were investigated at static and after fatigue loading. Also transmitted waveforms of a FBG attached to a surface of single layer E-Glass/Vinylester composite sample which has a purposely created hole closer to attached FBG sensor were examined in order to understand the FBG response in a vicinity of a void/damage, under static loading situation. As a consequence, some conclusions were made on the sensitivity and durability of the use of FBG sensors fabricated by conventional writing techniques in long term health monitoring system of composite structures.
A proposed fibre optic time domain optical coherence tomography system using a micro-photonic stationary optical delay line
Conventional time domain Optical Coherence Tomography (OCT) relies on a reference Optical Delay Line (ODL). These reference ODLs require the physical movement of a mirror to scan a given depth range. This movement results in instrument degradation. We propose a new optical fibre based time domain OCT system that makes use of a micro-photonic structure as a stationary ODL. The proposed system uses an in-fibre interferometer, either a Michelson or a Mach-Zhender. The reference ODL makes use of a collimator to expand the light from the optical fibre. This is them expanded in one dimension via planar optics, that is, a cylindrical lens based telescope, using a concave and convex lens. The expanded beam is them passed through a transmissive Spatial Light Modulator (SLM), specifically a liquid crystal light valve used as an optical switch. Light is then reflected back through the system off the micro-photonic structure. The micro-photonic structure is a one dimensional array of stagged mirror steps, called a Stepped Mirror Structure (SMS). The system enables the selection of discrete optical delay lengths. The proposed ODL is capable of depth hoping and multicasting. We discuss the fabrication of the SMS, which consists of eight steps, each approximately 150 μm high. A change in notch frequency using an in-fibre Mach Zhender interferometer was used to gauge the average step height. The results gave an average step height of 146 μm.
Use of first-order diffraction wavelengths corresponding to dual-grating periodicities in a single fiber Bragg grating for simultaneous temperature and strain measurement
S. P. Yam, Z. Brodzeli, S. A. Wade, et al.
A fiber Bragg grating sensor fabricated by a phase mask with 536 nm uniform pitch is presented. Two peaks/dips occur, at 785 and 1552 nm, due to reflection/transmission at the Bragg wavelength and at double the Bragg wavelength, and arising from FBG periodicities associated with half the phase mask periodicity and the phase mask periodicity, respectively. It provides simultaneous measurement of temperature and longitudinal strain, with similar intensities in both wavelengths making it better suited for long-distance operation and multiplexing compared with similar schemes.
Novel in-line fiber-optic etalon formed by hollow-core photonic crystal fiber
Y. J. Rao, T. Zhu, X. C. Yang, et al.
A novel fiber-optic in-line etalon is proposed and demonstrated, formed by splicing a section of hollow-core photonic crystal fiber (HCPCF) in between two single-mode fibers, for the first time to our knowledge. Such a HCPCF-based etalon acts as an excellent optical waveguide to form a Fabry-Perot interferometer and hence allows the cavity length to be as long as several centimeters with good visibility as the transmission loss of the HCPCF is much smaller than that of a hollow core fiber, this offers great potential to generate a practical dense fiber-optic sensor network with spatial-frequency division-multiplexing. This novel etalon is demonstrated for strain measurement and the experimental results show that a good visibility of 0.3 and a strain accuracy of better than ±5με are achieved.
Distributed intrusion detection based on combination of phi-OTDR and POTDR
Y. J. Rao, J. Z. Li, Z. L. Ran, et al.
A distributed optical fiber intrusion detection system, based on the combination of the phase-sensitive optical time-domain reflectometer (φ-OTDR) and the polarization optical time domain reflectometer (POTDR), is proposed and demonstrated. The wavelet transform method and peak-enhancing signal processing are used to de-noise the sensing data and achieve high SNR. Both the φ-OTDR and the POTDR share the same optical devices and work together to enhance the veracity of detecting and locating the intrusion perturbation. Experimental results show that perturbation detection with 100% veracity is achieved over a 14km long fiber link with a spatial resolution of 50m by means of the dual outputs from the φ-OTDR and the POTDR simultaneously.
Neural networks improving robustness on fiber Bragg gratings interrogation systems under optical power variations
Celso L. N. Veiga, Leonardo S. Encinas, Antonio C. Zimmermann
The herein article presents a signal processing methodology based on the process knowledge learned by Artificial Neural Networks - ANN aiming to compensate the undesirable power variations of the light in a Fiber Bragg Grating - FBG demodulation system. Conventional ratiometric signal conditioning requires the acquisition of the intensity light signal related to the power light source, minimizing only linear variations of the light imposed to the interrogation system. The proposed method brings better benefits, particularly when the measuring range of the system shall be extended, because of the redundant information generated by the addition of more fixed filters, improving the generalization capacity of the ANN. A temperature interrogation system is also presented and arranged on a typical and useful demodulation architecture, which adopts three filters to extend the measuring range. Preliminary results from a temperature experiment showed the ANN ability to make the FBG demodulation system robust to light variations, including some non-linear characteristic.
A highly reliable liquid pressure sensor based on dual FBGs
It is still a big challenge to set up a durable and stable long-term liquid pressure monitoring system at many points for long pipeline under harsh environment. In this paper, according to the need from customers, a practical high-reliable liquid pressure sensor based on dual optical fiber Bragg grating (FBGs) has been studied and developed. The FBG-based liquid sensor structure has been brought forward and optimized, and its sensing principle has also been given in details. Besides, the novel sensor has been tested by serious experiments. The research results show that the FBG-based liquid pressure sensor has good linearity, repetition and immunity of temperature changes, and the theoretical sensitivity agrees well with that from the experimental results. Such kind of FBG-based liquid pressure sensor can be applied in practical applications.
Experimental investigation of RC beams using BOTDA(R)-FRP-OF
Zhi Zhou, Jianping He, Ying Huang, et al.
Brillouin based fiber optic sensing turns to be a promising technology for Structural Health Monitoring (SHM). However, the bare optical fiber is too fragile to act as a practical sensor, so high durability and large range (large strain) Brillouin distributed sensors are in great needs in field applications. For this reason, high durable and large range optical fiber Brillouin Optical Time Domain Analysis (Reflectometer) sensors packaged by Fiber Reinforcement Polymer (FRP), named BOTDA(R)-FRP-OF, have been studied and developed. Besides, in order to study the large strain, crack and slip between the rebar and concrete in reinforced concrete (RC) beams using BOTDR(A) technique, five RC Beams installed with BOTDA(R)-FRP-OF sensors have been set up. And the damage characteristics of the RC beams were investigated by comparing the strain measured by the BOTDA(R)-FRP-OF sensors and the strain from traditional electric strain gauges and Fiber Bragg Grating (FBG) sensors, respectively. The test results show that the BOTDA(R)-FRP-OF sensor can effectively detect the damage (including crack and slip) characteristic of RC beam, and it is suitable for the long-term structural health monitoring on concrete structures such as bridge, big dam and so on.
Long-range quasi-distributed high temperature sensing based on fiber Bragg grating imbedded in high thermal conductive sheath cable
W. Ha, J. Kim, M. Park, et al.
In this paper, we experimentally demonstrate the potential of quasi-distributed high temperature sensor based on fiber Bragg grating (FBG) utilizing high thermal conductive sheath, which can be a cost-effective alternative for conventional distributed temperature sensors based on Raman, Brillouin, and Rayleigh scattering. A unique Fire Sensing Cable (FSC) used in this experiment is constructed from a 304 stainless steel sheath with 16 optical fibers imbedded in a conductive fluid. One of the fibers contains FBGs for temperature sensing. Total of seventy seven FBGs were serially inscribed with the spacing of six meter over the total length of 468 meter. FSC was heated by various hot zones formed by IR furnace and nitrogen heat nozzle, as the shifts of FBGs were monitored. Although FBGs were 6 meter apart each other, high thermal conductivity of the stainless steal sheath made it possible to check temperature change in the region between gratings. These preliminary results clearly show a high potential of FBGs combined with FSC in applications of quasi-distributed fire sensing cables and monitoring systems.
Low cost interrogation technique for a FBG sensor for combined transverse and longitudinal strain measurement
Z. Brodzeli, G. W. Baxter, S. F. Collins, et al.
A sensor based on a Bragg grating (FBG) fabricated in Hi-Bi optical fiber allowed measurement of transverse and longitudinal strains. A novel interrogation technique that enables information about transverse and longitudinal strain to be deduced from changes in FBG reflectance spectra is proposed. The scheme enables translation of spectral information into optical power received at a pair of sensor heads.
Polymer/Structured Fibers
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Single-mode polymer optical fiber sensors for high-strain applications
Sharon Kiesel, Kara Peters, Tasnim Hassan, et al.
We demonstrate the measurement of the phase shift in a polymethylmethacrylate single-mode optical fiber interferometer, operating at a wavelength of 632.8 nm, up to 15.8% nominal strain in the fiber. The phase-displacement sensitivity is measured to be 1.39 × 107 rad m-1 for this strain range. This strain range is well beyond that previously measured for polymer Bragg gratings and silica optical fiber sensors.
The role of material properties in the strain testing using microstructured polymer optical fibres (mPOF)
Maryanne C. J. Large, Joshua Moran, Lin Ye
Optical fibre sensors have conventionally been made of silica. Polymer optical fibres have a much lower Young's modulus, and higher elastic limit than silica, and can be incorporated into a large range of materials. Whilst these properties make them attractive for using in mechanical sensing, using polymers also brings complexity because of their viscoelastic response. In this work, we use long period gratings (LPG) in microstructured polymer optical fibre (mPOF) as an optical sensor. The effects of stress and strain on the sensor are decoupled and analyzed independently. It has been proposed that the relaxation of stress in the optical fibre during loading would have a significant effect on the interpretation of the optical sensor output. However through the experiments and modelling in this study it has been shown that the effect of stress is minimal.
A POF-based distributed strain sensor for detecting deformation of wooden structures
This report presents a feasibility test of the distributed strain sensor based on plastic optical fiber (POF) for detecting deformation of wooden structures. First, a simple method to fix POF cable onto wooden structures is developed, where the dimensions of the fixing plate are determined so as to minimize the OTDR responses due to the fixing tool as well as the slip between the POF cable and the structure. Second, the authors focus on a new function "memory effect" of the POF-based strain sensor. The strain once applied to the POF cable is memorized through the plastic deformation of the core material, and can be read out using OTDR even after the event. The characteristics of the memory effect and its life are discussed experimentally for tensile strain. Third, in this report, we showed that a 5-point measurement with the spatial resolution of around 5 m was possible for the axial elongation imposed on the POF. Then, we apply the present method for detection of deformations of wooden frame structures. We try to detect the direction and magnitude of deformations at four corners of a rectangular wooden frame using a POF cable and OTDR. The availability of the memory effect in multipoint measurements on wooden structures is also discussed.
Photonic bandgap fiber optical correlation spectroscopy gas sensor
We present results obtained from the first all-fiber, lensless, optical correlation spectroscopy gas sensor for acetylene (C2H2). In the reported sensing configuration, hollow-core photonic bandgap fiber (PBGF) is employed to contain all gas samples required for optical absorption measurements. This sensor relies upon comparison of the absorption spectrum of acetylene held in a 'reference gas cell' to that of a gas sample under test, which is contained in the 'measurement gas cell'. Ingress of the test gas mixture into the measurement cell is achieved via femtosecond laser-machined micro-channels running from the surface of the PBGF to its hollow core. Stable, lensless optical interrogation of the measurement cell is guaranteed by means of arc fusion splices to standard (solid-core) single-mode fiber (SMF). The reference cell is filled with acetylene at atmospheric pressure, and is permanently sealed at both ends by splices to SMF. Therefore, being constructed entirely from optical fiber, both the reference and measurement gas cells are inherently compact and coilable, and dispense with the need for lenses or other free-space optics for connection to the correlation spectroscopy system. We quantify the acetylene concentration of various test gas mixtures and compare our sensor's measured results with computer simulations.
The inner cladding mode in a photonic crystal fiber for temperature- and refractive index-independent strain sensing applications
Chengkun Chen, Albane Laronche, Géraud Bouwmans, et al.
Fiber Bragg gratings with strong resonance peaks for both Bragg and cladding modes are made in photonic crystal fiber modified with a germanium doped core. Experimental results for strain, temperature and refractive index sensitivities of fiber Bragg gratings are reported. We show the existence of an inner cladding mode that has the largest coupling from the core mode and that is insensitive to surrounding index changes. The core mode, inner cladding mode and outer cladding modes all have the same temperature sensitivity. By tracking the cladding mode resonances shifts relative to the core mode, a temperature and index insensitive strain sensor can be made.
Sensor Systems
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Ultra-long-distance (230 km) FBG sensor system
Takanori Saitoh, Kenichi Nakamura, Yoshifumi Takahashi, et al.
An ultra-long-distance Fiber Bragg Grating (FBG) sensor system using a high-speed swept-wavelength light source (HSLS) is proposed and demonstrated. The light output of the HSLS is amplified and turned on and off, and its timing is synchronized to the sweep signal of the HSLS to reduce optical noise caused by Rayleigh scattering from the transmission fiber. This system can detect changes in FBG reflection wavelengths even when the FBGs are located at a distance of 230 km.
Optical system with potential for remote health monitoring of subsea machinery
A prototype fibre optic sensing system is described with potential to remotely monitor the condition of 3 phase variable frequency sub-sea motors and electric submersible pumps. An indication that the integrity of a powerful electric motor may be compromised can be gained by spectral analysis of the stators drive current, the relative phases of the currents, the measurement of vibration at specific locations on the motor and the temperature of the bearings. The optical interrogation system is based on an imbalanced Mach Zehnder fibre interferometer, illuminated with a broad band source with FBG based current and vibration sensors. Signals from sensors operating at an effective distance of 7 km have been demonstrated.
Monitoring of flexible oil lines using FBG sensors
Sérgio R. K. Morikawa, Claudio S. Camerini, Daniel R. Pipa, et al.
Thorough the last two decades, oil and gas reservoirs discovered and developed in deep and ultra deep waters have continuously posed challenges to petroleum exploration and production activities in offshore basins. Maintaining optimum flow rates of oil and gas from subsea wellheads to surface processing facilities demands new technological solutions for petroleum companies operating in such frontiers. Integrity assurance of structures, equipment, and flow lines plays a major role in maximizing offshore production systems availability while at the same time keeping safety, operational, and environmental risks at minimum levels. In this scenario, implementation of permanent health monitoring solutions must take into account the environment of oil and gas production facilities, where installations in hazardous classified areas require explosion and fire-proof instrumentation. In this context, optical fiber sensors offer an attractive alternative to electrical sensing technologies, which, until now, have been the primary choice by maintenance personnel at offshore production units.
Underwater blast loading of a composite twisted rudder with FBGs
32 Fiber Bragg gratings (FBGs) were embedded in a full size, composite twisted rudder to monitor internal strains during underwater blast loading. During final fabrication, the fibers leading to sensors were broken rendering the embedded sensors useless. Time domain reflectometry located the breaks and suggested a likely approach to avoiding such problems in the future. An additional 8 FBGs were surface mounted on the rudder and used to collect data during the blast loading events. Data were successfully collected at rates up to 9700 Hz during 3 blasts, with strains approaching 4000 με and strain rates of up to 13 ε/s.
Postdeadline Papers
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Ultra-fast 31 kHz interrogation of FBG sensors using FDML wavelength swept laser
Ultra-fast 31.3 kHz interrogation is newly demonstrated for fiber Bragg grating (FBG) sensor system using Fourierdomain mode-locked (FDML) wavelength-swept laser. Higher speed interrogations are useful for the real-time monitoring of dynamic sloshing pressure and strain.
A multiplexed CW Brillouin system for precise interrogation of a sensor array made from short discrete sections of optical fibre
A novel configuration for precise temperature sensing in an array of optical fibre sections is reported. The sections are chosen to have different Brillouin shifts, to enable separation of scattered light signals in the frequency domain, rather than the traditional time domain, allowing lower-noise CW operation and greater precision due to the 100% duty cycle.
Novel all in-line photonic crystal fiber interferometer with liquid crystal transducer
A novel in-line photonic crystal fiber interferometer, in the Sagnac configuration consisted of a fused photonic coupler and a liquid crystal transducer is proposed and demonstrated for the first time to our best knowledge. System optimization for 532 nm wavelength is based on properties of the liquid crystal mixture, infiltrating air-holes of the photonic crystal fiber protecting its endlessly single mode operation. The fundamental device properties for the different applied temperature is demonstrated and discussed.
Correlation-based distributed measurement of SBS-generated dynamic grating spectrum in a polarization-maintaining fiber
The distribution of temperature-induced changes in Brillouin frequency shift and that of birefringence-determined frequency deviation in the spectrum of SBS-generated dynamic grating in a PMF have been measured with 1.2-meter spatial resolution and 110-meter measurement range. Synchronously controlled sinusoidal frequency-modulations are applied into two laser sources that are used for pump (probe) light and readout light, respectively, enabling distributed generation and detection of the dynamic grating.
Antibody immobilization within glass microstructured fibers: a route to sensitive and selective biosensors
T. M. Monro, Y. Ruan, H. Ebendorff-Heidepriem, et al.
Glass microstructured optical fibers have been rendered biologically active for the first time active via the immobilization of antibodies within the holes in the fiber cross-section. This has been done by introducing coating layers to the internal surfaces of soft glass fibers. The detection of proteins that bind to these antibodies has been demonstrated experimentally within this system via the use of fluorescence labeling. The approach combines the sensitivity resulting from the long interaction lengths of filled fibers with the selectivity provided by the use of antibodies.