This PDF file contains the front matter associated with SPIE Proceedings Volume 8351, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Based on many years research, a number of novel fiber-optic sensors and systems are developed by the Fiber Optics Group at University of Electronic Science & Technology of China (UESTC). This paper presents a review of the applications of these sensors and systems developed in recent years, including: (1) Micro fiber-optic Fabry-Perot interferometric sensors for high temperature strain measurement applications; (2) Fiber Bragg grating (FBG) sensors for safety monitoring applications in transportations industry; (3) Long-distance Brillouin optical time-domain analyzer (BOTDA) for high performance temperature/strain measurement; (4) Fiber-optic fences based on FBG and phasesensitive optical time-domain reflectometer (Φ-OTDR) for intrusion monitoring applications.

We have developed an FBG sensor with a strain resolution better than 10 nano-strain (10^-8) for geophysics applications. The sensor consists of a pair of identical FBGs, one for strain sensing and the other for reference. A narrow linewidth tunable laser is used to interrogate the two FBGs simultaneously. Cross-correlation algorithm is utilized to extract the Bragg wavelength difference between the FBGs with high precision. Multiplexed sensing is achieved using WDM technique. With this sensor, the crustal deformation induced by oceanic tide at Aburatsubo Bay in Japan is clearly observed with a strain resolution better than 10 nε. This is the first that 10 nε order static strain resolution is demonstrated with FBG sensors, providing a potential tool for the geophysics applications.

A fiber laser hydrophone (FLH) based on a flat diaphragm and an L shaped lever is presented. This hydrophone uses an L shaped lever to transfer the acoustic pressure induced defection of the flat diaphragm to the axial elongation of the fiber laser. The curve where the L shaped lever contacts the diaphragm is a segment of an Archimedes spiral, which is used to enhance the responsivity. To compensate the hydrostatic pressure, a capillary tube is fixed at the end of the hydrophone. Both theoretical and experimental investigations are presented in this paper. The result shows that the proposed design has a high sensitivity of a flat frequency response below 1 kHz.

A resonator fiber optic gyro (RFOG) based on a fiber-coupled semiconductor DFB-LD with an FPGA-based digital processor is set up. A bias stability of 23deg/h over one hour is successfully demonstrated. This is the best result in long time stability reported to date, to the best of our knowledge, for the RFOG based on a miniaturized laser source.

The sensitivity of a fibre Bragg grating (FBG) sensor fabricated in polymer optical fibre (POF) to hydrostatic pressure was investigated for the first time. In this initial investigative work a reflected Bragg response of a FBG fabricated in multimode microstructured POF (MMmPOF) was monitored, whilst the hydrostatic pressure was increased up to 10MPa. Positive sensitivities were observed, meaning a positive wavelength shift to increasing pressure, as opposed to negative sensitivities monitored when using a FBG sensor fabricated in silica optical fibre. The FBG sensors fabricated in the MMmPOF gave fractional changes in wavelength and hence sensitivities of at least 64.05×10^-6/MPa, which is some 25 times larger than the -2.50×10^-6/MPa sensitivity of a FBG sensor fabricated in silica optical fibre that was measured in this work. Furthermore this work highlighted a decrease in sensitivity of the FBG sensor fabricated in the MMmPOF by some 50% by sealing the holes of the mPOF at the tip of the fibre with an adhesive. This offers the potential to tailor the response of the sensor to hydrostatic pressure.

We introduce broadband and tunable Yagi-Uda-type plasmonic nanoantennas created by arrays of metal nanorods of varying length, and explore their use for nanoscale optical sensing. We suggest placing active nanoparticles, sensitive to chemical substances and biological agents, in close vicinity of individual nanoantenna elements at the points of subwavelength light confinement and enhancement. A change in the optical properties of the nanoparticles on exposure to e.g. inflammable gases influences the response of the nanoantenna at characteristic operating wavelengths given by the nanoantenna architecture. We also explore the possibility to dynamically adjust the operating band by using metalsemiconductor nanorods for nanoantenna elements and pumping them with a tightly focused laser beam. The operating band of more than 300 nm, all-optical tunability range of 200 nm and a high sensitivity due to subwavelength light confinement make the suggested nanoantennas attractive for nanoscale sensing applications, including real-time monitoring of low concentrations of gases and observation of chemical or biological events at the nanoscale.

A refractive index sensor using a pressure-induced long-period grating is proposed and demonstrated. The sensing element is made of a composite optical waveguide based on a single-mode fiber. The experimental results show that the sensitivity for LP₁₄ mode resonance is 72nm/RIU (refractive index unit) when the medium refractive index varies from 1.33 to 1.43.

The paper describes a new fiber optic sensor based on the Mach-Zehnder and Sagnac hybrid interferometer to measure the ground vibrations is investigated. The frequency characteristic of vibration signal is analyzed via fast Fourier transform (FFT) and Gabor transform. It provides highly sensitive for low frequency measurement. The fiber optic vibration sensing system presented in this research is appropriate to utilize for sensing ground vibration between 10 ~ 200Hz frequency range.

In this paper, we study the debris flow monitoring system. Two kinds of sensing system are studied and compared with their performance. The first sensor is a traditional geophone, while the second one is a fiber optic sensor. This sensing system is composed of a fiber optic sensor and a Sagnac interferometer. The optical sensor is constructed by a mandril wrapped with fiber. We compare the characteristic of those two sensor heads. The results indicate that the fiber optic interferometric sensor head (fiber optic geophone) has high resolution and its frequency response highly match with the traditional geophone. The results of experiments show that the performance of fiber optic geophone sensing system work well for low frequency range. According to our preliminary test, the dynamic range detected by the optic fiber sensor is 45 dB, while the frequency ranges is between 10 ~ 300 Hz.

The imperfection of optical devices in an optical imaging system deteriorates wavefront which results in aberration. This reduces the optical signal to noise ratio of the imaging system and the quality of the produced images. Adaptive optics composed of wavefront sensor (WFS) and deformable mirror (DM) is a straightforward solution for this problem. The need for a WFS in an AO system, raises the cost of the overall system, and there are also instances when they cannot be used, such as in microscopy. Moreover stray reflections from lens surfaces affect the performance of the WFS. In this paper, we describe a blind optimization technique with an in-expensive electronics without using the WFS to correct the aberration in order to achieve better quality images. The correction system includes an electromagnetic DM from Imagine, Mirao52d, with 52 actuators which are controlled by particle swarm optimization (PSO) algorithm. The results of the application of simulated annealing (SA), and genetic algorithm (GA) techniques that we have implemented in the sensor-less AO are used for comparison.

Using a Low Coherence Interferometry (LCI) model, a comparison of broadband single-Gaussian and multi-Gaussian light sources has been undertaken. For single-Gaussian sources, the axial resolution improved with source bandwidth, confirming the coherence length relation that resolution for single Gaussian sources improves with increasing spectral bandwidth. However, narrow bandwidth light sources resulted in interferograms with overlapping strata peaks and the loss of individual strata information. For multiple-Gaussian sources with the same bandwidth, spectral side lobes increased, reducing A-scan reliability to show accurate layer information without eliminating the side lobes. The simulations show the conditions needed for resolution of strata information for broadband light sources using both single and multiple Gaussian models. The potential to use the model to study LCI and OCT light sources, optical delays and sample structures can better characterise these LCI and OCT elements. Forecasting misinformation in the interferogram, may allow preliminary corrections. With improvements to the LCI-OCT model, more applications are envisaged.

A novel fiber temperature sensor with high sensitivity based on a Michelson interferometer in a single-mode fiber is constructed and demonstrated. The sensor consists of a peanut-shape structure and we demonstrated that the peanut-shape structure can couple the light energy of the core mode into the cladding and re-couple the light in the cladding into the core. The experimental results show that the device can be heated up to 900°C with the sensitive of 0.096nm/° when the sensor length L is ~21mm. Such kind of simple, low-cost, and highly sensitive fiber-optic temperature sensor would find applications in sensing fields.

A novel sensing scheme to measure strain and temperature simultaneously by using an off-axis single mode-multimode-single mode (SMS) fiber optical structure is proposed in this article. The dual-parameter measurement is achieved based on the obviously different strain and temperature responses of two loss peaks in the off-axis SMS transmission spectrum. In experimental, the sensitivities value of temperature and Strain of two loss peaks are measured to -8.2pm/με, -2.3 pm/με and 41.2pm C ° / , 16.0pm C° / , respectively.

We propose that phononic crystals could be used as a packaging method in a fiber optical vibrometer system to filter the vibration at unwanted frequency range. A simple FBG based vibrometer and a aluminum-silicone rubber based 1D phononic crystal with the designed phononic band gap are built up, and the corresponding experimental results are demonstrated to show the feasibility of our proposal. Our proposal also points out that optical fiber sensors could be an excellent candidate to research the inner acoustic response of more complex phononic crystals.

Self-mixing interferometry (SMI) signals are observed from a laser diode (LD) with optical feedbacks induced by an external target. SMI signals carry information related to both of the target and parameters of the LDs. However, the noise contained in SMI signals greatly degrades the applications of the SMI systems. This paper proposes a wavelet transform based de-noising method which can effectively eliminate noise while keeping an SMI waveform less changed. The proposed method is verified by both simulations and experiments.

This article presents a technique for modeling cavity optomechanical field sensors. A magnetic or electric field induces a spatially varying strain across the sensor. The effect of this strain is accounted for by separating the mechanical motion of the sensor into eigenmodes, each modeled by a simple harmonic oscillator. The force induced on each oscillator can then be determined from an overlap integral between strain and the corresponding eigenmode, with the optomechanical coupling strength determining the ultimate resolution with which this force can be detected.

This talk describes the embedded optical fiber sensor systems for smart aircraft composite structures. First, a summary of the current Japanese national project on structural integrity diagnosis of aircraft composite structures is described with special emphasis on the use of embedded small-diameter optical fiber sensors including FBG sensors. Then, some examples of life-cycle monitoring of aircraft composite structures are presented using embedded small-diameter optical fiber sensors for low-cost and reliable manufacturing merits.

Brillouin scattering in perfluorinated graded-index polymer optical fibers (PFGI-POFs) is potentially useful in developing high-accuracy distributed temperature sensors with reduced strain sensitivity. In this study, we investigate, both experimentally and theoretically, the influence of the fiber core diameter and length on the Brillouin gain spectra (BGS) in PFGI-POFs. First, we show that smaller core diameter drastically enhances the Stokes power using PFGI-POFs with 62.5-μm and 120-μm core diameters, and discuss the Brillouin threshold power. Then, we demonstrate that the PFGI-POF length has little influence on the BGS when the length is longer than 50 m. We also predict that, at 1.55-μm wavelength, it is difficult to reduce the Brillouin threshold power of PFGI-POFs below that of long silica single-mode fibers even if their core diameter is sufficiently reduced to satisfy the single-mode condition. Finally, making use of the enhanced Stokes signal, we confirm the Brillouin linewidth narrowing effect.

We demonstrate a fiber ring laser for high-resolution torsion measurement, where the laser cavity consists of a Mach-Zehnder interferometer (MZI) formed with a pair of long-period fiber gratings written in a twisted single-mode fiber (SMF) by a CO₂ laser. The emitting wavelength of the laser provides a measure of the rate of the torsion applied to the grating pair, while the direction of the wavelength shift indicates the sense direction of the applied torsion. The narrow linewidth and the large side-mode suppression ratio of the laser can provide a much more precise measurement of torsion, compared with passive fiber-optic torsion sensors. The torsion sensitivity achieved is 0.084 nm/(rad/m) in the torsion range ±100 rad/m, which corresponds to a torsion resolution of 0.12 rad/m, assuming a wavelength resolution of 10 pm for a typical optical spectrum analyzer.

In this paper, we have investigated cryogenic temperature response of long-period fiber gratings (LPFGs) inscribed on standard photosensitive single-mode fibers without any polymeric coatings. The resonance wavelength of the fabricated LPFG, which was ~1530.778 nm at room temperature (296 K), was monitored under various temperatures ranging from 77 K to 296 K. The temperature sensitivity of the resonance wavelength was measured as ~402.4 pm/K, and the adjusted R-square value of the linear fit of the temperature response curve was evaluated as 0.98144.

Bragg grating in a single-mode photosensitive polymer optical fiber (POF) with benzil dimethyl ketal (BDK)-doped in core has been inscribed through the Sagnac ring interference method. The Bragg wavelength of grating is about 1570nm. The stress and strain response of fiber Bragg grating (FBG) has been studied respectively. By fitting the experimental result, the strain sensitivity of FBG in POF has been found to be almost same to that of conventional silica fiber Bragg gratings. However, the stress sensitivity of FBG in POF is measured to be 421pm/MPa, which is 28 times higher than FBG in silica fiber. And such high stress sensitivity makes Bragg grating in a single-mode BDK-doped POF appear to be very attractive for constructing stress sensor with high resolution.

In this study, a fibre Bragg grating (FBG) was embedded beneath three common flooring materials acting as a pressure switch for in-ground intrusion detection. This is achieved using an intensiometric detection system, where a laser diode and FBG were optically mismatched so that there was a static dc offset from the transmitted and reflected optical power signals. As pressure was applied, in the form of a footstep, a strain induced wavelength shift occurred that could then be detected by converting the wavelength shift into an intensity change. The change in intensity caused a significant change in the DC offset which behaved as on optical switch. This switch could easily be configured to trigger an alarm if required. The intention is to use the FBG sensor as an in-ground intrusion detection pressure switch to detect an intruder walking within range of the sensor. This type of intrusion detection system can be applied to both external (in soil, etc) and internal (within the foundations or flooring of the home) security systems. The results show that a person's footstep can clearly be detected through solid wood flooring, laminate flooring, and ceramic floor tiles.

We design and fabricate a two elliptical cores hollow optical fiber, which has an about 60μm diameter hollow air hole centrally, a 125μm diameter cladding, two 8μm/4μm (major axis/minor axis) elliptical cores, and a 2μm thickness silica cladding between core layer and air hole. Its mode birefringence is consisted of geometry birefringence and self-stress birefringence. Based on the finite element method the birefringence characteristics are analyzed numerically at 200nm- 1800nm wavelength. We expect that the two elliptical cores hollow fiber has some potential applications in in-fiber interferometers with polarization maintaining, poling fiber and Bio-sensor based on evanescent wave field.

The coating process, of optic-fibers into a polymer matrix is a very difficult and delicate process due to the fragility of the fibers, which can get broken by the stresses and temperature imposed during processing. In this paper we introduce a new control system which is based on measurement of specific power changes in the laser transmitted signal thought the fiber. Those changes are produced by mechanical or thermal stresses on the fiber during processing. Those stresses normally generated by photoelastic effects on the fiber when it is pulled or heated, changing its optical properties. By a meticulous characterization of those effects we are able to establish a real time control system for the coating process, avoiding the deformation or even breaking of the fiber during coating.

A new kind of highly-sensitive refractometer is demonstrated based on the polarimetric interference of rectangular microfiber. The measured sensitivity is as high as 18,987nm per refractive index unit around refractive index of 1.33. The calculation is in good agreement with the experimental results. This device exhibits the performance of high sensitivity, easy implementation, high stability and repeatability.

We propose a novel relative humidity (RH) sensor based on hollow core fiber using direct absorption spectroscopic method in this paper. The wavelength scanning around water vapor absorption peak around 1368.59 nm is realized by injecting saw-tooth modulated current to a DFB laser diode. A reference signal is used as a zero absorption baseline and to help reduce the interference from DFB laser source and probed region. The humidity level is determined by the normalized voltage difference between reference signal and sensor signal at the peak of water vapor absorption. We demonstrate that a length of 5 cm hollow core fiber with a fixed small air gap between SMF and hollow core fiber as an opening achieves a humidity detection resolution of around 0.02%RH over the range 0 to 50%RH which does not require the use of any hygroscopic material.

We proposed a new structure for fiber lens to extend the working distance by applying polymer layer to the fiber lens. The simulation result shows that the working distance can be extended to larger than 10 times than a fiber lens without a coated layer. In simulation, the proposed structure extended the working distance to about 2,110 μm by using polymer layer with a refractive index of 1.3.

This paper presents a liquid level sensor with a double-fiber Fabry-Perot (F-P) cavity and a diaphragm serving as the sensing element. The end surfaces of the two fibers that integrated in a ferrule serve as the front surfaces of the F-P cavities, and the diaphragm (one of the standard components of a manometer) as the rear surface. The random difference in position between the two fiber ends makes a phase difference between the two F-P interferometers, and is used to interpret the direction of the pattern shifts with the variation of the F-P cavity length, which leads to a much lower technological requirement for the cavity manufacture and a more stable sensor. A prototype is fabricated to demonstrate the design, and the experimental results show a system accuracy of 1/2 fringe, refer to a height-resolution of 1mm.

Fiber Bragg gratings can be used for monitoring different parameters in a wide variety of materials and constructions. The interrogation of fiber Bragg gratings traditionally consists of an expensive and spacious peak tracking or spectrum analyzing unit which needs to be deployed outside the monitored structure. We present a dynamic low-cost interrogation system for fiber Bragg gratings which can be integrated with the fiber itself, limiting the fragile optical in- and outcoupling interfaces and providing a compact, unobtrusive driving and read-out unit. The reported system is based on an embedded Vertical Cavity Surface Emitting Laser (VCSEL) which is tuned dynamically at 1 kHz and an embedded photodiode. Fiber coupling is provided through a dedicated 45° micromirror yielding a 90° in-the-plane coupling and limiting the total thickness of the fiber coupled optoelectronic package to 550 μm. The red-shift of the VCSEL wavelength is providing a full reconstruction of the spectrum with a range of 2.5 nm. A few-mode fiber with fiber Bragg gratings at 850 nm is used to prove the feasibility of this low-cost and ultra-compact interrogation approach.

A novel tubular optical waveguide-based particle plasmon resonance (TOW-PPR) device for chemical and biochemical sensing is presented. The sensor is based on intensity measurement of consecutive total internal reflections (TIRs) along the wall of the gold nanoparticles-modified glass vial at a fixed wavelength from a miniaturized light emitting diode (LED). The extinction cross-section of self-assembled gold nanoparticles on the inner wall surface of a tubular glass vial changes with different refractive indexes (RIs) of surroundings in the vicinity of nanoparticles. In comparison with other evanescent wave based optical sensors, the TOW-PPR sensor possesses merits of being a wavelength-selectable optical waveguide sensor to fit application needs, microchamber of a defined sample volume, and itself of being a mechanical support for sensor coatings. The sensor resolution is estimated to be 2.7x10-6 RIU in measuring solutions of various RIs ranging from 1.343 to 1.403 obtained by dissolving sucrose in ultrapure water with a concentration between 6.8% and 41.7%. Moreover, the TOW-PPR microchamber was chemically modified with N-(2,4-dinitrophenyl)-6-aminohexanoic acid (DNP, MW = 297.27 Da) and has been shown to be able to detect different concentration of anti-dinitrophenyl antibody (anti-DNP, MW = 220 kDa) in buffer solutions. From corresponding calibrations, a detection limit of 1.21x10-10 g/ml by DNP-functionalized TOW-PPR sensor chip for anti-DNP detection is demonstrated. The device can be simply and inexpensively fabricated, and therefore is ideally suitable for disposable plasmonic sensors, especially promising for high-throughput biochemical sensing applications.

High speed random accessibility to arbitrary multiple points along an optical fiber is realized by a Brillouin Optical Correlation Domain Analysis (BOCDA) system with a time-division pump-probe generation scheme. In the BOCDA system, correlation between continuous pump and probe lightwave is synthesized by frequency modulation at a laser source, so that the stimulated Brillouin scattering takes place only at one selected point along an optical fiber where the two lightwaves are highly correlated. By sweeping the correlation position with changing the modulation parameters, distributed sensing can be realized by the system, but an important feature of the BOCDA system is random accessibility to an arbitrary point to be measured. Another feature of the BOCDA is high speed measurement capability, because the system is driven by the continuous lightwave. In this paper, the two features of the BOCDA, the random accessibility and the high speed measurement capability, are combined by introducing a time-division pump probe generation scheme, in which the Brillouin spectrum shape can be measured in a higher speed than the basic BOCDA . Simultaneous dynamic strain measurement at four points selected arbitrarily along an optical fiber is demonstrated with a total sampling rate of 200 samples/s.

We have realized phase encoding and sensing of signals for quantum cryptography in compact circuits made with standard silica-on-silicon technology. The circuits include Bragg grating filters allowing multichannel cryptography with dense channel spacing, and they are thermally balanced to avoid crosstalk.

This paper proposes a new method for measuring three-dimensional vibrations. By a spherical cooperative target, the system realizes interference from a spherical wave and a plane wave. It solves the problem of complex changes in interference fringes when two spherical waves are used to measure three-dimensional vibration. And the vibration calculation is very simple. Meanwhile, the interferometer integrates two interference arms into a beamsplitter by coating design and can monitor the stability of the system itself. Theoretical analysis and experiment are performed. The experiment results indicate that the method can monitor three-dimensional vibrations accurately.

We present and optical methane sensor that employs a Mach-Zehnder interferometer formed on a planar waveguide. The overclad of only one arm of interferometer is partially etched up to the boundary between the core and clad. Then, the etched region is coated by SnO2 thin layer and the sensor module is annealed at high temperature. When the fabricated sensor module is exposed to methane gas, the interferogram is changed and quickly saturated in 10 seconds.

Embedded sensors provide a high sensitivity to sub-surface damage due to their proximity to the damage features. In particular, fiber Bragg gratings (FBG) are easily embedded into laminates with a minimum of perturbation to the surrounding material microstructure. In this paper we summarize some recent advances derived from full-spectral interrogation of FBG sensors for structural health monitoring and damage identification in composites. In particular we present signals from the FBG reflected spectra that have been correlated to the progression of delamination due to multiple low-velocity impacts in woven composite laminates and foam-core sandwich composites. We also discuss recent advances in interrogation systems for these sensors which have permitted dynamic evaluation of these parameters. Finally, spectral distortion can lead to errors in the interpretation of strain values from the peak wavelength measurement when peak waveforms are assumed. We demonstrate that full-spectral interrogation can provide sensor specific error compensation for these measurements.

We demonstrate the thermal regeneration of fibre Bragg gratings inscribed by direct writing using a femtosecond, infrared laser into standard SMF-28 and pure silica core fibres. Post-H₂ loading was used. The regeneration process is shown to extend the temperature operation of these gratings up to 1200°C. The temperature durability of regenerated 193nm-written gratings in SMF-28 fibre is presented for comparison. The ability to enhance the temperature durability of femtosecond inscribed index changes has significance beyond fibre Bragg gratings; for example, the micromachining of photonic components such as planar waveguides.

The idea of fabricating fiber Bragg gratings during the drawing process of an optical fiber dates back almost 20 years. The application of a transverse holographic writing method on a fiber draw tower offers a promising solution for a highly effective Bragg grating production. Because of the high technology requirements it took more than 10 years to develop the method into a reliable process. The improvements in the technical development during the last five years enable today a cost efficient industrial production of draw tower grating (DTG®) arrays. In this paper we report about new possibilities of the improved process with respect to the grating type (type I gratings, type II gratings), the coating type (²ORMOCER®, metals) and the fiber diameter (125μm, 80μm and below). Furthermore, we present an example for the application of draw tower fiber Bragg gratings in sensing technologies for medical applications.

The inscription of fiber Bragg gratings was demonstrated by 193 nm ArF excimer laser in microfibers drawn from the standard single mode telecommunication fiber. Fiber Bragg gratings are directly inscribed in a series of microfibers with diameter ranged from ~10μm to 3.3 μm without any treatment to photosensitize the microfibers such as hydrogen loading, etc. Four reflection peaks are observed where three correspond to high order mode resonances. The resonance wavelength depends on the fiber diameter and it sharply blueshifts when the diameter is decreased below 10 μm. The gratings are characterized for their response to ambient refractive index. The higher order mode resonance exhibits higher sensitivity to refractive index.

Sensing and telecommunication applications requiring the bending of optical fibers to small diameters are on the increase. Recent work has shown that the centre wavelength of fiber Bragg gratings has a bend dependence the magnitude of which varies with the type of fiber in which the grating is written. In this work the basis of the centre wavelength shift is investigated by modeling the effects of several potential causes for standard and depressed cladding fiber designs. The majority of the expected affects, including bend induced stress and mode field deformation, were found to result in small wavelength shifts in the opposite direction to those observed experimentally. However, a new account of the shift, based on simplistic geometrical optics, does show wavelength changes in the observed direction, of up to -0.15 nm, which is in the range of the experimentally measured shifts.

We determine the noise coefficients of a Fiber Bragg Grating Accelerometer (FBGA) at static operation using Allan Variance Method. We describe the mechanical structure of the FBGA, as well as the embedded optical and electronic circuits used to acquire the experimental data. Comparing the Root Allan Variance Plot of our topology with two MEMS accelerometers plots, one from a theoretical article and another from a commercial datasheet, we observe that FBGA results show a relative low noise profile.

Weakly tilted fiber Bragg gratings (W-TFBGs) with a certain tilted angle are inscribed in the Ge-doped cladding rods of all-solid photonic band-gap fibers (AS-PBGF) by UV illumination. There are couplings not only forward-propagating LP₀₁ mode to counter-propagating LP01 mode but also the couplings to counter-propagating high order supermodes based on tilted refractive index modulation. The responses of the W-TFBGs to temperature and bend are investigated. The results indicate that the resonance peaks will shift red-side with increasing temperatures, and the sensitivities of different resonance peaks are very close in the same grating. When the bend is applied, the grids of W-TFBG will be compressed or stretched. Two resonance peaks will shift with increasing curvatures, which is related to the orientation of curvature. Therefore, it is potential to work as a directional bend sensor. For the fiber grating with high-order supermodes coupling, it could form fiber grating array by different levels. If every grating has individual response to surrounding, such a single W-TFBG could be used for one point and multi-parameter measurement. In addition, this work provides some insights into the mechanisms that contribute to the measured properties of TFBG in the photonic crystal fiber. It is also an effective method to investigate supermode properties of photonic crystal fiber.

Regeneration of fiber Bragg gratings has been shown to be an effective method for improving the temperature stability well beyond the limit of conventional gratings. Strong gratings, which require a high number of laser pulses, have been used mostly in the past for the additional regeneration process. Specific production methods such as draw tower inscription allow only single laser pulse illumination. Such a process can provide, however, versatile and cost effective Bragg grating arrays for sensor applications. Therefore, a combination of single pulse gratings and a regeneration process is of great practical interest. We have demonstrated that an increase of the temperature stability up to 800°C for arrays of single pulse gratings is possible. Furthermore we observe a stronger regeneration for 800 nm wavelength gratings with considerably higher reflectivity after the thermal process compared to gratings for the 1550nm wavelength range.

We demonstrate a structured fiber Bragg grating (FBG) sensor for the measurement of the refractive-index (RI) gradient of the inhomogeneous liquid medium. The double-layer fiber waveguide models and the transfer matrix method are utilized to calculate the reflection spectrum of structured FBG under inhomogeneous liquid medium, the refractive-index (RI) distribution of which is linear and range from 1.330 to 1.360, showing that the reflection spectrum of the structured FBG would split into several tiny resonant peaks, and the D-value of the wavelengths of the tow resonant peaks at the tow sides of reflection spectrum was approximately proportional to the RI gradient. In the experiment, a FBG was etched to a diameter of about 5.73μm for the RI gradient measurement of the diffusion process of the sucrose solution in the micro channel, the experimental results conformed the rationality of the simulated results, indicating the possibility of the RI gradient measurement by using the structured FBG sensors.

We present a theoretical model to study the static pressure distribution among the layers of an optical fiber cable spool based on the force analysis of the cable system. Using the distributed fiber Bragg grating (FBG) sensing technique, the static pressures within the fiber cable layers of the spool were measured according to the Bragg wavelength shifts of the FBGs embedded in the cable. The effects of the cable spool shrinkage owing to the pressure from outer fiber cable layers on the cable tension and the radial pressure were analyzed in detail. As a result, the relationship between the static pressure upon the fiber and the resulted Bragg wavelength shift of the FBG was deduced. The static pressure distribution of the fiber optical cable spool is obtained both in theory and experiment. Theoretical simulations coincide with experimental results. This technology provides us a real-time method to monitor the inner pressure among the fiber cable layers during the optical cable winding process.

WO₃-Pd and Pd-Ag composite films were deposited on the side-face of side-polished fiber Bragg grating as sensing element by magnetron sputtering process. Compared to common FBG coated with same hydrogen sensitive film, side-polished FBG significantly increase the sensor's sensitivity. When the hydrogen concentration is 4% and 8% in volume percentage, the maximum wavelength shift of side-polished FBG is about 25 and 55 pm respectively. The experiment results show the sensor's hydrogen response is reversible, side-polished FBG hydrogen sensor has great potential in hydrogen's measurement.

This paper presents theoretical and experimental results carried out on a simple structure based on bimetallic cantilever to enhance temperature sensitivity of fiber Bragg grating (FBG) sensors. Two metals of equal length and width but having different coefficients of thermal expansion (CTE) are bonded with electric arc welding to form the bimetallic strip and FBG was longitudinally affixed to that metallic strip having larger coefficient of thermal expansion. It was observed that the temperature sensitivity of the proposed FBG sensor has increased 5 times more compared to the bare FBG sensor. Moreover, the proposed sensor showed excellent linearity, reversibility, and repeatability.

Highly sensitive, accurate and stable high temperature (800 K) sensor based on Photonic Crystal Surface Plasmon Waveguides is proposed. The PCW is based on widely used lithographic and nano-fabrication compatible materials like TiO₂ and SiO₂. Gold has been used as a SPR active metal. Employing coupled mode theory, the sensitivity is found to be as high as ~ 66 pm/K.

A high sensitive fiber Bragg grating (FBG) geophone detecting system based on narrow line width distributed feedback (DFB) laser is realized by using filtering demodulation. Sensitivity of FBG geophone lies on the structure of the sensor shell and the shape of the reflectivity spectrum of FBG. Experiments on the detecting system's frequency character have been done. Results show that this geophone can detect the smallest acceleration of 1mm/s2 with a flat response from 5Hz to 40Hz.. The experiments on coal mine exhibit that the geophone can be used to measure microseismic signals. The detecting system shows great prospect in micro-seismic detection, and geological disasters detecting.

The online fabrication of distributed feedback (DFB) fiber laser with a compact and asymmetrical cavity structure was presented. A DFB fiber laser with the total length of 1.9cm and a nearly unidirectional output which had an over 10:1 ratio for the backward to forward output was achieved. The characteristics of small dimension and unidirectional output made it suitable for sensing applications. And the fabrication procedure was easy to be carried out.

Current study utilizes the corrugated long period fiber grating (CLPFG) edge filter and fiber Bragg grating (FBG) strain sensor to configure the high speed strain sensing system by intensity modulation. For static calibration, the FBG wavelength shift is linear with the modulated intensity by CLPFG while the linearity (R²) of the FBG intensity and strain is 0.994. For dynamic strain sensing, the performance of this system is good as the strain gage at 500Hz under the various strain fields. Experimental results also indicate that the optimal sensitivity is 11.08 mV/με.

We proposed an experimental investigation into the low-frequency intensity noise characteristics of erbium-doped distributed feedback fiber lasers (DFB-FL). And the paper presented a simple self-injection locking (SIL) configuration of DFB fiber laser to suppress the intensity noise. One of the reasons caused intensity noise is the existence of multimode in the DFB-FL. SIL inhibits other modes while enhances dominant mode. Process of locking mode occurred in the DFB-FL was measured in this paper. Comparison of the output powers with and without injection gives a sufficient proof, that it can realize the stable lasing by injecting the feedback laser into the cavity again. When the current of 980nm pump is about 175mA, the intensity noise is suppressed about 25 dB, and relaxation oscillation frequency decreased from 126.5 KHz to 60 KHz in this paper. The results have potential application in high sensitive fiber sensors and optical communication.

Long-period fiber gratings (LPFGs) written in nano-engineered bend insensitive single-mode fiber (NEBI-SMF) were reported. It is found that, only when the pitches of the gratings are in two wavelength ranges (270-305 μm and 420-480 μm), obvious resonance peaks can be obtained within the band of 1200-1650 nm, due to the cladding mode separation caused by the nano-engineered ring in the fiber cladding. The strain sensitivity of the LPFG with a pitch of 295 μm in the range of 270-305 μm is 2.8 pm/με, while the LPFG with a pitch of 470 μm in the range of 420-480 μm is insensitive to strain. The temperature sensitivities of the two LPFGs are 0.145 nm/^oC and 0.098 nm/^oC, respectively. Due to the special structure of the NEBI-SMF, more interesting phenomenon could be explored by carrying out further theoretical and experimental study of these novel LPFGs, such as the bending and twisting characteristics, etc.

The analysis of a novel demodulation technique for Fiber Bragg Grating (FBG) vibration sensors based on two parallel matching gratings has been carried out both theoretically and experimentally. The lineally model between transformed formula of optical power and the central reflection wavelength of sensing grating has been obtained. In addition, the FBG vibration sensor based upon cantilever with equalized strength is designed and the natural frequency of sensor has been obtained by calculations. The vibration experiment have been carried out to verify the feasibility of the modulation approach and the performance of the sensor, the results show that frequency measured by the FBG vibration sensor is agreement with the setting value. Moreover, the experiment also indicate that the sensor have a excellent frequency response at the measuring range of 0~30Hz, and the demodulation technique with two parallel matching gratings work well in the vibration sensing system.

A comparison is made between unpackaged and packaged distributed feedback (DFB) fibre lasers using the Michelson interferometer configuration for delayed self-heterodyne interferometery (MIDSHI) to ascertain the improvements to the external environmental noise, quantified by reductions in the Gaussian linewidth. Voigt fitting is used to extract and separate out the Lorentzian and Gaussian linewidth contributions and therefore the associated sources of noise. Significant improvements in the Gaussian linewidth were achieved as a result of significant reductions in the sensitivity of the DFB laser to external perturbations using packaging. However, a broadening of the laser Lorentzian linewidth was observed.

We present the transfer matrix based analysis of the distributed feedback (DFB) fiber laser with an extra weak optical feedback introduced by a fiber end facet directly. The lasing frequency and output power could be modulated by the modulation of the weak feedback parameters, including the phase and intensity of the feedback light. A corresponding simple intensity based DFB fiber laser vibrometer is proposed according to the analysis and the experimental results are given to prove it feasibility. With the advantages of simple and compact structure, the sensing scheme is expected to have broad applications.

A narrow-linewidth photonic crystal fiber (PCF) laser operating at room temperature with two Bragg gratings integrated directly is demonstrated. Fabrication of the Bragg grating in a photonic crystal fiber is investigated experimentally by phase mask method. Under the optimal experiment condition, we fabricate the optical fiber grating with four obvious peaks. Moreover, a continuous-wave all fiber laser operation at 1549.6nm of a diode-pumped PCF laser is fabricated. A constrained bandwidth of 50 pm is formed through locking the laser on the overlapping peak of one Bragg grating with the side lobes of the other. It is possible to achieve a high stability and beam quality laser, which has a great application potential in optical communication field in future.

This paper reports on a series of tests investigating the performance of Draw Tower Gratings (DTGs) combined with custom-designed broad area packaging and bonding techniques for high-strain sensing applications on Defence platforms. The sensors and packaging were subjected to a series of high-strain static and cyclic loading tests and a summary of these results is presented.

A liquid level sensor based on a long-period fiber grating is proposed. The principle of this type of sensor is based on the refractive index sensitivity of long-period fiber grating. As the cladding mode's effective refractive index depends on the refractive index of the surrounding material, the resonant wavelengths of the long period fiber grating will shift when the surrounding refractive index changes. By monitoring a given attenuation band's resonant wavelength shifts, one can measure the immersed lengths of long period fiber gratings and then the liquid level. A direct liquid level measurement is demonstrated by using a long-period fiber grating which was fabricated in a photosensitive B-Ge co-doped optical fiber from Fibercore Inc. (Fibercore PS 1250/1500). The long-period fiber grating was immersed in two solutions which have different refractive indexes. A maximum shift of 7.69 nm for 50 mm of solution which has the highest refractive index has been observed.

This paper reports an application of phase shifted fiber Bragg grating (PS-FBG) intensity-type acoustic sensor in a continuous and in-situ failure testing of an E-glass/vinylester top hat stiffener (THS). The narrow transmission channel of the PS-FBG is highly sensitive to small perturbation, hence suitable to be used in an effective acoustic emission (AE) assessment technique. The progressive failure of THS was tested under transverse loading to experimentally simulate the actual loading in practice. Our experimental tests have demonstrated, in good agreement with the commercial piezoelectric sensors, that the important failures information of the THS was successfully recorded by the simple intensity-type PS-FBG sensor.

We report the evidence of plasmonic-photonic resonances in hybrid metallo-dielectric quasi-crystal nanostructures composed of aperiodically-patterned low-contrast dielectric slabs backed on a metal layer. Via both experimental and numerical studies, we characterize these resonant phenomena with specific reference to the Ammann-Beenker (quasiperiodic, octagonal) tiling lattice geometry, and investigate the underlying physics. In particular, we show that, by comparison with standard periodic structures, a richer spectrum of resonant modes may be excited. Such modes are characterized by a distinctive plasmonic or photonic behavior, discriminated by their field distribution. Concerning the possible applications, we also explore the structure functionalization via nanosized high refractive index overlays (for resonance tuning and quality-factor enhancement), as well as its surface sensitivity to deposition of nanolayers of materials mimicking bio-molecular binding. Overall, our results indicate the possibility of exciting a wealth of resonant modes with state-of-the-art quality factors and sensing/tuning efficiencies, of potential interest for the development of high-performance optical devices for communications, energy and sensing applications.

We employ the photoinduced electron transfer (PET) effect within suspended-core microstructured optical fiber to authenticate a new type of fluorescence based sensor for ion detection. A sensor design based on a simple model PET-fluoroionophore system and small core microstructured optical fiber is shown and the operational performance of the sensor to different concentrations of sodium is investigated. Future approaches to improving the sensor's signal stability and sensitivity are discussed.

In this paper we describe a facile method for synthesizing gold triangular nanoframe from edge gold-coated silver nanoprism [Ag@(Au nanoframe)] with controlled ridge thickness and interior hollow diameter via chemical etching of silver from the gold coated Ag nanoprism with Hydrogen peroxide. Our process involves two major steps: (1) Formation of Ag@(Au nanoframe) by deposition of gold on the edges of Ag nanoprisms in room temperature (2) Etching of Ag atoms from the gold fame via H₂O₂ oxidation. The optical properties of the resulting nanoframe can be easily tailored in a broad range by controlling the ridge thickness or hole diameter by amount of H₂O₂ added into the reaction. Due to the changes to the optical spectra during etching, the nanoframe formation can be employed to detect H₂O₂ in a broad range of concentration down to 1 μM.

It is well known that surface-enhanced Raman scattering (SERS) substrates based on metal island films exhibit higher levels of enhancement when excited through a transparent base material than when excited directly through air. However, to our knowledge, the origin of this enhancement has never been satisfactorily explained. An initial suggestion that the additional enhancement was due to a "nearest layer effect" cannot account for the observation of additional enhancement for monolayer adsorbates. In this paper, finite difference time domain (FDTD) modelling is presented to show that the electric field intensity in between metal particles at the interface is higher for "far-side" excitation. This is reasonably consistent with the observed enhancement for silver islands on SiO2. The modelling results are in agreement with a simple physical model based on Fresnel reflection at the interface. This suggests that the additional enhancement is due to a near-field enhancement of the electric field due to the phase shift at the dielectric interface, when the light passes from the higher to the lower region of refractive index.

We present an experimental study of a fiber optic hydrogen gas sensor which works on the phenomenon of surface plasmon resonance. The sensor operates in intensity modulation scheme. The fiber optic probe was fabricated by removing a small section of the fiber cladding and symmetrically depositing a thin layer of indium tin oxide (ITO) by thermal evaporation technique onto the fiber core. The presence of hydrogen in the air around the ITO changes the dielectric function of ITO. The SPR spectra were obtained for 100% nitrogen as well as for a mixture of 4% hydrogen and 96% nitrogen. A sharp dip in the transmittance spectrum was observed in the case of mixture of 4% hydrogen and 96% nitrogen. The transmittance corresponding to the resonance wavelength was found to decrease with the increase in the exposure time of the hydrogen gas to ITO. The present sensor can be used for the online monitoring of hydrogen gas in various environments.

In this paper we present an experimental study on the surface plasmon resonance (SPR) based fiber optic sensor for the detection of hydrogen. Wavelength interrogation mode of operation has been used for sensing. The probe is fabricated by coating silver, silicon and palladium (Pd) layers over unclad core of the fiber. The fact that the presence of hydrogen in the air around the palladium changes the dielectric functions of palladium is utilized. The SPR spectra are obtained for 100% nitrogen as well as for a mixture of 4% hydrogen and 96% nitrogen. A shift in resonance wavelength is obtained. The shift initially increases with time and then saturates. The silicon layer enhances the shift in resonance wavelength.

The sensitivity is an important issue for intra-cavity absorption gas sensors (ICAGS). In this paper, the ICAGS based on erbium-doped fiber ring lasers (EDFRL) are modeled using propagation equations, from which the expressions of the signal-to-noise ratio (SNR) and the sensitivity of the system are deduced. The influence of the pump power and the total attenuation of the system on the performance of the ICAGS are simulated theoretically and measured experimentally. The absorption signal of acetylene is detected by adjusting the state of the system. And concentration calibration of acetylene is realized finally.

Using the technology of tunable diode laser absorption spectroscopy and the technology of micro-electronics, a fiber laser methane sensor based on the microprocessor C8051F410 is given. In this paper, we use the DFB Laser as the light source of the sensor. By tuning temperature and driver current of the DFB laser, we can scan the laser over the methane absorption line, Based on the Beer-Lambert law, through detect the variation of the light power before and after the absorption we realize the methane detection. It makes the real-time and online detection of methane concentration to be true, and it has the advantages just as high accuracy, immunity to other gases , long calibration cycle and so on. The sensor has the function of adaptive gain and self-diagnose. By introducing digital potentiometers, the gain of the photoelectric conversion operational amplifier can be controlled by the microprocessor according to the light power. When the gain and the conversion voltage achieve the set value, then we can consider the sensor in a fault status, and then the software will alarm us to check the status of the probe. So we improved the dependence and the stability of the measured results. At last we give some analysis on the sensor according the field application and according the present working, we have a look of our next work in the distance.

An evaluation model is proposed to estimate the fluorescence coupling efficiency of a small, capillary-shape fiber sensor, which takes advantage of the analysis approach for the coupling efficiency from a point lightsource to a fiber. To confirm the validity of the theoretical model, a group of 4 fiber-capillary units with increasing diameters and lengths are made and demonstrate with FITC solution. Both simulation and experiment results show that a triangle-arrangement of two excited fibers and one receiving fiber gives the best coupling efficiency of a capillary-shape fiber probe with a fixed diameter. The coupling efficiency is inversely proportion to the refractive index and attenuation coefficient of the fluorophore solution, besides being direct proportion to the core diameter R and the N.A., i.e., sinθ(θ is the receiving angle), of the receiving fiber within the distance from the fiber end to the limit decided by R/tanθ, and a fluorescence efficiency of 0.8% is demonstrated.

A surface plasmon resonance (SPR) based fiber optic biosensor has been fabricated and characterized for the detection of blood glucose. Optical fiber sensor was fabricated by first coating a 50 nm thick gold film on the bare core of optical fiber and then immobilizing glucose oxidase (GOx) over it. Aqueous glucose solutions of different concentrations were prepared. To mimic the blood glucose levels, the concentration of glucose solutions were kept equal to that in human blood. The refractive indices of these sample solutions were equal to that of water up to third decimal place. SPR spectra for the sensor were recorded for these glucose solutions. When the glucose comes in contact to glucose oxidase, chemical reactions take place and as a result, the refractive index of the immobilized GOx film changes, giving rise to a shift in the resonance wavelength. Unlike electrochemical sensors, the present sensor is based on optics and can be miniaturized because of optical fiber. The present study provides a different approach for blood glucose sensing and may be commercialized after optimization of certain parameters.

In this paper, a carbon nanotubes (CNTs) films around microfiber gas sensor is reported. The CNTs films are deposited uniformly on the surface of microfiber with Langmuir-Blodgett(LB) coating technology. The CNTs which are rank tightly perform as cladding of microfiber and show the well absorption characteristic when they are used for gas sensing. The experimental results have shown the variations of intensity of transmitting light while the concentration of acetone and xylene around CNTs films based microfiber are different, The changes of light intensity are 3.1dB and 9.5dB respectively, when acetone and xylene concentrations reached 1200ppm. As the gas vaporizing freely, the results also show the fine characteristic with real-time response. The results demonstrate that this type of CNTs films around microfiber structure has great potential applied in trace gases detecting in micro-scale.

Evanescent-wave gas sensing with tapered optical fibers (TOFs) and quartz-enhanced photoacoustic spectroscopy (QEPAS) is reported. The evanescent field of TOFs with diameter down to sub-wavelength is utilized for photoacoustic excitation in photoacoustic spectroscopy. A quartz tuning fork (QTF) with resonant frequency about ~32.75 kHz is used to detect the generated pressure wave. A normalized noise equivalent absorption coefficient of 1.5×10^-6 cm^-1 W/√Hz is achieved for acetylene detection with a fiber taper with a waist diameter of 1.1 μm. It is found that QEPAS with TOFs of sub-wavelength diameters exhibit comparable sensitivities with open path QEPAS but with additional advantages of lower insertion loss, easier alignment, and multiplexing capability.

Using a side polished standard fiber (SPF) as a sensor which is very sensitive to external refractive index, liquid crystal hybrid film mixed with Azobenzene(AZO) and ZLI811 is overlay on the polished region of the SPF, and the photorefractive effect of the film with UV light irradiation is studied. The mixture composed of liquid crystal, AZO, and ZLI811 was coated on the polishing area after the SPF was calibrated. The optical power transmission of the SPF changes when the photosensitive film on the SPF is under UV irradiation. Through curve of optical power transmission which functions as refractive index, refractive index change of liquid crystal hybrid film is measured. Our experimental result shows that the photosensitive thin film is a negative photosensitive material, and the refractive index changes from 1.474 to 1.470 under UV light irradiation. This photosensitive film material can be potentially used to create a new all-fiber optical-controllable components and sensors.

We propose to monitor the liquid-solid and gas-liquid phase transition of water based on FBG sensors. The naked FBGs and the packaged FBG temperature sensors are used to monitoring the liquid-solid phase transition of water at the same time in order to find its characteristics, including the supercooling state and the strain and pressure change introduced by the phase transition. Fourteen FBGs are packaged and arranged in a steam boiler in order to monitor the gas-liquid phase transition, including the temperature and pressure change inside the steam boiler and the strain of the boiler wall. The preliminary experimental results are demonstrated here.

Carbon dioxide is one of the important gas need to be detected in coal mine safety. In the mine limited ventilation environment, Concentration of carbon dioxide directly affects the health of coal miners. Carbon dioxide is also one of important signature Gas in spontaneous combustion forecasting of coal goaf area, it is important to accurately detect concentration of carbon dioxide in coal goaf area. This paper proposed a fiber carbon dioxide online sensing system based on tunable diode laser spectroscopy. The system used laser absorption spectroscopy and optical fiber sensors combined, and a near-infrared wavelength 1608nm fiber-coupled distributed feedback laser (DFB) as a light source and a 7cm length gas cell, to achieve a high sensitivity concentration detection of carbon dioxide gas. The technical specifications of sensing system can basically meet the need of mine safety.

Wavelength tunable distributed feedback laser diode (DFB-LD) were utilized to measure line 1368.597nm and line 1367.862 nm absorption character of water vapor, based on it, water vapor concentration can be measured by peak absorption rate according to Beer-Lambert law. Besides, we observe that the overlap between the line 1368.597nm and line 1367.862 nm appears and become serious with the increase of gas pressure, this agrees well with the theoretical prediction, and the overlap cause difficulty to determine the absorption peak value, a scheme is presented to cope with the difficulty, it takes advantage of the peak absorption difference between 1368.597nm and 1367.862 nm, and the difference value is used to calculate the water-vapor concentration.

The performance of an erbium-doped fiber (EDF) ring laser based intra-cavity gas sensor is investigated theoretically and experimentally. A theoretical model for analyzing the effects of the EDF parameters and the system parameters on the performance of this gas sensor was established using coupled rate equations and propagation equations. We investigated a number of specific cases and suggested practical choices of their parameters. Experiments with two cavity losses were conducted to test the system sensitivity enhancement and the trend of the results matched well with the theoretical prediction. The results showed sensitivity enhancement factors ranged from 17-20 in the experimental system can be achieved.

Focused ion beam (FIB) lithography was used to inscribe a periodic array of nanoholes directly on gold-coated optical fiber end-faces. The excitation of the surface plasmon polaritons of the nanohole arrays on the optical fiber end-faces provided the basis of a refractive index sensor for liquids. This optical fiber based surface plasmon resonance sensor is compact and has the potential to be used in biomedical applications. A sensitivity of approximately 294 nm per refractive index unit (RIU) has been demonstrated for this sensor.

A simple method of fabricating low loss microwire waveguides from silica nanoparticles via evaporative self-assembly is demonstrated. Light guidance within the microwires is characterised. The photonic microwires assemble into rectangular slab waveguides with a typical cross-sectional dimension of (20×10) μm and are up to 15 mm in length. Rhodamine B was incorporated into the structures and characterized with fluorescent microscopy, absorption spectroscopy and scanning electron microscopy (SEM). We discuss the relevance of these structures to sensing.

This paper describes the verification of a reproducible, highly sensitive, robust, and reliable SERS active substrate that is composed of periodic silver nanoparticle arrays encapsulated within large-area (1 in²) anodic aluminum oxide films. The well-organized spherical silver nanoparticles are electro-deposited at the interior bottom of alumina nanochannels. After chemically removing the residual aluminum, the exposed bottom alumina layer can be adopted as a sensitive SERS sensor but can avoid the oxidation and sulfidation corrosion of embedded silver. The encapsulated nanoparticle arrays provide strong and reproducible SERS signals of probe R6G and adenine molecules. The shelf life of the single-process fabricated SERS substrate is examined and over two months with repeatable SERS measurements and reproducible SERS signals. Avoiding the complicated and more expensive vacuum deposition process, the cost-effective and single electrochemical process fabricated SERS active substrate which can retain the most compromise Raman enhancing power and repeatable uses for at least two months is a promising sensor for a variety of practical applications.

We report novel living protein-doped planar waveguide, and real-time detection of an organophosphorus compound using a sol-gel silica planar waveguide doped with a green fluorescent protein and an organophosphorus hydrolase on a yeast-cell surface. The waveguide was pumped at 488 nm, and emitted green fluorescence at the far field. The green fluorescent light at 550 nm changed by 50% from the original power 1 min after application of the organophosphorus compound. The results enable the real-time detection of biochemical weapon and insecticide harmful for human body by using an in-line fiber sensor network.

We describe a fibre optic hydrophone array system that could be used for underwater acoustic surveillance applications e.g. military, counter terrorist and customs authorities in protecting ports and harbors, offshore production facilities or coastal approaches as well as various marine applications. In this paper we propose a new approach to underwater sonar systems using voltage-controlled Liquid Crystals (LC) and simple multiplexing method. The proposed method permits measurements of sound under water at multiple points along an optical fibre using low cost components (LC cells), standard single mode fibre, without complex interferometric measurement techniques, electronics or demodulation software.

Surface plasmon resonance (SPR) based fiber optic sensor has been studied for multichannel and multianalyte sensing. Simulations have been carried out for a fiber optic sensor having two sensing regions coated with silver and gold for multichannel and multianalyte sensing. The simulated results have been obtained for different combinations of refractive indices of the samples around the probes. To support simulations optical fiber SPR probes with two sensing regions coated with silver and gold have been fabricated. SPR spectra for these sensors have been recorded for aqueous sucrose solutions of varying refractive indices. The refractive index of the liquid samples around both the gold and silver coated regions was kept the same to see the potential of SPR based fiber optic multichannel sensing, while it was kept different for studies related to multianalyte sensing. Both the theoretical and experimental results match qualitatively. The SPR resonance wavelengths for gold and silver being different, these sensors can be utilized for both multichannel and multianalyte sensing.

A simple demonstration utilising the optical light source of an Android tablet to obtain the absorption spectra of Rhodamine dye stained self-assembled silica microwires is demonstrated. The spectrum is collected using a portable Spectrometer. This highlights the potential of tablet technology as portable optical hardware in its own right and we discuss how to potentially achieve complete integration of spectrometer onto the tablet.

A four-layer D-shaped optical fiber surface plasmon resonance (SPR) for high-sensitivity polarimetric strain sensor is proposed. In contrast to existing SPR-based sensors, which are based on changes in the refractive index of the over-layer, the sensor proposed in this study is based on the change in the refractive index of the fiber core in response to the application of an axial load. Specifically, the phase difference between the P- and S-waves after passing through the sensor under SPR conditions is measured using a common-path heterodyne interferometer and is used to determine the corresponding change in the refractive index of the core. The experimental results show that the sensitivity of the proposed sensor is around 2.19×104 Deg./ε, i.e., degree/strain. By contrast, that of a conventional (non-SPR) polarimetric fiber sensor is just 5.2×102 Deg./ε.

A novel approach to distributed radiation dosimetry is presented. Our approach uses optically stimulated luminescence in optical fibres to detect ionising radiation. This system is unique in that the optically stimulated luminescence mechanism occurs within the optical fibre itself, which then guides the resulting optical signal to a detector. Fluoride phosphate glass was identified as a suitable material, showing a strong optically stimulated luminescence response to ionising radiation. Optical fibres were fabricated from this glass and radiation-detection measurements performed. Radiation exposure was performed with a ⁹⁰Sr/⁹⁰Y beta source, optical stimulation was provided by a 532nm, 25mW diode laser. The luminescence signal was isolated using two Corning 7-59 filters and detected with an EMI 9635 QA photomultiplier tube. Detection of optically stimulated luminescence produced within the optical fibres is demonstrated. A relationship is shown between the intensity of the luminescence signal, and the applied radiation exposure. The optical fibres are shown to have a consistent response after repeated radiation exposures of 1380.5 ± 37.2 counts/sec. This demonstrates the capacity of the fibres to provide continuous and real-time detection.

In this work, we have experimentally studied the surface plasmon resonance (SPR)-based fiber-optic refractive index sensor introducing a layer of cobalt in addition to gold layer. The sensor is based on wavelength interrogation method. The advantage of cobalt is that it possesses both SPR and magnetic properties and hence can also be used for magnetic field sensing. Addition of a thin layer of cobalt to the SPR probe enhances the sensitivity of the sensor. Further, the operating wavelength can be tuned by varying the thickness of the cobalt layer. Experimental results show a red shift in the resonance wavelength with the increase in the refractive index of the sensing layer for a given thickness of the cobalt layer. Further, as the thickness of the cobalt layer increases, the sensitivity of the sensor increases. Use of cobalt in place of gold reduces the cost of the probe. In the bilayer metallic structure that has been studied, the ferromagnetic material (cobalt) induces the magneto-optic activity and the noble metal allows the excitation of non damped plasmons, which increases the electromagnetic field intensity inside the cobalt layer and enhances the sensitivity of the sensor.

In this paper, the Raman spectra of the cancer nude mouse serum were measured using surface-enhanced Raman scattering (SERS) with the silver colloid substrate. The result indicated that the SERS spectra of the serum increased several peaks compared with conventional Raman spectra. More ever, these peaks were so crucial for analysis of the serum component and structure so that the information of the protein, carbohydrate, lipid and other trace amounts component could be analyzed through SERS spectra. Therefore, SERS technique is reliably used to compare relative intensity shifts and to investigate the adsorption of biological molecular proteins on Ag nanoparticles.

Liquid crystal (LC) cells can be used in conjunction with optical fibres to develop cheap and efficient sensors, such as voltage sensors or hydrophones. In this paper we apply an effective tensor model to describe reflection from gold-coated deformed-helix ferroelectric liquid crystal (DHFLC) cells. We show that, depending on the polarisation of the incident light, it is possible to obtain a linear electro-optical response to the voltage applied to the cell. Theoretical results are compared with experimental results yielding accurate agreement.

Optical fibers are a unique medium to coat with functional sensor materials that change in refractive index upon adsorption/interaction with specific compounds. In this work, we demonstrate a simple technique to coat the end face of an optical fiber with the microporous MFI-type zeolite. The exposure of the zeolite films from air to water or to aqueous solutions of ethanol and isopropanol causes a distinct change in the film's refractive index. This change was then detected using a simple fiber optic refractive index sensor by monitoring the signal intensity reflected back from the coated fiber endface and as the zeolite is transferred between air, water and solutions containing ethanol and isopropanol. The zeolite coating was developed using the in-situ templated growth technique to grow the zeolite crystals on the cleaved endface of an optical fiber. Effective coating was achieved when the fiber was oriented horizontally in the hydrothermal reactor. The zeolite coated end face reflected less energy in water, at 0.0201 μW, and exhibited almost no change (~2% increase) with increasing ethanol concentration, but exhibited a 135% increase in reflected energy, i.e. 0.048 μW, in 100% ethanol. The zeolite therefore gave the sensor alcohol selectivity. Further work is exploring applicability for liquid phase chemical and water quality analysis.

In this paper we propose a new approach to fibre optic voltage sensors via voltage-controlled Liquid Crystals (LC), which would allow direct measurement of up to 400 kV/m electric fields at multiple points. In addition, a novel polarization independent fibre optic sensor configuration is presented that exhibits a linear electro-optic (EO) response to variations of the electrical field under test.

Recent results confirm the presence of molecular oxygen proving that recombination of dissociated silica bonds does not occur. This combined with the observation of nanopores within the nanograting structure in silica, leads to a new interpretation of femtosecond processing based on the unusual characteristics of quenching of tetrahedral silica compared to other glasses. This new approach suggests very different directions and implications for devices, including sensors, based on femtosecond laser processing of glasses.

Contact angle measurements of water on pathology grade borosilicate glass microscope slides before and after base piranha treatment are compared to treatment with 193nm laser irradiation. 193nm irradiation in the presence of hydrogen was also explored. Within experimental resolution, the observed changes in contact angle as a result of treatment either with base Piranha solution or with laser processing are identical. The contact angle, a, in both cases is reduced from a = (27 ± 6)º to a = (8 ± 3)º with treatment. However, for the piranha base method, there is an observed reversal over time either fully recovering or partially recovering within hours. By contrast, with laser processed, the increased surface wettability is retained with no change for more than 15 hours. In all cases, surface functionalisation, as measured by contact angle, with (3-mercaptopropyl)trimethoxysilane (MPTS) is found to be largely independent of any processing. We conclude that the method of contact angle as a means for qualitatively asserting improvements in attachment is unjustified.

The structure and physical properties of a thin titania sol-gel layer, prepared on silicon and silica surfaces by cold processing and spin-coating techniques, were examined. A series of spectroscopic (FTIR, UV-VIS spectroscopy and ellipsometry) and microscopic (light microscopy, SEM and EDS) techniques were used to examine the chemical and physical uniformities of the sol-gel layers. Conditions were established to generate uniform layers reproducibly. The high refractive index, selective binding to organic functional groups and the light and gas transmission properties of the titania layers can be successfully made use of for new optical sensor applications.

Based on recent studies of our group, we will present various methods of plasmonic field enhancement and hotspot generation. Especially, we will focus on the potential of utilizing localization of propagating surface plasmon polaritons (SPPs) for the sensor applications. The advantage of using localization of propagating SPPs instead of using directly excited localized SPPs will be investigated.

We investigate a powerful new sensing platform based on upconversion luminescence in NaYF4: Yb/Er nanocrystals loaded inside a suspended-core microstructured optical fibre. The use of a NIR source enables autofluorescence from the glass to be reduced compared to using visible sources for excitation of fluorescence. We demonstrate a substantial improvement in the detection limit that can be achieved in a suspended-core fibre sensor, with detection limits as low as 660 fM achieved. This is a factor of 15× better than the best results previously reported using Quantum dots in a similar fibre.

αIn this paper, real-time characterization of α-thrombin binding to single-strand DNA (ssDNA) aptamers by novel Si-based waveguide SPR biosensors has been investigated. The gold nanoparticles (AuNPs) modified with anti-thrombin antibodies were employed to bind with α-thrombin via strong antibody/antigen affinity for SPR signal amplification. The detection limit of 1 pM for -thrombin detection was achieved.

Multiplex fiber-optic biosensor implemented by integrating multiple particle plasmon resonances (PPRs), molecular bioassays, and microfluidics is successfully demonstrated. The multiple PPRs are achieved by chemical immobilization of silver nanoparticles (AgNPs) and gold nanorods (AuNRs) separately on two unclad portions of an optical fiber. The difference in morphology and nature of material of AgNPs and AuNRs are exploited to yield multiple plasmonic absorptions at 405 and 780 nm in the absorption spectrum measured from optical fiber by white light source illumination. Through the coaxial excitation of light-emitting diodes (LEDs) with 405 and 800 nm wavelengths, the distinct PPRs are advantageous for real-time and simultaneous detection of multiple analyte-probe pairs as AgNPs and AuNRs are separately functionalized with specific bio-probes. Here, the multi-window fiber-optic particle plasmon resonance (FO-PPR) biosensor has been shown to be capable of simultaneously detecting anti-dinitrophenyl antibody (anti-DNP, MW = 220 kDa) via N-(2,4-dinitrophenyl)-6-aminohexanoic acid (DNP, MW = 297.27 Da) functionalized AgNPs and streptavidin (MW = 75 kDa) via N-(3-aminopropyl)biotinamide trifluoroacetate (biotin, MW = 414.44 Da) functionalized AuNRs. The multiplex sensing chip possesses several advantages, including rapid and parallel detection of multiple analytes on a single chip, minimized sample to sample variation, reduced amount of sensor chip, and reduced analyte volume, hence it is ideally suitable for high-throughput multiplex biochemical sensing applications.

The integration of Raman-labeled nanoaggregate-embedded beads (NAEBs) for high performance SERS analysis of single mimic pathogen on a self-designed dielectrophoretic chip is demonstrated. The Raman tags called NAEBs are silica-coated, dye-induced aggregates of a small number of gold nanoparticles (AuNPs). In this work, NAEBs consisting of a Raman dye tetramethyl-rhodamine-5-isothiosyanate (TRITC) are chemically functionalized with streptavidin to detect biotin-functionalized polystyrene (PS) microspheres which mimic as pathogens. The sample solution of completely mixed streptavidin-functionalized NAEBs and biotin-functionalized PS microspheres is pumped into the microfluidic channel of a dielectrophoretic chip. By giving an AC voltage on the embedded electrodes, a single mimic pathogen can be caught via the non-contact dielectrophoretic force and suspended at the central cross of four aluminum electrodes for subsequent Raman spectroscopic detection. The SERS signal of TRITC is used as a spectral signature of specific mimic pathogen recognition, otherwise only the background Raman signal of a PS microsphere is observed. A pathogen-specific biosensor based on the dielectrophoresis-Raman spectroscopy system is developed, and the proof-ofconcept is confirmed by the specific molecular interaction model of streptavidin with biotin. Therefore, the on-chip multiplex SERS analysis of pathogens can be anticipated by employing different dye-tagged NAEBs simultaneously in a sample solution. We believe this bioassay has the ability to screen and detect multiple pathogens with minimal sample processing and handling even a small number of pathogens is present.

Plasmons based optical-fiber biosensors created from gold coating tilted Bragg gratings have been demonstrated. Plasmon resonances in the transmission are used to detect the banding of single stranded DNA (aptamer) and the further banding of target DNA (matched one).

A novel disk-like surface-enhanced Raman scattering (SERS) substrate for bacteria fingerprint discrimination is described. A simple synthesis method for dispersion gold nanoparticles (Au NPs) in the mesoporous silicas matrix with tuneable size and concentrations are also reported. Prepared Au NP-embedded complex matrix was thermal treated at 600 °C for cleaning protecting agent and impurity chemicals to obtain the bare gold NPs (~40 nm) embedded matrix. These prepared matrix present high surface area (≈ 300 m2g-1), large pore size (> 5.0 nm) and high metal NPs content (≈ 30 wt.%). Moreover, a filter-like substrate contains higher water permeability which targets can be filter out from sample solution and the substrates can also perform highly SERS signal compared with normal Raman spectra. Specially, SERS signals can be further adjusted by controlling the size of NPs.

Understanding the evaporation behavior of droplets on a flat substrate is very important for applications of many areas. In order to obtain quantitative three-dimensional imaging of droplet evaporation process, the dynamic digital holography has been employed. The off-axis holograms are recorded by a camera and the object waves are numerical reconstructed. The method can simultaneously provide an amplitude-contrast image and a quantitative phase-contrast image. The theory of digital holography is introduced and the experiment of water droplet evaporation is presented.

A new real non-invasive two-core single fiber optical tweezers is proposed and fabricated by fiber grinding and polishing technology. The yeast cells trapping performance of this special designed truncated cone tip fiber probe is demonstrated and investigated. The distributions of the optical field emerging from the truncated cone fiber tip are simulated by Beam Prop Method. Both axial and transverse trapping forces are calculated by FDTD method. This new optical tweezers can realize truly non-invasive remote trapping and manipulating bio-cells.

For a fiber with complex index profile, its density fluctuations change with position and it also introduces birefringence, hence the Brillouin frequency changes with position due to variation of modal index, and sound velocity has a range instead of being a constant. As a result, the single mode fibers support multiple Brillouin resonances varying in position, even with polarization scramblers (PS) of the pump and probe waves. For a Brillouin optical time domain analysis (BOTDA), at a specific location, because of the spatial resolution, the measured Brillouin frequency still gives a range, although PS can help to reduce this fluctuation, as the spatial resolution is much smaller than the beat length of single mode fiber (SMF). The measured Brillouin frequency variations in one position and its location dependence reflect the non-uniformity of the optical fiber, rather than the systematic error of the sensor detection system. When a fiber supports elliptical birefringence, then four Brillouin resonances can be found for an acoustically uniform fiber based on theoretical calculation of their eigenmodes. The beat of different Brillouin peak frequencies and their magnitudes change with temperature and strain, which can be used to measure temperature and strain simultaneously in LEAF fiber without the need of the sweeping Brillouin spectrum.

An analysis of the effect of weak feedback on Bragg grating fibre laser output parameters is presented and a simple sensor arrangement based on monitoring intensity fluctuations of a DFB fibre laser with a weak external reflector is considered. Calculations suggest that it may be possible, under certain conditions, to resolve changes to the length of the external cavity at close to the thermal noise limit. This introduces the possibility of achieving strain resolution in the sub-picostrain regime in the low frequency domain where resolution of conventional fibre laser sensors is limited by 1/f noise.

A frequency-sweep-free method for distributed Brillouin sensing is used to reconstruct the Brillouin gain spectrum of optical fibers at high speed. We experimentally demonstrate distributed strain measurements induced by 140Hz vibrations, with a spatial resolution of 5m.

We describe a novel distributed fiber optic sensor, which is able to map both strength and orientation of intense static magnetic fields in the area spanned by the fiber. The sensor is based on Faraday rotation and on polarization analysis of the field backscattered by the fiber due to Rayleigh scattering. Owing to a specific theoretical model, it is possible to isolate and measure the effect of magnetic field along the fiber, independently of its intrinsic birefringence. The small Verdet constant of standard silica fibers makes the proposed technique most suited to intense magnetic fields. Two different sensors based on this approach have been built and successfully tested in a 1.5 T magnetic resonance imaging scanner.

The ramifications of optical fiber vibrations on the calibration phase of slope-assisted fast distributed Brillouin optical time-domain analysis, is studied. It is theoretically and experimentally found that for not too severe vibrations the Brillouin gain spectrum, as determined by classical BOTDA, is only negligibly broadened, still enabling the correct estimation of its -3dB frequency points along the fiber.

We propose and experimentally demonstrate a novel simultaneous strain and temperature fiber optic sensor based on radio-frequency measurement. The sensing head is formed by two concatenated ultra-short distributed Bragg reflector lasers that operate in single longitude mode with two polarization modes. The total length of the sensing head is only 18 mm. The two lasers generate two polarization mode beat notes in the radio-frequency range which show different frequency response to strain and temperature. Simultaneous strain and temperature measurement can be achieved by radio-frequency measurement. This approach has distinctive advantages of ease of interrogation and avoidance of expensive wavelength detection.

Fiber Bragg Grating (FBG) is sensitive to the temperature as well when it is measuring the strain change, which is always avoided in most measurement applications. However, in this paper strain/temperature dual sensitivity is utilized to construct a special security fence with a second function of fire threat prediction. In an FBG-based fiber fence configuration, only by characteristics analysis and identification method, it can intelligently distinguish the different effects of personal threats and fires from their different trends of the wavelength drifts. Thus without any additional temperature sensing fittings or other fire alarm systems integrated, a normal perimeter security system can possess a second function of fire prediction, which can not only monitor the intrusion induced by personal actions but also predict fire threats in advance. The experimental results show the effectiveness of the method.

The influence of the non-local effect on sensing performance in long-distance Brillouin optical time-domain analyzer (BOTDA) based on bi-directional Raman amplification has been investigated theoretically. The results show that, the system error induced by non-local effect worsens with increased powers of probe and Raman pump waves.

We experimentally demonstrate distributed strain measurement with a high spatial resolution and a large dynamic range by proposing a system for Brillouin optical correlation domain reflectometry with an intensity modulation scheme. With the optimized intensity modulation, the optical power spectrum of the light source is properly modified so that the accumulated background noise in the Brillouin gain spectrum is significantly reduced. It is confirmed that the proposed system enables us to extend the maximum measurable strain up to ~7000 με, which is sufficient for practical applications of a distributed sensing, with 1-cm spatial resolution. This resolution is the best result ever reported in reflectometries based on spontaneous Brillouing scattering by using a conventional single mode fiber.

The raising demand for increase of efficiency and reduction of costs in power generation causes a mind change and promotes the commercial use of fiber optical sensors for health monitoring and control purposes.

In this paper, we report our recent work in an application of fiber Bragg grating (FBG) sensors in progressive failure monitoring of E-glass/vinylester top-hat stiffener (THS) composites. FBG sensor arrays were embedded at strategic points within the THS to monitor the onset and progress of failure modes as the THS undergone a transverse loading. Techniques to embed FBGs in-situ during composite structure fabrication are developed. Our experiments demonstrated that key structural failure information can be obtained from the analysis and assessment of data, such as average strain, strain gradient and full spectrum measurements, collected by the embedded FBG sensors.

Traditional electrical displacement sensors usually are big and insensitive, difficult to multiplex, therefore, they are not suitable for model test. In this paper, a novel subminiature multipoint FBG displacement sensor which has overcome the shortages of above displacement sensors is designed especially for the model test based on analysis of displacement detecting principle. It mainly consists of several FBGs, springs, crusts and the bases. FBGs which are sensitive device connect with springs in series. When key point moves, stretching deformation of spring will occur, so that FBG will receive axial force which will make central wavelength of FBG drifts. According to drift of center wavelength of the sensor, displacement of several points can be detected simultaneously. Calibration experiments of several sensors are carried out, in which it could get the conclusions that the sensitivity is about 1.3nm / mm and the linearity is over 0.99. FBG displacement sensors are embedded in the tunnel wall rock symmetrically to monitor precursory information of disaster. In the process of tunnel excavation, displacement increased gradually, and the detecting results had a strong symmetry.

Results of R and D of intelligent optical fiber sensors, in particular Fabry-Perot interferometer-based, Bragg grating-based and Doppler frequency-based sensors are presented. Advantages of using the intelligent OFS as self-checking pressure gauges, acoustic emission sensors and sensors of other physical quantities are considered. Presentations of the applications intelligent optical fiber measuring systems in nuclear, oil and gas industries of Russia are given.

This paper discusses the use of Fibre Bragg grating sensors (FBG) in structural health monitoring (SHM) of Fibre reinforced polymer (FRP) aerospace structures. The diminutive sensor provided the capability of embedding inside FRP structures in order to monitor vital potential locations for damage. Some practical problems associate with manufacturing process of FRP with embedded FBG sensors, interrelation of distortion to FBG spectra with damage, and interpretation of FBG spectral responses for identifying the damage will be discussed.

A calibration method for fiber Bragg grating (FBG) cryogenic temperature sensors based on look-up-table was proposed and demonstrated experimentally. The operating principles of different kind of FBG cryogenic temperature sensors are introduced. A statistical characterization of the data was carried out to verify the quasi-static condition of the measurement system by checking the stability of the measurement. Once verified this condition, the sensitivity curves of the sensors were determined by correlating the wavelength shift of the FBGs with the reference sensor measurements. On the basis of the sensitivity curves, the look-up-table (LUT) have been determined. The experimental data shows that the LUT fitting approach provides good and reliable performance in terms of accuracy and processing time.

An all-fiber wind direction sensor that used in wind power generation is introduced in this paper. The system based on Interferometer technology. The probe is designed as a fabry-perot cavity, which cavity length is changed with the wind directions. The system can calculate the wind direction by interference fringe period. The results of experiment showed that this sensor can monitor wind direction more exactly. The method is simple, sensitive with a good reproducibility.

The development and test of the fiber laser interrogation system is demonstrated in this paper. Unbalanced Michelson interferometer and digital phase-generated carrier (PGC) demodulation are adopted by the interrogation system. Interferometric interrogation principle and overall interrogation system are described. The interrogation system consists of digital PGC demodulation algorithm, data acquisition, photodiode amplifier and low-pass filter, PGC phase carrier generation and unbalanced Michelson interferometer. Realization methods and the performance of the above system components are discussed in detail. In order to simulate the wavelength shift induced by measurand, a standard wavelength shift signal generator is set up and its frequency response is tested. Interrogation experiment of acoustics signal in water is carried out, and the frequency response of the uncoated DFB fiber laser is obtained.

FBG strain sensing technology is used to dynamically detect tread wear of railway train wheels. Dozens of FBG track strain sensors are installed as lines along railway tracks in crosstie sections. Train wheels one by one roll on the track and load the sensors, groups of strain peak are taken. The strain curve of defective wheel appears a gap or with serration. By means of strain pulse processing program, tread wear and wheel health condition are obtained. FBG strain gauge is employed to increase the measuring sensitivity. Protecting methods for sensors and fiber are adopted to keep them surviving from harsh application environment. The examples of detecting results are given to show the validity of this FBG application.

A closed-loop resonator fiber optic gyro (R-FOG) with a precisely controlled bipolar digital serrodyne phase modulation scheme is experimentally demonstrated. The serrodyne modulation scheme serves multiple functions in the R-FOG, from reducing the backscattering induced performance degradation to achieving the closed-loop operation. To improve the backscattering suppression efficiency, a precise amplitude adjustment method using a gain variable amplifier and the oversampling technique is utilized to control the waveform of the bipolar digital serrodyne phase modulation. Compared with the amplitude control via adjusting the digital gain of the function generator, improved bias stability is realized. Moreover, the closed-loop operation is needed for the R-FOG to achieve high linearity in a wide dynamic range as the frequencies of both the clockwise (CW) and the counter clockwise (CCW) lightwaves are maintained at the resonator's resonant frequency. To balance the resonant frequency difference, an additional bipolar digital serrodyne waveform, with the slope proportional to the rotation speed to compensate for the resonant frequency difference, is superimposed on the original bipolar digital serrodyne waveform. Measurement results of different rotation speeds show good linearity thanks to the adoption of closed-loop operation.

The study evaluated damage detection of a tapered roller bearing using a non-contact photogrametric approach. Customized round tape was pasted on the bearing housing and GOM Pontos was used to measure the radial accelerations from the bearing housing. The data obtained from the the photogrammetric techniques was processed to detect damage of the bearing using statistical tools such as RMS, kurtosis. It was established that the phogrammetric approach detects bearing damage excellently.

This paper describes the application of Fibre Bragg Grating (FBG) based sensors for monitoring road pavement strains caused by mining induced ground subsidence as a result of underground longwall coal mining beneath a major highway in New South Wales, Australia. After a lengthy planning period, the risks to the highway pavement were successfully managed by the highway authority and the mining company through a technical committee. The technical committee comprised representatives of the mining company, the highway authority and specialists in the fields of pavement engineering, geotechnical engineering and subsidence. An important component of the management strategy is the installation of a total of 840 strain and temperature sensors in the highway pavement using FBG arrays encapsulated in glass-fibre composite cables. The sensors and associated demodulation equipment provide continuous strain measurements along the pavement, enabling on-going monitoring of the effects of mining subsidence on the pavement and timely implementation of planned mitigation and response measures to ensure the safety and serviceability of the highway throughout the mining period.

The suppression of nuisance alarms without degrading sensitivity in fibre-optic intrusion detection systems is important for maintaining acceptable performance. Signal processing algorithms that maintain the POD and minimize nuisance alarms are crucial for achieving this. A level crossings algorithm is presented for suppressing torrential rain-induced nuisance alarms in a fibre-optic fence-based perimeter intrusion detection system. Results show that rain-induced nuisance alarms can be suppressed for rainfall rates in excess of 100 mm/hr, and intrusion events can be detected simultaneously during rain periods. The use of a level crossing based detection and novel classification algorithm is also presented demonstrating the suppression of nuisance events and discrimination of nuisance and intrusion events in a buried pipeline fibre-optic intrusion detection system. The sensor employed for both types of systems is a distributed bidirectional fibre-optic Mach Zehnder interferometer.

In this article, we review R&D on optical fiber sensors at the National Engineering Laboratory for Optic Fiber Sensing Technologies at Wuhan University of Technology, both from industrial and fundamental aspects. New concepts of optical sensors combined micro-machining of novel fiber structure with sensitive thin film are also proposed and discussed.

The operation of Fiber Optic Gyro is based on the Sagnac Effect which states that light beams propagating along opposite directions in a rotating frame experience an optical path length difference. These two counter-propagating waves propagate within a closed fiber coil, and when this coil rotates the resultant phase difference is proportional to the rotation rate Ω. Fiber optic gyroscopes are desirable devices for many navigation and guidance applications because, being solid state devices, they have several major advantages including light weight, long working lifetimes, no moving parts and operate using low voltage power. In this paper the Optolink's single-axis and three-axis fiber optic gyroscopes are described. The Optolink's FOGs consist of the light-emitting diode, one or three photodetectors, circulators and polarization maintaining fiber couplers to divide the light into two or three parts, one or three sets of ring interferometers to sense one or three orthogonal angular rates, and installed PCB signal processing circuits. The ring interferometer consists of a multifunction integrated optic chip and polarization maintaining fiber coil, both these components are designed and fabricated by Optolink. The results illustrate the versatility of the technology, showing its potential to meet both the low-cost, compact sized needs of tactical guidance, as well as the very high performance needs of inertial navigation and precision applications. The optic and electronic blocks of closed-loop gyroscopes with integrated optic components are also considered in this paper.

An optical voltage sensor is proposed that exploits the electric field dependence of transmission of a Mach-Zehnder interferometer fabricated on basis of the channel waveguides in electro-optic LiNbO₃. The device works in a transmission scheme, utilizing the long fibre transmission lines for input and output optical signals. The sensor has been used to measure AC electric fields in a range from 0.005 to 56 kV/cm, resulting in a linear sensitivity that may be further improved by tailoring of the optical and geometrical parameters of the fibre-pigtailed Mach-Zehnder interferometer.

We incorporate for the first time optical coherence elastography (OCE) into a needle probe and demonstrate its ability to provide depth-resolved information about the mechanical properties of soft tissues. This allows analysis of tissues located much deeper than has previously been possible with other forms of OCE. OCE exploits the microscopic resolution of optical coherence tomography (OCT) to produce high-resolution maps of tissue mechanical properties. While OCE has potential to delineate diseased and healthy tissues (e.g., stiff tumor in soft tissue), standard techniques are limited by the penetration depth of OCT in tissue (2-3 mm). Our OCE needle probe overcomes this limitation, as it may be inserted deep within the body to perform measurements. We tested needle-based OCE in tissue-mimicking phantoms and ex vivo porcine airway tissue comprising layers of varying stiffness. Results demonstrate mechanical differentiation of tissues and identification of tissue interfaces. The proof-of-principle results presented here pave the way for future measurements in human breast tissue that will aim to establish needle-based OCE as a viable technique for intraoperative guidance of breast cancer surgery.

Brillouin scattering properties of optical fibers should be precisely investigated in advance for their applications to distributed strain/temperature sensing. Especially when the fibers are short, high-loss, or multi-mode, as in the case of polymer optical fibers, high-power pump is required, but commercially-available high-power lasers or optical amplifiers are expensive. In this paper, we propose a new method to enhance Brillouin scattering signals with a relatively low-cost low-power erbium-doped fiber amplifier by using pulsed pump light. When pulsed pump light with average optical power of 20 mW, duty ratio of 20%, and pulse period of 2 μs, was injected into a silica single-mode fiber, the Brillouin signal was enhanced by 25 dB compared to that with continuous-wave pump light having the same average power.

The novel concept of utilizing a random fiber laser (RFL) to extend the sensing distance of fiber-optic sensing systems is proposed for the first time to our knowledge. In this paper, two schemes based on the RFL with a fiber Bragg grating (FBG) are experimentally demonstrated to verify the concept. The first one is a 100km FBG temperature sensing system, in which a 100km RFL provides an effective way to enhance the sensing signal of the FBG sensor due to its strong lasing radiation across the 100km fiber span. It is the first time to find that the RFL without the FBG is a temperatureinsensitive distributed lasing cavity, which offers stable long-distance transmission for the sensing signal. The second one is a 100km Brilloiun optical time domain analyzer (BOTDA), in which the generated random lasing is used as a fully distributed Raman pump and hence stable Raman amplification can be obtained to enhance the Brilloiun sensing signal. In principle, such a novel concept can be adopted for any type of distributed fiber-optic sensors as the RFL can be used as a stable distributed Raman pump for sensing signal amplification along the whole length of the fiber.