This PDF file contains the front matter associated with SPIE Proceedings Volume 8924, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

we design a novel core-suspended capillary fiberhat the core is suspened in the air hole and close to the inner surface of the capillary, and experimentally demonstrate its fabrication technology. In addition, a method for linking a single mode fiber and a core-suspended fiber is proposed based on splicing and tapering at the fusion point between the two fibers. By combining with the optical time domain reflectometer technology, we construct a distributed gas sensor system to monitor greenhouse gas based on this novel fiber.

Optical fiber temperature sensors can provide accurate temperature information and adapt to different temperature environments well, so they have been widely used. Traditional optical fiber temperature sensors depend upon optical fiber grating or nonlinear back scatting, both of which need complex measurement systems and high cost. So, a simple and chip temperature sensing method was put forward based on fiber delay technology, and the temperature information was obtained by measuring additional delay of optical signal in fiber. Establishing an experiment system by using the frequency domain phase method, we obtained the delay coefficient which describes the relationship between delay and temperature, so that the feasibility of the method was proved.

Optically heated fiber Bragg gratings due to the absorption over the fiber core in rare-earth doped fibers are experimentally demonstrated. Bragg wavelength variations with pump power are measured for different fibers. We found that the Er/Yb-codoped fiber presents the strongest thermal effect, due to the high absorption. A maximum wavelength shift of 1.34 nm can be obtained when the 980 nm pump power is 358 mW under room temperature, suggesting the fiber is heated up to over 100 °C. Furthermore, the thermal effect is enhanced by pumping the surrounding air to close to vacuum. A wavelength shift of 1.69 nm is attained, due to the weakened ability of heat transfer at the silica-air interface. The optical heating presents a very short response time and can found applications in low temperature circumstances.

Enhancement of Brillouin scattering signal attenuating along optical fiber due to the inherent propagation loss can extend the sensing range or increase the sensing resolution of Brillouin distributed fiber-optic sensing. In this paper, we demonstrate a scheme to investigate the amplification effect of 980-nm pump on Brillouin gain spectrum in an erbiumdoped optical fiber (EDF). The Brillouin Stokes power is exponentially raised with increasing the pump power, indicating that adjusting the pump power can control the Brillouin signal in an EDF. We also show that drastic enhancement of Brillouin signal should be possible by using a high-power 980-nm pump laser.

We have recently reported azobenzene-coated fiber Bragg grating (FBG) for ultraviolet (UV) sensor. In this paper, we introduce an etched FBG for the strain sensitivity enhancement of the UV fiber grating sensors, which is inversely proportional to the fiber diameter. The sensitivity of the etched FBG with a diameter of ~60 μm is improved to be greater than twice of the original 125 μm fiber. In addition, the sensor system designed on the basis of the round-trip configuration can be used for many practical sensing applications in the field.

Fiber Bragg grating (FBG) is a passive optical fiber component with the refractive index modulated along the fiber length and has been widely applied in fiber sensing systems. High-temperature stable fiber gratings are promising for uses at high temperature and receive extensive attentions. In this paper, FBGs were inscribed in hydrogen loaded standard single mode fibers with 248 nm excimer laser, and regenerated gratings were obtained through heat treatment. The center wavelength of the regenerated FBG has a good linearity with temperature, and the reflectivity of the regenerated FBG can almost keep unchanged at 800 °C.

The absorption of Germanium (Ge) rises dramatically with decreased incident wavelength, in the absorption region of <1900nm, inversely no absorption of <1900nm, where the absorption would affect the measurement of refractive index. The band structure and optical properties of these crystals are calculated within the framework of density functional theory with local density approximation (DFT-LDA). The results show that the band gap is 0.571eV, which is closer to the experimental value as compared to Generalized Gradient Approximation (GGA) calculations. As the pressure increases from 0 to 2 GPa, restricted by experimental equipment, the indirect band gap increases linearly with the gradient of 4.29×10^-2 eV/GPa and the refractive index reduces linearly with the gradient of 5.903×10^-2 /GPa.

Optical fiber tweezers based on a graded-index multimode fiber (GIMMF) tip is proposed. Light propagation characteristics and gradient force distribution near the GIMMF tip are numerically investigated, which are further compared with that of optical fiber tips based on conventional single mode fibers. The simulated results indicated that by selecting optimal GIMMF length, the gradient force of the GIMMF tip tweezers is about 4 times higher than that of the SMF tip tweezers with a same shape. To prove the feasibility of such a new concept, optical trapping of yeast cells with a diameter of ~5 μm using the chemically-etched GIMMF tip is experimentally demonstrated and the trapping force is also calculated.

A refractive index insensitive temperature sensor based on coaxial dual-waveguide optical fiber was proposed and demonstrated. The coaxial fiber contains a central core along the fiber axis and an annular core between the inner/outer claddings. By inserting the coaxial fiber in between two single mode fibers through core-offset splicing, cladding modes are excited at the splice point and therefore a modal Mach-Zehnder interferometer is achieved. The effective refractive index of the inner cladding mode is independent of the external refractive index due to the existence of the annular core. Owing to the large thermo-optic coefficient difference between the coaxial fiber's core and cladding, the modal interferometer has high temperature sensitivity. Such an interferometer is extremely suitable for temperature measurement in wet or liquid environment.

We demonstrate an ultrasensitive temperature sensor by sealing a highly-birefringent microfiber into an alcoholinfiltrated copper capillary. With a Sagnac loop configuration, the interferometric spectrum is strongly dependent on the external refractive index (RI) with sensitivity of 36800nm/RIU around RI=1.356. As mainly derived from the ultrahigh RI sensitivity, the temperature response can reach as high as −14.72 nm/°C in the range of 30.9-36.9 °C. The measured response time is ~8s, as determined by the heat-conducting characteristic of the device and the diameter of the copper capillary. Our sensor is featured with low cost, easy fabrication and robustness.

We propose a novel dual optical fiber tweezers integrated in a four-core fiber which can trap, rotate and orient a micro particle immersed in a fluid medium. We design the structures and the functions of this dual optical fiber tweezers, and simulate the optical trapping forces, optical torques exerting on the micro particle. We also give out the experimental setup and the controlling method of this integrated dual optical fiber tweezers.

Broadband emission sources such as super luminous diodes and rare earth doped fibre for ASE sources have wide applications in optical fibre measurement and sensing systems. Recent intensive research has shown broadband luminescence in the range of 1100 to 1500 nm, across O, E and S bands of the telecommunications window from glasses or materials with Bi-doping and Bi/Er codoping. The broadband luminescence of active optical fibres in this wavelength range is particularly interesting for fibre amplifiers, lasers and ASE sources for optical communication and sensing applications. Here we report our recent development of Bi/Er/Al codoped phosphogermanosilicate optical fibre with ultra-broadband luminescence between 1000 to 1570 nm, covering O-, E-, S-, C-, and L-bands, when pumped by 532, 808, or 980 nm lasers. The new material composition of this optical fibres are potentially useful as gain media for ultrabroadband ASE sources, tunable fibre lasers or amplifiers.

We propose and demonstrate an all-fiber Bessel beam generator based on M-type optical fiber and graded-index optical fiber. We show that the output optical beam from the graded-index optical fiber end-face is a Bessel-like beam, which is generated by Fourier transform of a ring light that is generated by M-type optical fiber using graded-index optical fiber lens. We also study wave propagation in this generator using beam propagation method. The simulated results show that the output beam from this generator is rather like an ideal Bessel-Gaussian beam.

Three-component seismometer is widely used in oil or gas exploration, earth quake monitoring. In this paper, an allmetal 3-component optical fiber seismometer is proposed and experimentally demonstrated. The theoretical analysis is given based on electro-mechanical theory. Calibration results show that axis sensitivity is 41 dB (re: 0 dB=1 rad/g) with a fluctuation ±2 dB in frequency bandwidth of 5~400 Hz. A transverse sensitivity of about -40 dB is achieved. The fluctuation of the acceleration sensitivity for the three accelerometers in the seismometer is within ±2.5 dB. The minimum phase demodulation detection accuracy of the phase-generated carrier (PGC) is 10^-5 rad/√Hz, and the minimum detectable acceleration is calculated to be 90 ng/√Hz. With an all-metal structure, the proposed seismometer is expected to improve reliability of long-term use in harsh environment such as ocean bottom seismic wave monitoring in oil or gas exploration.

We proposed a closed-form all-in-fiber SCHF-SPR sensor. Using the dual-core directional microstructure for reference, we add a metal layer in the left core to directly enhance the overlapping area of the core mode and plasmonic mode. A theoretical analysis is carried out to simulate the resonant wavelength shift corresponding to RI. An average sensitivity of 2390.91nm/RIU in the RI range 1.33-1.43, and 9294.55nm/RIU in 1.44-1.54 with high linearity and sensitivity is achieved. This SCHF-SPR sensor has a good sensing performance on RI among the existing RI sensors.

A fiber optic relative-humidity sensor with a low-fineness Fabry-Perot cavity is proposed and demonstrated. Manufactured by e-beam evaporation, the Fabry–Perot cavity composed of five-layer dielectric oxides has columnar and porous structures, which is sensitive to relative-humidity change of environment. Experimental investigation shows that the proposed sensor exhibits a sensitivity of 0.42 nm/%RH when the ambient relative humidity changes from 15.2%RH to 74.3%RH.

An optical fiber Fabry-Perot (F-P) sensor with quartz diaphragm for gas pressure testing was designed and fabricated. It consisted of single-mode fiber, hollow glass tube and quartz diaphragm. It uses the double peak demodulation to obtain the initialized cavity length. The variety of cavity length can be calcultated by the single peak demodulation after changing the gas pressure. The results show that the sensor is small in size, whose sensitivity is 19 pm/kPa in the range of the 10 ~ 260 kPa gas pressure. And it has good linearity and repeatability.

In this paper, we propose two optical fiber sensing applications based on the pulse selection technique, in which an acousto-optic modulator (AOM) is employed to generate optical pulses and to choose the pulses traveling back to it. Firstly, we propose an interferometer configuration with optical path difference (OPD) amplified, which offers an alternative way to increase the interrogation resolution and develops some potential sensing applications which require high sensitivity. By adjusting the repetition interval, we can select the pulses which travel along the corresponding arms of the interferometer for any given trips. Secondly, we designed a Fiber Bragg Grating (FBG) sensing system with intelligent sensor management, which offers two work modes and improves the availability of information.

Carbon monoxide is one of the important gases need to be detected in coal mine safety. Detection technology based on signature gas is the primary means of spontaneous combustion forecasting of coal goaf area. Because of the high accuracy requirement of CO concentration in the coal mining applications, we had to introduce more data processig methods to improve the signal-to-noise ratio (SNR), finally to achieve the requirements of coal mining. Therefore, we used three data processing methods to eliminate noises of the CO sensing system which based on the tunable diode laser absorption spectroscopy (TDLAS): Fourier transform, least-squares fitting and Kalman filter. The results show that the combination of three data processing methods had a good inhibitory effect of random noise and interference fringes, etc. and significantly improved the system detection accuracy, the minimum detectable spectral absorption rate could be increased by an order of magnitude. So this high-resolution fiber CO sensing system can better meet the needs of coal mine safety.

For high-precision, the grating demodulator based on WDM theory is widely used. In order to satisfy the request of high-speed and high-precision grating demodulator using F-P tuned filter, a high-speed frequency swept laser light source based on semiconductor optical amplifier is designed. This light source uses the work pattern of Fourier Domain Mode Locking and ring cavity geometry. It can provide narrow band tuning light using for grating demodulation, and the tuned frequency is above 4000Hz, the bandwidth is 40nm. Its output light power is higher than 12dBm, and it can greatly improve the speed and SNR of grating demodulator. Under the conditions of swept speed above 4000Hz, the precision of grating demodulator using this light source can reach 2pm.

A dual-polarization fiber grating laser is proposed to sense a magnetic field by attaching the fiber laser to a copper wire. When an electrical current is injected into the copper wire and a perpendicular magnetic field is applied, the current generates Ampere force to squeeze the fiber laser and change the birefringence inside the laser cavity, resulting in beat note frequency change. The magnetic field induced beat note frequency change can be discriminated from environment disturbances by applying an alternating current, which therefore demonstrates a novel miniature fiber-optic magnetic field sensor with high sensitivity and inherent immunity to disturbances.

A novel curvature sensor comprize a section of multi-mode fiber and a up-taper is proposed and demonstrated experimentally. The whole fabrication process is quite simple and the sensor head is cost effective. Measurement results show that it has a maximum curvature sensitivity of -61.877nm/m^-1 at 1.1718m^-1 and -9.2115nm/m^-1 from 1.1718m^-1 to 1.6583m^-1. Temperature sensitivity of 89.01 pm/°C within the range of 20~80 °C has also been achieved, which implies the possibility for measurement of temperature. High sensitivity and low-cost make it a preferable candidate for curvature sensing in practical applications.

Digital proportional-integral (PI) controller is always adopted in the resonant frequency servo loop in a highperformance resonator fiber optic gyro (R-FOG). Large reset pulse at the output of the R-FOG occurs on the overflow reset of the digital PI controller, which limits the lock-in frequency accuracy and system response. To reduce the effect of the overflow reset in the digital PI, an auto-controlled reset technique is proposed and experimentally demonstrated. As a result, the time back to the lock-in state falls from 8 s to 5 ms. With the integration time of 1 s, the equivalent accuracy of the resonant frequency servo loop is improved to 0.18 deg/h.

A fiber in-line Michelson interferometer based on open micro-cavity is demonstrated, which is fabricated by femtosecond laser micromachining and thin film coating technique. In refractive index sensing, this interferometer operates in a reflection mode of detection, exhibits compact sensor head, good mechanical reliability, wide operation range and high sensitivity of 975nm/RIU (refractive index unit) at the refractive index value of 1.484.

This paper presents a fluorescence fiber probe design for temperature sensor based on lifetime measurement and focuses on the structural and coupling analysis between the stimulated fluorescence area to light-source and optic fiber. A theoretical model taking advantage of geometric optics is built to estimate the effectiveness of the probe design. A standard 62.5/125μm multimode fiber with a spherical end and least squares fitting method are adopted in the sensing system to demodulate the fluorescence lifetime. Experiment results of temperature range from 17°C to 77°C demonstrate an efficiency increment of 82.36%, which matches well with the simulation.

A side-polished plastic optical fiber is proposed as the line source of a linear fiber array in a liquid level sensor. We hope the leakage light power of side-polished plastic optical fiber along the axial direction is constant. To that end, the transmission characteristics of the line source is investigated, and a formula describing the relationship between the polished depth and the side leak light power is developed with a simple method. A 300 mm long gradient side-polished plastic optical fiber is fabricated according to the theoretical conclusion, its side-leak light power is measured and the measurement results are discussed.

The orientation of nematic liquid crystal (NLC) can be used in biosensor. The sensing characteristics of side-polished fiber (SPF) for determination of azimuthal orientation of NLC have been investigated. The relationship between the azimuthal angle of NLC director and the optical transmission power in SPF was derived by empirical approach. Experimental results showed that the azimuthal transition of liquid crystal affected the optical transmission power in SPF. While the azimuthal angle increased from 0° to 90°, the optical transmission power increased by 28.10dB, which is similar to the variation tendency of the empirical analysis. When it changes from 0° to 30°, the azimuthal angle is linear to the change of optical transmission power. The respondence of azimuthal angle for optical sensing is averagely 0.359dB/°. Experiments indicate that SPF can be used in determination of the azimuzal transition of NLC. It would be used for a new fiber optical biosensor based on the SPF and NLC.

A tip-timing method based on fiber Bragg grating magnetically coupling sensor is proposed to study and analyze the ventilator blade vibration, aiming at realizing long-distance and non-contact real-time online safety monitoring of blade vibration. Fiber grating magnetic coupling sensors has advantages such as explosion-proof, protection against harsh environment with humid air, full of dust and greasy dirt, capable of achieving long-distance signal transmission.

High current sensitivity is obtained based on a microfiber that is wrapping around a chrome-nickel (CrNi) wire. Due to the strong heating effect of the CrNi wire with the flowing electric current, the mode index and the loop length of microfiber are changed, resulting in the shift of resonant wavelength. The measured current responsivity is as high as 220.65nm/A², which is in two or three magnitude orders than the previously-obtained ones. We study the influence of component size to the structure performance, which is useful for future applications of current sensing or tuning devices.

We demonstrated an active radiation hardening technology for fiber optic source developed for high performance fiber optic gyroscope. The radiation characteristic of erbium-doped fiber was studied experimentally. The radiation induced attenuation (RIA) at 980nm pump light was identified to be the main reason for the degradation and there was photo-bleaching effect in EDF too. A variable parameters control technology was proposed and taken to keep the 980nm and 1550nm light energy stable and high stability and radiation-resistance fiber source with gauss profile spectrum was realized .The source can stand against more than 50 krad (Si) total radiation dose.

A novel intensity-modulated strain sensor based on a fiber in-line Mach-Zehnder interferometer is proposed and demonstrated, which is constructed by splicing a thin core fiber between two single mode fibers with a core offset. Such an interferometer exhibits a large fringe visibility of more than 15 dB. When used in axial strain sensing from 0 to 400 με, the interferometer operates at intensity mode of detection with a high sensitivity of -0.023 dB/μεwithout the cross sensitivity between temperature and strain. Its ease of fabrication, high strain sensitivity and intensity mode of detection makes it a low-cost alternative to existing sensing applications.

A distributed feedback (DFB) fiber laser with a ratio of backward to forward output power of 1:100 was composed by a 45mm length asymmetrical phase-shifted fiber grating fabricated on 50mm erbium-doped photosensitive fiber. Forward output laser was amplified using a certain length of Nufern EDFL980-Hp erbium-doped fiber to absorb surplus pump power after the active phase-shifted fiber grating and get population inversion. Using OptiSystem software, the best fiber length of the EDFL to get the highest gain was simulated. In order to keep the amplified laser with narrow line-width and low noise, a narrow-band light filter consisted of a FBG with the same Bragg wavelength as the laser and an optical circulator was used to filter the ASE noise of the out-cavity erbium-doped fiber. The designed laser structure sufficiently utilized the pump power, a DFB fiber laser of 32.5mW output power, 11.5 kHz line width, and -87dB/Hz relative intensity noise (RIN) at 300mW of 980 nm pump power was brought out.

We demonstrate femtosecond laser micro-machining and inscription of micro-optical structures, such as ring and disk resonators, Mach-Zender interferometers, and complex microfluidic devices, in a novel optical flat-fibre chip. In addition, we fill the channels with functional materials that can be used for sensing applications. Furthermore, direct write femtosecond-laser inscribed Bragg gratings are written in the Ge-doped flat-fibre core at 1547.8 nm. The flat-fibre chip offers a unique degree of freedom by allowing surface and sub-surface devices to be integrated onto an optical platform with the potential for straightforward incorporation into integrated photonic circuits or optofluidic devices.

Fiber-optic strain sensors are increasingly used in very different technical fields. Sensors are provided with specifications defined by the manufacturer or ascertained by the interested user. If deformation sensors are to be used to evaluate the long-term behavior of safety-relevant structures or to monitor critical structure components, their performance and signal stability must be of high quality to enable reliable data recording. The measurement system must therefore be validated according to established technical rules and standards before its application and after. In some cases, not all details of the complex characteristic and performance of applied fiber-optic sensors are sufficiently understood, or can be validated because of a lack of knowledge and methods to check the sensors’ behavior. This contribution focusses therefore on the importance of serious validation in avoiding a decrease or even deterioration of the sensors’ function. Methods for validation of applied sensors are discussed and should reveal weaknesses in validation of embedded or integrated fiber-optic deformation and/or strain sensors. An outlook to some research work that has to be carried out to ensure a well-accepted practical use of fiber-optic sensors is given.

A novel class of polarization converters (PCs) in highly birefringent (Hi-Bi) microfibers is proposed and investigated numerically by use of the coded full vectorial finite difference beam propagation method. The PCs could be implemented by inducing periodic deformations along the surface of a Hi-Bi microfiber. Simulation shows that complete conversion between two linearly polarized eigen modes may be achieved with a device as short as 150 μm.

In this paper, we reveal characteristics of static and dynamic distributed strain measurement using a long-gauge fiber Bragg grating (FBG) and a Delayed Transmission/Reflection Ratiometric Reflectometry (DTR³) scheme. The DTR³ scheme has capability of detecting distributed strain using the long-gauge FBG with 50-cm spatial resolution. Additionally, dynamic strain measurement can be achieved using this technique in 100-Hz sampling rate. We evaluated strain sensing characteristics of the long-gauge FBG attached on 2.5-m aluminum bar by a four-point bending equipment. Experimental results showed that the DTR³ using the long-gauge FBG could detect distributed strain in static tests and resonance frequency of structure in free vibration tests. As a result, it is suggested that the DTR³ scheme using the longgauge FBG is attractive to structural health monitoring (SHM) as dynamic deformation detection of a few and tensmeters structure such as the airplane wing and the helicopter blade.

A novel temperature demodulation method which eliminates the impact of Rayleigh scattering on Raman distributed temperature sensors (RDTS) using anti-Stokes light only is presented. This method utilizes two sections of reference fiber which are placed into temperature control chambers with different temperatures, such that the impact caused by the variation of laser’ power and the Rayleigh scattering is eliminated by the two reference temperatures. In the experiment, the temperature error caused by the Rayleigh scattering was decreased by 0.6℃ and 1.7℃ at 30℃ and 50℃compared with conventional method respectively.

This paper gives an experimental study on Brillouin scattering property in an all solid photonics bandgap fiber (ASPBGF) using tapering technique. There are four Brillouin resonance peaks, one from the pure silica core and three from microstructure cladding of the AS-PBGF. We report Brillouin frequency shift and linewidth of the fiber. Because these four peaks show the different temperature and strain dependence, the simultaneous measurement of temperature and strain can be achieved.

We demonstrate a high-spatial-resolution fast Brillouin optical time-domain analysis scheme based on frequency agility and differential double-pulse for distributed dynamic measurement. The frequency-agility probe wave is obtained from the second-order sideband of the modulated light by using frequency-agility microwave signal from a wideband arbitrary waveform generator. The differential double-pulse technique is proposed to improve the spatial resolution while keeping the capability of dynamic measurement. In experiment, a spatial resolution of 20 cm is achieved by using a 52/50 ns differential double-pulse, and the distributed vibration measurement is demonstrated over a 50-m Panda fiber with a maximum vibration frequency of up to 50 Hz. With only five averages, the standard deviation of the strain accuracy is of 14με;.

A lowcost Fiber Bragg Grating (FBG) Sensing System based on code division multiplexing access (CDMA) technology is proposed. The system using semiconductor optical amplifier and a broadband source is experimented. Without a tunable laser source or electro-optic switch driven, the price of system is very low. CDMA is used to separate each reflected sensor. The experimental results show that theory is correct.

A novel data processing algorithm named “2-FFT” for multi-point disturbances detection and location in an in-line Sagnac sensing system is proposed and demonstrated. When multiple disturbances are applied onto the sensing fiber at the same time, the frequency response curve of the modulated phase will be superposed by each null frequency curve of the single disturbance. However, by applying a second-time FFT to the frequency spectrum, the location corresponding to each disturbance point could be simply extracted and determined. Based on the theoretical and the experimental investigation, the “2-FFT” algorithm is demonstrated to be reasonable and efficient.

A differential double-pulse pair Brillouin optical time-domain analysis (DDP-BOTDA) combined with the double-pulsed technique and the differential pulse-width pair technique is proposed and simulated to detect small temperature and strain changes. Using a symmetrical double-pulse pair, the system can detect small Brillouin shift with high spatial resolution and large dynamic range. Sub-meter spatial resolution is decided by the difference between the pulse-width and the peak and valley of the spectrum which is derived from differential pump depletion signals, and detectable Brillouin shift is less than 1 MHz.

A distributed fiber sensor which can simultaneously measure the strain and vibration of fiber is proposed. Only the Brillouin scattering is used for the measurement with a heterodyne detection scheme. In the Brillouin scattering, the Brillouin frequency shift is utilized for the strain measurement and the state of polarization is utilized for the vibration measurements. Experimental results proved a distributed fiber strain and vibration sensor which can achieve 11.5 km sensing distance, 10 m spatial resolution, 26 Hz frequency measurement range, 0.8 Hz frequency resolution and 0.1 MHz uncertainty of Brillouin frequency measurement.

A novel distributed Raman amplification (DRA) scheme based on ultra-long fiber laser (UL-FL) pumping with a ring cavity rather than a linear cavity is proposed and demonstrated, for the first time. As a typical application of the proposed configuration, ultra-long-distance distributed sensing with Brillouin optical time-domain analysis (BOTDA) over 142.2km fiber with 5m spatial resolution and ± 1.5℃ temperature uncertainty is achieved, without any repeater, for the first time. The key point for the significant performance improvement is the system could offer both of uniform gain distribution and considerably suppressed pump-probe relative intensity noise (RIN) transfer, by optimized design of system structure and parameters.

A fiber optic Fabry-Perot (FP) hydrophone with hydrostatic pressure compensation was demonstrated. A polyimide (PI) diaphragm attached on the end of an Acrylonitrile Butadiene Styrene (ABS) tube was used as the sensing element. A pair of grooves was designed in an inner ABS tube to connect the Fabry-Perot cavity with the outside environment, which made the hydrophone hydrostatic pressure compensated. The operation principle, design and testing of polyimide diaphragm-based sensor were described. Experiment results show that it has not only high stability in different hydrostatic pressures, but also flat frequency response of about 158 ±3 dB within 300-3000 Hz.

We present that an improved optical fiber acoustic emission sensor has been applied to the hydraulic decoking on-line monitoring system for the first time, meanwhile the characteristics of the improved acoustic emission sensor are analyzed. The actual research results of China Petrochemical Wuhan Petrochemical Corporation Group show that hydraulic decoking on-line monitoring system can monitor the real-time and accurate states of hydraulic decoking based on the optical fiber acoustic emission sensor technology, the system can realize the automation of hydraulic decoking monitoring effectively.

On the basis of the analysis of the current hydraulic decoking monitoring system, it is proposed that use optical fiber Bragg grating (FBG) vibration sensor and fiber Fabry-Perot (FP) acoustic sensors to online monitor vibration signal and audio signal hydraulic of the coke drum in the running state progress, analysis the vibration sensor and acoustic sensor used in the system. Based on the actual monitoring results in Sinopec Wuhan Branch , the fiber optic acoustic emission sensors is more suitable for the hydraulic decoking online monitoring system than the FBG vibration sensor ,which can more accurate monitor of hydraulic decoking.

A 4-element wavelength division multiplexed linear array of asymmetric distributed feedback fiber lasers (DFB-FL), pumped at 1480nm is reported. A very desirable feature of asymmetric DFB-FL is unidirectionality, and relevant principle is presented. Larger output powers are obtained from shorter ends of all the four asymmetric DFB-FLs which are fabricated in our laboratory by phase mask moving method. This obvious advantage has important applications to design sensor array. And furthermore, many experiments are completed to confirm it. Output flatness of the sensor array system presents a good performance with the applications of asymmetric DFB-FLs.

An acoustic emission (AE) linear location system is proposed, which employs fiber Bragg gratings (FBGs) as AE sensors. It is demonstrated that the FBG wavelength can be modulated as static case when the grating length is much shorter than the AE wavelength. In addition, an improved AE location method based on Gabor wavelet transform (WT) and threshold analysis is represented. The method is testified through AE linear location experiments based on a tunable narrow-band laser interrogation system using ultra-short FBG sensors as AE sensors. Results of the experiments show that 86% of the linear location errors are less than 10mm.

A dual-wavelength distributed feedback fiber laser with two symmetrical π phase shifts is fabricated and investigated. The stable operation in single polarization and dual wavelengths with 20 pm separation is achieved. It shows good performances including low relative intensity and narrow linewidth.

Accurate measurement of energy is a technical difficulty that various microseismic monitoring systems are facing. In this article, we applied the groundbreaking fiber optics microseismic monitoring system to mine rock burst monitoring for the first time around the world. We suggest to calculate microseismic energy via the duration of vibration. Precise picking of P wave first arrival and end point is essential to microseismic energy calculation. According to the huge energy difference before and after the arrival of the seismic wave, we use the sliding time-window energy ratio method to pick the first arrival and end point, and put forward the quantitative relationship between the sliding time-window width TWL and the sampling frequency as well as the signal dominant frequency for the first time. The results of P wave automatically picking are almost the same as those manually picked. However the end point may need to be corrected if wave distortion occurred.

The mine hoist operation status is closely related to the vibration signal of the hoist various components. using optical fiber sensing technology, this paper designed a hoist fault diagnosis system based on vibration spectrum analysis. Through rapid demodulation of real-time vibration signal, the system realized vibration spectrum analysis to various parts of the hoist. The test results show that the system can achieve effective monitoring of the various parts of the hoist operating status, provide an important basis for fault diagnosis.

A fiber optic white-light interferometry based on cross-correlation calculation is presented. The detected white-light spectrum signal of fiber optic extrinsic Fabry-Perot interferometric (EFPI) sensor is firstly decomposed by discrete wavelet transform for denoising before interrogating the cavity length of the EFPI sensor. In measurement experiment, the cross-correlation algorithm with multiple-level calculations is performed both for achieving the high measurement resolution and for improving the efficiency of the measurement. The experimental results show that the variation range of the measurement results was 1.265 nm, and the standard deviation of the measurement results can reach 0.375 nm when an EFPI sensor with cavity length of 1500 μm was interrogated.

Cerenkov radiation can be observed easily as a shimmer of blue light from the water in boiling- and pressurized-water reactors, or spent fuel storage pools. In this research, we fabricated the fiber-optic Cerenkov radiation sensor using a Gdfoil, rutile crystal and optical fiber for detecting neutrons. Also, the reference sensor for measuring background gammarays was fabricated with the rutile crystal and optical fiber. The neutron fluxes could be obtained by measuring the signal difference between two sensors. To characterize the fiber-optic Cerenkov radiation sensor, we measured neutron fluxes using a Cf-252 neutron source according to depths of polyethylene. As the results, the counts of fiber-optic Cerenkov radiation sensor were higher than those of reference sensor due to additional interactions between Gd-foil and neutrons. Also, the counts of Cerenkov radiation decreased with increasing polyethylene thickness. It is anticipated that the novel and simple fiber-optic Cerenkov radiation sensor using the Cerenkov effect can be widely used to detect the neutrons in hazardous nuclear facilities.

We demonstrate a low pulse repetition frequency (LPRF) Q-switched erbium-doped fiber (EDF) lasers based on acoustic optical modulator (AOM). The single wavelength fiber laser has a stable output at 1553 nm. In Q-switched operation, a pulse train with 3.3μs width and a repetition rate of 1kHz is obtained. The dual wavelength fiber laser is based on fiber Bragg gratings (FBGs) and a Faraday rotator mirror (FRM) as the laser cavity, which has a stable output at 1545 nm and 1557 nm with similar peak power and same repetition rate.

An optical fiber distributed sensing system merged Mach-Zehnder interferometer (MZI) and phase-sensitive optical time domain reflectometer (φ-OTDR) for vibration measurement with wide frequency response and spatial resolution is proposed and demonstrated. Two acoustic optical modulators (AOM) are adopted to generate narrow pulses and wide pulses respectively on both ends of sensing fiber with a time difference. Narrow pulses are used to generate Rayleigh backscattering light, which locates the vibration point, while wide pulses interfere with reference light as a MZI to obtain frequency response. To simulate the high frequency responses of crack in civil structures, the sudden break of pencils adjacent to fiber loop has been measured. The experimental results show 5 m spatial resolution and up to 6.3 MHz frequency response with 50 ns pulse width are achieved in 1150 m sensing distance.

Cerenkov radiation occurs when charged particles are moving faster than the speed of light in a transparent dielectric medium. In optical fibers, the Cerenkov light also can be generated due to their dielectric components. Accordingly, the radiation-induced light signals can be obtained using optical fibers without any scintillating material. In this study, to measure the intensities of Cerenkov radiation induced by gamma-rays, we have fabricated the fiber-optic Cerenkov radiation sensor system using silica optical fibers, plastic optical fibers, multi-anode photomultiplier tubes, and a scanning system. To characterize the Cerenkov radiation generated in optical fibers, the spectra of Cerenkov radiation generated in the silica and plastic optical fibers were measured. Also, the intensities of Cerenkov radiation induced by gamma-rays generated from a cylindrical Co-60 source with or without lead shielding were measured using the fiberoptic Cerenkov radiation sensor system.

An all optical fibre based sensing configuration designed to measure the changes in differential length of two independent Fabry-Perot cavities at widely separated locations in an environment where strong temperature gradients may exist is demonstrated. Two Fabry-Perot sensing cavities are formed between the cleaved end of a fibre and a reflective surface. The presented technique is based on low coherence tandem interferometry incorporating high coherence interferometry as a calibration measurement.

Capacity of the sensor network is always a bottleneck problem for the novel FBG-based quasi-distributed fiberoptical defending system. In this paper, a highly sensitive sensing network with FBG vibration sensors is presented to relieve stress of the capacity and the system cost. However, higher sensitivity may cause higher Nuisance Alarm Rates (NARs) in practical uses. It is necessary to further classify the intrusion pattern or threat level and determine the validity of an unexpected event. Then an intelligent identification method is proposed by extracting the statistical features of the vibration signals in the time domain, and inputting them into a 3-layer Back-Propagation(BP) Artificial Neural Network to classify the events of interest. Experiments of both simulation and field tests are carried out to validate its effectiveness. The results show the recognition rate can be achieved up to 100% for the simulation signals and as high as 96.03% in the real tests.

The porous properties of self-assembled waveguides made up of nanoparticles are characterised. Atomic force microscopy (AFM) reveals predominantly hcp or fcc packing suggesting a remarkably well ordered and distributed porous structure. N² adsorption studies estimate a surface area SA ~ 101 m²/g, a total interstitial volume V_i ~ 1.7 mL/g and a pore size distribution of r ~ (2 - 6) nm. This distribution is in excellent agreement with the idealised values for identically sized particles obtained for the octahedral and tetrahedral pores of the hcp and fcc lattices, estimated to lie within and r_tet ~ (2.2 – 3.3) nm and roct ~ (4.2 – 6.2) nm for particles varying in size over 20 to 30 nm. Optical transmission based percolation studies reveal rapid penetration of Rhodamine dye (< 5 s) with very little percolation of larger molecules such as ZnTPP observed under similar loading conditions. In the latter case, laser ablation was used to determine the transport of hydrated Zn²⁺ to be D ~ 3 x 10^-4 nm²s^-1. By comparison, ZnTPP was not able to percolate into the wire over the time of exposure, t = 10 mins, effectively demonstrating the self-assembled structure acting as a molecular sieve. We discuss the potential of such structures more broadly and conclude that the controllable distribution of such nano-chambers offers the possibility of amplifying, or up-scaling, an otherwise local interaction or nanoreactions to make detection and diagnostics much simpler; it also opens up a new approach to material engineering making new composites with periodic nanoscale variability. These and other unique aspects of these structures are embodied in an overall concept of lab-in-wire, or similar self-assembled structures, extending our previous concept of lab-in-fibre from the micro domain into the nano domain.

Recent work on characterising viscosity of silica fibres using regenerated gratings is described. Some of the broader implications for all fibre sensors are outlined.

In this study, we fabricated a fiber-optic radiation sensor using three kinds of inorganic scintillation crystals with the same dimension, such as LYSO:Ce, YSO:Ce, and BGO. Gamma-ray energy spectra for Cs-137 were measured with three kinds of inorganic scintillators to select an optimum scintillator that is suitable to use for gamma-ray energy spectroscopy. The total counts of the scintillating lights, were also obtained according to the activity of Cs-137. As a result, the energy spectra measured using the three scintillators were clearly different, thereby they showed clear distinction about the energy resolution and position of the inherent photopeak of Cs-137. Although all scintillators had a linear response over the activity of Cs-137, we selected LYSO:Ce as an optimum scintillator because it provided good energy resolution and the highest light output in our experimental setup.

We have made lead (II) tetrakis (4-cumylphenoxy) phthalocyanine (PbTCPc) films with various concentrations in plasticized poly (methyl methacrylate) (PMMA) and poly (acrylic tetraphenyl diaminobiphenylamine) (PATPD) matrices, and investigated nonlinear transmission properties with a Nd:YAG laser (532 nm, 5ns). Our results demonstrate a solid state PbTCPc nonlinear absorber, whose performance is comparable to that of low concentration solutions of the dye, that can be fabricated by mixing the dye in a plasticized polymer matrix.

In this paper, a novel method to sensing the complex refractive index (CRI) of graphene waveguide (GW) is demonstrated. Theoretical analysis and simulated results indicate the spectral properties of evanescent wave guided by microfiber would be modulated by the GW nearby. In experiment, evanescent waves with wavelength from 1510nm to 1590nm transimitting on the surface of the GW for a few centimeters, which are launched and collected by specially designed microfiber knot sensors (MFKSs). Repeated experiments and statistic results verifie that the CRI of the GW varies from 2.59-i2.66 to 2.51-i2.84 for 1510nm-1590nm band. Such an application of MFKS is suitable not only for the GW, but also for other thin films, which would be significant for the design and research of state-of-art optical devices.

D-shaped optical fibres are coated with silica nanoparticles by horizontal dip and slide method. Visual determination of film coverage is difficult. Thick coatings are discernible through thin film interference coloring but thinner coatings require SEM imaging. Here, we show that fluorescence imaging, using Rhodmaine B in this example, can provide some qualitative assessment of coverage.

Integrated optical waveguide sensors are usually fabricated using materials like silicon, silica, SU-8, etc. Their fabrication requires clean room processes which are expensive and time-consuming. We demonstrated the fabrication of PDMS based optical waveguide in non-cleanroom environment using soft lithography technique. A master-mold was fabricated using Acralyn. PDMS polymer was chosen for waveguide fabrication, as it provides low refractive index contrast in the sensing region. These PDMS waveguides were found to be 5-times more sensitive than SU-8 waveguides. High sensitivity along with mechanical robustness and ease of fabrication of PDMS waveguides provides a promising and versatile platform for biosensor application.

The wrist-pulse is a kind of signals, from which a lot of physiological and pathological status of patients are deduced according to traditional Chinese medicine theories. This paper designs a new optic fiber wrist-pulse sensor that based on a group of FBGs. Sensitivity of the optic fiber wrist-pulse measurement system reaches 0.05% FS and the range reaches 50kPa. Frequency response is from 0 Hz to 5 kHz. A group of typical pulse signal is given out in the paper to compare different status of patient. It will improve quantification of pulse diagnosis greatly.

An air-silica microstructure optical fiber based on anti-resonant reflecting optical waveguide (ARROW) principle was used to develop spectral absorption gas sensor. The ARROW fiber has an air core and an air cladding layer. An ARROW fiber with length of 725 mm was used to construct a sensing system to detect acetylene gas. The gas was injected into the fiber from one end of the fiber. The transmission spectra were collected using an optical spectrum analyzer. The results indicate that the system can detect the gas of different concentrations and has good system linearity. The response time of the system is about 200 s.

This paper describes an optical fiber oxygen sensor based on wavelength scanning and spectrum absorption technique. An open path optical gas chamber is employed to analyze the absorption lines of oxygen in visible region. The oxygen sensor works in the concentration range 0-100% oxygen with good performance in stability and sensitivity. The precious is less 0.5% over 30 hours in atmosphere. The results show that it will have a great potential application in the harsh environments.

A novel bio-detecting chip configuration based on the fiber surface plasmon enhancement mechanism is proposed and analyzed. Our improvement is proposing to couple the specialized shell-isolated gold nanoparticles into the sensing region of the opened fiber-integrated microfluidic chip, and achieving drastic surface plasmon enhancement by employing the guided optical mode. Simulation shows that the optical intensity distribution near the surface of exposed fiber hole is enhanced drastically, which could be beneficial to the fluorescence or Raman enhancement. Our work could contribute to searching novel microfluidic chip based bio-detecting methods such as for tracing poisonous and harmful substances detection.

In trace water vapor direct absorption spectroscopy, the absorption signal is buried in noise and up and downs of the light intensity, an effective signal extraction method is vital. In the basis of double-beam differential absorption, division method in voltage and an approach based on balanced ratiometer detection (BRD) were studied. Voltage division has an excellent stability to temperature variation, mechanical extrusion and fiber bend loss. As to the BRD method, it has an outstanding self-adjusting capability and it can also avoid an excess phase difference caused by current-to-voltage converting circuit, thus this method has a high sensitivity. Furthermore, a so called dual-peak method based on the differential value of two adjacent absorption lines is introduced, the differential value proved has a linear relation with water vapor concentration, and this method provides a way to measure the concentration at high pressure. In addition, the influence of water vapor inside the optical components has been discussed.

Because of its special structure, photonic crystal fiber(PCF) has shown great potential in gas sensing. Probe beam with the test gas can directly interact within a PCF. PCF gas sensor with a very small amount of gas can be interact with light in optical fiber in a long distance. And you can change the parameters of the fibers can be improved sensor sensitivity, etc. The status of solid core PCF and hollow-core PCF as a gas sensor is introduced respectively in this paper.

Wavelength, linewidth and divergence angle of light source are crucial in high precision SPR measurement and investigated respectively in this paper. Theoretical modeling and simulation results show that the resonance angle is more sensitive to short wavelength, and both linewidth and divergence angle broaden and reduce the depth of the resonance peak. Increment of linewidth and divergence angle can also result in a larger resonance angle.

In this study, we report a miniaturized optical sensor for direct detection of vapors of nitro-based explosives using gold nanoparticle (AuNP) coated SU-8 polymer optical waveguides. S-shaped waveguide geometry was chosen due its enhanced evanescent field sensitivity. Light was coupled into the waveguide structure to evanescently excite the localized surface plasmon resonance (LSPR) modes of the immobilized AuNP. The AuNP were functionalized with 4- mercaptobenzoic acid (4-MBA) which acts as the receptor for nitro-based explosives. The AuNP coated SU-8 optical waveguide sensor demonstrated an ability to detect 10 parts per billion (ppb) concentration of explosive analytes.

A hollow-core photonic crystal fiber (HC-PCF)-based gas sensor is proposed and numerically investigated through the finite element method. To obtain higher relative sensitivity coefficient γ and the better sensing properties of the gas sensor, the floriated structure of the central hole of HC-PCF is optimized. Numerical investigation shows that γ is high and relatively stable to changes of the diameter of air holes in a wide range of wavelength of 1.5-1.7μm, which is very beneficial for sensor fabrication. A lower confinement loss and the flatness are also exhibited with the HC-PCF. And the highest γ of 0.9998 of the floriated structure of the central hole can be obtained than the circular ones of 0.9435 at the wavelength of 1.56μm.

A study of polymer photonic crystal fiber (PCF) sensor coated with smart composite materials for measurements of refractive index of analyte is presented in this paper. The proposed sensor combines the characteristics of polymer PCF and composite material, which can make the confinement loss lower than the silica PCF duo to the double interaction of the polymer and silver film. The results obtained in this study demonstrate that polymer PCF sensors coated with composite material and with the polymer PCF’s advantages, the sensor’s feasibility can be improved further and it can be applied in a broad field, especially in biosensing platforms.

We report the fabrication of in-line fiber-optic photonic microcells by post-processing commercial photonic crystal fibers. With such microcells, novel photonic devices such as in-fiber amplifiers, grating filters, and accelerometers are created.

Aiming at exiting linear temperature fire detection technology including temperature sensing cable, fiber Raman scattering, fiber Bragg grating, this paper establish an experimental platform in cable tunnel, set two different experimental scenes of the fire and record temperature variation and fire detector response time in the processing of fire simulation. Since a small amount of thermal radiation and no flame for the beginning of the small-scale fire, only directly contacting heat detectors can make alarm response and the rest of other non- contact detectors are unable to respond. In large-scale fire, the alarm response time of the fiber Raman temperature sensing fire detector and fiber Bragg grating temperature sensing fire detector is about 30 seconds, and depending on the thermocouples’ record the temperature over the fire is less than 35℃ in first 60 seconds of large-scale fire, while the temperature rising is more than 5℃/min within the range of ± 3m. According to the technical characteristics of the three detectors, the engineering suitability of the typical linear heat detectors in cable tunnels early fire detection is analyzed, which provide technical support for the preparation of norms.

One of the most important equipment in high voltage power grid system is power transformer, however there are still some limitations on traditional methods of online partial discharge monitoring. Considering the advantages of optical fiber sensing technology, in this paper we do some research on fiber optics F-P sensing which can be used in transformer on online partial discharge monitoring. It also contributes to the improvement of the reliability of power system safety monitoring. This paper designs an equipment scheme for fiber optics F-P sensor, strictly fabricates the sensor according to the fabrication procedure. Moreover, we build a reasonable signal demodulation system for fiber optics F-P sensing, doing a preliminary analysis of online partial discharge signal monitoring,Partial discharge online monitoring system including different intensity discharge with a same sensing distance and a same intensity discharge with different sensing distances. Finally we make a detailed analysis of experimental result.

In order to measure the distance between switch point and stock rail in railway system high precision, a wide range and high precision fiber Bragg grating (FBG) displacement sensor is designed. The sensitivity as well as the measurement range of the senor is increased through the effective cooperation of the spring and equal strength beam. At the same time, differential compensation method is exploited for eliminating temperature effects, which brings further improvement of the sensitivity as well. Test results show that, in the range of 160 mm, the precision of the sensor is 0.017 mm.

Because of the high degree of railway’s electromagnetic radiation and the vulnerability of the traditional electronic sensor, the safety monitoring of railway’s protective net in slopes is an important process. Based on fiber grating’s such advantages as freedom from electromagnet, and the convenient linkage of signal, this thesis formulated tension sensor and acceleration sensor on the basis of protective net’s characteristics. By conducting the impulse test on the protective net that is installed with sensor, we collected the mechanics’ parametric variation during the whole process of impact. The fiber grating sensor used in the test was stable and reliable.

Based on the technology of the spectrum absorption and the FBG, the monitoring system realize on line detection of the concentration of methane and oxygen, the temperature and the pressure of the gas in pipeline, and in order to improve the accuracy of the gas detection, we induce the compensation to the gas concentration using the data of the temperature and the pressure. In order to have a effective utilization of the methane in the coal mine gas drainage system, we have to have a accurate measurements of the concentration, the temperature and the pressure of the gas in pipeline. At the same time the dynamic monitoring of the concentration of Oxygen is a sign of the leakage of the pump. This paper gave some data detected in the field of the coal mine gas drainage system.

This paper presents the application of the FBG sensing technology for train overload and unbalanced load monitoring. A type of FBG strain gauges is designed，which can avoid chirped FBG, and enhance sensitivity. A sensor installation method is worked out for nondestructive detecting, enabling sensors to adapt to adverse circumstance by installing FBG sensing device on steel rails, and making use of real time wavelength offset value of FBG sensors, and the dynamic detection of wheel axle load can be achieved. Comparing dynamic axle load distribution of the two tracks, the unbalanced load conditions of carriages can be obtained. The sum of axle load of a carriage turns out to be the total weight of the carriage. Meanwhile, the monitoring system possesses a function of monitoring wheel tread defect.

（1National Engineering Laboratory for Fiber Optic Sensing Technology, 2Key Laboratory of Fiber Optic Sensing Technology and Information Processing, Wuhan University of Technology, Wuhan, 430070, China） Abstract: In view of the high voltage, strong magnetic field environment of high voltage switchgear, the isolation contact temperature measurement scheme of optical fiber based on wireless sensor technology realizes the contact temperature monitoring of high-voltage switchgear. In this scheme, good thermal conductivity and insulation ceramic materials are selected as outer jacket material sensing probe, and the program has a good solution to the problem of high and low voltage isolation; Combination of optical fiber composite insulator for wireless sensing, solves the problem of high voltage insulation, but also to avoid the "creeping" phenomenon due to dust. The package structure and reasonable installation solve the cross sensitivity of strain. Application shows that the precision of temperature measurement of the system can reach ± 0.5 ℃ and can work in a variety of harsh environment. It can improve the reliability of the operation of electrical equipment significantly and has considerable practical value for the normal operation of the whole power system.

Microseismic monitoring is essential for rock burst predication in coal mines. However, the existing monitoring instruments based on electric geophone have inherent limitations and hardly progress further. This paper presents the design and implementation of a novel microseismic monitoring system using fiber optic sensing and distributed data acquisition techniques. The technical details including seismic sensor, interrogation system, and seismic substation are introduced. The results show that the system achieves a bandwidth of 0.5-400 Hz and a dynamic range of 80 dB. The location accuracy reaches 10 m by reasonable configuration of sensors, and so it is particularly suitable for precision mine microseismic monitoring.

Safety must always prevail in Nuclear Power Plants (NPPs), as shown at Fukushima-Daiichi. So, innovations are clearly needed to strengthen instrumentations, which went inoperative during this nuclear accident as a consequence of power supply losses. Possible improvements concern materials and structures, which may be remotely monitored thanks to Optical Fiber Sensors (OFS). We detail topics involving OFS helpful for monitoring, in nominal conditions as well as during a severe accident. They include distributed sensing (Rayleigh, Raman, Brillouin) for both temperature sensing and structure monitoring as well as H₂ concentration and ionizing radiation monitoring. For future plants, Fiber Bragg Grating (FBG) sensors are considered up to high temperature for sodium-cooled fast reactor monitoring. These applications can benefit from fiber advantages: sensor multiplexing, multi-km range, no risk-to-people, no common failure mode with other technologies, remote sensing, and the ability to operate in case of power supply lost in the NPP.

For real-time dosimetry in both radiation therapeutic and diagnostic applications, a newly-designed dual-mode fiberoptic dosimeter was developed using a scintillating probe and a Cerenkov probe. In this study, we measured the scintillating and Cerenkov lights simultaneously and analyzed the light intensities and spectra of their light signals for the performance evaluation of the proposed fiber-optic dosimeter.

Coal mine belt transport system is the most important transportation system, directly determines the normal operation of coal mine production safety, so it is necessary to secure real-time online monitoring of running status. Based on distributed optical fiber temperature measurement technology, developed a coal mine belt conveyor running state online monitoring system, achieved to monitor the Real-time temperature of mainly electromechanical device and all the belt line. Field data analysis showed that coal mine belt conveyor state on-line monitoring system of based on DTS can real-time accurately monitor the temperature and belt conveyor running state, to guarantee the coal belt conveyor safe operation and offer a strong support.for the realization of the state maintenance of equipment.

In the field of oil well logging, real-time monitoring of fluid flow parameter provides a scientific basis for oil and gas optimization exploration and increase of reservoir recovery, so the non-intrusive flow test method based on turbulent vibration is proposed. The specific length of sensor fiber wound tightly around the outer wall of the pipe is connected with the optical fiber gratings at both ends, the sensor fiber and the optical fiber gratings compose the flow sensing unit. The dynamic pressure is generated by the turbulence when fluid flows through the pipe, and the dynamic pressure results in the light phase shift of the sensor fiber. The phase information is demodulated by fiber optic interferometer technology, time division multiplexing technology and Phase Generated Carrier modulation and demodulation techniques. The quadratic curve relationship between phase change and flow rate is found by experimental data analysis, and the experiment confirms the feasibility of optical fiber flow test method with non-intrusive and implements the realtime monitoring of flow.

Optical modes of a microbubble are studied both theoretically and experimentally. It is shown that the thermal red shift of the whispering gallery mode can be counteracted by selecting a suitable wall thickness and core material. Furthermore, the temperature sensitivity can be enhanced by selecting the appropriate wall thickness and core fluid such that a significant blue shift up to 30GHz/K is possible. Calculated shift rates are compared to preliminary results.

This paper investigates the transmission spectral properties of tilted long period fiber gratings (TLPFGs) written in fiber tapers with different radiuses. We found that the tilted angle, the radius of fiber and the external refractive index both have influences on the transmission spectral by simulations. With the decrease of the radius of the fiber taper and the increase of refractive index, the resonant wavelength of the tilted LPFG was found to shift towards shorter wavelength. Experimental results show the agreement with the simulation predictions. The TLPFG inscribed in fiber taper also brings the high sensitivity of external refractive index as 566.7 nm/RIU.

In this paper, we demonstrate a hydrostatic pressure sensor based on a liquid filled solid-core photonic crystal fiber (PCF). A single cladding hole of the PCF is selectively filled with the assistance of femtosecond laser micromachining. The filled PCF presents several loss dips in the transmission spectrum due to the resonant couplings from the core mode to the LP11 liquid modes. Pressure measurement is performed by monitoring the wavelength shift of the dips. The pressure sensitivities are -0.452 and -0.621nm/MPa for two of them, respectively.

A silicon steel sheet is proposed in this paper to work as a magnetic field concentrator to enhance the sensitivity of a Faraday effect based magnetic field sensor using a dual-polarization fiber grating laser. When the silicon steel sheet is placed close to the cavity of the fiber grating laser, the magnetic field is concentrated around the silicon steel sheet and hence the fiber grating laser experience stronger magnetic field than the case without the silicon steel sheet, which results in a larger magnetic field induced beat note frequency change after photodetection of the two orthogonally polarized laser outputs. With the same axial magnetic field, the experiment results confirm that the sensitivity of the sensor with a silicon steel sheet is improved over the one without a silicon steel sheet, which validates our proposal.

Intracranial pressure is an important monitoring indicator of neurosurgery. In this paper we adopt all-fiber FP fiber optic sensor, using a minimally invasive operation to realize real-time dynamic monitoring intracranial pressure of the hemorrhage rats, and observe their intracranial pressure regularity of dynamic changes. Preliminary results verify the effectiveness of applications and feasibility, providing some basis for human brain minimally invasive intracranial pressure measurement.

Two measuring methods of wide absorption spectrum by DFB-LDs are presented in detecting water vapor absorption line. One is subsection scanning method, it takes advantage of wide spectrum tuning range by temperature modulation and fast spectrum tuning speed by current modulation, specifically, this method is realized by dividing a target spectral region into several sections which corresponding to specific temperature of DFB-LD, and scanning every section by current modulation for hundreds times and average the data to raise SNR, combining all sections to get the whole spectrum. An accuracy of 10 ppmv had been obtained in the measurement of water vapor with a 10-cm path length by this method. Another is data fitting method, based on absorption line-shape function, the absorption line can be described by fitting with partial measured data. The fitting absorption line is fitted well with the measured data, and the square of correlation coefficient (R-square) is no less than 0.99.

Chemical etching process for PANDA polarization-maintaining fiber (PMF) in HiBi fiber loop mirror (FLM) is studied detailedly in this paper. The PMF is inserted into the FLM whose etched length is about 3cm. Due to decrease of the fiber diameter, the whole wavelengths of transmission dips shift to the short wavelength because of the reduction of birefringence when the PMF is etched. The result shows that the wavelength spacing between two interference minima increases from 19nm to 22nm when chemical etching ends, the thinned PMF is sensitive to the external environment and can be applied to many biochemistry sensing applications.

We propose and experimentally demonstrate a compact in-line micro-fiber inclinometer based on deformation of FBG, where the micro-fiber FBG beam is fabricated by special chemical etching method and the fiber pendulum is gained by splicing a section of hollow core fiber filling with tin to the end of the micro-fiber beam. The experiment results show that as the inclination angle increasing from0⁰ to 20⁰, the increments of the transmission loss and Bragg wavelength of the sensor are 1.81dB, and 0.035nm, respectively. Simultaneously, the change of the bandwidth at -25dBm increases linearly from 0.86nm to 1.048nm and the bandwidth sensitivity to inclination angle is 7.24pm/deg. On the other hand, temperature cross issue is solved by monitoring the bandwidth at -25dBm because the bandwidth sensitivity to temperature is 0.089pm/℃from 20℃ to 200℃.

We demonstrate a temperature-independent displacement sensor by inscribing a periodic grating in a microfiber taper with assistance of the 193-nm ultraviolet exposure technique. The obtained bandwidth is as large as 29.64nm for the grating with diameter of 3.8~6.38μm and length of 6.2mm, respectively. When the displacement is increased from 0 to 1.08mm, the reflecting bandwidth reduces to 3.38nm gradually, producing an average sensitivity of around −22.8nm/mm. The minimum displacement of measurement is ~4.39×10⁻⁴mm considering the wavelength resolution of 10pm in the optical spectrum analyzer. Moreover, the temperature-cross sensitivity is suppressed.

A micro Fabry-Perot (MFP) filter is proposed and fabricated by twisting a section of microfiber into two Sagnac loop mirrors. With the co-operation of this MFP filter and a section of highly nonlinear fiber, we propose and experimentally demonstrate a multi-wavelength Erbium-doped fiber ring laser (EDFRL) based on the inhomogeneous loss mechanism. When the pump current is set at 450mA, 22-lasering wavelengths with the identical wavelength space of 0.22nm and side-mode suppression ratio (SMSR) above 30dB are achieved. Within the period of one hour’s monitoring, the fluctuation of the output power is less than 0.943dB.

We demonstrate a miniaturized fiber in-line Mach–Zehnder interferometer high-temperature sensor based on inner aircavity adjacent to the fiber core, fabricated by femto-second laser micromachining and fusion splicing technique. Such a device is robust and insensitive to ambient refractive index change, with high temperature sensitivity of ~43.2 pm/°C, up to 1000°C,while exhibiting low cross-sensitivity to strain.

In this invited paper, we glance at the history of plasmonic sensors and provide the optimization study of representative plasmonic sensors such as surface plasmon resonance (SPR) sensors, localized SPR sensors, and fiber grating SPR sensors. The key variables of specific plasmonic sensors are numerically examined and compared. Furthermore, we discuss the recent developments and prospect on various plasmonic sensors.

Highly birefringent (Hi-Bi) microfiber-based fiber loop mirrors (FLMs) are studied for gas pressure measurement. A elliptical microfiber is made by tapering a femtosecond laser-processed single mode fiber and demonstrated a very high birefringence of up to 10^-2 . The microfiber is housed within a pressure tube with which gas pressure measurement is carried out. The robust microfiber sensor demonstrates a pressure sensitivity of 6 pm/kPa with a temperature cross-sensitivity of less than 0.01 nm/K.

Optical fiber-tip air bubbles are demonstrated for pressure sensing with ultrahigh sensitivity. The air bubble locates in the end facet of a single mode fiber (SMF) that spliced with a silica tube, which is naturally formed and acts as a compressible Fabry-Pérot interferometer (FPI) cavity when immersing the silica tube into liquid. The proposed device exhibits pressure sensitivity of <1000 nm/kPa. This kind of compressible FPI cavity may find potential applications in highly sensitive pressure and/or acoustic sensing.

FBG-based perimeter security is a new security method. It can be distributed security and intelligent addressing. So far, it has been widely used in a variety of security. During the idle time of fiber Bragg grating (FBG) perimeter security defense system, the available FBG perimeter sensor can be utilized as temperature sensor, frequency sensor and acceleration sensor according to its characteristics. The sensor can collect more real-time environment information that make the defense system functions more perfect and more powerful. All of this information can help us to understand the changes in the environment and avoid some accidents.

Polymer micro-fibers with inscribed Bragg gratings are reported in this paper. By implementing a two-stage fabrication process a 16 μm diameter micro-fiber is fabricated with an inscribed 10 mm long Bragg grating which exhibits a peak reflected wavelength circa 1530 nm. The growth dynamics of the polymer micro-fiber Bragg grating are also observed and analyzed. A maximum reflectivity of 5% is obtained after an exposure time of 3 minutes to a 50 mW power He-Cd laser of 325 nm wavelength. The temperature characterization of the micro-fiber Bragg grating with different diameters is also presented. The fabricated micro-fiber Bragg grating can be used as sensors for high sensitivity measurements in a number of application areas.

A novel method was proposed to improve hydrogen sensitive performance of fiber Bragg grating (FBG) hydrogen sensor. The hydrogen performance of the sensor can be greatly improved by combing Pt/WO3 composite film annealed under 315°C for 1 h and temperature sensitive FBG. At room temperature of 25°C, FBG coated with Pt/WO3 composite film has 536 pm wavelength shift towards 10000 ppm hydrogen, and hydrogen detection threshold of FBG hydrogen sensor can reach to 200 ppm. The hydrogen performance of FBG hydrogen sensor was studied under different humidity, and ambient humidity has little effect on the hydrogen performance of FBG hydrogen sensor.

An interrogation system based on two semiconductor optical amplifiers for weak fiber Bragg gratings(FBGs) was proposed in this study. The first Semiconductor Optical Amplifier (SOA) was used to modulate the light and the second SOA separated the signal through delayed switching. The proposed system has lower insertion loss and higher spatial resolution, and can interrogate time-division and wavelength-division multiplexed FBG array. Up to 50 FBGs, with a reflectivity of 0.2% and a spatial resolution of 5m along the optical fiber, were distinguished to demonstrate the interrogation system.

A Mach-Zehnder interferometer (MZI) based on a pair of long period gratings (LPGs) fabricated by silica microfiber for sensing applications is demonstrated. Each LPG with only 6 deformations was fabricated by using a pulsed CO2 laser to periodically modify the surface of the microfiber through only one scanning cycle. Owing to the relatively large effective refractive index (RI) difference between the fundamental and higher order modes of the microfiber LPG, the size of the microfiber MZI can reach as short as 8.84mm when the diameter of the microfiber is 9.5μm. The microfiber MZI can exhibit a high sensitivity of around 2225nm per refractive index unit and temperature sensitivity of only 11.7 pm/°C. Featured with the easy fabrication, excellent compactness, high sensitivity and stability, the microfiber MZI has potential in the microfiber-based devices and sensors.

In this paper, the output beat signal of the polarimetric heterodyning fiber grating laser sensor has been stabilized based on the investigation of polarization effect on the beat frequency. The short-term frequency fluctuation has been reduced from 1.5 MHz to about 0.1 MHz and the resolution of the sensors is greatly improved.

We present an optical fiber bend sensor with enhanced resolution based on the principle of a Mach-Zehnder interferometer in transmission. The sensor is based on two identical Long-Period Gratings separated by approximately 100 mm in a D-shaped single-mode optical fiber. The sensor provides a narrow resonance bandwidth compared to a typical resonance from a Long-Period Grating. The sensor was recoated with low refractive index polyimide and embedded on a fiber-glass base plate before it was characterized as a bending sensor.

We propose a laser sensor system which uses fiber Bragg gratings as laser cavity mirrors as well as sensors. With a spectrometer demodulation, a low-cost, more robust, and faster sensor functions have been demonstrated compared with the conventional wavelength-swept laser demodulation. Some of the multiple FBG sensors showed unstable lasing characteristics, leading to missing measurands. Polarization scrambling has been used to alleviate the problem. With fast polarization disturbances in the fiber-optic laser cavity, more FBG sensor outputs could be generated consistently and data acquisition rate has increased more than 5 times.

Fiber Bragg Grating (FBG) sensing technology was used to monitor a crevice of continuous beam joint and rails near rail expansion devices on a viaduct. The monitoring items consisted of rail temperature, rail displacement, viaduct beam displacement, and strain of sliding rail of rail expansion device. Strain sensor was a prefabricate FBG strain gauge; displacement sensor with different scale used a FBG stress ring; and the FBG of temperature sensor was pre-drawn and fixed in a metal tube. The monitoring results matched to the manual testing and theoretical estimate.

This work presents an application of reactive ion etching (RIE) for effective tuning of spectral response and the refractive-index (RI) sensitivity of diamond-like carbon (DLC) nano-coated long-period gratings (LPGs). The technique allows for an efficient and well controlled etching of the DLC by means of O₂ and CF₄ plasma. The effect of DLC nanocoating etching on spectral properties of the LPGs is discussed. We correlated the decrease in DLC thickness with the shift of the LPG resonance wavelength. The thinning of the overlay effectively changes the distribution of the cladding modes and thus it also has an impact on the device’s RI sensitivity. The advantage of this approach is a capability for post-processing of the nano-coated structures with a good precision (etching rate from 4.6 to 8.1 nm/min for O₂ plasma), cleaning the samples and their re-coating according to requested needs.

We have investigated the possibility to use a step-chirped fiber Bragg grating array for a time-delay-spectrometer. This concept allows a simultaneous spectral and temporal characterization of pulsed light in the nanosecond regime which can also be applied for the investigation of single pulses. A spectral resolution in the 100 picometer range has been achieved and used for the characterization of laser pulses in the nanosecond range.

Microstructured optical fibers are usually divided into two different types of fibers: solid-core photonic crystal fibers and air-core photonic bandgaps fibers. This paper presents long period fiber gratings written in both solid-core PCFs and aircore PBGs by use of a CO₂ laser. A sensitive stain sensor was demonstrated by use of a CO₂-laser-written long period fiber grating in a solid-core photonic crystal fiber. An in-fiber polarizer based on a long period fiber grating was written by use of a focused CO₂ laser beam to notch periodically on a solid-core photonic crystal fiber. Moreover, a novel long period fiber grating was written in air-core photonic bandgap fibers by use of a CO₂ laser periodically collapse air holes in the fiber cladding.

The FBG strain sensors were applied to the Dongtan Mine to monitor the stress variation of the lined wall in the gateway retained along goaf of No. 3203 coal mining face on line. The results showed that the FBG strain sensor with high measuring range could measure the stress variation accurately during the support process of the gateway retained along goaf and could provide the basis to further optimize the support structure and to determine the support plan of the gateway retained along the goaf. The FBG micro-seismic sensors were used in Xinglong Mine to detect micro-seismic signal. The signals are well received and analyzed to determine the earthquake source and do warming. The FBG sensors and detecting system show great prospect in micro-seismic detection, and geological disasters detecting.

This paper addresses the metrological stability of spectral measurements performed with a smart FBG sensing instrument. With a sophisticated tracking system based on a real-time drift compensation, we obtained, during 16 days, an unrivalled measurement stability, as low as: 0.0074 fm/h with a standard deviation: 0.032 pm. This level of performance opens the way, not only to high quality metrology, but also to long-term structure monitoring.

Fiber Bragg Grating (FBG) sensing technology was used to dynamically monitor multiple parameters of railway switch machine poles, including time of movement, direction and quantity of loading and locking force, and states of loading resistance. Ring shape FBG strain gauge and strain sensibilized methods significantly increased the monitoring sensitivity. Installing approaches adapted the harsh environment in railway application. The monitoring results showed that for a Siemens S700K switch machine, its pole pressured stroke took 5s. Maximum load: -5.9kN, average load: -3.3kN. Vibration caused by resistance exists, its period: 0.1s, range: 0.5kN~1.6kN. After the stroke, the locking force was kept at -0.6kN. In tensile stroke, it also took 5s. Maximum load: 6.8kN, average load: 5.5kN. Vibration period: 0.1s, range: 0.7kN~2kN. Locking force: 0.2 kN. This long-term and on-line detecting method could meet railway switch condition monitoring demands of more than 100,000 switch machines in this country.

In this paper, we study spectral characteristics of long-period double-helix chiral fiber gratings fabricated by a mechanical stepping system. By discussing the effects of the step of the stepping system on the spectral characteristics, we suggest the selection of the step in the fabrications.

We demonstrated a simple method for temperature-independent refractive index measurement by use of two cascaded fiber Bragg gratings fabricated in single-mode fiber and microfiber, respectively. The reflective peaks of the two FBGs exhibit almost identical temperature sensitivity of 10.1 pm/°C and different responses to ambient refractive index. Based on the differential measurement method, of the issue of temperature cross-sensitivity for FBG sensors is solved. The refractive-index sensitivity of the sensor is 17.22 nm/RIU when the diameter of microfiber is 6.5 μm.