This PDF file contains the front matter associated with SPIE Proceedings Volume 10618, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

In this paper, we proposed a distributed stress sensor based on white light interferometer. The measurement including two steps: firstly, the moveable mirror of Michelson interferometer scans to detect the interferogram, and the position of dynamic stress can be obtained from the interferogram. Secondly, the moveable mirror of Michelson interferometer adjusted to compensate the optical path difference generated in the polarization maintaining fiber, and the photodiode detect the interference intensity. By applying wavelet transform to the detect signal, the frequency of dynamic stress can be demodulate. In our experiments, the measurement errors for 100 Hz and 1 kHz sinusoidal stress are 0.26 Hz and 0.3 Hz, respectively. And 20 Hz - 60 Hz chirp signal is also measured successfully. In the end, the harmonics in the time frequency distribution image and the factors resulting in the measurement error are discussed in detail.

An improved data processing and analysis method is proposed to realize simultaneous monitor of multiple vibrations using polarization optical time domain reflectometry system. In our method, a differential trace of the frequency component along the fiber is got by doing subtraction of the distance traces with different number of vibrations at a certain frequency, and the vibrations vibrating at different time can be located by analyzing the response power variation of the differential trace. For multiple vibration points vibrating with the same frequency and at the same time, multiple vibration events can also be distinguished by extracting the modulated frequency component, and the frequency component is obtained at the starting or ceasing state of the vibrations because the initial phases of vibration sources are unsteady and different. With our method, a POTDR sensing system which can simultaneously monitor multiple vibration points over 3km with 10m spatial resolution is demonstrated.

Fiber distributed acoustic sensing (FDAS) systems have been widely used in many fields such as oil and gas pipeline monitoring, urban safety monitoring, and perimeter security. An event recognition method for fiber distributed acoustic sensing (FDAS) systems is proposed in this paper. The Mel-frequency cepstrum coefficients (MFCC) of the acoustic signals collected by the FDAS system are computed as the features of the events, which are inputted into a convolutional neural network (CNN) to determine the type of the events. Experimental results based on 2300 training samples and 946 test samples show that the precision, recall, and f1-score of the classification model reach as high as 98.02%, 97.99%, and 97.98% respectively, which means that the combination of MFCC and CNN may be a promising event recognition method for FDAS systems.

Polarization Optical Time Domain Reflectometer (POTDR) can be used to detect the external vibration information by measuring the change of state of polarization (SOP) of the Rayleigh backscattering along the sensing fiber. However, the traditional POTDR system is suffer from the false negative when the vibrations along the fiber are with the same frequency. In this article, we propose and numerically simulated a scheme of POTDR system which can be used to detect multi-vibration with the same frequency. By scanning the SOP of the probe pulse, a series of vibration spectra along the fiber are obtained. The sum of these vibration spectra whose amplitudes are theoretical immune to certain SOP of the probe pulse and birefringence of the sensing fiber is used to analyze the external vibration information. The proposed system with input SOPs of uniform distribution and random distribution are analyzed by numerical simulation, respectively. The misdiagnosis rate of detecting multi-vibrations with different frequencies are greatly reduced. In addition, multi-vibrations with same frequency detection system using POTDR is successfully achieved by analyzing the amplitude change of the add up spectra along the sensing fiber, which would greatly promote the development of POTDR.

The use of a distributed optical fiber sensor based on optical frequency-domain reflectometry (OFDR) is proposed for drilling monitoring of carbon fiber reinforced polymer (CFRP) plates. The OFDR sensor response provides information of the drilling-induced temperature and strain over the CFRP plate within a 2D area closely located to the drilled hole. The different stages of the drilling process can be easily identified over time. In addition, a time-frequency analysis based on short-time Fourier transform allows the monitoring of the dynamic strain spectral content generated over the CFRP plate during drilling. Besides the spectral components resulting from the spindle rotation speed of the drill, this analysis allows for the detection of eventual microcracks and delamination of the CFRP plate, as experimentally verified.

In this paper, a double-sideband heterogeneous with suppressed carrier (DSBH-SC) pulse modulation method for fiber-optic distributed acoustic sensing is proposed. An electro-optic in-phase/quadrature (I/Q) modulator is used to realize carrier-suppressed double-sideband heterogeneous pulse modulation in which the positive and the negative optical sidebands can carry independent modulation signals. Due to the modulation curve of the electro-optic I/Q modulator irregularly, the factors that influence the performance of the DSBH-SC are analyzed from modulation amplitude and frequency. The analysis shows that the constant frequency modulation on the lower optical sideband while a stable wide band linear frequency chirping on the upper optical sideband can be obtain in appropriate modulation conditions. It presents a method of digital subcarrier modulation for distributed optical sensing.

Dynamic population gratings recorded in rare-earth-doped optical fibers, which are promising substitutes of photorefractive crystals for adaptive interferometric detections of mechanical vibrations and laser-induced ultrasound especially in industrial conditions, is formed by two counter-propagating mutually coherent laser recording waves via local saturation of the fiber optical absorption or gain (in optically pumped fibers). The dynamic population gratings are very attractive for different applications such as single-frequency cw fiber lasers, tunable narrow-band fiber optical filters, fiber optical sensors, adaptive interferometers, etc. The detection configuration will have an all-fiber design and will be based only on commercially available elements. In this work, we report an optical fiber adaptive vibrometer based on dynamic population grating in Er-doped optical fiber. A linear interferometer utilized for adaptive detection of mechanical vibrations. The two-wave mixing signal appears here as a result of nonlinear interaction between the direct wave R and the back propagating phase modulated wave S, which is reflected from the vibrating surface of a piezoelectric vibrating mirror. This all-fiber detection system has a fast response, is easy to prepare, which can be a potential method for detection of mechanical vibrations.

In this paper we report the development and field test of a high sensitivity fiber Bragg grating (FBG) geophone for geophysical imaging and monitoring application. A high sensitivity FBG geophone is designed, and its sensitivity is about 1000pm/g. The wavelength change of the FBG geophone is interrogated by using interferometric demodulation method, and the demodulation system noise is below 10^-3 pm/ √Hz . And the minimum detectable seismic signal is below 1μg/ √Hz . We are presenting field test results for the FBG geophone and comparing its performance with regular exploration geophones. In comparison, FBG geophone has the advantages of higher signal-to-noise ratio and better low-frequency response. This work shows that using FBG technology to develop geophone for oil and gas exploration is both advantageous and feasible.

Aiming at the impact damage monitoring requirements of aircraft fuselage and wing structure, in this paper, a fast loading identification method based on fiber Bragg grating (FBG) sensor honeycomb layout form is proposed. Firstly, the FBG honeycomb topology network is constructed, which has good scalability and high monitoring efficiency. Secondly, the impact response signal of fiber grating is processed by fractal filter method, then the energy amplitude of the fifth order wavelet transform is chosen as the characteristic parameter of the impact response. Thirdly, a FBG impact response model is established by using a few prior samples. On that basis, according to the location feature of the fiber sensors, a cell location and coordinate location method based on honeycomb cell is proposed to realize fast impact location for four edges clamped plate structures. The research shows that in a random honeycomb monitoring unit which side length is 250mm, 9 randomly chosen simulated impact points are identified with an average error of about 20mm. This method does not require a large number of prior samples, and is suitable for the conventional low speed fiber grating sampling mode. It has excellent environment adaptability and fast response ability.

Long period grating (LPG) is a kind of optical fiber sensing element which is sensitive to the change of refractive index in external environment. Magnetic fluid has the characteristic of changing its refractive index under different magnetic field. In this paper, a novel method for measuring magnetic field of optical fiber is proposed by combining magnetic fluid with LPG and fiber Bragg grating (FBG). Firstly, the LPG is encapsulated in a capillary glass tube filled with magnetic fluid, the shift of the LPG transmission spectrum under different magnetic field is obtained by a optical spectrum analyzer(OSA), the transmission spectrum is shifted by 2.194nm when the range of magnetic field is 0~30mT. On this basis, in order to realize the rapid monitoring of magnetic field, a composite structure of LPG and FBG in series is proposed. The structure is immersed in capillary glass tube filled with magnetic fluid, the external magnetic field information can be detected according to the change of the amplitude of FBG reflection spectrum. When the magnetic field varies, the refractive index of the magnetic fluid will change. Although the FBG is insensitive to the refractive index, its reflection intensity can be modulated due to the shift of the LPG transmission spectrum with the magnetic field. The results show that the maximum sensitivity can reach 0.042dB/mT when the magnetic field range is 0~30mT. This novel fiber grating composite sensing structure can provide a basis for further development of magnetic field monitoring based on intensity modulation.

This paper reports testing results of radiation resilient fiber Bragg grating (FBG) in radiation resistant fibers in the nuclear reactor core at MIT Research Reactor Lab. FBGs were fabricated by 140-fs ultrafast laser pulse using a phase mask approach. In-core test of fiber Bragg gratings was carried out in the core region of a 6-MW research reactor at temperature > 600°C and an average fast neutron (>1 MeV) flux >1×10¹⁴ n/s/cm². First 100-day tests of FBG sensors shows less than 5 dB reduction in FBG peak strength after over 1×10²⁰ n/cm² of accumulated fast neutron dosage. To test temporal responses of FBG sensors, a number of reactor anomaly events were artificially created to abruptly change reactor power, temperature, and neutron flux over short periods of time. The thermal optical coefficients and temporal responses of FBG sensors are determined at different accumulated dosages of neutron flux. Results presented in this paper reveals that temperature-stable Type-II FBGs fabricated in radiation-hardened fibers could be used as sensors to perform in-pile measurements to improve safety and efficiency of existing and next generation nuclear reactors.

We report a single mode-bare core multimode-single mode (SBMS) optical fiber sensor, for environmental parameters in-situ monitoring. Compared with the reflection structure and the transmission structure of the SBMS optical fiber sensors, we found that the repeatability and stability results of the reflection structure were much better than that of the transmission structure’s. The principle of this experimental design is based on the optical fiber which can be transmitted by the outside temperature modulation. Because the parameters of the light transmitted in the single mode-multimode single mode (SMS) fiber structure are subject to the change of the external physical factors, this type of fiber optic temperature sensor is made by multiple modes of transmission in a multimode fiber. As the light source transmits a distance in the multimode fiber, it will change greatly, making the input light and the final output light produce a great difference. While the length of the bare core multimode fiber was around 8.1cm, the temperature cross-sensitivity of the device had good linearity and was around 0.009075nm/°C , from 50 °C to 350 °C. Furthermore, the increased temperature curve was almost coincided with the decreased temperature curve.

In order to verify the performance of space deployable structures before launch, separation and deployment tests should be carried out in large space environment simulation chamber, in which a simulated on-orbit environment can be achieved. In separation and deployment tests, high-speed camera system is often employed to capture the test image. The high-speed camera system is also exposed to the cryogenic and vacuum environment in large space environment simulation chamber. Consequently, cryogenic and vacuum adaptability of the system should be very strong to withstand the extreme environment in space environment simulation chamber. A common solution is using optical chamber. The equipment was set in a pressurized chamber which can insulate inner environment from the outer vacuum environment, and the gas in the chamber can also help to heat convection, therefore heat generated by the device can be transferred to the chamber wall. This paper aims to explore the thermal design of optical chamber for high-speed camera or other special equipment used in extreme environment. Using rule number analysis method, Heat transfer model in vacuum and ambient environment had been built to analyze the characteristics of heat transfer under different thermal power, characteristic length, and environment. recommended limits were delivered by the rule number analysis. CFD method was applied to verify the rule number analysis above. The two methods above reached a similar result, which demonstrated the effectiveness of the analysis.

We developed a novel lab-on-a-chip device with the capability of rapidly pre-concentrating for Raman detection that use gold bead as the solid carrier of biomolecules. The device combines an array of patterned plasmonic surface (i.e. gold nano-ellipses), as the bead manipulation element. The purpose of gold bead manipulation is to provide sample pre-concentration in close proximity of the Raman detecting region. In the presence of an external uniform electric field, the gold ellipses create local electric field gradients (which is usually called hot spots) that capture the gold beads. The location of hot spots within a plasmonic nanostructure is polarization dependent, and inhomogeneous electric field between two adjacent nano-ellipses perpendicular to each other leads to highly unbalanced trap potential that give the chance of transferring trapped particles in a given direction through rotating the polarization. Nano-optical conveyor belts with staircase pattern of nano-ellipses were arranged with their terminus collected at detection area to gather biomolecules. With the capacity to transfer biomolecules precisely, our design offers an attractive scheme for rapid, high throughput and highly sensitive sensing of low abundance analytes.

In optical fiber spectroscopy research, adsorbent is frequently used on gas sensing detection. But traditional solid adsorbent have some adverse effect for optical transmission. In this paper, liquid film is used as the CO adsorbent. The base tube is hollow core waveguide. Liquid is coated to the inner surface of the hollow core waveguide. And the both end of the tube are packaged to FMA905 connector. The surface of the liquid film is smooth. So it has small scattering and high detection efficiency. The sensor with 48cm length is used to CO detection. The limit detection concentration can be achieved about 20 ppmv.

Breath analysis is an attractive method for disease diagnosis and therapeutic monitoring, due to its high potential for non-invasive medical diagnostics. Among numerous analysis techniques, tunable diode laser-based absorption spectroscopy (TDLAS) is an excellent method for detection of gas concentration, since it presents advantages of high sensitivity, good selectivity, fast response and high temporal resolution. In this study, state-of-the-art quantum cascade laser based gas sensor is demonstrated as a promising new tool for noninvasive, real-time identification and quantification of trace gases in human breath for clinical uses. Details of selection of spectroscopic parameters and primary lab studies conducted on CO, H2O and N2O molecules in exhaled breath are presented, together with suggestions on the future direction of this challenging analytical field.

This article introduced a new type of normally closed micro-valve (NCV) equipped with curved channels and trapezia-shaped valve seat, which could solve the issues of large area of dead zone, high threshold pressure and slow response speed of NCV in the current microfluidic oscillators. The new type of NCV has a three-layered structure with a top controlling layer, medium membrane layer and the bottom feedback layer. The membrane channel in the feedback layer is specifically deigned as curved to decrease the dead zone area. The valve seat is designed as a trapezoid to reduce the adhesion between the membrane and the valve seat and the threshold pressure of the NCV , and to improve the response speed of the system .The results of simulation study on COMSOL shows that this micro-valve structure reduces the NCV threshold pressure by 45% and the oscillation period of the micro-oscillator by 36%. This article conducted further simulation studies on the factors that influence the oscillation period of micro-oscillator. When enlarging inlet flow rate of micro-oscillator, lowering NCV threshold pressure and decreasing valve seat angle, the oscillation period would be reduced. Otherwise, the oscillation period will be increased.

In this paper, an optical fiber Fabry–Perot (F-P) pressure sensor based on micro-electro-mechanical system (MEMS) techniques is presented. We use SOI wafer and Pyrex glass wafer with micro-circular shallow pit array to fabricate the sealed F-P cavity structure by employing Au-Au thermal-compression bonding technique which avoids the gas releasing due to chemical reaction during anodic bonding process. The loaded pressure on the silicon diaphragm is transferred to cavity length information and measured by using polarization low-coherence interference demodulator. The response range and sensitivity of this pressure sensor can be simply altered by adjusting the parameters of radius and thickness of silicon diaphragm. This batch fabrication process is helpful for keeping performance consistency of the sensors. Fabrication and experimental investigation of the sensors are described. Results show that the sensor exhibits a relatively linear response within the pressure variation range of 3-283kPa with a sensitivity of 23.63 nm/kPa and the repeatability of the sensor is about 0.119%F.S. Additionally, the temperature dependency is approximately linear with 1.7nm/°C from -20°C to 70°C.

Color filter is the key component of the detector of space optical-remote-sensing camera. It is used for multispectral band-pass filtering and for the encapsulation of detector. Color filter is more complicated than the panchromatic or monochromatic filter. Physical dimension of filter substrate, light window size, black layer outline size and on-filter alignment mark are the feature sizes of a color filter. This article gives the designing and calculating method of these feature sizes. Analysis of influences on detector and camera resulting from the designing and manufacturing error is also proposed, such as filter-and-die alignment precision, detector butting on focal plane assembly, and spectral response characteristic of the camera. Finally a designing and application example of a color filter on some camera is given.

A high sensitivity strain sensor based on cascaded cladding mode resonant double-clad fiber (DCF) and simple mode fiber is proposed. The basic principle of the sensor is analyzed, and the preparation of the sensor is performed. In different length of double-clad fiber, the strain sensing characteristics are analyzed detailedly. Experimental results show that, as the length of the connected double-clad fiber increases, the trough of the resonant spectrum will gradually increase. That is, the length of the access DCF is inversely proportional to the free spectral range. With the increase of tensile force, the resonance spectrum is blue shift, and the tension sensitivity can be up to -1.87nm/mε.

In this paper, a simple structure, low-cost all-fiber laser self-mixing vibration sensing system is designed for monitoring the health status of thin-walled structures which are workpieces in machining, for resolving the interferential problems with the existing vibration measurement system, caused by the cruel environment such as electromagnetic interference, humidity. In this system, a distributed feedback all-fiber laser with ultra-short cavity length is used as the light source, and the real-time monitoring of vibration state of plate under different positions of forced vibration sources is observed. The experimental results show that when the forced vibration source located at the free end or the restricted end of the plate, the measurable self-mixing signals (signal-to-noise ratio up to 30dB) is available at any position. Moreover, it will help us to analysis the specification and the physical mechanism of the forced vibration, by studying this all-fiber laser self-mixing vibration sensor in detail.

Surface Plasmon resonance (SPR) technique is gradually growing as a research focus in optical area, which has been widely applied in many disciplines. The fiber-based SPR sensor, combining the advantages of fiber and SPR phenomenon, will lead to more tremendous application areas. The design and fabrication of different fiber SPR sensors are always be focuses of researchers in recent year, but the characteristic wavelength demodulation of the SPR sensor didn’t obtain enough attention. In this paper, the detection system for a fiber-based SPR sensor was presented first, and the detection mechanism of the refractive index sensing was obtained theoretically. Based on the theoretical simulation and analysis, the analytical expression of the all-phase low-pass filters was deduced, which is used for the de-noising of the original spectrum for the SPR sensing system, leading to resonance wavelength extraction only by calculating the derivative of the de-noised signal. So the resonance wavelength of the SPR sensor can be easily obtained by using this simple demodulation algorithm. Based on the realization of the system, the refractive index sensing of alcohol solution was carried out. And a good linear relationship between the refractive index of the solution and the characteristic wavelength of the SPR sensor can be obtained, with refractive index sensitivity and fitting error of 2048.5 nm/RIU and 5.69 nm respectively.

We demonstrate a high-sensitivity fiber-optic Fabry-Perot acoustic sensor based on a thin Parylene-C diaphragm. The vacuum thermal evaporation deposition method is used to fabricate the Parylene-C nanofilm, which possesses strong adhesion and good compactness. Based on these characteristics, the Parylene-C diaphragm is fabricated with 9 mm in diameter and 500 nm in thickness. The noise limited equivalent acoustic signal level is 33.5 μPa/Hz^1/2 at the frequency of 30 Hz. The pressure sensitivities of the acoustic sensor are more than 1000 mV/Pa at the frequency from 10 Hz to 30 Hz. The fundamental resonance frequency of the Parylene-C diaphragm is about 13 Hz. The acoustic sensor is applied in a multiple trace gas detection system based on photoacoustic spectroscopy. The detection limits of acetylene (C₂H₂), carbon monoxide (CO) and carbon dioxide (CO₂) are achieved to be 0.25, 0.32 and 1.1 parts-per-million, respectively.

A systematic error calibration method is presented to improve the measurement accuracy of lateral shearing interferometry (LSI). This method is used to remove the most significant errors: geometric optical path difference (OPD) and detector tilt error. Difference fronts in the 0° and 90° directions are used to reconstruct wavefront using difference Zernike polynomial fitting. And difference fronts in the 45° and 135° directions are also used to reconstruct wavefront. The coefficient differences between the reconstructed wavefront are generated from geometric OPD and detector tilt error. The relationship between Zernike coefficient differences and systematic parameters are presented based on shear matrix. Thus, the distance of diffracted light converging point (d) and detector tilt angle can be calculated from the coefficient difference. Based on the calculated d and detector tilt angle, the geometric OPD and detector-tilt induced systematic errors are removed and the measurement accuracy of LSI is improved.

Pipeline leakage is an important security issue, which directly affects the normal operation of life and production. The development of optical fiber sensing technology is fast and must be the trend of pipeline monitoring. The research of pipeline leak characteristics based on optical fiber monitoring data will become more and more important. This paper puts forward a series of characteristic indicators of pipeline leakage. The characteristics of gas pipeline leakage and liquid pipeline leakage are compared and analyzed, and the commonness and individuality of pipeline leakage are studied, whose researches are proved through practical experiments.

Fiber laser sensor based on multimode interference (MMI) effect can achieve high sensitivity with lower temperaturestrain cross sensitivity by designing optimally the MMI structure. An erbium-doped fiber laser for temperature, stress and refractive sensing based on single mode fiber spliced a short section of no-core fiber was proposed in this paper. The optical field characteristics of this MMI structure have been analyzed, indicating the spectral filtering effect existed. An erbium-doped fiber laser with the MMI structure inserted as the sensor element, the enhanced sensing sensitivity is achieved on the sensing experiments of ambient temperature, mechanical stress and liquid refractive index. The sensitivity of this MMI-based fiber laser sensor is up to 13.24 pm/°C with the measured range from 30 °C to 220 °C, 1.29pm/με from 0 to 7776.05με, 180.21nm/RIU from 1.34 to 1.42, respectively.

This paper illustrates the principle of several common distributed fiber sensing techniques, especially Brillouin optical time domain reflectometry (BOTDR) and optical time domain reflectometry (OTDR). By measuring the frequency shift of spontaneous Brillouin scattering light in fiber, BOTDR could simultaneously monitor both strain and temperature with a high spatial resolution. But the spontaneous Brillouin scattering signal is so weak that it has a high demand of the laser generator and the signal-to-noise ratio of the whole system. Therefore, the BOTDR system is usually too complex, expensive and difficult to be widely used. Unlike BOTDR, OTDR utilizes Rayleigh scattering to measure the loss of fiber. Rayleigh scattering signal is much stronger than spontaneous Brillouin scattering signal, thus OTDR system has the advantages of high sensitivity, long distance and relatively low price. These advantages make OTDR very suitable for wide application in the field of slope monitoring, especially in remote areas where the geographical environment is complex and are difficult for staff to stay.

This paper designed and implemented a slope monitoring and warning system based on the technology of optical time domain reflectometry(OTDR). The test result shows that the system has high sensitivity, strong real-time and provides user friendly interface.

The 16-channel multi-longitudinal mode fiber laser sensor array is investigated experimentally by the wavelength/frequency division multiplexing technique. In the proposed sensing system, a 4×4 sensor array is established by a few different coupling-ratio couplers, and four different fiber Bragg gratings (FBG) with different center wavelengths are used as four different sensing units. In each sensor unit, four parallel fiber laser sensors have the same operating wavelengths FBGs, but their effective laser cavity lengths slightly different from each other. Every cavity is formed by a fiber Bragg grating (FBG) serving as one reflection mirror, a piece of erbium-doped fiber (EDF) acting as the gain medium, and a Faraday rotator mirror (FRM) serving as other reflection mirror. When the pump power is higher than threshold value, the 16-channel fiber laser sensor array is stimulated stably. The frequency of the beat signal of the fiber laser sensor with different cavity lengths is used to realize frequency division multiplexing, and the wavelength division multiplexing is realized according to the operation wavelength of the fiber laser. The beat frequency signals are generated on a photodetector(PD), and monitored by a frequency spectrum analyzer(FSA). By tracking the shift of the beat frequency, all of the 16 laser sensors can be demodulated and real-time discriminated. The result of the experiment shows that different channels can be demodulated independently. The applications of the sensor array for strain and temperature measurements are also investigated. The strain or temperature information can be extracted from the change of the beat frequency signals according to the wavelength-frequency division multiplexing and the beat signal demodulation. The proposed hybrid multiplexing system can greatly reduce the weight, volume, and cost of the fiber laser sensors system while increasing the amount of the sensors multiplexable, which making it very competitive in some applications fields requiring large scale arrays such as space vehicles, marine infrastructure systems and constructional engineering.

Aiming at the low-speed impact load localization and vibration testing requirements of aerospace composite flexible structure, The Fiber Bragg Grating sensor network monitoring system is established. The increasing sampling technique is used to process the impact response signal, then the generalized cross-correlation delay estimation method is used to extract the time difference relationship between the sensor response signals. On this basis, the rapid identification of the impact position of the composite flexible structure is realized by considering the position information of the sensor comprehensively. The experimental results show that the area of six impact sample points and the specific coordinates of the location can be accurately identify respectively by this method. The average error of the coordinate positioning is about 3cm. The self-vibration mode and the natural frequency of the composite structure are achieved by using Fiber Bragg Grating sensor network monitoring system simultaneously. The finite element model of the composite structure with triangular section is established by using Patran. The natural frequency of the simulation is in good agreement with the experimental result, which proves that the Fiber Bragg Grating sensor has good vibration test performance.

In this paper, the vibration performance and damage types of carbon fiber composite materials were investigated based on FBG sensing technology. The free end of a carbon fiber composite cantilever beam was hit by a falling ball to generate a resonance in the cantilever. The resonance frequency was measured and the damping loss factor was calculated based on which the vibration characteristic of the carbon fiber composite was analyzed. After that, a man-made damage (a small hole) was introduced into the cantilever and the resonance frequency was measured again. The result was compared with the frequency without damage, so that the damage type could be judged. The result provides a reference to the study of the vibration performance and damage monitoring of carbon fiber composite materials.

Due to some limitations of traditional methods about oil temperature and level monitoring in transformer conservators, an intelligent monitoring system based on fiber Bragg grating sensors to monitor the change of oil temperature and level in transformer is proposed in this paper. This system is composed of five parts: fiber Bragg grating sensors, sensor data processing and storage, intelligent evaluation of the characteristic information of the transformer, cooperation of the monitoring and evaluation results. The oil level sensor is composed of a fiber Bragg grating sensor and a C-type spring tube, and the oil level can be monitored by the relationship between pressure and height of the liquid pressure. This method can improve the stable operation reliability of the transformer without electricity detection. The experimental results show that the central wavelength of the fiber Bragg grating sensor changes linearly with the oil temperature and level in the transformer. The intelligent monitoring system can be achieved in high voltage, electromagnetic interference and other complex environments without electricity detection, which can greatly improve the safety and reliability of the transformer.

Fano resonance is investigated by finite element method in plasmonic waveguide system which comprise a stub and a side coupled split ring resonator. We show that Fano resonance wavelength has a linear relation with refractive index of the material. Based on the sensitivity to the circumstance, a high performance refractive index sensor is proposed. This sensor can take advantage of easy on-chip integration of SPPs and high sensitivity of Fano resonance. This work may provide guidance for the design of on-chip nanosensors and other applications in integrated optical circuit.

A novel fiber-optic Fabry–Perot accelerometer (FOFPA) based on a spherical air bubble cavity is demonstrated. The cavity is fabricated by corroding a fiber end to form a groove and then arc discharging several times to form a spherical bubble. The bubble diameter and wall thickness are about 130 μm and 5 μm, respectively. Experimental results show that the resonance frequency of the accelerometer is 1520 Hz, the signal to noise ratio (SNR) is 40 dB at 706 Hz under 2 mg acceleration excitation, the voltage sensitivity is 14.16 V/g, and the minimum detectable acceleration of the measuring system is 20 μg/sqrt Hz at 706 Hz. Moreover, the accelerometer has a very low temperature sensitivity of 1.7 pm/°C, which means that FOFPA is basically immune to environmental temperature variation. Thus with advantages of miniaturization and simple structure, the FOFPA can be applied widely in the field of vibration measurements.

The phase-shifted sensitivity of an interferometer can be enhanced by increasing the group index. In this paper, we experimentally demonstrate a slow light sensor by placing an active fiber Bragg grating (FBG) in one arm of the Michelson’s interferometer. A 25 KHz AC voltage was applied to a piezoelectric (PZT) set nearby the active FBG. Once the wavelength is varied to near the FBG band edge, the maximum phase-shifted amplitude appears, which is about 1.8 rad and is 4 times greater than that when wavelength is near the center of the reflection band. The active FBG is pumped by a 980 nm laser diode, which can help us to stabilize the system works in the slow light regime to obtain the maximum phase shift. It provides a very simple approach to increase the phase-shifted sensitivity, which is likely to have important applications for strain and acoustic sensors.

An improved fiber sensor consisting of a fiber Bragg grating (FBG) and an extrinsic Fabry-Perot interferometric (EFPI) sensor is proposed. The interferometric cavity of the improved sensor is composed of a glass capillary tube and two sections of single-mode fiber (SMF), the segment near one of the SMF’s end faces has a FBG. One of the two aligned SMFs is free along the axial direction in the testing specimen, which is different from the traditional structure. During the cryogenic test, only the glass tube and the free SMF with a FBG which exposed outside the glass tube part will be encapsulated by cryogenic adhesives on the testing oxygen-free copper specimen. The temperature and strain performance of the testing oxygen-free copper specimen were studied at high vacuums and low temperatures range 273 K to 30 K. The testing result was agreed well with the theoretical values. The improved sensor is compact, easy in fabrication and has high potentials in cryogenic temperature applications.