This PDF file contains the front matter associated with SPIE Proceedings Volume 11607, including the Title Page, Copyright information, and Table of Contents

A unique multi-parameter sensor for distributed measurement of temperature and strain based on spontaneous Brillouin scattering in communication optical fiber is proposed, which is an excellent candidate for the crosstalk effects in conventional Brillouin sensing network. In experimental section, the discrimination of strain and temperature is successfully demonstrated by analyzing the unequal sensing coefficients of the Brillouin frequency shifts generated by different acoustic modes. The Brillouin frequency shifts of first two three peaks are successfully measured to discriminate the strain and temperature with an accuracy 19.48με and 0.93°C in 10km sensing range. The proposed distributed Brillouin optical fiber sensor allows simultaneously temperature and strain measurement, thus opening a door for practical application such as smart grid.

In practical application, it is found that single-path phase-sensitive optical time-domain reflectometers (φ-OTDR) is susceptible to noise and random interference, which increases the probability of missing detection over external perturbations by conventional amplitude demodulation. In the work, a dual-channel system based on two fibers extracted from an armored four-core cable is investigated to enhance the robustness of the φ-OTDR. In signal demodulation, by combining the conventional differential accumulation algorithm (DAA) and standard deviation algorithm (SVA) a multipath information fusion algorithm (MIFA) is accordingly proposed to conclude whether the vibration signal is present. The MIFA-based dual-channel φ-OTDR is experimentally demonstrated on a highway of 9 km to position a running vehicle, indicating a considerable performance improvement of vibration identification compared to the DAA and SVA.

Optical frequency-domain reflectance (OFDR) has been widely used in vibration measurement due to its unique advantages over optical time-domain reflectometry (OTDR). It should be noted that, however, OFDR requires long measurement time and shows poor sensitivity when applied to measure vibration signal over long distance. In the work, an algorithm is presented to automatically detect and locate the vibration signals. Firstly, we perform cross-correlation analysis in a moving window between the beating signals without and with vibration, and find the maximum cross-correlation coefficients in all windows to reconstruct them into a cross-correlation curve. Secondly, an automatic decision threshold curve is designed to conclude whether there is any vibration over the sensing fiber. Lastly, the cross-correlation curve is compared with the threshold to locate the vibration. We experimentally test the algorithm in an OFDR system and locate a PZT vibration at 26.96 km, which demonstrates its validity in terms of detecting external disturbances over a relative long distance.

This paper proposed and demonstrated a novel distributed optical fiber vibration sensor with high sensitivity and high accuracy based on time delay estimation. The light source is divided into two wavelength bands by a wavelength division multiplexer to form two Sagnac interferometers. The dual Sagnac interferometer can detect the interference signals of different bands modulated by the same disturbance, and then obtain the corresponding phase difference by demodulating the interference signals. Based on the time delay estimation algorithm, the phase difference is used to construct two composite signals with time delay, and then the time delay is extracted by cross-correlation to determine the location of vibration. A positioning software is developed based on LabVIEW. Through the vibration simulation experiment driven by piezoelectric transducer (PZT), it is proved that the sensor can realize the disturbance positioning above 400 Hz. The experimental results show that the sensing distance of the sensor can reach 100 km, and the positioning error is within ± 30 m. It can be widely used in long-distance perimeter security

The characteristics of bi-periodic sensitivity of semiconductor laser and its application in the incoherent light detection sensor are studied. From the simulation results, it can be found that the unmoving point of an optoelectronic time-delay feedback semiconductor laser shifts when there is external light injection, two unmoving points are conduced to show, and implies high instability dynamics existing in the system. So the external light injection will inevitably result in destructing the referent laser state condition and changing the state, thus the incoherent light intensity change can be monitored via detecting the referent state change. In this paper, a bi-periodic optical pulse is generated by the optoelectronic time-delay feedback semiconductor laser, and the bi-periodic laser system is used as a sensor for incoherent light detection. A bi-periodic state in the laser is a highly unstable nonlinear dynamic state, it is very sensitive to external conditions and influences. When a beam of external incoherent light enters into the bi-periodic laser sensor, it will inevitably lead to the destruction of the bi-periodic state condition and the state variation. A novel bi-periodic laser incoherent light detection sensor is proposed based on the above principle. By using this sensor, the injected incoherent light can be used as the sensor's recognition signal, and by detecting the change of the laser output behavior, the external incoherent light intensity can be measured. The simulation results show that the sensor has high ability to recognize the injected incoherent light and can measure it accurately. The results of the proposed sensor are quite useful for the research of new laser sensor and application of photoelectric detection technology

A distributed optical fiber pressure sensor based on Brillouin scattering technique is proposed and experimentally demonstrated, where double-layer polymer coatings are used on the single-mode fibers (SMF) to improve the Brillouin frequency shift (BFS) pressure sensitivity. The single-coated and double-coated fibers are designed to demonstrate their BFS pressure sensitivity, where the outer coating radius of double-coated fibers are 450 μm, 1000 μm and 1500 μm, respectively. Experimental results show that the BFS pressure sensitivity are -0.74 MHz/MPa, -1.61 MHz/MPa, -2.59 MHz/MPa and -3.51 MHz/MPa in the pressure range of 0-30 MPa for above four kinds of fibers. According to the experimental results, it can be concluded that the BFS pressure sensitivity can be improved with increasing of outer coating radius or decreasing of outer coating Young's modulus and Poisson's ratio. The maximum BFS pressure sensitivity is measured about 5 times higher than single-coated SMF, it is of great significance for SMF to be used in practical distributed pressure measurement.

A novel hybrid BOTDR and Φ-OTDR system for simultaneous static and dynamic measurements is proposed. Employing the division of both backscattering light and local light, a double coherent detection configuration is achieved to extend the sensing range and demodulate the phase quantitively. With the independent detection of Brillouin scattering light and Rayleigh scattering light, the demodulation error in BOTDR is avoided while the signal-to-noise ratio of Φ-OTDR is enhanced. Experiment for simultaneously measuring temperature and vibration is carried out, which proves the sensing range of the hybrid system is 49.5km with 20m spatial resolution. The measurement uncertainty of BOTDR is verified to be 2.821MHz, and the maximum frequency response range of Φ-OTDR is 900Hz. Experimental results indicate the proposed system is specialized in dealing with both static and dynamic situations simultaneously.

In this paper, the composite interferometric distributed optical fiber vibration sensing technology based on a two-path unbalanced Mach-Zehnder/Sagnac linear interferometric structure is proposed. Firstly, the laser interference mechanism and vibration positioning principle of this system are theoretically analyzed, and the vibration positioning algorithm with the time-delay estimation based on the improved generalized cross-correlation principle is proposed. Secondly, the experimental system is built and double photodetectors are used to obtain the two-path interferometric signal with a certain time delay, and the high-precision time delay signal is obtained with the help of conjugate multiplication and digital filtering algorithm. The experimental results show that the system can accurately locate different types of vibration signals with a 65 km sensing fiber, and the location limitation of broadband vibration signals for a single-channel interferometric structure can be resolved. This system is expected to be popularized and applied in fields such as leakage monitoring of coalbed methane pipelines.

Four kinds of passive phase demodulation algorithms based on 3×3 couplers are introduced and analyzed in this paper. The performance of these algorithms in noisy environment are theoretically investigated and simulation under five conditions including ideal situation, amplitude noise, phase noise, coupler asymmetry, and weak signal is employed. The proposed arctangent scheme utilizing three outputs is designed and implemented in hardware system based on programmable logic devices and high speed digital-to-analog converters. The performance of the proposed hardware scheme is verified experimentally by applying into the optical fiber interference system.

In view of the limitations of the traditional Brillouin optical time domain analysis (BOTDA) system such as low sampling rate, large transmission and storage space, a fast BOTDA scheme based on compressed sensing technology has been proposed to realize the random frequency sampling of Brillouin gain spectrum (BGS). The proposed scheme uses a data-adaptive sparse base obtained by the principle component analysis algorithm to realize the sparse representation of Brillouin spectrum. Then, it can be reconstructed successfully with orthogonal matching-pursuit algorithm. Compared with the traditional uniform spectrum sampling with a step size of 4 MHz, the proposed compressed sampling scheme can recover the BGS using 30% of the frequency. With fewer sampling frequencies, compressed sensing technology can improve the sensing performance of traditional fast BOTDA, including increasing the sampling rate by 3.3 times and reducing the amount of data storage by 70%.

In this paper, we analyzed the Brillouin scattering characteristics in micro-nano fibers. According to the elastic mechanics equation and the Helmholtz equation, the mathematical model of the acoustic wave field and the optical field in the cylindrical waveguide with the sub-wavelength scale were established. According to the relationship between intrinsic acoustic mode and dispersion, the mechanism of Brillouin scattering in micro-nano fiber was analyzed. Considering the effects of electrostriction and radiation pressure comprehensively, the influence of two main physical effects, photo-elastic effect and moving-boundary effect on Brillouin gain in the process of acousto-optic coupling was studied. On this basis, the influence of the structure, material, and size of the micro-nano fiber on the Brillouin frequency shift and gain was analyzed and verified experimentally by Brillouin optical correlation domain analysis.

A novel demodulation method for the sensing system based on an identical weak fiber Bragg grating (IWFBG) array is proposed in this paper. With the help of a wavelength-swept laser, the reflection spectrum and transmission spectrum of an FBG can be mapped into two pulse signals with opposite polarity in time domain, both of which contain the wavelength information of the FBG. Therefore, improved signal intensity and sensing performance can be obtained when the reflection and transmission spectra of the FBG are both adopted for demodulation. A simulation has been done to a quasi-distributed sensing system based on the IWFBG array. The results show that the improvement of the signal intensity is related to the number of the FBGs with the same center Bragg wavelength. The location of the event is realized through the intensity comparison of the pulse signals, and the wavelength change of the FBG can be directly obtained by monitoring the time delay difference between the reference pulse and the sensing pulse.

Partial discharge is a common insulation fault problem in power system. It will concomitance have ultraviolet light, infrared light, visible light, and local temperature rise. Accordingly, Partial discharge detection based on optical fiber ultraviolet sensing technology can be an effective and feasible insulation fault diagnosis scheme applied to power system. ZnO-nanorods have great development potential in ultraviolet detection due to its high exciton binding energy. From the three parties of controllable preparation of nanometer ZnO material, preparation of optical fiber ultraviolet sensing unit and design of optical path structure, this paper combines theoretical analysis method with experimental analysis method to give a deep analysis. Take advantage of the excellent sensing characteristics of micro-nano fiber, we proposed and designed a FLRD(Fiber Loop Ring Down)-based optical fiber ultraviolet sensing system used for partial discharge diagnosis. It can achieve a high sensitivity of 37.57 ns/nWcm⁻² for ultraviolet sensing ranging from 3.18mWcm^-2 to 9.55mWcm^-2. Compared to existing ZnO UV detectors, the proposed system has advantage of simple to make, resist the influence of light source fluctuation, higher stability, higher sensitivity, and also it can realize long range detection. It provides a novel and effective reference for the research of fiber-based partial discharge detection in the electrical field.

Nowadays, Microwave photonics has been extensively studied. Microwave photonic filter(MPF) is a new method in recent years that is widely used in optical sensing, which is a new method developed in recent years. In microwave photonic sensing technology, microwave photonic interference is the key method. In this experiment, the microwave photonic interference technology is used to complete the identification of different types of fiber connector, which can be identify optical fiber connectorr or certain types of optical devices in the optical fiber sensing link. MPF is formed by Mach-Zehnder interferometer(MZI) composed of coupler and optical fiber. People usually use the optical path differences between the upper and lower arms to form microwave photon interferometer for optical sensing. We form the optical path difference by adding optical fibers of different lengths. The formation of MPF is due to the interference of light modulated by the microwave signal interferometer. We has found that the different fiber connector of the optical fiber also have a greater impact on the performance of the microwave photonic filter. This paper selects the optical fiber of 3 meter with different fiber connectors, and measures optical power and radio frequency intensity at different temperature. This paper mainly discusses the differences of different connectors of the fiber and the microwave photonic sensing at different temperatures.

Submarine optical cables placed on the seabed are easily to suffer from damage and interference in submarine environment. In order to ensure the safety of submarine optical cable, distribution fiber-optic sensing technology is used for submarine optical cable safety monitoring. In the method, long submarine optical cables firstly are divided into several parts, then optical signals and ambient sounds in each part are collected and analyzed, finally the interference types and sources are judged based on signal above through the system host. Fiber optic sensing methods, which is mainly divided into scattering fiber optic sensing and reflective grating sensing, will affect the effectiveness of submarine optical cable safety monitoring greatly. Common scattering optical fiber sensing methods include optical time domain reflection (OTDR), polarized optical time domain reflection (POTDR), phase-sensitive optical time domain reflection (Phase-OTDR) and Brillouin optical time domain reflection (BOTDR), which all have the disadvantages of short range, low resolution. Reflective grating sensing for monitoring requires a large signal bandwidth and is costly. Consequently, a novel sensing method is proposed in this paper, which combines multiple sensing techniques such as Phase-OTDR, POTDR and BOTDR with frequency division multiplexing (FDM), wavelength division multiplexing (WDM) and time division multiplexing (TDM).

Fiber optic distributed acoustic sensing (DAS) is a novel technology for seismic data acquisition and particular suitable for vertical seismic profiling, near surface structure imaging and natural seismic monitoring. In this paper, a series of field trials verifying the performance of DAS for detecting marine seismic data are conducted in the geological condition of lagoon. The results show DAS can detect surface waves and longitudinal waves generated by artificial earthquake, and the surface waves have higher main frequency and wider bandwidth and the wave field information of seismic data is more abundant compared to geophone under the same source and the same offset condition.

With the development of offshore wind power generation technology, the power of wind turbine is increasing, and the bearing capacity of pile foundation is very important to the safety of fan operation. In order to ensure safe and reliable operation of the fan, it is necessary to carry out load test on the pile foundation in advance so as to detect/check its relevant performance parameters. In this paper, we set up a Brillouin optical time domain reflectometry (BOTDR) system with 1m spatial resolution to measure the strain of the pile foundation of the offshore wind generator through horizontal loading test. From the experimental data collected from the test, the strain distribution of the pile foundation under horizontal load can be obtained. Meanwhile, by analyzing the relationship between the horizontal load and the maximum strain, the horizontal bearing capacity of the pile foundation can exceed the expected maximum load of 700kN. According to the test results, we believe that the technique of BOTDR can be used for detection of offshore wind generator pile foundation.

A novel pattern recognition method based on relevant vector machine for optical fiber vibration sensor is proposed to meet the requirement of accurate identification of long-distance pipeline leakage. The sensing system is based on Sagnac interferometer, which is suitable for vibration signal detection. The initial vibration signals are firstly pretreated by the wavelet de-noising method. Then, the wavelet decomposition algorithm is utilized to obtain decomposition coefficients at all levels to build feature vectors. Furthermore, the relevant vector machine is presented as a classifier to identify three types of vibration signals, including pipeline leakage, human tapping and human walking. Experimental results demonstrate that the proposed method can discriminate three threat events with an average recognition rate above 85% with a 4-km-long sensing fiber, which can satisfy actual application requirements.

The security pre-warning system of underground pipelines was traditionally designed by electronic sensors, usually suffering from intrinsic flawssuch as too scattered monitoring points and poor anti-interference performance. To overcome these disadvantages, a distributed optical fiber temperature and strain sensing system based on Brillouin Optical Time Domain Reflectometer (BOTDR) is designed and developed for underground pipelines security monitoring. In this paper, the sensing mechanism of temperature and strain sensing is analyzed and a BOTDR experimental scheme is presented. Meanwhile, the kernel software program is developed for signal demodulation. Then, the integrated BOTDR instrument is designed compactly and evaluated by temperature and strain measurement experiments, for respectively simulating pipeline leakage and deformation. The experimental results show that the sensing range of 10.268 km is achieved with a spatial resolution of 1.15 m. The nonlinear error is less than 1% FSS over the temperature and strain change of 30~90°C and 0-15000με.

Brillouin optical time domain reflectometer (BOTDR) has attracted extensive attention due to its advantages of one-end access and long-distance measurement. The measurement accuracy and sensing range of BOTDR are affected by the system signal-to-noise ratio (SNR), which is closely related to the characteristics of the probe light pulse. In this paper, the influence of two characteristics of probe light on SNR is theoretically analyzed and experimentally verified, including the extinction ratio (ER) and peak power. Firstly, the theoretical model of probe pulse extinction ratio (ER) and SNR in the BOTDR is established, and the SNR distribution versus different ER is analyzed. Both numerical simulation and experimental verification show that the SNR was enhanced with the increase of ER. Besides, the SNRs under different pulse peak power are also evaluated. The experimental results show that the SNR increases along with the peak power at the beginning but decreases when the peak power exceed a certain value. The research results provide a reference for selecting the appropriate probe pulse features in BOTDR for higher SNR.

Phase-sensitive optical time-domain reflectometry (φ-OTDR) has been widely used in many situations. In order to simplify the system structure and reduce costs, a new phase demodulation method is developed for φ-OTDR based on coherent detection. It works by extracting the time domain signals at two points in the disturbance area, and that could construct a pair of IQ component containing the disturbance phase information. Compared with most commonly used digital quadrature demodulation, the digital coherent signal is not required. And the need for high speed sampling frequency is reduced. The PZT induced vibration is applied to a certain section of fiber, which is used to introduce phase disturbance. Experimental results show that the phase change caused by external disturbance can be successfully demodulated in a sensing fiber of 22km, and a simple system structure is realized. When the central frequency of the beat signal is 200 MHz, the need for sampling rate can be reduced to 156MSa/s or less. Amplitude modulated disturbance tests show a reasonable linear response of the system with the R-square of 0.963.

The recognition of vehicle load in motion has always been an important problem to be solved in pavement. In this paper, an improved fiber Bragg grating (FBG) based sensor has been developed to measure the vehicle load transferred pressure in the asphalt pavement structures. Cyclic loading tests have been conducted to calibrate the structural and sensing properties of the FBG sensors. The proposed sensors have been further used in ZhangBian highway to measure the vehicle load induced pressures in asphalt pavement. The results indicate that the improved sensors own high survival rate to resist the harsh construction condition in pavements and the quick recovery speed validates the feasibility of the proposed sensors to recognize the vehicle load in motion.

In order to solve the problem that traditional piezoelectric sensors (PZT) cannot be implanted into the material to monitor the internal sound field transmission of the material, an unbalanced Michelson interferometer is used to build an acoustic signal based on a phase shift fiber Bragg grating (PSFBG) Monitoring system, carried out acoustic signal transmission detection experiment, compared the signal characteristics of PSFBG and PZT two sensors; and studied the sensitivity and temperature stability of PSFBG signal. The results show that the sensitivity of PSFBG is higher than that of the commercial R15a acoustic emission PZT sensor, and the volume is much smaller than that of PZT. It can be applied to the detection of sound field transmission inside the material; it can work stably under a wide temperature threshold (- 20°C ~80°C) environment, with amplitude variation not more than 5%; The self-built PSFBG demodulation system is used to measure the acoustic signal in real time.