WO2017107657A1 - 一种基于非对称双Mach-Zehnder干涉的分布式光纤扰动定位系统及其定位方法 - Google Patents

一种基于非对称双Mach-Zehnder干涉的分布式光纤扰动定位系统及其定位方法 Download PDF

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WO2017107657A1
WO2017107657A1 PCT/CN2016/103521 CN2016103521W WO2017107657A1 WO 2017107657 A1 WO2017107657 A1 WO 2017107657A1 CN 2016103521 W CN2016103521 W CN 2016103521W WO 2017107657 A1 WO2017107657 A1 WO 2017107657A1
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disturbance
signal
time
frequency
light source
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刘琨
刘铁根
江俊峰
马春宇
柴天娇
何畅
田苗
李志辰
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Tianjin University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • G01D5/35329—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using interferometer with two arms in transmission, e.g. Mach-Zender interferometer
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
    • G08B13/181—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems
    • G08B13/183—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier
    • G08B13/186—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier using light guides, e.g. optical fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • G01D5/35335—Aspects of emitters or receivers used by an interferometer in an optical fibre sensor arrangement
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
    • G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors

Definitions

  • the invention belongs to the field of sensing and detecting technology, and particularly relates to a distributed optical fiber disturbance sensing positioning system based on asymmetric interference.
  • the Mach-Zehnder distributed optical fiber perturbation sensing system uses optical wave interference technology to realize intrusion detection and localization, with long-distance monitoring, high-precision positioning, low energy dependence, high environmental tolerance, Anti-electromagnetic interference, corrosion resistance and other characteristics.
  • Shangran Xie, et, al. Positioning error prediction theory for dual Mach-Zehnder interferometric vibration sensor, Journal of Lightwave Technology, 2011, 29: 362-368 analyzed the accuracy of various noises in the system. Influence and predict the system positioning accuracy under different SNR. Qinnan Chen, et, al.
  • the positioning accuracy of the dual Mach-Zehnder distributed optical fiber perturbation sensing system can reach 20m (sampling rate 10MS/s, theoretical precision is 10m).
  • the influence of backscattering noise on the signal-to-noise ratio of the system becomes more and more obvious, which seriously affects the positioning accuracy of the system and limits the sensing distance of the system.
  • the object of the present invention is to solve the problem that the dual Mach-Zehnder distributed optical fiber disturbance sensing system has a low signal-to-noise ratio when the sensing distance is long due to the backscattering effect, and proposes an asymmetric double Mach-Zehnder distributed optical fiber. Disturbance sensing system.
  • the system uses the optical filtering method to eliminate the influence of the backscattered light of the fiber on the signal, and greatly improves the signal-to-noise ratio of the system in long-distance applications.
  • a distributed optical fiber disturbance localization system based on asymmetric double Mach-Zehnder interference characterized in that the system comprises:
  • DFBs distributed feedback lasers
  • DWDM dense wavelength division multiplexer
  • Optical circulator used to transmit the light emitted by the light source to the object to be detected and collect the reflected signal light;
  • DWDM Two commercial single-channel DWDMs with a working wavelength of around 1500 nm, the spectral transmission range only includes The wavelength of a light source used by the system;
  • Photodetector Indium gallium arsenide photodetector (PD), receiving optical signals, performing photoelectric conversion and amplification;
  • Fiber coupler 3dB fiber coupler for 1:2 splitting
  • Polarization controller adjust the polarization state of the two interfering signals to ensure signal visibility
  • Sensing cable G.652D communication cable for sensing external disturbances and conducting optical signals
  • the sampling rate is 10MS/s dual channel data acquisition card (DAQ), and the voltage signals of the two photodetectors are collected and sent to the computer for processing;
  • DAQ dual channel data acquisition card
  • Processing unit including a general-purpose computer and an embedded computing system, the interference signal received by the acquisition card is processed to finally obtain the disturbance information.
  • the backscattered light filtering device composed of the light source and the corresponding DWDM is a combination of an arbitrary wavelength light source and an optical filter.
  • a fiber coupler is used instead of the optical circulator.
  • the present invention also provides a positioning method that can be applied to the above system, and obtains a time-frequency distribution of a perturbed frame signal by using a time-frequency analysis method based on a short-term average frequency, and performs a point near the maximum point of the frequency as an effective signal segment. Correlation delay estimation, obtain the delay d, and then obtain the disturbance position x.
  • the specific algorithm flow is as follows:
  • the time-frequency distribution curve of the disturbance signal in the method is obtained by any other time-frequency analysis method to obtain a time-frequency distribution curve of the disturbance signal, and then the cross-correlation is performed to obtain the time delay d, thereby obtaining the disturbance position x.
  • the invention has the beneficial effects that, unlike the conventional dual Mach-Zehnder distributed optical fiber disturbance sensing system, the system of the invention uses two narrowband light sources and a corresponding dense wavelength division multiplexer (DWDM) is added in front of the detector.
  • DWDM dense wavelength division multiplexer
  • the backscattered noise of the fiber is greatly filtered out, and the problem that the signal to noise ratio is too low when the sensing distance is long due to the backscattering effect is solved.
  • the positioning method that can be used in the above system is obtained by using a fast time-frequency analysis method based on short-term average frequency to obtain the time-frequency distribution of the perturbed frame signal, and the point near the maximum frequency point is used as the effective signal segment for cross-correlation delay estimation. The delay is obtained, and the disturbance position is obtained.
  • the method can locate the asymmetric disturbance signal in the system and has high positioning accuracy and stability.
  • FIG. 1 is a schematic diagram of a positioning of a distributed optical fiber disturbance positioning system
  • FIG. 2 is a schematic diagram of a distributed optical fiber disturbance positioning system
  • Figure 3 is an original signal diagram of the disturbance signal
  • Figure 4 is a time-frequency distribution diagram of the disturbance signal
  • the principle of the distributed optical fiber sensing system based on the asymmetric double Mach-Zehnder interference principle is shown in Fig. 1.
  • the two lights emitted by the light source 1 and the light source 2 propagate in the clockwise and counterclockwise directions respectively in the sensing loop. And the interference occurs at the opposite coupler.
  • the light propagation path emitted by the light source 1 is C1-PC1-C2-C3-C4-DWDM2-PD2.
  • the light propagation path emitted by the light source 2 is C4-PC2-C3-C2-C1-DWDM1-PD1.
  • C1 and C4 are circulators
  • C2 and C3 are 3dB couplers
  • PC1 and PC2 are polarization controllers
  • DWDM1 and DWDM2 are dense wavelength division multiplexers
  • PD1 and PD2 are photodetectors.
  • the present invention also provides a high precision positioning method based on the above system:
  • the delay d is estimated by performing cross-correlation operation on two interfering signals.
  • the two interference signals detected by the detectors PD1 and PD2 are inconsistent and cannot be directly correlated. Delay estimate. These two interference signals can be expressed as:
  • I 1 (t) and I 2 (t) are the two-way interference signal intensity
  • ⁇ 1 and ⁇ 2 are the wavelengths of the light source 1 and the light source 2, respectively
  • f(t) is the change of the optical path difference caused by the disturbance.
  • ⁇ 1 and ⁇ 2 are initial phase differences
  • n 1 (t) and n 2 (t) are respective circuit noises.
  • the frequencies of I 1 (t) and I 2 (t) are proportional to f(t) and f(td), respectively. Therefore, in order to obtain the delay d, the time-frequency distribution of the two signals can be obtained first, and then the time-frequency distribution of the two signals is normalized and cross-correlated.
  • Embodiment 1 Distributed Optical Fiber Disturbance Sensing System for Positioning
  • light source a wavelength bandwidth of a densely distributed wavelength division multiplexer (DWDM) in a narrow bandwidth distributed feedback laser (DFB) with a wavelength of 1550 nm or less;
  • DWDM densely distributed wavelength division multiplexer
  • DFB narrow bandwidth distributed feedback laser
  • optical circulator used to transmit the light emitted by the light source to the object to be detected and collect the reflected signal light.
  • the fiber coupler can be used instead;
  • 3a, 3b, DWDM commercial single-channel DWDM near the operating wavelength of 1500nm, wherein the spectral transmission range of 3a includes the center wavelength of the light source 1b, and the spectral transmission range of 3b includes the central wavelength of the light source 1a;
  • photodetector Indium gallium arsenide photodetector (PD), receiving optical signals, photoelectric conversion and amplification.
  • PD Indium gallium arsenide photodetector
  • polarization controller adjust the polarization state of the two interference signals to ensure the visibility of the signal.
  • sensing cable G.652D communication cable for sensing external disturbances and conducting optical signals;
  • data acquisition card sampling rate of 10MS / s dual-channel data acquisition card (DAQ)
  • DAQ dual-channel data acquisition card
  • Processing unit including a general-purpose computer and an embedded computing system, processing the interference signal received by the acquisition card, and finally obtaining the disturbance information.
  • Embodiment 2 Distributed optical fiber sensing localization algorithm based on zero-crossing rate analysis
  • the data acquisition card collects two signals and sends the signals to the computer.
  • the time-frequency analysis of the perturbed frame signal is obtained by the computer based on the time-frequency analysis method of the short-term average frequency, and the point near the maximum point of the frequency is used as the effective signal segment for cross-correlation delay estimation.
  • the parameters of the system are set as follows: the total length of the sensing fiber is 61km, of which 1km is armored cable, and the remaining 60km is bare fiber.
  • the wavelengths of light source 1a and light source 1b are 1555.74nm and 1549.95nm, respectively, and the power is 10mW.
  • the center wavelengths of the DWDMs are 1550.12 nm and 1550.92 nm, respectively, and the bandwidth is ⁇ 0.22 nm.
  • the sampling frequency of the acquisition card is 10 M/s, the sampling time is 0.3 s, and the sampling time corresponding to the effective signal points is set to 0.02 s.
  • the cable is struck at 800m of the cable.
  • the original signal collected by the system is shown in Figure 3. It can be seen that the two signals in the dotted line and the solid line have a high signal-to-noise ratio, and there is an obvious time between the two signals. Delay.
  • Figure 4 is a time-frequency distribution diagram of the signal. It can be found that the two time-frequency distribution curves of the solid line of the dotted line are basically the same, so the delay can be obtained by cross-correlation.
  • the probability of positioning error within 50 m is 80%, and the mean square error is 42.25 m. With high positioning accuracy and reliability.

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Abstract

一种基于非对称双Mach-Zehnder干涉的分布式光纤扰动定位系统，与传统的双Mach-Zehnder分布式光纤扰动传感系统不同，该系统使用两个窄带光源(1a，1b)和在探测器（4a，4b）前加入了相应的密集波分复用器DWDM（3a，3b），能够滤除光纤背向散射噪声，解决由于背向散射影响在传感距离较长时信噪比过低的问题。一种能够用于以上系统的定位方法，该方法利用基于短时平均频率的快速时频分析方法得到扰动帧信号的时频分布，并将频率最大点附近的点作为有效信号段进行互相关时延估计求得时延，进而获得扰动位置。该方法能够对系统中非对称扰动信号进行定位，具有较高的定位精度和稳定性。

Description

一种基于非对称双Mach-Zehnder干涉的分布式光纤扰动定位系统及其定位方法 技术领域
本发明属于传感及检测技术领域，特别涉及一种基于非对称干涉的分布式光纤扰动传感定位系统。
背景技术
双马赫-曾德(Mach-Zehnder)型分布式光纤扰动传感系统采用光波干涉技术实现入侵扰动检测及定位，具有长距离监控、高精度定位功能、低能源依赖性、高环境耐受性、抗电磁干扰、抗腐蚀等特性。近年来，谢尚然等(Shangran Xie,et,al.Positioning error prediction theory for dual Mach-Zehnder interferometric vibration sensor,Journal of Lightwave Technology,2011,29:362-368)分析了系统中多种噪声对定位精度的影响，并对不同信噪比下的系统定位精度进行预测。陈沁楠等(Qinnan Chen,et,al.An Elimination Method of Polarization-Induced Phase Shift and Fading in Dual Mach-Zehnder Interferometry Disturbance Sensing System,Journal of Lightwave Technology,2013,31:3135-3141)通过高效偏振控制方法对系统中偏振噪声进行补偿，提高了系统定位精度。黄翔东等(Xiangdong Huang,et,al.Configurable Filter-Based Endpoint Detection in DMZI Vibration System,Photoics Technology Letters,2014,26:1956-1959)利用全相位滤波器对扰动起始点准确定位。
目前，当传感距离较短时，双Mach-Zehnder分布式光纤扰动传感系统的定位精度可以达到20m以内(采样率10MS/s，理论精度为10m)。然而受限于系统光路结构，随着传感距离增加，光纤中背向散射噪声对系统信噪比影响愈发明显，严重影响系统定位精度，制约着该系统的传感距离。
发明目的
本发明的目的是解决双Mach-Zehnder分布式光纤扰动传感系统由于背向散射影响在传感距离较长时信噪比过低的问题，提出一种非对称型双Mach-Zehnder分布式光纤扰动传感系统。该系统利用光学滤波的方法消除光纤背向散射光对信号的影响，大大提高了系统在长距离应用时的信噪比。
发明的本技术方案是：
一种基于非对称双Mach-Zehnder干涉的分布式光纤扰动定位系统，其特征在于该系统包括：
光源：采用两个波长为1550nm附近窄带宽分布式反馈激光器(DFB)，两光源波长差大于本系统所用密集波分复用器(DWDM)的波长间隔；
光环行器：用来将光源发出的光传输到待检测物体并收集反射信号光；
DWDM：工作波长1500nm附近两个商用单通道DWDM，光谱透射范围分别只包含 系统所用的一只光源的波长；
光电探测器：铟镓砷光电探测器(PD)，接收光信号，进行光电转换并放大；
光纤耦合器：3dB光纤耦合器，用于1:2分光；
偏振控制器：调整两路干涉信号偏振态，保证信号可见度；
传感光缆：G.652D通信光缆，用于感知外界扰动及传导光信号；
数据采集卡：采样率为10MS/s双通道数据采集卡(DAQ)，对两个光电探测器的电压信号进行采集，并送入计算机处理；
处理单元：包括通用计算机和嵌入式计算系统，采集卡接收的干涉信号进行处理，最终获取扰动信息。
进一步的，光源和相应的DWDM所构成的背向散射光滤除装置为任意波长光源和光滤波器组合。
进一步的，当光源功率较大时，采用光纤耦合器替代光环行器。
本发明还提供了一种可以应用与上述系统的定位方法，利用基于短时平均频率的时频分析方法得到扰动帧信号的时频分布，并将频率最大点附近的点作为有效信号段进行互相关时延估计，求得时延d，进而获得扰动位置x，具体算法流程如下：
1)设一对阈值门限δ1、δ2和一个幅值阈值ε，其中δ1<0，δ2>0且|δ1|＝|δ2|＝ε(为了滤除电路噪声，2ε需要大于噪声的幅值)。针对任意一个阈值门限，求得过阈值点位置的公式如下：
Figure PCTCN2016103521-appb-000001
其中x(m)为信号段中第m点的幅值，Ci(m)为所求的过阈值点位置，把δ＝δ1、δ＝δ2分别代入公式中并依次对一帧点数为N的信号进行处理即可求得各自的过门限点位置C1(m)和C2(n)，m,n∈[1,N-1]。
2)取C1(m)和C2(n)中大于0的项按从小到大共同排序，我们选取其中满足C1(m)<C2(n)的相邻两项来确定信号的过零点位置Z(k)，其中Z(k)＝[C1(m)+C2(n)]/2，k＝1,2,3...，位于相邻两过零位置间信号的短时平均频率可以表示为：f(k)＝1/[Z(k+1)-Z(k)]；
3)对求得的短时平均频率点进行三次样条差值拟合，用拟合曲线来代表信号的时频分布，将频率最大点附近的点作为有效信号段，对两路有效信号的时频分布曲线进行归一化和时域上的互相关估计，即可确定时延d，进而算出扰动位置x。
进一步的，所述方法中扰动信号的时频分布曲线为现有其他任一时频分析方法获得扰动信号的时频分布曲线，再进行互相关求得时延d，进而获得扰动位置x。
本发明有益效果是：与传统的双Mach-Zehnder分布式光纤扰动传感系统不同，本发明系统使用两个窄带光源和在探测器前加入了相应的密集波分复用器(DWDM)，能够大大滤除光纤背向散射噪声，解决由于背向散射影响在传感距离较长时信噪比过低的问题。同时， 提供的能够用于以上系统的定位方法，利用基于短时平均频率的快速时频分析方法得到扰动帧信号的时频分布，并将频率最大点附近的点作为有效信号段进行互相关时延估计求得时延，进而获得扰动位置。该方法能够对系统中非对称扰动信号进行定位，具有较高的定位精度和稳定性。
附图说明
图1是分布式光纤扰动定位系统定位原理图；
图2是分布式光纤扰动定位系统示意图；
图3是扰动信号的原始信号图；
图4是扰动信号的时频分布图；
具体实施方式
1、本发明所提供的非对称型双Mach-Zehnder光纤扰动传感系统原理如下：
基于非对称型双Mach-Zehnder干涉原理的分布式光纤传感系统原理如图1所示，光源1和光源2发出的两束光在传感环路中分别沿顺时针和逆时针方向传播，并在对端的耦合器发生干涉。由光源1发出的光传播路径为C1-PC1-C2-C3-C4-DWDM2-PD2。光源2发出的光传播路径为C4-PC2-C3-C2-C1-DWDM1-PD1。其中，C1、C4为环形器，C2、C3为3dB耦合器，PC1、PC2为偏振控制器，DWDM1、DWDM2为密集波分复用器，PD1、PD2为光电探测器。设两个光电探测器PD1和PD2检测到同一扰动事件的时间分别为t1和t2，d＝t1-t2，L为传感光缆的长度,x为扰动点距离耦合器C2的位置，其定位公式为
x＝(L-vd)/2
式中，v为光波在单模光纤中的传播速度，单位m/s，其中v＝c/n，c是光在真空中的速度(3×108m/s)，n是光纤的折射率。
2、本发明同时提供了一种基于上述系统的高精度定位方法：
在传统的双Mach-Zehnder分布式光纤扰动定位系统中，时延d是通过对两路干涉信号进行互相关运算来进行估计的。本发明提供的基于非对称型双Mach-Zehnder原理的系统中，由于光源1和光源2的波长不同，由探测器PD1和PD2检测到的两路干涉信号具有不一致性，无法通过直接互相关进行时延估计。这两路干涉信号可以表示为：
Figure PCTCN2016103521-appb-000002
式中，I1(t)、I2(t)为两路干涉信号光强，λ1、λ2分别为光源1和光源2的波长，f(t)为扰动引起的光程差变化，φ1、φ2为初始相位差，n1(t)、n2(t)为各自的电路噪声。在滤除电路噪声的条件下，I1(t)、I2(t)的频率分别与f(t)和f(t-d)成正比。因此，为了求时延d，可以先获得两路信号的时频分布，再对两路信号的时频分布进行归一化和互相关。
本发明中我们先用双门限过零检测的方法滤除电路噪声并找出扰动信号的过零点位置，再利用相邻过零点之间的信号点数的倒数来估计该段信号的平均频率，并对平均频率点进行三次样条差值拟合，得到信号的时频分布；最后对时频分布曲线进行互相关求得时延d，具体算法流程如下所示：
1)设一对阈值门限δ1、δ2和一个幅值阈值ε，其中δ1<0，δ2>0且|δ1|＝|δ2|＝ε(为了滤除电路噪声，2ε需要大于噪声的幅值)。针对任意一个阈值门限，求得过阈值点位置的公式如下：
Figure PCTCN2016103521-appb-000003
其中x(m)为信号段中第m点的幅值，Ci(m)为所求的过阈值点位置，把δ＝δ1、δ＝δ2分别代入公式中并依次对一帧点数为N的信号进行处理即可求得各自的过门限点位置C1(m)和C2(n)，m,n∈[1,N-1]。
2)取C1(m)和C2(n)中大于0的项按从小到大共同排序。我们选取其中满足C1(m)<C2(n)的相邻两项来确定信号的过零点位置Z(k)，其中Z(k)＝[C1(m)+C2(n)]/2，k＝1,2,3...。位于相邻两过零位置间信号的短时平均频率可以表示为：f(k)＝1/[Z(k+1)-Z(k)]。
3)对求得的短时平均频率点进行三次样条差值拟合，用拟合曲线来代表信号的时频分布。将频率最大点附近的点作为有效信号段，对两路有效信号的时频分布曲线进行归一化和时域上的互相关估计，即可确定时延d，进而算出扰动位置x。
实施例1：用于定位的分布式光纤扰动传感系统
该系统结构如图2所示，包括9个部分：
1a、1b，光源：采用波长为1550nm附近窄带宽分布式反馈激光器(DFB)，两光源波长差大于3)中密集波分复用器(DWDM)的波长间隔；
2a、2b，光环行器：用来将光源发出的光传输到待检测物体并收集反射信号光，当光源功率较大时，可采用光纤耦合器替代；
3a、3b，DWDM：工作波长1500nm附近商用单通道DWDM，其中3a的光谱透射范围包含光源1b的中心波长，3b的光谱透射范围包含光源1a的中心波长，；
4a、4b，光电探测器：铟镓砷光电探测器(PD)，接收光信号，进行光电转换并放大。
5a、5b，光纤耦合器：3dB光纤耦合器，用于1:2分光；
6a、6b，偏振控制器：调整两路干涉信号偏振态，保证信号可见度。
7，传感光缆：G.652D通信光缆，用于感知外界扰动及传导光信号；
8，数据采集卡：采样率为10MS/s双通道数据采集卡(DAQ)，对两个光电探测器4a和4b的电压信号进行采集，并送入计算机处理。
9，处理单元：包括通用计算机和嵌入式计算系统，对采集卡接收的干涉信号进行处理，最终获取扰动信息。
实施例2、基于过零率分析的分布式光纤传感定位算法
如图2所示，数据采集卡采集两路信号并将信号送入计算机。计算机基于短时平均频率的时频分析方法得到扰动帧信号的时频分布，并将频率最大点附近的点作为有效信号段进行互相关时延估计。
以下对图2所示的系统，用某次定位实例来说明计算过程：
该系统的参数设定如下：传感光纤总长度为61km，其中1km为铠装光缆，其余60km为裸纤，光源1a和光源1b的波长分别为1550.74nm和1549.95nm，功率均为10mW，两个DWDM的中心波长分别为1550.12nm和1550.92nm，带宽均为±0.22nm，采集卡的采样频率为10M/s，采样时间为0.3s，有效信号点数对应的采样时间设为0.02s。
在光缆的800m处敲击光缆，系统采集到的原始信号如图3所示，可以看出图中虚线和实线两信号具有较高的信噪比，且两信号之间有一个明显的时延差。图4是信号的时频分布图，可以发现虚线实线两条时频分布曲线趋势基本一致，因此可以利用互相关求得时延。
为了说明该算法的有效性，在800m处以敲击方式进行200组定位实验，定位误差分布如下表所示。
Figure PCTCN2016103521-appb-000004
在61km的传感距离下，定位误差在50m以内的概率达到80％，均方差为42.25m。具有较高的定位精度和可靠性。

Claims (5)

  1. 一种基于非对称双Mach-Zehnder干涉的分布式光纤扰动定位系统，其特征在于该系统包括：
    光源：采用两个波长为1550nm附近窄带宽分布式反馈激光器(DFB)，两光源波长差大于本系统所用密集波分复用器(DWDM)的波长间隔；
    光环行器：用来将光源发出的光传输到待检测物体并收集反射信号光；
    DWDM：工作波长1500nm附近两个商用单通道DWDM，光谱透射范围分别只包含系统所用的一只光源的波长；
    光电探测器：铟镓砷光电探测器(PD)，接收光信号，进行光电转换并放大；
    光纤耦合器：3dB光纤耦合器，用于1:2分光；
    偏振控制器：调整两路干涉信号偏振态，保证信号可见度；
    传感光缆：G.652D通信光缆，用于感知外界扰动及传导光信号；
    数据采集卡：采样率为10MS/s双通道数据采集卡(DAQ)，对两个光电探测器的电压信号进行采集，并送入计算机处理；
    处理单元：包括通用计算机和嵌入式计算系统，采集卡接收的干涉信号进行处理，最终获取扰动信息。
  2. 根据权利要求1所述的基于非对称双Mach-Zehnder干涉的分布式光纤扰动定位系统，其特征在于，光源和相应的DWDM所构成的背向散射光滤除装置为任意波长光源和光滤波器组合。
  3. 根据权利要求1所述的基于非对称双Mach-Zehnder干涉的分布式光纤扰动定位系统，其特征在于，当光源功率较大时，采用光纤耦合器替代光环行器。
  4. 一种用于权利要求1所述系统的定位方法，其特征在于：
    利用基于短时平均频率的时频分析方法得到扰动帧信号的时频分布，并将频率最大点附近的点作为有效信号段进行互相关时延估计，求得时延d，进而获得扰动位置x，具体算法流程如下：
    1)设一对阈值门限δ1、δ2和一个幅值阈值ε，其中δ1<0，δ2>0且|δ1|＝|δ2|＝ε；针对任意一个阈值门限，求得过阈值点位置的公式如下：
    Figure PCTCN2016103521-appb-100001
    其中x(m)为信号段中第m点的幅值，Ci(m)为所求的过阈值点位置，把δ＝δ1、δ＝δ2分别代入公式中并依次对一帧点数为N的信号进行处理即可求得各自的过门限点位置C1(m)和C2(n)，m,n∈[1,N-1]；
    2)取C1(m)和C2(n)中大于0的项按从小到大共同排序，选取其中满足C1(m)<C2(n)的相 邻两项来确定信号的过零点位置Z(k)，其中Z(k)＝[C1(m)+C2(n)]/2，k＝1,2,3...，位于相邻两过零位置间信号的短时平均频率可以表示为：f(k)＝1/[Z(k+1)-Z(k)]；
    3)对求得的短时平均频率点进行三次样条差值拟合，用拟合曲线来代表信号的时频分布，将频率最大点附近的点作为有效信号段，对两路有效信号的时频分布曲线进行归一化和时域上的互相关估计，即可确定时延d，进而算出扰动位置x。
  5. 根据权利要求4所述的定位方法，其特征在于，所述扰动信号的时频分布曲线为现有技术任一时频分析方法获得扰动信号的时频分布曲线，再进行互相关求得时延d，进而获得扰动位置x。
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