WO2014012411A1 - 基于脉冲编码和相干探测的botda系统 - Google Patents
基于脉冲编码和相干探测的botda系统 Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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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
- G01D5/35338—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 other arrangements than interferometer arrangements
- G01D5/35354—Sensor working in reflection
- G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
- G01D5/35364—Sensor working in reflection using backscattering to detect the measured quantity using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/322—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres using Brillouin scattering
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
- G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
- G01M11/3118—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR using coded light-pulse sequences
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/39—Testing of optical devices, constituted by fibre optics or optical waveguides in which light is projected from both sides of the fiber or waveguide end-face
Definitions
- the invention relates to a BOTDA system based on pulse coding and coherent detection, and belongs to the field of distributed optical fiber sensing technology. Background technique
- Brillouin Optical Time-Domain Analysis based on fiber-stimulated Brillouin scattering is a sensing technology with long-distance, high-accuracy temperature and strain measurement capabilities in many distributed fiber optic sensors. It has great application prospects in structural health monitoring of large civil engineering, communication optical cables, oil and gas pipelines, etc.
- BOTDA Brillouin Optical Time-Domain Analysis
- the frequency difference between the two optical waves transmitted in opposite directions in the optical fiber is within the Brillouin gain range, they generate a stimulated Brillouin action through the acoustic wave field, whereby energy transfer occurs between the two beams.
- Coherent detection based optical time domain reflectometer which uses coherent detection to detect Rayleigh scattering signals, effectively suppresses the influence of spontaneous emission noise (ASE) on Rayleigh scattering power, and is very suitable for applications such as seabed Long distances such as fiber optic cable and link detection of multiple fiber amplifiers.
- C0TDR is widely used for monitoring the loss, fault point, connection point and breakpoint of ultra-long-haul fiber links. It is indispensable for transoceanic cables. Monitoring tools.
- the traditional B0TDA system generally adopts the direct detection mode. Due to the nonlinear effect of the fiber, the maximum optical power allowed by the probe light and the pump light is limited, so the sensing performance of the B0TDA is limited.
- the effective sensing length of traditional B0TDA based on direct detection method is generally less than 40km.
- B0TDA has the disadvantage of being unable to work when a breakpoint occurs in the fiber link due to the need for double-ended access, which greatly limits the application of B0TDA.
- the need for health monitoring and major disaster prevention of various large-scale infrastructures has increased, and higher requirements have been placed on long-distance distributed optical fiber temperature and strain sensing networks. Summary of the invention
- the object of the present invention is to provide a long-distance coherent detection Brillouin optical time domain analyzer integrating COTDR instead of the traditional direct detection B0TDA, which can realize long-distance temperature or strain sensing, when the sensing fiber has a breakpoint. ,
- the system can locate the breakpoint.
- the object of the present invention is to overcome the shortcomings of the above method and system that the signal-to-noise ratio, spatial resolution and measurement accuracy are not high enough, and propose a pulse-based pulse with high gain, long sensing distance, high system signal-to-noise ratio and high measurement accuracy.
- a long-distance coherent detection Brillouin optical time domain analyzer integrating COTDR, including a narrow linewidth laser, a first coupler, a second coupler, a microwave signal source, Electro-optic modulator, isolator, long-distance sensing fiber, optical circulator, 3dB coupler, pulse modulator, erbium-doped fiber amplifier, scrambler, pulse signal generator, balanced photodetector, electrical spectrum analyzer, data Processing module, acousto-optic modulator; wherein:
- the narrow linewidth laser emits continuous light divided into two continuous lights by the first coupler: a first continuous light, a second continuous light, wherein the first continuous light is modulated by a pulse modulator controlled by a pulse signal generator Pumping pulsed light, the pump pulsed light is amplified by the erbium-doped fiber amplifier to the required optical power, and then injected into the optical circulator through the first port of the optical circulator through the scrambler, and then the second circulator by the optical circulator The port is output to the long-distance sensing fiber of the long-distance sensing fiber.
- the pump light pulse modulated by the pulse modulator becomes a detection signal light.
- the backward Rayleigh scattered light is injected into the second port of the optical circulator, and then enters the 3dB coupler through the third port of the optical circulator and is coherently mixed with the local oscillator, and then detected by the balance detector, the electric spectrum analyzer
- the long-distance coherent detection Brillouin optical time domain analyzer of the fused COTDR of the present invention further includes a first polarization controller disposed between the first coupler and the pulse modulator, and a second coupler disposed at the second coupler a second polarization controller with the electro-optic modulator; wherein the first polarization controller is for controlling a polarization state of light incident on the electro-optic modulator, and the second polarization controller is for controlling an injection pulse modulator The polarization state of light.
- the frequency of the microwave control signal output by the microwave signal source is about a Brillouin frequency shift of the long-distance sensing fiber.
- the first continuous light is frequency-shifted by the frequency shifter; and then used as the local oscillator;
- the coded pump pulse modulated by the first electro-optic modulator is a coded pump pulse light of a Hadamard sequence or a Golay complementary sequence.
- the first electro-optic modulator modulates the output of the Hadamard sequence or the coded pump pulse light of the Golay complementary sequence as the detection signal light
- the backward Rayleigh scattered light enters the 3dB coupler through the 3rd port of the optical circulator and is coherently detected by the balance detector after coherent mixing with the local oscillator.
- the digital signal processing unit controls the pulse signal source to generate an encoded electrical pulse of a Hadamard sequence or a Golay complementary sequence, and performs synchronous control on the spectrum analyzer.
- the sweep measurement of the Brillouin spectrum is achieved by adjusting the value of the modulation frequency of the microwave signal source.
- the system uses both pulse coding technology and coherent detection technology.
- Fig. 4 is a graph showing the results of COTDR test performed by the present invention when the A terminal of the long distance sensing fiber is disconnected.
- Figure 1 9, frequency shifter; 10, narrow linewidth laser; 11, first polarization-maintaining coupler; 12, second polarization-maintaining coupler; 13, first electro-optic modulator; 14, pulse signal source; , second electro-optic modulator; 16, scrambler; 17, microwave signal source; 18, test light; 19, optical circulator; 20, 3dB coupler; 21, balanced photodetector; 22, electric spectrum analyzer; 23.
- Digital signal processing unit Digital signal processing unit. detailed description
- the narrow linewidth laser 10 having a 3 dB line width of less than 1 MHz has a frequency of outgoing light of f.
- the laser emits continuous light and is divided into two continuous lights by the first polarization maintaining coupler 11: the first continuous light is frequency-shifted by the frequency shifter 9; the latter is used as the local oscillator of the subsequent coherent detection;
- the second polarization-preserving coupler 12 is further divided into two continuous lights: one of the continuous lights is modulated by the first electro-optic modulator controlled by the pulse signal source 14 to form a coded pulse of a Hadamard sequence or a Golay complementary sequence, and the code length is pulsed according to the actual situation.
- the two detection sidebands are injected from the other end of the test fiber, and the coded pump pulse light transmitted in the opposite direction undergoes stimulated Brillouin scattering in the test fiber, and the probe signal light after the stimulated Brillouin action passes through the aura shape
- the third port 19 into the The 3dB coupler 20 is coherently detected by the balanced photodetector 21 after being coherently mixed with the local oscillator.
- the processing unit 24 can obtain the time-domain power curve of the intermediate frequency/word after decoding and accumulating the intermediate frequency electrical signals collected by the electrical spectrum analyzer, and adjust the output of the microwave source 17 at a certain frequency interval in the Brillouin spectrum range.
- Signal frequency / according to the method of obtaining the time domain power curve of the intermediate frequency signal distributed along the fiber, the time domain power curve of a series of intermediate frequency signals can be obtained, and the series of time domain power curves are reformed according to the size of the intermediate frequency.
- a Brillouin gain spectrum along the fiber distribution can be obtained, The abundance spectrum is subjected to Lorentz fitting, and the Brillouin frequency shift along the fiber distribution is obtained. According to the relationship between temperature and strain and Brillouin frequency shift, temperature or strain distributed measurement is realized.
- the coded pump pulse light in the present invention is formed by modulating continuous light output from a narrow linewidth laser 10 by a correlation sequence, and these correlation sequences are two or more sequence groups consisting of "1" and they are
- the autocorrelation function is an integer multiple of the ⁇ function. Since the light pulse can only be unipolar, when the sequence contains the element "-1", the bipolar sequence can be used as the difference between the two unipolar sequences. Said, and the system response of the bipolar sequence can be subtracted from the response of the two unipolar sequences. During decoding, the system response of the bipolar sequence is cross-correlated with the correlation sequence, and the estimated value of the system response is obtained by accumulating, thereby realizing signal decoding.
- the Hadamard sequence and the Golay complement sequence are commonly used correlation sequences, and they have good correlation. According to the coding principle, the improvement of the signal-to-noise ratio obtained by using the N-bit Hadamard sequence and the Golay complement sequence are as follows: N 2
- the time-sequenced coded pump pulse light modulated by the first electro-optic modulator 13 becomes the probe pulse light, and the backward Rayleigh scattered light enters through the third port of the optical circulator.
- the 3dB coupler is coherently mixed with the local oscillator, it is detected by the balanced photodetector 21, and the intermediate frequency of the spectrum analyzer 22 is selected as f.
- the intermediate frequency electrical signal is acquired and the digital signal processing unit is used. 23 After decoding and accumulating processing, the power curve of 0TDR in the time domain is obtained, and the function of breakpoint detection is realized.
- the invention simultaneously adopts a pulse coding technique and a coherent detection method, which can improve the signal-to-noise ratio of the B0TDA system, improve the measurement accuracy of the temperature and strain, and increase the sensing distance; and use the time-series coding laser pulse to improve the system signal-to-noise ratio while
- the spatial resolution can be improved by reducing the symbol width of the encoded pulse.
- the symbol width can be as small as the optical phonon lifetime of 10 ns, and the corresponding spatial resolution can reach lm.
- Coherent detection makes the B0TDA system have a breakpoint monitoring function. It can effectively overcome the shortcomings of traditional B0TDA that need double-ended access to breakpoints, and enhance the adaptability and practicability of B0TDA sensing system.
- the ultra-long-distance coherent detection Brillouin optical time domain analyzer of the fused COTDR of the present invention specifically includes: a laser 30 having a line width of less than 1 MHz emits continuous light of 1550 nm (power is 16 dBm), and the coupler 31 is divided into two.
- the pulse modulator 21 controlled by the pulse signal generator 44 is modulated into a 50 ns pump light pulse, and the pulse modulator 41 is a lithium niobate intensity electro-optic modulator with an extinction ratio of 40 dB due to the polarization of the light by the electro-optic modulator.
- the other continuous light is further divided into two paths by the coupler 32: one of the continuous lights is shifted by the acousto-optic modulator 30-1 as the local oscillator, and the frequency shift of the acousto-optic modulator 30-1 / ⁇ SOMHz; A continuous light is frequency-shifted/backed by the electro-optic modulator 35 having a bandwidth greater than 12 GHz as the detection signal light, and the magnitude of the frequency shift/ is controlled by the microwave signal source 34, which is a Brillouin frequency shift of the optical fiber medium, and the electro-optic modulator 35
- the former polarization controller 33 controls the polarization state of the incident light; the detection signal light modulated by the electro-optic modulator 35 has two sidebands symmetric, and the sideband detection light is separated from the original continuous light by about 11 GHz, in order to reduce the pumping.
- the long-distance sensing fiber 37 is simultaneously injected from the A end of the long-distance sensing fiber 37, and then stimulated Brillouin scattering occurs in the long-distance sensing fiber 37 with the relatively transmitted pump pulse light.
- the two sidebands are detected by the balance detector 45 after being coherently mixed with the local oscillator by the 3-port coupler 39 of the optical circulator 38.
- the bandwidth of the balance detector 45 is greater than 12 GHz, and the electrical spectrum analyzer 46 is used.
- the data processing module 47 For observing and collecting the intermediate frequency electrical signal output by the balance detector 45, the data processing module 47 performs data processing on the signal collected by the electrical spectrum analyzer 46 to obtain a Brillouin frequency shift distribution along the fiber, according to Brillouin frequency shift and temperature.
- the relationship between strain and strain ie the demodulation principle of temperature and strain, enables the distributed measurement of temperature or strain.
- Fig. 3 is a view showing the distribution of the Brillouin frequency shift along the length of the fiber measured by the long-distance coherent detection Brillouin optical time domain analyzer of the fusion COTDR of the present invention.
- the Brillouin frequency shift is divided into two segments. This is because the sensing fiber is composed of two fibers with different Brillouin frequency shifts.
- the length of the previous fiber is about 48km, and the length of the latter fiber is about 24km.
- the long-distance coherent detection Brillouin optical time domain analyzer of the fused COTDR when the long-distance sensing fiber 17 has a break point, the pump light pulse modulated by the pulse modulator 21 becomes a detecting pulse, and the backward direction thereof
- the Rayleigh scattered light enters the 3dB coupler 39 through the 3-port coupler 38 of the optical circulator 38 and is coherently mixed with the local oscillator light, and is detected by the balance detector 46, and the intermediate frequency of the electric spectrum analyzer 46 is selected as 80 MHz in "Zero-Span".
- the mode after multiple averaging, obtains the power curve of 0TDR in the time domain, and realizes the function of C0TDR breakpoint detection.
- Figure 4 is a graph showing the results of the C0TDR test performed by the present invention when the end of the long-distance sensing fiber is broken.
Abstract
一种基于脉冲编码和相干探测的BOTDA系统,包括窄线宽激光器(10),两个保偏耦合器(11,12),微波信号源(17),两个电光调制器(13,15),测试光纤(18),光环形器(19),3dB耦合器(20),扰偏器(16),脉冲信号源(14),平衡光电探测器(21),频谱分析仪(22),数字信号处理单元(23),移频器(9)。该系统同时采用了脉冲编码技术和相干检测方法,可提高BOTDA的信噪比、测量精度和增加传感距离,并且该系统具有断点监测功能,能有效克服传统BOTDA需要双端接入带来出现断点不能工作的缺点,增强传感系统的适应能力和实用性。
Description
基于脉冲编码和相干探测的 BOTDA系统
技术领域
本发明涉及一种基于脉冲编码和相干探测的 BOTDA系统, 属于分布式光纤传感技 术领域。 背景技术
基于光纤受激布里渊散射的布里渊光时域分析仪 (Brillouin Optical Time-Domain Analysis, BOTDA)是众多分布式光纤传感器中具有长距离、 高测量精度温度和应变测量 能力的传感技术, 在大型土木工程、 通信光缆、 油气管道等的结构健康监测中有着巨大 的应用前景。 在这种技术中, 当光纤中相向传输的两束光波的频率差在布里渊增益范围 内时, 它们通过声波场发生受激布里渊作用, 由此两束光之间发生能量转移, 当两束光 的频率差等于光纤的布里渊频移(Brillouin frequency shift, BFS)时, 能量转移量最大, 这 个布里渊频移 (BFS)与温度和应变之间存在一个线性关系,因此通过测量两束光波能量转 移量最大时的频率差, 进而测得布里渊频移 (BFS), 根据布里渊频移 (BFS)与温度和应变 之间存在一个线性关系就可以实现温度和应变的分布式传感。
基于相干检测的光时域反射仪 (C0TDR),该技术利用相干检测的方法来探测瑞利散射 信号, 有效抑制了自发辐射噪声 (ASE )对瑞利散射功率的影响, 非常适合用于诸如海底 光缆等长距离并且存在多个光纤放大器的链路检测, C0TDR广泛应用于超长距离光纤链路 的损耗、 故障点、 接续点和断点等事件的监测, 是跨洋海缆的不可或缺的监测工具。 传统的 B0TDA系统一般采用直接探测方式, 由于光纤非线性效应的存在, 探测光和 泵浦光所允许的最大光功率受到限制, 因此 B0TDA的传感性能受到限制。 基于直接探测 方法的传统 B0TDA的有效传感长度一般小于 40km。此外, B0TDA存在由于需要双端接入 而带来的当光纤链路中出现断点时不能工作的缺点,这极大的限制了 B0TDA的应用场合。 而近年来, 随着电力传输网络的发展, 各种大型基础设施的健康监控和重大灾害防治需 要的增加, 对长距离分布式光纤温度、 应变传感网络提出了更高的要求。 发明内容
本发明的目的是, 提出一种融合 COTDR的长距离相干检测布里渊光时域分析仪代 替传统直接检测的 B0TDA, 可以实现长距离的温度或应变传感, 当传感光纤出现断点时,
系统能对断点进行定位。 本发明的目的还在于, 克服上述方法与系统存在信噪比、 空间 分辨率和测量精度不够高的缺点, 提出一种增益高、 传感距离长、 系统信噪比和测量精 度高的基于脉冲编码和相干探测的具有断点定位功能的 B0TDA系统。
本发明为达到上述目的, 采用如下技术方案: 一种融合 COTDR的长距离相干检测 布里渊光时域分析仪, 包括窄线宽激光器, 第一耦合器, 第二耦合器, 微波信号源, 电 光调制器, 隔离器, 长距离传感光纤, 光环形器, 3dB耦合器, 脉冲调制器, 掺铒光纤放 大器, 扰偏器, 脉冲信号发生器, 平衡光电探测器, 电频谱分析仪, 数据处理模块, 声 光调制器; 其中:
所述窄线宽激光器发出连续光经第一耦合器分成两路连续光: 第一路连续光、 第二 路连续光, 其中, 第一路连续光经由脉冲信号发生器控制的脉冲调制器调制成泵浦脉冲 光,所述泵浦脉冲光经掺铒光纤放大器放大到所需光功率后,经扰偏器由光环形器的第 1 端口注入光环形器, 然后由光环形器的第 2端口输出至长距离传感光纤的 B端口进入长 距离传感光纤;
第二路连续光经第二耦合器再分成两路连续光: 其中一路连续光经声光调制器移频 后作为本振光; 另一路连续光经电光调制器移频 /后作为探测信号光,移频量 /的值由 微波信号源控制,由电光调制器调制的探测信号光具有对称的两个探测边带,两个探测边 带经隔离器后同时从长距离传感光纤的 A端注入长距离传感光纤, 与相向传输的泵浦脉 冲光在长距离传感光纤中发生受激布里渊散射作用,然后两个探测边带经光环形器的第 3 端口进入 3dB耦合器与所述本振光相干混频后由平衡探测器探测,所述电频谱分析仪根据 观测和采集平衡探测器输出的中频电信号获取布里渊增益谱, 所述数据处理模块对电频 谱分析仪采集到的布里渊增益谱进行洛伦茨拟合得到沿光纤的布里渊频移分布, 根据布 里渊频移与温度和应变的解调关系, 实现光纤分布式温度或应变的传感。
进一步的, 本发明的融合 COTDR的长距离相干检测布里渊光时域分析仪, 所述脉 冲信号发生器用于控制脉冲调制器的同时, 还对电频谱分析仪进行同步触发控制。
进一步的, 本发明的融合 COTDR的长距离相干检测布里渊光时域分析仪, 所述长 距离传感光纤为长度超过 70km的普通单模光纤。
进一步的, 本发明的融合 COTDR的长距离相干检测布里渊光时域分析仪, 当所述 长距离传感光纤出现断点时, 所述脉冲调制器调制的泵浦光脉冲成为探测信号光, 其后 向的瑞利散射光注入光环形器的第 2端口后, 经光环形器的第 3端口进入 3dB耦合器与 本振光相干混频后由平衡探测器探测, 电频谱分析仪的中心频率设置在中频/, F = 处,
并采用 "零范围"模式, 经多次平均后获取瑞利散射光的时域曲线分布, 实现 C0TDR断 点检测的功能。
进一步的, 本发明的融合 COTDR的长距离相干检测布里渊光时域分析仪, 还包括 设置在第一耦合器与脉冲调制器之间的第一偏振控制器、 以及设置在第二耦合器与电光 调制器之间的第二偏振控制器; 其中, 所述第一偏振控制器用于控制射入电光调制器的 光的偏振态, 所述第二偏振控制器用于控制射入脉冲调制器的光的偏振态。
进一步的, 本发明的融合 COTDR的长距离相干检测布里渊光时域分析仪, 所述微 波信号源输出的微波控制信号的频率约为长距离传感光纤的一个布里渊频移。
进一步的, 本发明的融合 COTDR的长距离相干检测布里渊光时域分析仪, 所述微 波信号源控制移频量 /的值, 即为控制探测光和泵浦脉冲光之间的频率差, 通过不断调 节微波信号源的调制频率改变探测光和泵浦脉冲光之间的频率差, 实现布里渊频谱的扫 一种基于脉冲编码和相干探测的 BOTDA系统, 包括移频器、 窄线宽激光器、 第一 保偏耦合器、 第二保偏耦合器、 第一电光调制器、 脉冲信号源、 第二电光调制器、 扰偏 器、 微波信号源、 测试光纤、 光环形器、 3dB耦合器、 平衡光电探测器、 频谱分析仪、 数 字信号处理单元, 窄线宽激光器发出连续光经第一保偏耦合器分成两路连续光: 第一路 连续光、 第二路连续光, 其中,
第一路连续光经移频器移频 /;后作为本振光;
第二路连续光经第二保偏耦合器再分成两路连续光: 其中一路连续光经经由脉冲信 号源控制的第一电光调制器调制成编码泵浦脉冲, 所述编码泵浦脉冲光经扰偏器后由光 环形器的第 1端口注入, 然后由光环形器的第 2端口输出至测试光纤的一端; 另一路连 续光经第二电光调制器移频 /后作为探测信号光,移频量 /的值由微波信号源控制,由第 二电光调制器调制的探测信号光具有对称的两个探测边带, 两个探测边带从测试光纤的 另一端注入, 与相向传输的编码泵浦脉冲光在测试光纤中发生受激布里渊散射作用, 经 过受激布里渊作用后的探测信号光经光环形器的第 3端口进入 3dB耦合器与所述本振光 相干混频后由平衡探测器进行相干检测, 平衡探测器输出的中频电信号由频谱分析仪观 测和采集, 数字信号处理单元对电频谱分析仪采集到的中频电信号进行解码、 累加处理 得到布里渊增益谱, 并对所获得的布里渊增益谱进行洛伦兹拟合得到沿光纤的布里渊频 移分布, 在根据布里渊频移与温度和应变的解调关系, 实现光纤分布式温度或应变的传 感。
进一步的, 所述平衡探测器是频率响应大于 12GHz的光电探测器。
进一步的, 所述移频器的频移量/ i超过 80MHz。
进一步的,所述第一电光调制器调制输出的编码泵浦脉冲是 Hadamard序列或 Golay 互补序列的编码泵浦脉冲光。
本发明的基于脉冲编码和相干探测的 B0TDA系统, 当所述测试光纤出现断点时, 所述第一电光调制器调制输出的 Hadamard序列或 Golay互补序列的编码泵浦脉冲光作为 探测信号光, 其后向的瑞利散射光经光环形器的第 3端口进入 3dB耦合器与所述本振光 相干混频后由平衡探测器进行相干检测,此时所述电频谱分析仪采用 "Zero-Span"模式提 取中频/ IF= y;的中频信号, 经多次累加平均后得到瑞利散射的 0TDR功率分布曲线, 实现 断点检测功能。
进一步的,所述数字信号处理单元控制着脉冲信号源产生 Hadamard序列或 Golay互 补序列的编码电脉冲, 并对频谱分析仪作同步控制。
进一步的, 通过调节所述微波信号源调制频率/的值, 实现布里渊频谱的扫频测量。 进一步的, 该系统同时采用了脉冲编码技术和相干探测技术两种技术。
本发明采用以上技术方案与现有技术相比, 具有以下有益效果:
本发明采用相干检测技术代替传统直接检测的方法, 有效提高 B0TDA系统的信噪比 和动态范围,在无光放大器的情况下,传感长度超过 70km;本发明采用双边带探测方法, 可以有效的减小传统 B0TDA中的非局域效应,提高长距离测量的精度;本发明的 B0TDA 相对于传统的 B0TDA, 由于采用相干检测的方法, 系统中不再需要窄带宽的光滤波器, 提高了系统的稳定性; 本发明将具有单端接入和超长距离断点检测能力的 C0TDR融合到 相干探测的 B0TDA系统中, 在传感光纤出现断点时, 系统能工作在 C0TDR断点检测模式, 有效克服传统 B0TDA在传感光纤出现断点不能工作且无法对断点定位的缺点, 增强传感 器的实用性。
本发明同时采用脉冲编码技术和相干检测结合的方法,可提高 B0TDA系统的信噪比、 改善温度和应变的测量精度和增加传感距离;采用 Hadamard序列或 Golay互补序列的编 码泵浦脉冲光, 在提高系统信噪比同时又可通过减小编码脉冲的码元宽度来提高系统的 空间分辨率, 码元宽度可以小到与光纤声子寿命 10ns相当, 对应空间分辨率可达到 lm; 采用相干探测使得系统具有断点监测功能, 能有效克服传统 B0TDA需要双端接入带来出 现断点不能工作的缺点, 增强传感系统的适应能力和实用性。 本发明实现长距离的温度 或应变传感, 当传感光纤出现断点时, 系统具有对断点进行定位的功能, 同时具有高的
空间分辨率、 测量精度高, 传感距离长, 信噪比高。 附图说明
图 1是本发明基于脉冲编码和相干探测的 BOTDA系统示意图。
图 2是本发明的融合 COTDR的长距离相干检测布里渊光时域分析仪示意图。
图 3是本发明的融合 COTDR的长距离相干检测布里渊光时域分析仪所测得的布里 渊频移沿光纤长度的分布图。
图 4是当长距离传感光纤的 A端断开时, 本发明实现的 COTDR测试结果图。 图 1中: 9、 移频器; 10、 窄线宽激光器; 11、 第一保偏耦合器; 12、 第二保偏耦合 器; 13、 第一电光调制器; 14、 脉冲信号源; 15、 第二电光调制器; 16、 扰偏器; 17、 微波信号源; 18、 测试光线; 19、 光环形器; 20、 3dB耦合器; 21、平衡光电探测器; 22、 电频谱分析仪; 23、 数字信号处理单元。 具体实施方式
下面结合附图和实施例对本发明的技术方案作进一步详细说明和描述。
如图 1所示,一种基于脉冲编码和相干探测的 BOTDA系统包括移频器 9、窄线宽激 光器 10、 第一保偏耦合器 11、 第一保偏耦合器、 第一电光调制器 13、 脉冲信号源 14、 第二电光调制器 12、 扰偏器 16、 微波信号源 17、 测试光纤 18、 光环形器 19、 3dB耦合 器 20、 平衡光电探测器 21、 频谱分析仪 22和数字信号处理单元 23。
假设 3dB线宽小于 1MHz的窄线宽激光器 10出射光的频率为 f。, 激光器发出连续光 经第一保偏耦合器 11分成两路连续光: 第一路连续光经移频器 9移频 /;后作为后续相干 探测的本振光; 第二路连续光经第二保偏耦合器 12再分成两路连续光: 其中一路连续光 经由脉冲信号源 14控制的第一电光调制器调 13制成 Hadamard序列或 Golay互补序列的 编码脉冲,编码长度根据实际情况由脉冲信号源 14设定, 所述编码泵浦脉冲光经扰偏器 16后由光环形器 19的第 1端口注入,然后由光环形器 19的第 2端口输出至测试光纤 18 的一端; 另一路连续光经第二电光调制器 15移频 /后作为探测信号光, 移频量 /的值由 微波源 17控制,由第二电光调制器 15调制的探测信号光具有对称的两个探测边带,两个 探测边带从测试光纤的另一端注入, 与相向传输的编码泵浦脉冲光在测试光纤中发生受 激布里渊散射作用,经过受激布里渊作用后的探测信号光经光环形器 19的第 3端口进入
3dB耦合器 20与所述本振光相干混频后由平衡光电探测器 21进行相干检测。根据相干检 测原理, 平衡光电探测器 21输出拍频信号的光电流为: t (0 = 2R,]PLP (l + 8SBS (vs , z))2 x∞8(2π ΙΡί + Α ) ( 1 ) 式 (1)中, gsss是受激布里渊增益, R为平衡光电探测器的响应度, i\和 ΡΡ分别是本振光 的功率和探测光的功率, /IF是拍频信号频率 (也称为中频), 是本振光和探测光的相位 差。 将电频谱分析仪的中心频率设置在中频/ IF处, 并采用 "Zero-Span"模式, 数字信号 处理单元 24对电频谱分析仪采集到的中频电信号进行解码、累加处理后则可以获取中频 / 言号的时域功率曲线。在布里渊频谱范围内按一定频率间隔调节微波源 17的输出信号 频率 /, 按前面所述获取中频信号沿光纤分布的时域功率曲线的方法, 可以得到一系列中 频信号的时域功率曲线, 按中频的大小将这一系列时域功率曲线重整后, 可以获得沿光 纤分布的布里渊增益谱, 对布里渊增益谱进行洛伦兹拟合, 得到沿光纤分布的布里渊频 移, 根据温度和应变与布里渊频移关系, 实现温度或应变分布式测量。
温度和应变的解调原理如下:
布里渊频移变化量 Δ ^与温度和应变的线性关系为:
AvB = CvTAT + CvsAs (2) 式 (2)中 ΔΓ为温度的变化量, 为应变的变化量, Cv 和 Cvs分别是布里渊频移的温 度系数和应变系数, 这些系数通过已知条件的实验进行标定, 根据测得的布里渊频移变 化量和 (2)式, 实现温度或应变的分布式传感。
脉冲编码和解码原理:
本发明中的编码泵浦脉冲光是由相关序列对窄线宽激光器 10输出的连续光进行调制 而成, 这些相关序列是有两个或者多个由 和 " 1 "组成的序列组, 且它们的自相关 函数和为 δ函数的整数倍, 由于光脉冲只能为单极性, 因此当序列中含有元素 " -1 "时, 可将该双极性序列用两个单极性序列的差表示, 而该双极性序列的系统响应可以由这两 个单极性序列的响应相减得到。 解码时将双极性序列的系统响应与该相关序列做互相关 后累加可以得到系统响应的估计值, 从而实现信号的解码。
Hadamard序列和 Golay互补序列是常用的相关序列, 它们具有很好的相关性, 由编码 原理可知, 采用 N位的 Hadamard序列和 Golay互补序列可获得的信噪比改善分别为:
N2
GH = 「 (3)
GG = (4) G 2
断点监测原理为:
当测试光纤 18出现断点时, 所述第一电光调制器 13调制的具有时间序列的编码泵 浦脉冲光成为探测脉冲光, 其后向的瑞利散射光经光环形器的第 3端口进入 3dB耦合器 与本振光相干混频后由平衡光电探测器 21 探测, 将频谱分析仪 22 的中频选为 f、, 在 "Zero-Span"模式, 采集中频电信号并由对数字信号处理单元 23其进行解码、累加处理 后则得到时域下 0TDR的功率曲线, 实现断点检测的功能。
本发明同时采用了脉冲编码技术和相干检测方法, 可提高 B0TDA系统的信噪比、 改 善温度和应变的测量精度和增加传感距离; 采用时间序列编码激光脉冲, 在提高系统信 噪比同时又可通过减小编码脉冲的码元宽度来提高空间分辨率, 码元宽度可以小到与光 纤声子寿命 10ns相当,对应空间分辨率可达到 lm;采用相干探测使得 B0TDA系统具有断 点监测功能, 能有效克服传统 B0TDA需要双端接入带来出现断点不能工作的缺点, 增强 B0TDA传感系统的适应能力和实用性。
参照图 2,本发明的融合 COTDR的超长距离相干检测布里渊光时域分析仪,具体为: 线宽小于 1MHz的激光器 30发出 1550nm的连续光(功率为 16dBm),耦合器 31分成两路, 一路经由脉冲信号发生器 44控制的脉冲调制器 21调制成 50ns的泵浦光脉冲,脉冲调制 器 41为铌酸锂强度电光调制器, 消光比为 40dB, 由于电光调制器对光的偏振态敏感, 所 以为了减小偏振态的影响, 在脉冲调制器 41前放置了偏振控制器 40用于控制入射光的 偏振态,光脉冲经掺铒光纤放大器 42放大到所需光功率 (脉冲峰值功率为 20dBm左右)后 经扰偏器 43注入光环形器 38的 1端口, 由光环形器 38的 2端口出射后, 从长距离传感 光纤 37的 B端进入长距离传感光纤 37。
另一路连续光经耦合器 32再分成两路: 其中一路连续光经声光调制器 30— 1移频 j 后作为本振光, 声光调制器 30-1的频移量/ ^SOMHz ; 另一路连续光经带宽大于 12GHz的 电光调制器 35移频/后作为探测信号光, 移频量/的大小由微波信号源 34控制, 约为光 纤介质的一个布里渊频移, 电光调制器 35前的偏振控制器 33控制入射光的偏振态; 由 电光调制器 35 调制的探测信号光有对称的两个边带, 边带探测光与原连续光差频约为 11GHz , 为了减小泵浦衰竭造成的非局域效应, 采用双边带探测技术, 即两个边带探测光
经隔离器 36后同时从长距离传感光纤 37的 A端注入长距离传感光纤 37, 然后与相对传 输的泵浦脉冲光在长距离传感光纤 37中发生受激布里渊散射作用,然后两个边带探测光 经光环形器 38的 3端口进入 3dB耦合器 39与本振光相干混频后由平衡探测器 45探测; 平衡探测器 45的带宽大于 12GHz, 电频谱分析仪 46用于观测和采集平衡探测器 45输出 的中频电信号, 数据处理模块 47对电频谱分析仪 46采集到的信号进行数据处理得到沿 光纤的布里渊频移分布, 根据布里渊频移与温度和应变的关系, 即温度和应变的解调原 理, 实现温度或应变的分布式测量。
本发明的相干检测布里渊光时域分析仪利用光纤中受激布里渊散射效应, 采用相干 检测技术和双边带探测方式制成的布里渊光时域分析仪。
脉冲信号发生器 44用于控制脉冲调制器 21的同时, 对电频谱分析仪 46进行同步触 发控制。
微波信号源 44输出的微波控制信号的频率约为长距离传感光纤 37 的一个布里渊频 移; 所述微波信号源 44控制探测光和泵浦脉冲光之间的频率差, 通过不断调节微波信号 源 34的调制频率改变探测光和泵浦脉冲光之间的频率差, 完成布里渊频谱的扫频测量; 所述电频谱分析仪 26获取布里渊增益谱;数据处理模块 47对电频谱分析仪 46采集到的 布里渊增益谱进行洛伦茨拟合得到沿光纤的布里渊频移分布, 根据布里渊频移与温度和 应变的关系, 实现温度或应变的分布式传感。
图 3是本发明的融合 COTDR的长距离相干检测布里渊光时域分析仪所测得的布里 渊频移沿光纤长度的分布图。 图中布里渊频移分成两段, 这是因为传感光纤由两段布里 渊频移不同的光纤组成, 前一段光纤长约 48km, 后一段光纤长度约为 24km, 图中的小插 图为后一段光纤接近末端处的布里渊频移分布的放大图,其中在 24km末端约 50m的光纤 的温度与其余光纤的温度实际相差约 32.7°C, 而放大图中两部分光纤的布里渊频移相差 约 34.2MHz, 与实际温度相符 (布里渊频移温度系数取 l . lMHz/°C;)。
所述融合 C0TDR的长距离相干检测布里渊光时域分析仪, 当长距离传感光纤 17出现 断点时, 所述脉冲调制器 21调制的泵浦光脉冲成为探测脉冲, 其后向的瑞利散射光经光 环形器 38的 3端口进入 3dB耦合器 39与本振光相干混频后由平衡探测器 46探测,将电 频谱分析仪 46的中频选为 80MHz,在" Zero-Span"模式,经多次平均后则得到时域下 0TDR 的功率曲线, 实现 C0TDR断点检测的功能。 图 4是当长距离传感光纤的末端断开时, 本 发明实现的 C0TDR测试结果图。
本发明采用相干检测方法提高 B0TDA的信噪比, 采用双边带的探测方式减小系统的
非局域效应, 有效提高了 B0TDA系统的传感距离, 并将具有单端接入和超长距离断点检 测能力的 C0TDR融合到相干探测的 B0TDA系统中, 在传感光纤 37出现断点时, 系统能工 作在 C0TDR断点检测模式, 有效克服传统 B0TDA在传感光纤出现断点不能工作且无法对 断点定位的缺点, 增强传感器的实用性。
虽然本发明已以较佳实施例公开如上, 但它们并不是用来限定本发明, 本领域的开 发人员可以对本发明的实施例进行各种改动和变型而不脱离本发明的精神和范围。这样, 倘若本发明实施例中的这些修改和变型属于本发明权利要求及其等同的范围之内, 则本 发明中的实施例也包含这些改动和变型在内。 因此本发明的保护范围应当以本申请的权 利要求所界定的为准。
Claims
1. 一种基于脉冲编码和相干探测的 B0TDA 系统, 包括窄线宽激光器(10)、 第一保 偏耦合器(11)、 第二保偏耦合器(12)、 微波信号源(17)、 测试光纤(18)、 光环形器 (19)、 3dB耦合器 (20)、 平衡光电探测器 (21)、 扰偏器(16)、 电频谱分析仪 (22)和数字信 号处理单元(23), 窄线宽激光器(10)发出连续光经第一保偏耦合器(11)分成两路连续 光: 第一路连续光、 第二路连续光, 其特征在于: BOTDA 系统还包括移频器 (9)、 第一 电光调制器(13)、 脉冲信号源(14)、 第二电光调制器(15)其中:
第一路连续光经移频器 (9)移频 f、后作为本振光;
第二路连续光经第二保偏耦合器(12)再分成两路连续光: 其中一路连续光经由脉冲 信号源(14)控制的第一电光调制器(13)调制成泵浦脉冲, 所述泵浦脉冲光经扰偏器(16) 后由光环形器(19)的第 1端口注入, 然后由光环形器(19)的第 2端口输出至测试光纤(18) 的一端; 另一路连续光经第二电光调制器(15)移频 /后作为探测信号光, 移频量 /的值 由微波信号源(14)控制, 由第二电光调制器(15)调制的探测信号光具有对称的两个探测 边带, 两个探测边带从测试光纤(18)的另一端注入, 与相向传输的泵浦脉冲光在测试光 纤(18)中发生受激布里渊散射作用, 经过受激布里渊作用后的探测信号光经光环形器(19) 的第 3 端口进入 3dB耦合器 (20)与所述本振光相干混频后由平衡光电探测器 (21)进行相 干检测, 平衡光电探测器 (21)输出的中频电信号由电频谱分析仪 (22)观测和采集, 数字 信号处理单元 (23)对电频谱分析仪 (22)采集到的中频电信号进行相应的处理得到布里渊 增益谱; 并对所获得的布里渊增益谱进行洛伦兹拟合得到沿光纤的布里渊频移分布, 在 根据布里渊频移与温度和应变的解调关系, 实现光纤分布式温度或应变的传感。
2. 根据权利要求 1所述基于脉冲编码和相干探测的 BOTDA系统, 其特征在于: 所 述平衡光电探测器 (21)是频率响大于 12GHz的光电探测器。
3. 根据权利要求 1所述基于脉冲编码和相干探测的 BOTDA系统, 其特征在于: 所 述移频器(9)的移频量超过 80MHz。
4. 根据权利要求 1所述基于脉冲编码和相干探测的 BOTDA系统, 其特征在于: 所 述数字信号处理单元 (23)控制着脉冲信号源 (14)产生 Hadamard序列或 Golay互补序列的编 码电脉冲, 并对电频谱分析仪 (22)作同步控制。
5.根据权利要求 1 所述基于脉冲编码和相干探测的 BOTDA系统, 其特征在于: 所 述第一电光调制器 (13)由脉冲信号源 (14)控制, 其输出的是 Hadamard序列或 Golay互补序 列的编码泵浦脉冲光。
6. 根据权利要求 1所述基于脉冲编码和相干探测的 BOTDA系统, 其特征在于: 当 所述测试光纤(18)不出现断点时, 所述平衡光电探测器 (21)输出拍频信号的光电流为: (0 = 2R^PLP (l + gSBS (vs , z))2 X οο8(2π ΙΡί + Αφ)
其中, gsss是受激布里渊增益, R为平衡光电探测器的响应度, / 和 ΡΡ分别是本振光的 功率和探测光的功率, /IF是拍频信号频率 (也称为中频), 是本振光和探测光的相位 差; 当所述测试光纤(18)出现断点时, 所述第一电光调制器(13)调制输出的具有时间序 列的 Hadamard序列或 Golay互补序列的编码泵浦脉冲光作为探测信号光, 其后向的瑞利 散射光经所述光环形器(19)的第 3 端口进入 3dB耦合器 (20)与所述本振光相干混频后由 平衡光电探测器 (21)进行相干检测,此时所述电频谱分析仪 (22)采用 "Zero-Span "模式提 取频率 /IF= /;的中频信号, 经多次累加平均后得到瑞利散射的 0TDR功率分布曲线, 实现 断点检测功能。
7. 根据权利要求 1所述基于脉冲编码和相干探测的 BOTDA系统, 其特征在于: 所 述电频谱分析仪(22)的中心频率设置在中频/ IF处, 并采用 "Zero-Span "模式, 所述数字 信号处理单元 (23)对所述电频谱分析仪 (22)采集到的中频电信号进行解码、 累加处理后 则可以获取中频/ ^信号的时域功率曲线。
8.根据权利要求 1所述基于脉冲编码和相干探测的 BOTDA系统, 其特征在于: 通 过调节所述微波信号源(17)调制频率/的值, 实现布里渊频谱的扫频测量。
9. 一种融合 COTDR 的长距离相干检测布里渊光时域分析仪, 其特征在于: 包括窄 线宽激光器(10), 第一耦合器(11), 第二耦合器(12), 微波信号源(14), 电光调制器 ( 15), 隔离器(16), 长距离传感光纤(17), 光环形器(18), 3dB耦合器(19), 脉冲调制器 (21), 掺铒光纤放大器(22), 扰偏器(23), 脉冲信号发生器(24), 平衡光电探测器 (25), 电频谱分析仪 (26), 数据处理模块 (27), 声光调制器 (30) ; 其中:
所述窄线宽激光器(10)发出连续光经第一耦合器(11)分成两路连续光: 第一路连续 光、 第二路连续光, 其中,
第一路连续光经由脉冲信号发生器(24)控制的脉冲调制器 (21)调制成泵浦脉冲光, 所述泵浦脉冲光经掺铒光纤放大器(22)放大到所需光功率后, 经扰偏器 (23)由光环形器 ( 18)的第 1 端口注入光环形器(18), 然后由光环形器(18)的第 2 端口输出至长距离传感 光纤(17)的 B端口进入长距离传感光纤(17);
第二路连续光经第二耦合器(12)再分成两路连续光: 其中一路连续光经声光调制器 (30)移频/ 1后作为本振光; 另一路连续光经电光调制器(15)移频/后作为探测信号光, 移
频量 f 的值由微波信号源(14)控制,由电光调制器(15)调制的探测信号光具有对称的两个 探测边带, 两个探测边带经隔离器(16)后同时从长距离传感光纤(17)的 A 端注入长距离 传感光纤(17), 与相向传输的泵浦脉冲光在长距离传感光纤(17)中发生受激布里渊散射 作用, 然后两个探测边带经光环形器(18)的第 3 端口进入 3dB耦合器(19)与所述本振光 相干混频后由平衡探测器(25)探测,所述电频谱分析仪(26)根据观测和采集平衡探测器 (25)输出的中频电信号获取布里渊增益谱, 所述数据处理模块 (27)对电频谱分析仪 (26) 采集到的布里渊增益谱进行洛伦茨拟合得到沿光纤的布里渊频移分布, 根据布里渊频移 与温度和应变的解调关系, 实现光纤分布式温度或应变的传感。
10. 根据权利要求 1所述融合 COTDR的长距离相干检测布里渊光时域分析仪, 其 特征在于: 当所述长距离传感光纤(17)出现断点时, 所述脉冲调制器(21)调制的泵浦光 脉冲成为探测信号光, 其后向的瑞利散射光注入光环形器(18)的第 2 端口后, 经光环形 器(18)的第 3 端口进入 3dB耦合器(19)与本振光相干混频后由平衡探测器 (25)探测, 电 频谱分析仪 (26)的中心频率设置在中频/, F = /;处, 并采用 " Zero-Span"模式, 经多次平 均后获取瑞利散射光的时域曲线分布, 实现 C0TDR断点检测的功能。
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