WO2022227948A1 - 一种损耗与振动同步监测的相干及偏振衰落抑制方法 - Google Patents

一种损耗与振动同步监测的相干及偏振衰落抑制方法 Download PDF

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WO2022227948A1
WO2022227948A1 PCT/CN2022/082419 CN2022082419W WO2022227948A1 WO 2022227948 A1 WO2022227948 A1 WO 2022227948A1 CN 2022082419 W CN2022082419 W CN 2022082419W WO 2022227948 A1 WO2022227948 A1 WO 2022227948A1
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polarization state
amplitude
distribution matrix
phase
polarization
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French (fr)
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张益昕
陈晓红
张旭苹
佟帅
梁蕾
万一鸣
王峰
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南京大学
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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
    • G01M11/3145—Details of the optoelectronics or data analysis
    • 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
    • G01M11/02—Testing optical properties
    • 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
    • G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
    • 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
    • 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
    • G01H9/006—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors the vibrations causing a variation in the relative position of the end of a fibre and another element
    • 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
    • G01M11/3181—Reflectometers dealing with polarisation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Definitions

  • the invention relates to a coherence and polarization fading suppression method for synchronous monitoring of loss and vibration, and belongs to the technical field of optical fiber sensing.
  • Coherent Optical Time Domain Reflectometry uses coherent detection to convert Rayleigh Backscattering Signal (RBS) optical signals into electrical signals at a specific intermediate frequency. By performing electrical narrowband filtering on the intermediate frequency signal, most of the ASE noise is suppressed, so that it can monitor multi-relay ultra-long-distance optical fiber communication lines.
  • COTDR technology has continued to improve. It mainly relies on frequency division multiplexing technology to improve the bandwidth utilization efficiency of monitoring channels and shorten the measurement time. However, in terms of its target parameters, it is still limited to monitoring fiber loss parameters. As a result, the COTDR-based optical fiber link monitoring system can only perform post-event fault diagnosis and location.
  • ⁇ -OTDR Phase-sensitive Optical Time-Domain Reflectometry
  • ⁇ -OTDR and COTDR use lasers with narrow linewidth and small frequency drift as light sources
  • the heterodyne detection ⁇ -OTDR and COTDR systems are also highly similar in structure.
  • the combination of ⁇ --OTDR and COTDR technology can be considered.
  • the polarization scrambler is often used to quickly perturb the polarization state of the Optical Local Oscillator (OLO) light to suppress the polarization fading noise caused by the mismatch between the polarization state of the RBS and the OLO.
  • OLO Optical Local Oscillator
  • the amplitude discrimination-based demodulation method can usually only perform qualitative measurements, and cannot reconstruct the time-frequency characteristics of the disturbance event with high fidelity.
  • the phase detection type demodulation method utilizes the linear relationship between the phase change of the RBS and the dynamic strain in the local area of the fiber, which can accurately restore the disturbance events and improve the accuracy of subsequent pattern recognition.
  • the intensity of some areas of the fiber tends to be zero, and the phase demodulation results in these areas are prone to a sharp deterioration of the signal-to-noise ratio, resulting in frequent false alarms.
  • the technical problem to be solved by the present invention is to provide a coherence and polarization fading suppression method for synchronous monitoring of loss and vibration, adopting a new design method, which can realize early warning of disturbance events while monitoring the loss of optical fiber links.
  • the present invention adopts the following technical solutions: the present invention designs a coherence and polarization fading suppression method for synchronous monitoring of loss and vibration, based on the two-way orthogonal polarization state intermediate frequency obtained by adopting polarization diversity detection method for the fiber to be tested signal, perform the following steps A to F:
  • Step A For the P-polarized state intermediate frequency signal and the S-polarized state intermediate-frequency signal in the two-way orthogonal polarization state intermediate-frequency signal respectively, perform IQ demodulation, obtain the P-polarized state amplitude distribution matrix, P-polarized state corresponding to the P-polarized state intermediate-frequency signal. state phase distribution matrix, and the S-polarization state amplitude distribution matrix and S-polarization state phase distribution matrix corresponding to the S-polarized state intermediate frequency signal, and then enter step B; wherein, the amplitude distribution matrix represents the distribution of signal amplitude over time and distance, and the phase distribution The matrix represents the distribution of the signal phase over time and distance;
  • Step B According to the P polarization state amplitude distribution matrix and the S polarization state amplitude distribution matrix, obtain the P polarization state disturbance position and the S polarization state disturbance position respectively, and then enter step C;
  • Step C Respectively for the P polarization state amplitude distribution matrix and the S polarization state amplitude distribution matrix, according to the preset size time domain window TWsize, divide along the time axis, and obtain the signal interval of each TWsize duration corresponding to the P polarization state amplitude distribution matrix , and the signal interval of each TWsize duration corresponding to the S-polarization state amplitude distribution matrix, and then enter step D;
  • Step D For each signal interval divided by the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix, respectively, calculate the first amplitude of the P-polarization state and the S-polarization state in the spatial resolution width before the perturbation position of the current signal interval respectively.
  • Step E Based on the P-polarization state phase distribution matrix and the S-polarization state phase distribution matrix, for each signal interval divided by the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix, first select the corresponding P-polarization state and S-polarization state.
  • the polarization state phase and the position corresponding to the larger first amplitude eigenvalue within the spatial resolution width before the disturbance position in the current signal interval are taken as the polarization state phase before the disturbance position in the current signal interval; at the same time, the P polarization state and S polarization state are selected
  • the polarization state corresponds to the polarization state phase and the position corresponding to the larger second amplitude eigenvalue within the spatial resolution width after the disturbance position in the current signal interval, as the polarization state phase after the disturbance position in the current signal interval; then for the current signal interval
  • the phase difference operation is performed on the selected polarization state phases before and after the disturbance position to realize phase extraction, and the phase signal of the disturbance position in the current signal interval is obtained; then the phase signal of the disturbance position in each signal interval is obtained to realize the reconstruction of the phase signal of the disturbance position, and then enter the step F;
  • Step F Perform phase unwinding according to the reconstructed phase signal at the disturbance position in each signal interval, and restore the fiber expansion and contraction situation at the disturbance position caused by the external disturbance signal, that is, obtain the disturbance monitoring result of the fiber under test.
  • step A based on the P-polarized state amplitude distribution matrix and the S-polarized state amplitude distribution matrix obtained in step A, it also includes performing the following steps I to step II to realize the acquisition of the fiber loss monitoring result to be measured:
  • Step 1 Sequence along the time axis, respectively carry out the square sum processing to the P polarization state amplitude distribution matrix and the S polarization state amplitude distribution matrix, obtain the square sum result of the P polarization state amplitude distribution matrix, and the S polarization state amplitude distribution matrix sum of squares result, Then enter step II;
  • Step II Accumulate and average the result of the square sum of the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix square sum result to obtain the loss monitoring result of the fiber to be tested.
  • the step D includes the following:
  • step D1 For each signal interval divided by the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix respectively, perform steps D1 to D2 to obtain the spatial resolution of each signal interval of the P-polarization state and the S-polarization state before and after the disturbance position.
  • Step D1 According to the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix, obtain the minimum amplitude values of each spatial position in the current signal interval before the P-polarization state and the S-polarization state perturbation position, and within the spatial resolution width range, respectively, and select The maximum amplitude value of the minimum amplitude values corresponding to the P-polarization state and the S-polarization state respectively, as the first amplitude eigenvalues corresponding to the P-polarization state and the S-polarization state respectively before the respective disturbance positions in the current signal interval, respectively denoted as A p ra and A s ra , where the subscript ra represents the position of the first amplitude eigenvalue before the respective disturbance positions in the signal interval corresponding to the P polarization state and the S polarization state;
  • Step D2 According to the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix, respectively obtain the minimum amplitude value of each spatial position within the spatial resolution width range after the P-polarization state and the S-polarization state perturbation position in the current signal interval, and select
  • the maximum amplitude values of the respective minimum amplitude values corresponding to the P-polarization state and the S-polarization state, respectively, are the second amplitude eigenvalues corresponding to the respective disturbance positions of the current signal interval for the P-polarization state and the S-polarization state, respectively denoted as A p rb and A s rb , where the subscript rb represents the position of the second amplitude eigenvalue after the perturbation position of the P-polarization state and the S-polarization state, respectively.
  • the phase selection of the polarization state before and after the disturbance position of each signal interval in the step E includes:
  • the P polarization state phase is selected before the perturbation position in the signal interval, and the P polarization state phase is selected after the perturbation position;
  • the S-polarization state phase is selected before the perturbation position in the signal interval, and the S-polarization state phase is selected after the perturbation position.
  • the method for suppressing coherence and polarization fading for synchronous monitoring of loss and vibration according to the present invention adopts the above technical solution compared with the prior art, and has the following technical effects:
  • the invention designs a coherence and polarization fading suppression method for synchronous monitoring of loss and vibration.
  • the polarization diversity measurement method solves the problem of polarization state between ⁇ -OTDR and COTDR.
  • the ability to identify small loss events can be enhanced. It can reconstruct the vibration signal with high fidelity, thus effectively reducing the false alarm rate of external disturbance early warning.
  • FIG. 1 is a schematic diagram of a system architecture of a coherence and polarization fading suppression method for synchronous monitoring of loss and vibration designed by the present invention
  • FIG. 2 is a schematic diagram of the optical fiber connection to be tested in the design of the present invention.
  • Fig. 3 is the coherence and polarization fading suppression method flow chart of the loss and vibration synchronous monitoring designed by the present invention
  • Fig. 4 is the amplitude waterfall diagram between 2s near the P-state PZT in the embodiment
  • Fig. 5 is 216 curve loss test results in the embodiment
  • FIG. 7 is the phase information extracted from the two states and the reconstruction result after optimization in the embodiment.
  • Fiber to be tested 1 1. Fiber to be tested 2
  • Fiber to be tested 2 3. Cylindrical cylindrical piezoelectric ceramic for experiment.
  • the present invention designs a coherence and polarization fading suppression method for synchronous monitoring of loss and vibration.
  • the method is implemented based on a specifically designed system architecture.
  • the system specifically includes a laser , optical couplers, acousto-optic modulators, optical amplifiers, circulators, pre-amplification polarization diversity receivers (Pre-PDR), polarization controllers, control and processing modules, data acquisition cards (DAQ), pulse signal generators, And P-polarized state signal filtering device and S-polarized state filtering device.
  • the laser is connected to the control and processing module, and the laser sweeps frequency based on the preset frequency sweep speed from the control and processing module to generate a continuous optical signal;
  • the optical output end of the laser is connected to the input end of the optical coupler, and the optical coupler targets the
  • the received continuous optical signal is divided into beams, and the detection optical signal and the local oscillator optical signal are obtained respectively;
  • the local oscillator optical signal output end of the optical coupler is connected to the input end of the polarization controller, and the polarization controller is used for the received local oscillator light.
  • the polarization state of the signal is adjusted; the detection optical signal output end of the optocoupler is connected to the input end of the acousto-optic modulator, and the acousto-optic modulator is controlled by the pulse modulation signal output by the pulse signal generator for the received detection signal.
  • the optical signal is modulated to obtain probe optical pulses and frequency-shifted.
  • the output end of the acousto-optic modulator is connected to the input end of the optical amplifier, and the acousto-optic modulator transmits the detection light pulse to the optical amplifier for amplification processing; the output end of the optical amplifier is connected to the circulator, and the optical amplifier transmits the detection light pulse to the ring
  • the circulator transmits the probe light pulse to the fiber to be tested, and receives the RBS signal returned by the fiber to be tested;
  • the pre-amplification polarization diversity receiver (Pre-PDR) is connected to the circulator and the polarization controller respectively, and the pre-amplification type polarization diversity receiver (Pre-PDR) is connected to the circulator and the polarization controller.
  • the Amplifying Polarization Diversity Receiver receives the RBS signal from the circulator and the local oscillator optical signal from the polarization controller respectively, and realizes the coherent processing of each polarization state in the RBS signal and the local oscillator optical signal, respectively obtaining The P polarization state intermediate frequency signal and the S polarization state intermediate frequency signal are output.
  • the P-polarized state signal filtering device and the S-polarized state signal filtering device have the same structure, respectively filter-amplify-re-amplify the P-polarized state intermediate frequency signal and the S-polarized state intermediate frequency signal from the output end of the pre-amplification polarization diversity receiver (Pre-PDR). Filter processing to update and output the polarization state intermediate frequency signal.
  • Pre-PDR pre-amplification polarization diversity receiver
  • the output ends of the P-polarization signal filtering device and the S-polarization signal filtering device are connected to the two input ends of the data acquisition card (DAQ), and the data acquisition card (DAQ) outputs the updated polarization from the two polarization state signal filtering devices.
  • the state intermediate frequency signal is collected, and transmitted to the control and processing module for data processing, and the coherence and polarization fading suppression method for synchronous monitoring of loss and vibration is implemented; the pulse signal generator is based on the output of the data acquisition card (DAQ).
  • the clock signal synchronized with the polarization state intermediate frequency signal generates a pulse modulation signal for driving the acousto-optic modulator to generate the detection pulse light, and sends it to the acousto-optic modulator.
  • the two polarization state signal filtering devices in the system respectively include a first bandpass filter, a low-noise electrical amplifier, and a second bandpass filter.
  • the first The input end of the band-pass filter constitutes the input end of the polarization state signal filtering device
  • the output end of the first band-pass filter is connected to the input end of the corresponding low-noise electrical amplifier
  • the output end of the low-noise electrical amplifier is connected to the corresponding second band-pass filter
  • the output end of the second bandpass filter constitutes the output end of the corresponding polarization state signal filtering device
  • the first bandpass filter is used to filter out the unwanted signal and broadband noise in the received polarization state intermediate frequency signal, and executes
  • the first-stage filtering process realizes the update of the polarization state intermediate frequency signal
  • the low-noise electrical amplifier is used to amplify and update the polarization state intermediate frequency signal output by the first bandpass filter
  • the second bandpass filter realizes the update of the polarization
  • the erbium-doped fiber amplifier is specifically selected; for the laser, the narrow linewidth tunable laser is specifically selected.
  • the system constructed based on the above practical application specifically implements the coherence and polarization fading suppression method designed by the present invention for synchronous monitoring of loss and vibration.
  • the following steps A to F are specifically performed.
  • Step A For the P-polarized state intermediate frequency signal and the S-polarized state intermediate-frequency signal in the two-way orthogonal polarization state intermediate-frequency signal respectively, perform IQ demodulation, obtain the P-polarized state amplitude distribution matrix, P-polarized state corresponding to the P-polarized state intermediate-frequency signal. state phase distribution matrix, and the S-polarization state amplitude distribution matrix and S-polarization state phase distribution matrix corresponding to the S-polarized state intermediate frequency signal, and then enter step B; wherein, the amplitude distribution matrix represents the distribution of signal amplitude over time and distance, and the phase distribution The matrix represents the distribution of the signal phase over time and distance.
  • Step B According to the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix, obtain the P-polarization state perturbation position and the S-polarization state perturbation position, respectively, and then proceed to step C.
  • Step C Respectively for the P polarization state amplitude distribution matrix and the S polarization state amplitude distribution matrix, according to the preset size time domain window TWsize, divide along the time axis, and obtain the signal interval of each TWsize duration corresponding to the P polarization state amplitude distribution matrix , and the signal interval of each TWsize duration corresponding to the S-polarization state amplitude distribution matrix, and then enter step D.
  • Step D For each signal interval divided by the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix, respectively, calculate the first amplitude of the P-polarization state and the S-polarization state in the spatial resolution width before the perturbation position of the current signal interval respectively.
  • step D is specifically designed to perform steps D1 to D2 for each signal interval divided by the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix to obtain each signal interval of the P-polarization state and the S-polarization state.
  • Step D1 According to the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix, obtain the minimum amplitude values of each spatial position in the current signal interval before the P-polarization state and the S-polarization state perturbation position, and within the spatial resolution width range, respectively, and select The maximum amplitude value of the minimum amplitude values corresponding to the P-polarization state and the S-polarization state respectively, as the first amplitude eigenvalues corresponding to the P-polarization state and the S-polarization state respectively before the respective disturbance positions in the current signal interval, respectively denoted as A p ra and A s ra , where the subscript ra represents the position of the first amplitude eigenvalue before the disturbance position in the signal interval corresponding to the P polarization state and the S polarization state, respectively.
  • Step D2 According to the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix, respectively obtain the minimum amplitude value of each spatial position within the spatial resolution width range after the P-polarization state and the S-polarization state perturbation position in the current signal interval, and select
  • the maximum amplitude values of the respective minimum amplitude values corresponding to the P-polarization state and the S-polarization state, respectively, are the second amplitude eigenvalues corresponding to the respective disturbance positions of the current signal interval for the P-polarization state and the S-polarization state, respectively denoted as A p rb and A s rb , where the subscript rb represents the position of the second amplitude eigenvalue after the perturbation position of the P-polarization state and the S-polarization state, respectively.
  • Step E Based on the P-polarization state phase distribution matrix and the S-polarization state phase distribution matrix, for each signal interval divided by the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix, first select the corresponding P-polarization state and S-polarization state.
  • the phase and position of the polarization state corresponding to the larger first amplitude eigenvalue (max ⁇ A p ra ,A s ra ⁇ ) in the spatial resolution width before the disturbance position in the current signal interval are taken as the current signal interval before the disturbance position.
  • Polarization state phase select the polarization corresponding to the second amplitude eigenvalue (max ⁇ A p rb ,A s rb ⁇ ) corresponding to the larger second amplitude eigenvalue (max ⁇ A p rb ,A s rb ⁇ ) in the spatial resolution width after the disturbance position of the current signal interval corresponding to the P polarization state and the S polarization state
  • the phase of the polarization state after the disturbance position in the current signal interval is used as the polarization state phase; then the phase difference operation is performed on the polarization state phase selected before and after the disturbance position in the current signal interval to realize phase extraction and obtain the phase of the disturbance position in the current signal interval. and then obtain the phase signal of the disturbance position in each signal interval, realize the reconstruction of the phase signal of the disturbance position, and then enter step F.
  • phase selection of the polarization state before and after the disturbance position of each signal interval in step E includes:
  • the P polarization state phase is selected before the perturbation position in the signal interval, and the P polarization state phase is selected after the perturbation position;
  • the S-polarization state phase is selected before the perturbation position in the signal interval, and the S-polarization state phase is selected after the perturbation position.
  • Step F According to the reconstructed phase signal of the disturbance position in each signal interval, phase unwinding is performed, and the fiber expansion and contraction situation at the disturbance position caused by the external disturbance signal is restored, that is, the disturbance monitoring result of the fiber to be tested is obtained.
  • step A based on the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix obtained in step A, the following steps I to II are also included to realize the acquisition of the monitoring result of the fiber loss under test:
  • Step 1 Sequence along the time axis, respectively carry out the square sum processing to the P polarization state amplitude distribution matrix and the S polarization state amplitude distribution matrix, obtain the square sum result of the P polarization state amplitude distribution matrix, and the S polarization state amplitude distribution matrix sum of squares result, Then enter step II;
  • Step II Accumulate and average the result of the square sum of the P-polarization state amplitude distribution matrix and the S-polarization state amplitude distribution matrix square sum result to obtain the loss monitoring result of the fiber to be tested.
  • the system uses a narrow linewidth tunable NKT laser with a wavelength of 1550.12nm and a linewidth of 3.7kHz as the light source, and its optical frequency is tuned by a programmable driver controlled by the control and processing module.
  • the continuous light output by the NKT laser is divided into two parts by a 90:10 optical coupler, of which 90% of the light is used as the probe light, and the 10% of the light is used as the local oscillator light.
  • the probe light is modulated into a 200MHz frequency-shifted light pulse by an acousto-optic modulator, and then the power is amplified by an optical amplifier.
  • the spatial resolution within 100m is sufficient to meet the requirements.
  • the modulation pulse of the acousto-optic modulator in the experiment adopts a pulse width of 1us and a period of 1ms.
  • the frequency sweep speed of 5MHz/s is selected in the experiment, which is enough to effectively suppress the influence of coherent fading on the loss measurement accuracy without sacrificing the disturbance event identification ability of ⁇ -OTDR.
  • the probe pulse light amplified by the optical amplifier is injected into the fiber to be tested through the 2 ports of the circulator.
  • the fiber to be tested 1 and the fiber to be tested 2 are single-mode fibers with lengths of about 71 km and 1 km, respectively.
  • An optical fiber of about 30 m was wound on the surface of the cylindrical cylindrical piezoelectric ceramic (PZT) used for the experiment to simulate the vibration of the external sound field.
  • PZT cylindrical cylindrical piezoelectric ceramic
  • a 30Hz sine wave was applied to the PZT to simulate the sensing fiber being disturbed by the external sound field.
  • the RBS light generated in the fiber is returned through the 2 port of the circulator, and is output by the 3 port and received by the pre-amplification polarization diversity coherent receiver (Pre-PDR) together with the local oscillator light. Adjust the polarization state to equalize the IF signal intensity of the P state and S state output by the Pre-PDR, so that the average intensity is as consistent as possible.
  • the coherent beat frequency generates P-state and S-state intermediate frequency signals, which are further filtered and amplified by a band-pass filter with a center frequency of 200MHz and a low-noise amplifier, and finally collected by a data acquisition card (DAQ), and transmitted to the control and
  • DAQ data acquisition card
  • the processing module performs data processing.
  • the system sampling rate is 1.25GSa/s.
  • the bandwidth of the first band-pass filter and the second band-pass filter range from 195MHz to 205MHz, and the gain of the low-noise amplifier is 27dB.
  • the function of the polarization state signal filtering device is mainly to filter out useless signals. At the same time amplify the weak electrical signal generated by photoelectric conversion.
  • the P-state amplitude distribution matrix and the S-state amplitude distribution matrix are respectively divided into the time domain along the time axis according to the time domain window TWsize of a preset size.
  • the time-domain window TWsize is set here to be 20 points, that is, 0.02s.
  • the two-state amplitude distribution matrix is divided into 428 signal intervals with end-to-end and equal width respectively.
  • phase difference operation is performed on the selected polarization state phases before and after the disturbance position in the current signal interval to realize phase extraction and obtain the phase signal of the disturbance position in the current signal interval. Then, the phase signals of the disturbance positions in 428 signal intervals are obtained to realize the reconstruction of the phase signals of the disturbance positions.
  • the fluctuations of the COTDR curves obtained by calculating the P state and the S state are 0.24dB and 0.35dB respectively, and the fluctuation of the COTDR curve obtained by accumulating and averaging the two states is 0.09B. It can be seen that by using the coherent and polarization fading suppression method for synchronous monitoring of loss and vibration provided by the present invention, not only a better coherent fading noise suppression effect can be obtained, but also the ability to identify small loss events can be enhanced.
  • FIG. 7 the phase extraction results before and after the optimization of the method provided by the present invention are shown.
  • Figure 7(c) shows the sum of the amplitudes of the ra and rb positions in the TWsize time domain of the amplitudes obtained by the demodulation of the P-state and S-state RBS signals above.
  • the distorted positions in (a) and (b) of Fig. 7 are both positions with weak amplitude.
  • (d) in FIG. 7 corresponds to the amplitude selection strategy in (c) in FIG. 7 , in the current time domain window, the one with the largest total amplitude eigenvalue is selected for phase extraction.
  • the blue domain indicates that the P state is selected
  • the red domain indicates that the S state is selected.
  • the vibration signal can be reconstructed with high fidelity, and the loss and vibration monitoring with a single-ended sensing distance of at least 71.9km can be synchronously realized.

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Abstract

本发明涉及一种损耗与振动同步监测的相干及偏振衰落抑制方法，在仅使用普通单模传感光纤的前提下，基于偏振分集的测量方式，解决了Φ-OTDR和COTDR在偏振态问题上的冲突，并且对于损耗参量的监测，不仅能够获得更好的相干衰落噪声抑制效果，还能够增强微小损耗事件的识别能力，同时对于扰动参量的监测，能够抑制相干衰落对Φ-OTDR相位解调的影响，高保真地重构振动信号，从而有效地降低外部扰动预警的误报率。

Description

一种损耗与振动同步监测的相干及偏振衰落抑制方法 技术领域
本发明涉及一种损耗与振动同步监测的相干及偏振衰落抑制方法，属于光纤传感技术领域。
背景技术
相干光时域反射仪(Coherent Optical Time Domain Reflectometry，COTDR)采用相干探测将瑞利背向散射信号(Rayleigh Backscattering Signal，RBS)光学信号转换为某一特定中频的电学信号。通过对该中频信号进行电学的窄带滤波，抑制绝大部分的ASE噪声，从而使其能够监测多中继超长距离光纤通信线路。近年来，COTDR技术仍有持续改进，主要依托频分复用技术提高监测通道的带宽利用效率，缩短测量耗时，但就其目标参量而言仍局限在对光纤损耗参量的监测。这就造成基于COTDR的光纤链路监测***仅能够进行事后的故障诊断与定位。事实上，在出现真正的不可逆转的损伤之前，虽然损耗值尚未出现明显的变化，但线路周边环境中的潜在威胁常通过直接接触或间接的振动信号传递，对光缆形成扰动，从而为提前预警提供依据。在扰动监测方面，相位敏感型光时域反射仪(Phase-sensitive Optical Time-Domain Reflectometry，Φ-OTDR)凭借灵敏度高和响应速度快的优点成为现阶段海缆监测技术的研究热点。
考虑到Φ-OTDR和COTDR都使用线宽窄、频率漂移小的激光器作为光源，并且在结构上外差探测Φ-OTDR与COTDR***也具有高度的相似性。为了满足光纤监测***对振动和损耗同步监测的需求，可以考虑将Φ--OTDR与COTDR技术进行结合。但是两种测量原理的融合，存在诸多矛盾和问题，例如：(1)Φ-OTDR***为了能够获得较高的监测精度，相邻RBS曲线之间必须具备较高的相似性，因此需要一个频率稳定的光源，而COTDR则需要进行主动扫频和多点数字平均技术来抑制相干衰落噪声，产生对光源工作模式的需求冲突；(2)对于Φ-OTDR而言，偏振态的改变会在检测信号中引入随时间变化的偏振分量，影响振动测量精度。而COTDR中常采用扰偏器对光本振光(Optical Local Oscillator，OLO)光的偏振态进行快速扰动，以抑制由于RBS与OLO偏振态不匹配导致的偏振衰落噪声，这与Φ-OTDR希望偏振态高度稳定的要求相矛盾；(3)目前Φ-OTDR解调方法有两种：鉴幅型和鉴相型。鉴幅型解调方法根据RBS的幅度信息快速定位振动事件。由于RBS的幅度变化与振动事件引起的光纤动态应变没有明确的线性关系，因此鉴幅型解调方法通常仅能够做定性测量，无法高保真地重构扰动事件的时频特征。鉴相型解调方法利用RBS的相位变化与光纤局部区域的动态应变之间的线性关系，可以精准还 原扰动事件，提升后续模式识别的准确性。但是由于相干衰落，光纤某些区域强度趋近于零，在这些区域相位解调结果很容易出现信噪比的急剧恶化导致频繁的误报警。
发明内容
本发明所要解决的技术问题是提供一种损耗与振动同步监测的相干及偏振衰落抑制方法，采用全新设计方法，在实现光纤链路损耗监测的同时，能够实现扰动事件的预警。
本发明为了解决上述技术问题采用以下技术方案：本发明设计了一种损耗与振动同步监测的相干及偏振衰落抑制方法，基于针对待测光纤采用偏振分集探测方式获得的两路正交偏振态中频信号，执行如下步骤A至步骤F：
步骤A.分别针对两路正交偏振态中频信号中的P偏振态中频信号与S偏振态中频信号，执行IQ解调，获得P偏振态中频信号所对应的P偏振态幅度分布矩阵、P偏振态相位分布矩阵，以及S偏振态中频信号所对应的S偏振态幅度分布矩阵、S偏振态相位分布矩阵，然后进入步骤B；其中，幅度分布矩阵表示信号幅度随时间、距离的分布，相位分布矩阵表示信号相位随时间、距离的分布；
步骤B.根据P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，分别获得P偏振态扰动位置和S偏振态扰动位置，然后进入步骤C；
步骤C.分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，按预设大小时域窗口TWsize，沿时间轴进行划分，获得P偏振态幅度分布矩阵所对应的各个TWsize时长的信号区间，以及S偏振态幅度分布矩阵所对应的各个TWsize时长的信号区间，然后进入步骤D；
步骤D.分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵划分后的各信号区间，计算P偏振态和S偏振态分别对应当前信号区间扰动位置前空间分辨率宽度内的第一幅度特征值、以及所在位置；同时，计算P偏振态和S偏振态分别对应当前信号区间扰动位置后空间分辨率宽度内的第二幅度特征值、以及所在位置；进而分别获得P偏振态与S偏振态各个信号区间扰动位置前和扰动位置后空间分辨率宽度内的第一幅度特征值和第二幅度特征值，以及该第一幅度特征值和第二幅度特征值所对应的位置，然后进入步骤E；
步骤E.基于P偏振态相位分布矩阵与S偏振态相位分布矩阵，分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵划分后的各信号区间，首先选择P偏振态和S偏振态对应当前信号区间扰动位置前空间分辨率宽度内较大的第一幅度特征值所对应的偏振态相位、以及所在位置，作为当前信号区间扰动位置前的偏振态相位；同时，选择P偏 振态和S偏振态对应当前信号区间扰动位置后空间分辨率宽度内较大的第二幅度特征值所对应的偏振态相位、以及所在位置，作为当前信号区间扰动位置后的偏振态相位；然后对当前信号区间扰动位置前后所选的偏振态相位进行相位差运算，实现相位提取，获得当前信号区间扰动位置的相位信号；进而获得各个信号区间扰动位置的相位信号，实现扰动位置相位信号重构，然后进入步骤F；
步骤F.根据各信号区间扰动位置的重构相位信号，执行相位解缠绕，还原由外部扰动信号所引起的扰动位置处的光纤伸缩情况，即获得待测光纤的扰动监测结果。
作为本发明的一种优选技术方案，基于步骤A所获P偏振态幅度分布矩阵与S偏振态幅度分布矩阵，还包括执行如下步骤I至步骤II，实现对待测光纤损耗监测结果的获得：
步骤I.沿时间轴顺序，分别对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵进行平方和处理，获得P偏振态幅度分布矩阵平方和结果，以及S偏振态幅度分布矩阵平方和结果，然后进入步骤II；
步骤II.针对P偏振态幅度分布矩阵平方和结果与S偏振态幅度分布矩阵平方和结果，进行累加平均处理，获得待测光纤的损耗监测结果。
作为本发明的一种优选技术方案，所述步骤D包括如下：
分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵划分后的各信号区间，执行步骤D1至步骤D2，获得P偏振态与S偏振态各信号区间扰动位置前和扰动位置后空间分辨率宽度内的第一幅度特征值和第二幅度特征值，以及该第一幅度特征值和第二幅度特征值所对应的位置，然后进入步骤E；
步骤D1.根据P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，分别获得当前信号区间P偏振态和S偏振态扰动位置前、空间分辨率宽度范围内各空间位置的最小幅度值，并选取P偏振态和S偏振态分别所对应该各最小幅度值中的最大幅度值，作为P偏振态和S偏振态分别对应当前信号区间各自扰动位置前所对应的第一幅度特征值，分别记为A p ra和A s ra,其中下标ra表示P偏振态、S偏振态分别对应信号区间各自扰动位置前第一幅度特征值所在位置；
步骤D2.根据P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，分别获得当前信号区间P偏振态和S偏振态扰动位置后、空间分辨率宽度范围内各空间位置的最小幅度值，并选取P偏振态和S偏振态分别所对应该各最小幅度值的最大幅度值，作为P偏振态和S偏振态分别对应当前信号区间各自扰动位置后所对应的第二幅度特征值，分别记为A p rb和A s rb,其中下标rb表示P偏振态、S偏振态分别对应信号区间各自扰动位置后第二幅度 特征值所在位置。
作为本发明的一种优选技术方案，所述步骤E中各信号区间扰动位置前、后的偏振态相位选择包括：
(1)信号区间扰动位置前选择了P偏振态相位，扰动位置后选择了P偏振态相位；
(2)信号区间扰动位置前选择了P偏振态相位，扰动位置后选择了S偏振态相位；
(3)信号区间扰动位置前选择了S偏振态相位，扰动位置后选择了P偏振态相位；
(4)信号区间扰动位置前选择了S偏振态相位，扰动位置后选择了S偏振态相位。
本发明所述一种损耗与振动同步监测的相干及偏振衰落抑制方法，采用以上技术方案与现有技术相比，具有以下技术效果：
本发明所设计一种损耗与振动同步监测的相干及偏振衰落抑制方法，在仅使用普通单模传感光纤的前提下，基于偏振分集的测量方式，解决了Φ-OTDR和COTDR在偏振态问题上的冲突，并且对于损耗参量的监测，不仅能够获得更好的相干衰落噪声抑制效果，还能够增强微小损耗事件的识别能力，同时对于扰动参量的监测，能够抑制相干衰落对Φ-OTDR相位解调的影响，高保真地重构振动信号，从而有效地降低外部扰动预警的误报率。
附图说明
图1是本发明所设计损耗与振动同步监测的相干及偏振衰落抑制方法的***架构示意图；
图2为本发明所设计中待测光纤连接示意图；
图3是本发明所设计损耗与振动同步监测的相干及偏振衰落抑制方法流程图；
图4是实施例中P态PZT附近2s间的幅度瀑布图；
图5是实施例中2 16条曲线损耗测试结果；
图6是实施例中损耗测试结果局部放大图；
图7是实施例中两态提取的相位信息及经过优选后的重建结果。
其中，1.待测光纤1，2.待测光纤2，3.实验用圆筒形柱状压电陶瓷。
具体实施方式
下面结合说明书附图对本发明的具体实施方式作进一步详细的说明。
本发明设计了一种损耗与振动同步监测的相干及偏振衰落抑制方法，该方法是基于具体所设计的***架构去实现执行的，实际应用设计中，如图1所示，该***具体包括激光器、光耦合器、声光调制器、光放大器、环形器、预放型偏振分集接收器(Pre-PDR)、 偏振控制器、控制及处理模块、数据采集卡(DAQ)、脉冲信号发生器、以及P偏振态信号滤波装置和S偏振态滤波装置。
其中，激光器与控制及处理模块相连，激光器基于来自控制及处理模块的预设扫频速度进行扫频，产生连续光信号；激光器的光输出端对接光耦合器的输入端，由光耦合器针对所接收的连续光信号进行分束，分别获得探测光信号与本振光信号；光耦合器的本振光信号输出端对接偏振控制器的输入端，由偏振控制器针对所接收的本振光信号的偏振态进行调整；光耦合器的探测光信号输出端对接声光调制器的输入端，由声光调制器在脉冲信号发生器所输出脉冲调制信号的控制下、针对所接收到的探测光信号进行调制，获得探测光脉冲，并进行移频。
声光调制器的输出端对接光放大器的输入端，由声光调制器将探测光脉冲输送至光放大器进行放大处理；光放大器的输出端对接环形器，由光放大器将探测光脉冲输送至环形器，由环形器将探测光脉冲传输至待测光纤，并接收待测光纤返回的RBS信号；预放型偏振分集接收器(Pre-PDR)分别与环形器、偏振控制器相连接，由预放型偏振分集接收器(Pre-PDR)分别接收来自环形器的RBS信号、以及来自偏振控制器的本振光信号，并实现RBS信号中各偏振态与本振光信号的相干处理，分别获得P偏振态中频信号和S偏振态中频信号进行输出。
P偏振态信号滤波装置和S偏振态信号滤波装置结构相同，分别针对来自预放型偏振分集接收器(Pre-PDR)输出端的P偏振态中频信号和S偏振态中频信号进行滤波-放大-再滤波处理，实现偏振态中频信号的更新、并输出。
P偏振态信号滤波装置和S偏振态信号滤波装置的输出端对接数据采集卡(DAQ)的两路输入端，由数据采集卡(DAQ)对来自两路偏振态信号滤波装置输出更新后的偏振态中频信号进行采集，并传输至控制及处理模块进行数据处理，执行所述一种损耗与振动同步监测的相干及偏振衰落抑制方法；脉冲信号发生器基于与数据采集卡(DAQ)所输出各偏振态中频信号相同步的时钟信号，生成用于驱动声光调制器产生探测脉冲光的脉冲调制信号，并输送至声光调制器。
实际设计应用中，该***中的两路偏振态信号滤波装置分别均包括第一带通滤波器、低噪声电学放大器、第二带通滤波器，两路偏振态信号滤波装置结构中，第一带通滤波器的输入端构成偏振态信号滤波装置的输入端，第一带通滤波器的输出端对接对应低噪声电学放大器的输入端，低噪声电学放大器的输出端对接对应第二带通滤波器的输入端，第二带通滤波器的输出端构成对应偏振态信号滤波装置的输出端；第一带通滤波器用于滤除所 接收偏振态中频信号中的无用信号、以及宽带噪声，执行第一级滤波处理，实现对偏振态中频信号的更新；低噪声电学放大器用于针对第一带通滤波器输出的偏振态中频信号，实现放大更新；第二带通滤波器用于针对对应低噪声电学放大器输出的偏振态中频信号，滤除其中的无用信号、以及宽带噪声，执行第二级滤波处理，实现对偏振态中频信号的更新输出。
并且在实际的***搭建中，针对光放大器，具体选用为掺铒光纤放大器；针对激光器，具体选用窄线宽可调激光器。
基于上述实际应用所搭建的***，具体执行本发明所设计损耗与振动同步监测的相干及偏振衰落抑制方法，基于针对待测光纤采用偏振分集探测方式获得的两路正交偏振态中频信号，实际应用中，如图3所示，具体执行如下步骤A至步骤F。
步骤A.分别针对两路正交偏振态中频信号中的P偏振态中频信号与S偏振态中频信号，执行IQ解调，获得P偏振态中频信号所对应的P偏振态幅度分布矩阵、P偏振态相位分布矩阵，以及S偏振态中频信号所对应的S偏振态幅度分布矩阵、S偏振态相位分布矩阵，然后进入步骤B；其中，幅度分布矩阵表示信号幅度随时间、距离的分布，相位分布矩阵表示信号相位随时间、距离的分布。
步骤B.根据P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，分别获得P偏振态扰动位置和S偏振态扰动位置，然后进入步骤C。
步骤C.分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，按预设大小时域窗口TWsize，沿时间轴进行划分，获得P偏振态幅度分布矩阵所对应的各个TWsize时长的信号区间，以及S偏振态幅度分布矩阵所对应的各个TWsize时长的信号区间，然后进入步骤D。
步骤D.分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵划分后的各信号区间，计算P偏振态和S偏振态分别对应当前信号区间扰动位置前空间分辨率宽度内的第一幅度特征值、以及所在位置；同时，计算P偏振态和S偏振态分别对应当前信号区间扰动位置后空间分辨率宽度内的第二幅度特征值、以及所在位置；进而分别获得P偏振态与S偏振态各个信号区间扰动位置前和扰动位置后空间分辨率宽度内的第一幅度特征值和第二幅度特征值，以及该第一幅度特征值和第二幅度特征值所对应的位置，然后进入步骤E。
实际应用当中，上述步骤D具体设计，分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵划分后的各信号区间，执行步骤D1至步骤D2，获得P偏振态与S偏振态 各信号区间扰动位置前和扰动位置后空间分辨率宽度内的第一幅度特征值和第二幅度特征值，以及该第一幅度特征值和第二幅度特征值所对应的位置，然后进入步骤E。
步骤D1.根据P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，分别获得当前信号区间P偏振态和S偏振态扰动位置前、空间分辨率宽度范围内各空间位置的最小幅度值，并选取P偏振态和S偏振态分别所对应该各最小幅度值中的最大幅度值，作为P偏振态和S偏振态分别对应当前信号区间各自扰动位置前所对应的第一幅度特征值，分别记为A p ra和A s ra,其中下标ra表示P偏振态、S偏振态分别对应信号区间各自扰动位置前第一幅度特征值所在位置。
步骤D2.根据P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，分别获得当前信号区间P偏振态和S偏振态扰动位置后、空间分辨率宽度范围内各空间位置的最小幅度值，并选取P偏振态和S偏振态分别所对应该各最小幅度值的最大幅度值，作为P偏振态和S偏振态分别对应当前信号区间各自扰动位置后所对应的第二幅度特征值，分别记为A p rb和A s rb,其中下标rb表示P偏振态、S偏振态分别对应信号区间各自扰动位置后第二幅度特征值所在位置。
步骤E.基于P偏振态相位分布矩阵与S偏振态相位分布矩阵，分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵划分后的各信号区间，首先选择P偏振态和S偏振态对应当前信号区间扰动位置前空间分辨率宽度内较大的第一幅度特征值(max{A p ra,A s ra})所对应的偏振态相位、以及所在位置，作为当前信号区间扰动位置前的偏振态相位；同时，选择P偏振态和S偏振态对应当前信号区间扰动位置后空间分辨率宽度内较大的第二幅度特征值(max{A p rb,A s rb})所对应的偏振态相位、以及所在位置，作为当前信号区间扰动位置后的偏振态相位；然后对当前信号区间扰动位置前后所选的偏振态相位进行相位差运算，实现相位提取，获得当前信号区间扰动位置的相位信号；进而获得各个信号区间扰动位置的相位信号，实现扰动位置相位信号重构，然后进入步骤F。
实际应用中，步骤E中各信号区间扰动位置前、后的偏振态相位选择包括：
(1)信号区间扰动位置前选择了P偏振态相位，扰动位置后选择了P偏振态相位；
(2)信号区间扰动位置前选择了P偏振态相位，扰动位置后选择了S偏振态相位；
(3)信号区间扰动位置前选择了S偏振态相位，扰动位置后选择了P偏振态相位；
(4)信号区间扰动位置前选择了S偏振态相位，扰动位置后选择了S偏振态相位。
为抑制相干及偏振衰落提供了多种选择，从而实现更好的相干及偏振衰落抑制效果。
步骤F.根据各信号区间扰动位置的重构相位信号，执行相位解缠绕，还原由外部扰 动信号所引起的扰动位置处的光纤伸缩情况，即获得待测光纤的扰动监测结果。
实际应用中，基于步骤A所获P偏振态幅度分布矩阵与S偏振态幅度分布矩阵，还包括执行如下步骤I至步骤II，实现对待测光纤损耗监测结果的获得：
步骤I.沿时间轴顺序，分别对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵进行平方和处理，获得P偏振态幅度分布矩阵平方和结果，以及S偏振态幅度分布矩阵平方和结果，然后进入步骤II；
步骤II.针对P偏振态幅度分布矩阵平方和结果与S偏振态幅度分布矩阵平方和结果，进行累加平均处理，获得待测光纤的损耗监测结果。
将本发明所设计损耗与振动同步监测的相干及偏振衰落抑制方法，应用于实际当中，以长距离海缆监测为例，结合附图对本发明的技术方案做进一步的详细说明：
如图1所示，***采用波长为1550.12nm、线宽为3.7kHz的窄线宽可调谐NKT激光器作为光源，通过控制及处理模块控制的可编程驱动器对其光频率进行调谐。NKT激光器输出的连续光被90:10的光耦合器分成两部分，其中90％的一路作为探测光，10％的一路作为本振光。探测光经声光调制器被调制为200MHz频移的光脉冲，再利用光放大器进行功率放大。针对长距离海缆监测海上定位的需求，100m以内的空间分辨率足以满足要求。因此实验中声光调制器的调制脉冲采用1us脉宽，周期为1ms。为了确保Φ-OTDR对外部扰动的测量精度，同时抑制RBS曲线的幅度波动，根据Φ-OTDR对相邻RBS曲线相关度的要求，以及扫频速度与调制信号脉宽、周期之间的关系，实验中选取了5MHz/s的扫频速度，这足以有效地抑制相干衰落对损耗测量精度的影响，而不牺牲Φ-OTDR的扰动事件识别能力。经光放大器放大后的探测脉冲光通过环形器的2端口注入待测光纤。
基于图2所示，待测光纤1和待测光纤2分别为长度约71km和1km的单模光纤。在实验用圆筒形柱状压电陶瓷(PZT)表面缠绕了约30m光纤，用于模拟产生外界声场的振动。实验中，对PZT施加了30Hz的正弦波模拟传感光纤受到外部声场扰动。
光纤中产生的RBS光经环形器的2端口返回，并由3端口输出后与本振光被预放型偏振分集相干接收器(Pre-PDR)接收，其中本振光一路通过偏振控制器实现对其偏振态的调整，以均衡Pre-PDR输出的P态和S态的中频信号强度，使其平均强度尽量一致。相干拍频产生P态和S态两路中频信号，再分别经中心频率为200MHz的带通滤波器和低噪声放大器进一步滤波和放大，最终由数据采集卡(DAQ)进行采集，传输至控制及处理模块进行数据处理。***采样率为1.25GSa/s。其中，第一带通滤波器和第二带通滤波器的带宽通带范围为195MHz～205MHz，低噪声放大器的增益为27dB，该偏振态信号 滤波装置的作用主要是为了滤除无用的信号，同时放大光电转换产生的微弱电信号。
采集后的数据处理如图3所示，具体过程如下：
(1)分别对采集到的两路中频信号(P态和S态)分别进行IQ解调，获得两态中频信号的幅度分布矩阵A p m×n和A s m×n，以及相位分布矩阵Φ p m×n和Φ s m×n，其中，A和Φ均为由时间行和距离列组成的m×n列的矩阵，二者中每一行分别代表着幅度和相位随距离的分布，每一列分别代表着幅度和相位随时间的变化。
(2)根据P态幅度分布矩阵和S态幅度分布矩阵，分别获得P偏振态扰动位置和S偏振态扰动位置，如图4所示，为P态PZT附近2s间的幅度瀑布图，图中虚线区域可以清楚地看到约71.9km处检测到了一个周期性的信号。
(3)分别对P态幅度分布矩阵和S态幅度分布矩阵，按预设大小时域窗口TWsize，沿时间轴进行时域划分。考虑到海底扰动事件的低频特性，这里设置时域窗口TWsize选择为20个点，即0.02s。将两态幅度分布矩阵分别划分为首尾相接且等宽度的428个信号区间。
(4)沿被划分的428个信号区间的时间轴，比较两态幅度分布矩阵在当前时域宽度TWsize下扰动位置前的第一幅度特征值和扰动位置后的第二幅度特征值，选择两态当前信号区间扰动位置前空间分辨率宽度内较大的第一幅度特征值(max{A p ra,A s ra})所对应的偏振态相位及所在位置ra，作为扰动位置前的偏振态相位；同时，选择两态当前信号区间扰动位置后空间分辨率宽度内较大的第二幅度特征值(max{A p rb,A s rb})所对应的偏振态相位及所在位置rb，作为扰动位置后的偏振态相位。对当前信号区间扰动位置前后所选的偏振态相位进行相位差运算，实现相位提取，获得当前信号区间扰动位置的相位信号。进而获得428个信号区间扰动位置的相位信号，实现扰动位置相位信号重构。
(5)对重构的相位信号进行解缠绕，还原由外部扰动信号引起的扰动位置处的光纤伸缩情况，获得扰动监测结果，从而实现对外部扰动信号的感测。
(6)分别对两态幅度矩阵A p m×n和A s m×n沿时间轴进行平方，得到两态幅度矩阵的平方和AP和AS。
(7)对两态平方和矩阵AP和AS再进行累加平均，得到AT曲线，从而获得损耗监测结果，如图5所示。其中，图5中的(a)和(b)分别为P偏振态和S偏振态各自获得的2 16条RBS曲线进行平均的结果，图5中的(c)为两态RBS曲线总条数平均的改进结果，可以看到将两态的RBS曲线进一步平均后，得到的COTDR曲线更加平滑，获得了59.2dB的总动态范围，对应的单程动态范围(Single-Way Dynamic Range，SWDR)为 29.6dB。图6为图5中30km～40km的局部放大图，经计算P态和S态获得的COTDR曲线的波动分别为0.24dB和0.35dB，将两态累加平均获得COTDR曲线的波动为0.09B。可见，利用本发明提供的一种损耗与振动同步监测的相干及偏振衰落抑制方法，不仅能够获得更好的相干衰落噪声抑制效果，还能够增强微小损耗事件的识别能力。
如图7所示，展示了经过本发明提供的方法优选前后的相位提取结果。为了能够凸显偏振分集幅度优选的效果，在已知施加信号频率的基础上，我们对各自鉴相结果进行带通滤波。由上至下，图7中(a)和(b)分别为P态和S态各自RBS的重构振动信号波形图，可以看到未进行本发明的优选算法之前，两态RBS提取的相位信号均存在多处畸变；图7中(c)展示了上文P态和S态RBS信号解调得到的幅度在TWsize时域内ra和rb位置的幅度总和。与相应的信号强度相比，图7中(a)和(b)中的失真位置均为幅值较弱的位置。图7中(d)对应了图7中(c)的幅值选择策略，在当前时域窗口内选择最大总幅度特征值的一方进行相位提取。其中，蓝色域表示选择了P态，红色域表示选择了S态，从图中可以看到，随着时间的推移，其相位提取一直在两个偏振态中跳转，从而获得了如图7中(e)所示的重建相位信号波形图。
可见，利用本发明提供的一种损耗与振动同步监测的相干及偏振衰落抑制方法，能够高保真地重构振动信号，并且同步实现了单端传感距离至少71.9km的损耗与振动监测。
上面结合附图对本发明的实施方式作了详细说明，但是本发明并不限于上述实施方式，在本领域普通技术人员所具备的知识范围内，还可以在不脱离本发明宗旨的前提下做出各种变化。

Claims (4)

  1. 一种损耗与振动同步监测的相干及偏振衰落抑制方法，其特征在于：基于针对待测光纤采用偏振分集探测方式获得的两路正交偏振态中频信号，执行如下步骤A至步骤F：
    步骤A.分别针对两路正交偏振态中频信号中的P偏振态中频信号与S偏振态中频信号，执行IQ解调，获得P偏振态中频信号所对应的P偏振态幅度分布矩阵、P偏振态相位分布矩阵，以及S偏振态中频信号所对应的S偏振态幅度分布矩阵、S偏振态相位分布矩阵，然后进入步骤B；其中，幅度分布矩阵表示信号幅度随时间、距离的分布，相位分布矩阵表示信号相位随时间、距离的分布；
    步骤B.根据P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，分别获得P偏振态扰动位置和S偏振态扰动位置，然后进入步骤C；
    步骤C.分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，按预设大小时域窗口TWsize，沿时间轴进行划分，获得P偏振态幅度分布矩阵所对应的各个TWsize时长的信号区间，以及S偏振态幅度分布矩阵所对应的各个TWsize时长的信号区间，然后进入步骤D；
    步骤D.分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵划分后的各信号区间，计算P偏振态和S偏振态分别对应当前信号区间扰动位置前空间分辨率宽度内的第一幅度特征值、以及所在位置；同时，计算P偏振态和S偏振态分别对应当前信号区间扰动位置后空间分辨率宽度内的第二幅度特征值、以及所在位置；进而分别获得P偏振态与S偏振态各个信号区间扰动位置前和扰动位置后空间分辨率宽度内的第一幅度特征值和第二幅度特征值，以及该第一幅度特征值和第二幅度特征值所对应的位置，然后进入步骤E；
    步骤E.基于P偏振态相位分布矩阵与S偏振态相位分布矩阵，分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵划分后的各信号区间，首先选择P偏振态和S偏振态对应当前信号区间扰动位置前空间分辨率宽度内较大的第一幅度特征值所对应的偏振态相位、以及所在位置，作为当前信号区间扰动位置前的偏振态相位；同时，选择P偏振态和S偏振态对应当前信号区间扰动位置后空间分辨率宽度内较大的第二幅度特征值所对应的偏振态相位、以及所在位置，作为当前信号区间扰动位置后的偏振态相位；然后对当前信号区间扰动位置前后所选的偏振态相位进行相位差运算，实现相位提取，获得当前信号区间扰动位置的相位信号；进而获得各个信号区间扰动位置的相位信号，实现扰动位置相位信号重构，然后进入步骤F；
    步骤F.根据各信号区间扰动位置的重构相位信号，执行相位解缠绕，还原由外部扰动信号所引起的扰动位置处的光纤伸缩情况，即获得待测光纤的扰动监测结果。
  2. 根据权利要求1所述一种损耗与振动同步监测的相干及偏振衰落抑制方法，其特征在于：基于步骤A所获P偏振态幅度分布矩阵与S偏振态幅度分布矩阵，还包括执行如下步骤I至步骤II，实现对待测光纤损耗监测结果的获得：
    步骤I.沿时间轴顺序，分别对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵进行平方和处理，获得P偏振态幅度分布矩阵平方和结果，以及S偏振态幅度分布矩阵平方和结果，然后进入步骤II；
    步骤II.针对P偏振态幅度分布矩阵平方和结果与S偏振态幅度分布矩阵平方和结果，进行累加平均处理，获得待测光纤的损耗监测结果。
  3. 根据权利要求1或2所述一种损耗与振动同步监测的相干及偏振衰落抑制方法，其特征在于：所述步骤D包括如下：
    分别针对P偏振态幅度分布矩阵和S偏振态幅度分布矩阵划分后的各信号区间，执行步骤D1至步骤D2，获得P偏振态与S偏振态各信号区间扰动位置前和扰动位置后空间分辨率宽度内的第一幅度特征值和第二幅度特征值，以及该第一幅度特征值和第二幅度特征值所对应的位置，然后进入步骤E；
    步骤D1.根据P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，分别获得当前信号区间P偏振态和S偏振态扰动位置前、空间分辨率宽度范围内各空间位置的最小幅度值，并选取P偏振态和S偏振态分别所对应该各最小幅度值中的最大幅度值，作为P偏振态和S偏振态分别对应当前信号区间各自扰动位置前所对应的第一幅度特征值，分别记为A p ra和A s ra,其中下标ra表示P偏振态、S偏振态分别对应信号区间各自扰动位置前第一幅度特征值所在位置；
    步骤D2.根据P偏振态幅度分布矩阵和S偏振态幅度分布矩阵，分别获得当前信号区间P偏振态和S偏振态扰动位置后、空间分辨率宽度范围内各空间位置的最小幅度值，并选取P偏振态和S偏振态分别所对应该各最小幅度值的最大幅度值，作为P偏振态和S偏振态分别对应当前信号区间各自扰动位置后所对应的第二幅度特征值，分别记为A p rb和A s rb,其中下标rb表示P偏振态、S偏振态分别对应信号区间各自扰动位置后第二幅度特征值所在位置。
  4. 根据权利要求1所述一种损耗与振动同步监测的相干及偏振衰落抑制方法，其特征在于，所述步骤E中各信号区间扰动位置前、后的偏振态相位选择包括：
    (1)信号区间扰动位置前选择了P偏振态相位，扰动位置后选择了P偏振态相位；
    (2)信号区间扰动位置前选择了P偏振态相位，扰动位置后选择了S偏振态相位；
    (3)信号区间扰动位置前选择了S偏振态相位，扰动位置后选择了P偏振态相位；
    (4)信号区间扰动位置前选择了S偏振态相位，扰动位置后选择了S偏振态相位。
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