A phase-sensitive optical time domain reflectometer and a method for eliminating polarization dependent loss

Abstract

The application provides a phase-sensitive optical time domain reflectometer, which comprises a polarization diversity receiving module, an amplification circuit and a signal acquisition and processing unit; a controller of the polarization diversity receiving module can adjust a first transimpedance amplifier, a second transimpedance amplifier and a gain multiple of the amplification circuit according to first photodetector information and the like sent by the signal acquisition and processing unit, so that the total gain of X-state electric polarization signals and Y-state electric polarization signals output by the amplification circuit is consistent, the problem of original output power imbalance is overcome from the perspective of ensuring responsivity and amplification multiple, then a polarization compensation coefficient is generated according to a preset rule to compensate for power imbalance caused by the polarization diversity receiving module manufacturing process. The application further discloses a method for eliminating polarization-dependent loss.

Description

Technical Field

[0001] This invention relates to the field of distributed optical fiber sensing technology, and in particular to a phase-sensitive optical time-domain reflectometer and a method for eliminating polarization-dependent loss. Background Technology

[0002] Distributed fiber-optic acoustic sensors (DAS) can detect and locate strain signals occurring at any position on a distributed optical fiber in real time. They offer advantages such as high measurement accuracy, resistance to electromagnetic interference, corrosion resistance, and the ability to achieve long-distance distributed sensing, making them widely used in oil and gas pipelines, security boundary demarcation, and other fields. Currently, most distributed fiber-optic acoustic sensor systems employ phase-sensitive optical time-domain reflectometry (PDDR). Related technologies, specifically: phase-sensitive optical time-domain reflectometer. Coherent detection technology is generally used, in which a narrow-linewidth light source is modulated into a pulse signal and injected into the sensing fiber. The reflected Rayleigh backscattering (RBS) signal is mixed with the intrinsic signal for coherent detection, and then demodulation is performed to obtain the intensity and phase information of the Rayleigh backscattering (RBS).

[0003] Existing technologies typically employ the following techniques to eliminate polarization-dependent losses in distributed fiber optic acoustic transmission systems: using phase-sensitive optical time-domain reflectometers... The receiver splits the Rayleigh backscattered (RBS) light into two orthogonal polarization states: X and Y. After processing and demodulating the two signals, the final intensity and phase information are obtained by averaging, thus eliminating polarization-dependent noise. However, this phase-sensitive optical time-domain reflectometer... The process requires the use of polarization-splitting devices, and signals of different polarization states will pass through independent photoelectric detection devices and electrical signal amplification circuits. Therefore, the intensity of the X-state and Y-state signals after processing is inconsistent, resulting in fluctuations in the final demodulated intensity information and the inability to eliminate polarization-related losses. Summary of the Invention

[0004] In view of the above problems, it is necessary to propose a phase-sensitive optical time-domain reflectometer. The present invention proposes a method for eliminating polarization-dependent losses to solve or partially solve the above problems. The technical solution proposed by the present invention is as follows:

[0005] A phase-sensitive optical time-domain reflectometer includes a polarization diversity receiver module, an amplifier circuit, and a signal acquisition and processing unit, wherein:

[0006] The polarization diversity receiving module includes a polarization beam splitter, a first polarization-maintaining coupler, a second polarization-maintaining coupler, a third polarization-maintaining coupler, a fourth polarization-maintaining coupler, a fifth polarization-maintaining coupler, a first photodetector, a second photodetector, a third photodetector, a fourth photodetector, a fifth photodetector, a multi-channel optical switch, a first mixer, a second mixer, a first balanced receiver, a first transimpedance amplifier, a second balanced receiver, a second transimpedance amplifier, and a controller;

[0007] The input end of the polarization beam splitter is used to receive Rayleigh backscattered light, and the output end of the polarization beam splitter is connected to the second polarization-maintaining coupler and the third polarization-maintaining coupler respectively to output two orthogonal X-state light polarization state signals and Y-state light polarization state signals.

[0008] The input of the second polarization-maintaining coupler is connected to the polarization beam splitter, and the output is connected to the first photodetector and the multi-channel optical switch, respectively.

[0009] The input end of the third polarization-maintaining coupler is connected to the polarization beam splitter, and the output end is connected to the second photodetector and the multi-channel optical switch, respectively.

[0010] The input terminal of the first polarization-maintaining coupler is used to receive the intrinsic optical signal, and the output terminal of the first polarization-maintaining coupler is connected to the fourth polarization-maintaining coupler and the fifth polarization-maintaining coupler respectively.

[0011] The input terminal of the fourth polarization-maintaining coupler is connected to the first polarization-maintaining coupler, and the output terminal is connected to the third photodetector and the multi-channel optical switch, respectively.

[0012] The input terminal of the fifth polarization-maintaining coupler is connected to the first polarization-maintaining coupler, and the output terminal is connected to the fourth photodetector and the multi-channel optical switch, respectively.

[0013] The input terminals of the multi-channel optical switch are respectively connected to the second, third, fourth, and fifth polarization-maintaining couplers, the output terminals are respectively connected to the first mixer, the second mixer, and the fifth photodetector, and the control terminal is connected to the controller to selectively connect the input terminals and the output terminals under the control of the controller.

[0014] The output of the first mixer is connected to the input of the first balanced receiver, and the output of the second mixer is connected to the input of the second balanced receiver.

[0015] The input terminal of the first balanced receiver is connected to the first mixer, and the output terminal is connected to the first transimpedance amplifier. The input terminal of the second balanced receiver is connected to the second mixer, and the output terminal is connected to the second transimpedance amplifier. The first transimpedance amplifier circuit and the second transimpedance amplifier circuit are respectively used to output the X-state electrically polarized signal and the Y-state electrically polarized signal to the amplifier circuit.

[0016] The signal acquisition and processing unit is connected to the first photodetector, the second photodetector, the third photodetector, the fourth photodetector, the fifth photodetector, the amplifier circuit, and the controller, respectively. In the debugging state, it acquires the output signals of the first, second, third, fourth, and fifth photodetectors, as well as the X-state and Y-state electropolarized signals output by the amplifier circuit, and sends them to the controller. In the working state, it multiplies the real-time acquired X-state or Y-state electropolarized signal by the polarization compensation coefficient fed back by the controller, and demodulates the intensity and phase information according to the corresponding demodulation algorithm.

[0017] The controller is used to, when the signal acquisition and processing unit is in the debugging state, cause the multi-channel optical switch to first operate in the first state to obtain the relative relationship between the first, second, third, fourth, and fifth photodetectors. Then, it switches the multi-channel optical switch to the second state to receive the X-state and Y-state electropolarized signals output by the amplifier circuit. It adjusts the gain ratios of the first and second transimpedance amplifiers and the amplifier circuit to make the gain ratios of the X-state and Y-state electropolarized signals consistent. Then, it uses the relative relationship and the values ​​of the first, second, third, and fourth photodetectors when the multi-channel optical switch is switched to the second state to generate a polarization compensation coefficient and send it to the signal acquisition and processing unit. The controller is also used to, when the signal acquisition and processing unit is in the working state, cause the multi-channel optical switch to operate in the second state.

[0018] Furthermore, when the signal acquisition unit processes the second state, the multi-channel optical switch is used to connect the output terminals of the second and fourth bias-maintaining couplers to the two input terminals of the first mixer; and to connect the output terminals of the third and fifth bias-maintaining couplers to the two input terminals of the second mixer.

[0019] Furthermore, the polarization compensation coefficient is:

[0020] α1=K1 / K2

[0021] α2=K2 / K1

[0022] in:

[0023]

[0024]

[0025] α1 is the polarization compensation coefficient corresponding to the X-state electropolarized signal, α2 is the polarization compensation coefficient corresponding to the Y-state electropolarized signal, I1, I2, I3, and I4 are the current values ​​when the first, second, third, and fourth photodetectors are connected to the fifth photodetector, respectively, and P1, P2, P3, and P4 are the power values ​​of the corresponding fifth photodetectors; I5 and I6 are the currents of the first and second photodetectors when the second polarization-maintaining coupler is connected to the first mixer, and the third polarization-maintaining coupler is connected to the second mixer, respectively; I7 and I8 are the currents of the third and fourth photodetectors when the fourth polarization-maintaining coupler is connected to the first mixer, and the fifth polarization-maintaining coupler is connected to the second mixer, respectively, and N is the current value for obtaining I5, I2, I3, and I4. 6、 The number of times I7 and I8.

[0026] Furthermore, the phase-sensitive optical time-domain reflectometer also includes a coherent light source and a chirped light pulse generation module. The output of the coherent light source is connected to both the chirped light pulse generation module and the polarization diversity receiving module, respectively, to input the intrinsic light signal generated by the coherent light source into the polarization diversity receiving module. The input of the chirped light pulse generation module is connected to the coherent light source, and its output is connected to the polarization diversity receiving module, to input the Rayleigh backscattered light output by the chirped light pulse generation module into the polarization diversity receiving module.

[0027] Furthermore, the coherent light source includes a narrow linewidth laser module and a polarization-maintaining fiber coupler. The output end of the narrow linewidth laser module is connected to the polarization-maintaining fiber coupler, and the output end of the polarization-maintaining fiber coupler is connected to a polarization diversity receiving module and a chirped light pulse generating module, respectively.

[0028] Furthermore, the chirped optical pulse generation module includes an acousto-optic modulator, a first erbium-doped fiber amplifier, a circulator, and a second erbium-doped fiber amplifier. The input end of the acousto-optic modulator is connected to a coherent light source, and the output end is connected to the first erbium-doped fiber amplifier. The output end of the first erbium-doped fiber amplifier is connected to the circulator. The circulator is also connected to the sensing fiber and the second erbium-doped fiber amplifier, respectively, for outputting the optical signal input to the circulator to the sensing fiber, and for receiving Rayleigh backscattered light generated by the sensing fiber and inputting it to the second erbium-doped fiber amplifier.

[0029] Furthermore, the first and second photodetectors are avalanche diodes, and the third, fourth, and fifth photodetectors are photodiodes.

[0030] Furthermore, the multi-channel optical switch includes four first multi-channel optical switches and one second multi-channel optical switch. The first multi-channel optical switch includes one input terminal and two output terminals; the second multi-channel optical switch includes four input terminals and one output terminal. The input terminal of each first multi-channel optical switch is used to connect to the second, third, fourth, and fifth polarization-maintaining couplers, respectively. One output terminal of each first multi-channel optical switch is used to connect to one input terminal of the second multi-channel optical switch, and the other output terminal is used to connect to the first and second mixers. The output terminal of the second multi-channel optical switch is used to connect to the fifth photodetector.

[0031] On the other hand, the present invention also discloses a method for eliminating polarization-dependent loss, applied to the above-mentioned phase-sensitive optical time-domain reflectometer, the method for eliminating polarization-dependent loss includes the following steps:

[0032] When the signal acquisition and processing unit is in the debugging state, the multi-channel optical switch is controlled to work in the first state, and the relative relationships of the first photodetector, the second photodetector, the third photodetector, the fourth photodetector and the fifth photodetector are obtained respectively.

[0033] Switch the multi-channel optical switch to the second state to receive the X-state and Y-state electrically polarized signals output by the amplifier circuit. Adjust the gain ratio of the first transimpedance amplifier, the second transimpedance amplifier, and the amplifier circuit to make the gain ratio of the X-state and Y-state electrically polarized signals the same.

[0034] Using the aforementioned relative relationship and the values ​​of the first, second, third, and fourth photodetectors when the multi-channel optical switch is switched to the second state, a polarization compensation coefficient is generated and sent to the signal acquisition and processing unit.

[0035] Based on the above technical solution, the beneficial effects of the present invention compared with the prior art are as follows:

[0036] The phase-sensitive optical time-domain reflectometer of the present invention includes a polarization diversity receiving module, an amplification circuit, and a signal acquisition and processing unit. The signal acquisition and processing unit is in both a debugging state and a working state. The multi-channel optical switch of the polarization diversity receiving module can be in either a first state or a second state. When the signal acquisition and processing unit is in the debugging state and the multi-channel optical switch is in the first and second states sequentially, the controller of the polarization diversity receiving module can adjust the gain ratio of the first transimpedance amplifier, the second transimpedance amplifier, and the amplification circuit according to the information such as the X-state electropolarized signal and the Y-state electropolarized signal output by the first photodetector, the second photodetector, the third photodetector, the fourth photodetector, the fifth photodetector, and the amplification circuit sent by the signal acquisition and processing unit. This ensures that the total gain of the X-state electropolarized signal and the Y-state electropolarized signal output by the amplification circuit is consistent, overcoming the problem of unbalanced output power from the perspective of ensuring responsivity and amplification ratio. Then, a polarization compensation coefficient is generated according to a preset rule to compensate for the power imbalance caused by the manufacturing process of the polarization diversity receiving module. This invention solves the problem of inconsistent intensity of the X-state and Y-state electrically polarized signals output by the amplifier circuit through two approaches, which can avoid fluctuations in intensity information during final demodulation and effectively eliminate polarization-related losses. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a phase-sensitive optical time-domain reflectometer according to Embodiment 1 of the present invention;

[0038] Figure 2 This is a schematic diagram of the structure of a polarization diversity receiving module in Embodiment 1 of the present invention;

[0039] Figure 3 This is a schematic diagram of a multi-channel optical switch according to Embodiment 1 of the present invention;

[0040] Figure 4 This is a flowchart illustrating a method for eliminating polarization-dependent loss in Embodiment 2 of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0042] Example 1

[0043] A phase-sensitive optical time-domain reflectometer, combined with Figure 1 , Figure 2As shown, the phase-sensitive optical time-domain reflectometer includes at least a polarization diversity receiver module 80, an amplifier circuit 90, and a signal acquisition and processing unit 100, wherein:

[0044] The polarization diversity receiving module 80 includes a polarization beam splitter 801, a first polarization-maintaining coupler 809, a second polarization-maintaining coupler 802, a third polarization-maintaining coupler 807, a fourth polarization-maintaining coupler 810, a fifth polarization-maintaining coupler 812, a first photodetector 803, a second photodetector 808, a third photodetector 811, a fourth photodetector 813, a fifth photodetector 818, a multi-channel optical switch 817, a first mixer 804, a second mixer 814, a first balanced receiver 805, a first transimpedance amplifier 806, a second balanced receiver 815, a second transimpedance amplifier 816, and a controller (not shown in the figure). It is understood that the output of the polarization beam splitter 801 is also two orthogonal polarization-state signals, while the output of the polarization-maintaining coupler is a signal of the same polarization state.

[0045] The input terminal of the polarization beam splitter 801 is used to receive Rayleigh backscattered light, and the output terminal of the polarization beam splitter 801 is connected to the second polarization-maintaining coupler 802 and the third polarization-maintaining coupler 807 respectively to output two orthogonal X-state light polarization state signals and Y-state light polarization state signals.

[0046] The input of the second polarization-maintaining coupler 802 is connected to the polarization beam splitter 801, and its output is connected to the first photodetector 803 and the multi-channel optical switch 817, respectively. The input of the third polarization-maintaining coupler 807 is connected to the polarization beam splitter 801, and its output is connected to the second photodetector 808 and the multi-channel optical switch 817, respectively. The input of the first polarization-maintaining coupler 809 is used to receive the intrinsic optical signal, and its output is connected to the fourth polarization-maintaining coupler 810 and the fifth polarization-maintaining coupler 812, respectively. The input of the fourth polarization-maintaining coupler 810 is connected to the first polarization-maintaining coupler 809, and its output is connected to the third photodetector 811 and the multi-channel optical switch 817, respectively. The input of the fifth polarization-maintaining coupler 812 is connected to the first polarization-maintaining coupler 809, and its output is connected to the fourth photodetector 813 and the multi-channel optical switch 817, respectively. The preferred splitting ratio of the first polarization-maintaining coupler 809 is 50:50, and the preferred splitting ratio of the second polarization-maintaining coupler 802, the third polarization-maintaining coupler 807, and the fourth polarization-maintaining coupler 810 is 1:99, wherein 1% of the light enters each photodetector.

[0047] In some embodiments, preferably, since the light signal of the Rayleigh backscattered light is generally small, the first photodetector 803 and the second photodetector 808 can be avalanche diodes, while the third photodetector 811, the fourth photodetector 813, and the fifth photodetector 818 can be general photodiodes.

[0048] The input terminals of the multi-channel optical switch 817 are connected to the second polarization-maintaining coupler 802, the third polarization-maintaining coupler 807, the fourth polarization-maintaining coupler 810, and the fifth polarization-maintaining coupler 812, respectively. The output terminals are connected to the first mixer 804, the second mixer 814, and the fifth photodetector 818, respectively. The control terminal is connected to a controller to receive control from the controller to operate in either a first state or a second state. In the first state, the first photodetector 803, the second photodetector 808, the third photodetector 811, and the fourth photodetector 813 are each connected to the fifth photodetector 818 one by one. In the second state, the first photodetector 803, the second photodetector 808, the third photodetector 811, and the fourth photodetector 813 are simultaneously connected to the first mixer 804 and the second mixer 814.

[0049] In some embodiments, such as Figure 2 As shown, the multi-channel optical switch 817 includes nine ports, where port a is connected to the second polarization-maintaining coupler 802, port b is connected to the third polarization-maintaining coupler 807, port c is connected to the fourth polarization-maintaining coupler 810, port d is connected to the fifth polarization-maintaining coupler 812, ports e and f are connected to the two inputs of the first mixer 804, ports g and h are connected to the two inputs of the second mixer 814, and port i is connected to the fifth photodetector 818. The multi-channel optical switch 817 can be controlled by a controller such that at any given time, only one of the following connections—port a and port i, port b and port i, port c and port i, and port d and port i—is connected; or, at any given time, port i is connected to port e, port b is connected to port 7, port c is connected to port e, and port d is connected to port h.

[0050] Preferably, in some embodiments, considering the versatility of the multi-channel optical switch 817, such as... Figure 3 As shown, the preferred multi-channel optical switch 817 includes four first multi-channel optical switches 8171 and one second multi-channel optical switch 8172. Each first multi-channel optical switch 8171 includes one input terminal and two output terminals; the second multi-channel optical switch 8172 includes four input terminals and one output terminal. For ease of understanding, it can be... Figure 3 and Figure 2A detailed comparison of the nine-port multi-channel optical switch 817 is provided. The first multi-channel optical switch 8171 has input port a, one output port e, and the other output port connected to the second multi-channel optical switch 8172. The second multi-channel optical switch 8171 has input port b, one output port g, and the other output port connected to the second multi-channel optical switch 8172. The third multi-channel optical switch 8171 has input port c, one output port f, and the other output port connected to the second multi-channel optical switch 8172. The fourth multi-channel optical switch 8171 has input port d, one output port h, and the other output port connected to the second multi-channel optical switch 8172. The output port of the second multi-channel optical switch 8172 is port i, used for connection to the fifth photodetector 818.

[0051] The output of the first mixer 804 is connected to the input of the first balanced receiver 805, and the output of the second mixer 814 is connected to the input of the second balanced receiver 815.

[0052] The input terminal of the first balanced receiver 805 is connected to the first mixer 804, and the output terminal is connected to the first transimpedance amplifier 806. The input terminal of the second balanced receiver 815 is connected to the second mixer 814, and the output terminal is connected to the second transimpedance amplifier 816. The first transimpedance amplifier circuit 90 and the second transimpedance amplifier circuit 90 are respectively used to output the X-state electropolarized signal and the Y-state electropolarized signal to the amplifier circuit 90.

[0053] The signal acquisition and processing unit 100 is connected to the first photodetector 803, the second photodetector 808, the third photodetector 811, the fourth photodetector 813, the fifth photodetector 818, the amplifier circuit 90, and the controller, respectively. In the debugging state, it acquires the output signals of the first photodetector 803, the second photodetector 808, the third photodetector 811, the fourth photodetector 813, and the fifth photodetector 818, as well as the X-state and Y-state electropolarized signals output by the amplifier circuit 90, and sends them to the controller. In the working state, it multiplies the real-time acquired X-state or Y-state electropolarized signal by the polarization compensation coefficient fed back by the controller, and demodulates the intensity and phase information according to the corresponding demodulation algorithm.

[0054] The controller is used to, when the signal acquisition and processing unit 100 is in the debugging state, cause the multi-channel optical switch 817 to first operate in the first state, obtain the relative relationship between the first photodetector 803, the second photodetector 808, the third photodetector 811, the fourth photodetector 813, and the fifth photodetector 818, and then switch the multi-channel optical switch 817 to the second state, receive the X-state electropolarized signal and the Y-state electropolarized signal output by the amplifier circuit 90, adjust the gain ratio of the first transimpedance amplifier 806, the second transimpedance amplifier 816, and the amplifier circuit 90 so that the gain ratio of the X-state electropolarized signal and the Y-state electropolarized signal are consistent, and then use the relative relationship and the values ​​of the first photodetector 803, the second photodetector 808, the third photodetector 811, and the fourth photodetector 813 when the multi-channel optical switch 817 is switched to the second state to generate a polarization compensation coefficient and send it to the signal acquisition and processing unit 100; the controller is also used to, when the signal acquisition and processing unit 100 is in the working state, cause the multi-channel optical switch 817 to operate in the second state.

[0055] Specifically, when the signal acquisition and processing unit 100 is in the debugging state and the multi-channel optical switch 817 is in the first state, it acquires the first power value P1 and the second power value P2 of the fifth photodetector 818 when the fourth polarization-maintaining coupler 810 and the fifth polarization-maintaining coupler 812 are connected to the fifth photodetector 818 one by one. Understandably, in practical applications, the signal acquisition and processing unit 100 should also be equipped with logarithmic amplifiers, acquisition and processing units, etc., for connection to each photodetector, to convert the current signal output by the photodetector into the required digital voltage signal and power signal.

[0056] When the multi-channel optical switch 817 is in the second state, the X-state electropolarized signal voltage value V1 and the Y-state electropolarized signal voltage value V2 output by the amplifier circuit 90 are acquired.

[0057] Adjust the gains of the first transimpedance amplifier 806, the second transimpedance amplifier 816, and the amplifier circuit 90 so that the first power value P1 and the second power value P2 satisfy: V1 / V2=P1 / P2.

[0058] Understandably, the amplifier circuit 90 may include a first amplifier circuit 90 and a second amplifier circuit 90 connected to the first transimpedance amplifier 806 and the second transimpedance amplifier 816, respectively. When adjusting the gain of the first transimpedance amplifier 806, the second transimpedance amplifier 816, and the amplifier circuit 90, the first transimpedance amplifier 806 and the second transimpedance amplifier 816 can be set to the same gain first, and the first amplifier circuit 90 and the second amplifier circuit 90 can also be set to the same gain. Then, the gain of each device can be gradually increased or decreased until V1 / V2 = P1 / P2, so that the total gain of the X-state electropolarized signal and the Y-state electropolarized signal output by the amplifier circuit 90 is consistent, thus overcoming the original problem of unbalanced output power from the perspective of ensuring responsivity and amplification factor.

[0059] On the other hand, due to manufacturing processes, the loss of the same signal from different input ports to the output port of the multi-channel optical switch 817 may vary, thus introducing polarization-dependent losses. Therefore, the relative relationships between each input and output port can be pre-calibrated to find the device characteristics and generate a polarization compensation coefficient to eliminate polarization-dependent losses. For example, when the multi-channel optical switch 817 is in its first operating state, the current values ​​I1, I2, I3, and I4 of the first photodetector 803, second photodetector 808, third photodetector 811, fourth photodetector 813, and fifth photodetector 818, and the corresponding power values ​​P1, P2, P3, and P4 of the fifth photodetector 818, are obtained. Assuming P1 = a*I1 + b, the signal power of input port 1 can be changed multiple times to determine the values ​​of parameters a and b, thus obtaining the relationship between the first photodetector 803 and the fifth detector. Similarly, the relationship between the second photodetector 808, the third photodetector 811, the fourth photodetector 813, and the fifth detector can be obtained. In practical applications, the output signals of each photodetector can be collected multiple times to improve the accuracy of the calibration of the relative relationships.

[0060] When the multi-channel optical switch 817 is in its second operating state, the output terminals of the second polarization-maintaining coupler 802 and the fourth polarization-maintaining coupler 810 are connected to the two input terminals of the first mixer 804; the output terminals of the third polarization-maintaining coupler 807 and the fifth polarization-maintaining coupler 812 are connected to the two input terminals of the second mixer 814. Understandably, due to manufacturing limitations, the beam splitting of the polarization beam splitter 801 and the first polarization-maintaining coupler 809 is generally not ideal. Therefore, the polarization compensation coefficient can be set by determining the relationship between the X-state and Y-state electrically polarized signals output by the amplifier circuit 90 and the input intrinsic signal and Rayleigh backscattered light. The output signals of the first photodetector 803, the second photodetector 808, the third photodetector 811, and the fourth photodetector 813 can be used to represent the intrinsic signal and Rayleigh backscattered light.

[0061] Considering the polarization-related losses introduced by the aforementioned manufacturing process, the following polarization compensation coefficients can be generated:

[0062] α1=K1 / K2

[0063] α2=K2 / K1

[0064] in:

[0065]

[0066]

[0067] α1 is the polarization compensation coefficient corresponding to the X-state electropolarized signal, α2 is the polarization compensation coefficient corresponding to the Y-state electropolarized signal, I1, I2, I3, and I4 are the current values ​​when the first photodetector 803, the second photodetector 808, the third photodetector 811, and the fourth photodetector 813 are connected to the fifth photodetector 818 one by one, and P1, P2, P3, and P4 are the power values ​​of the corresponding fifth photodetector 818; I5 and I6 are the currents of the first photodetector 803 and the second photodetector 808 when the second polarization-maintaining coupler 802 is connected to the first mixer 804 and the third polarization-maintaining coupler 807 is connected to the second mixer 814; I7 and I8 are the currents of the third photodetector 811 and the fourth photodetector 813 when the fourth polarization-maintaining coupler 810 is connected to the first mixer 804 and the fifth polarization-maintaining coupler 812 is connected to the second mixer 814, and N is the current value for obtaining I5, I6, and I7. 6、 The number of times I7 and I8.

[0068] With this design, when the signal acquisition and processing unit 100 is in operation, the X-state electropolarized signal output by the amplification unit is multiplied by the polarization compensation coefficient α1, or the Y-state electropolarized signal is multiplied by the polarization compensation coefficient α2 to compensate for polarization correlation loss. Then, the intensity and phase information are demodulated according to the corresponding demodulation algorithm (such as I / Q quadrature phase demodulation). Since polarization correlation loss represents the inconsistency between the optical power and the total amplification of the receiving circuit between two orthogonal polarization states, compensating for either polarization state signal can achieve the effect of equalization between the two polarization states.

[0069] The phase-sensitive optical time-domain reflectometer of the present invention includes a polarization diversity receiving module 80, an amplification circuit 90, and a signal acquisition and processing unit 100. The signal acquisition and processing unit 100 is in a debugging state and a working state, respectively, and the multi-channel optical switch 817 can be in a first state or a second state. When the signal acquisition and processing unit 100 is in the debugging state and the multi-channel optical switch 817 is in the first and second states sequentially, the controller of the polarization diversity receiving module 80 can adjust the gain ratio of the first transimpedance amplifier 806, the second transimpedance amplifier 816, and the amplifier circuit 90 according to the information such as the X-state electropolarized signal and Y-state electropolarized signal output by the first photodetector 803, the second photodetector 808, the third photodetector 811, the fourth photodetector 813, the fifth photodetector 818, and the amplifier circuit 90. This ensures that the total gain of the X-state electropolarized signal and the Y-state electropolarized signal output by the amplifier circuit 90 is consistent, overcoming the original problem of unbalanced output power from the perspective of ensuring responsivity and amplification. Then, a polarization compensation coefficient is generated according to a preset rule to compensate for the power imbalance caused by the manufacturing process of the polarization diversity receiving module 80. This invention solves the problem of inconsistent intensity of the X-state electropolarized signal and the Y-state electropolarized signal output by the amplifier circuit 90 through two approaches, avoiding fluctuations in intensity information during final demodulation and effectively eliminating polarization-related losses.

[0070] In some embodiments, a phase-sensitive optical time-domain reflectometer further includes a coherent light source 1 and a chirped light pulse generation module 2. The output terminal of the coherent light source 1 is connected to the chirped light pulse generation module 2 and the polarization diversity receiving module 80, respectively, to input the intrinsic light signal generated by the coherent light source 1 into the polarization diversity receiving module. The input terminal of the chirped light pulse generation module 2 is connected to the coherent light source 1, and the output terminal is connected to the polarization diversity receiving module 80, for inputting the Rayleigh backscattered light output by the chirped light pulse generation module 2 into the polarization diversity receiving module.

[0071] Specifically, the coherent light source 1 includes a narrow linewidth laser module 10 and a sixth polarization-maintaining fiber coupler 20. The output end of the narrow linewidth laser module 10 is connected to the sixth polarization-maintaining fiber coupler 20, and the output end of the sixth polarization-maintaining fiber coupler 20 is connected to the polarization diversity receiving module and the chirped light pulse generating module 2, respectively.

[0072] The chirped optical pulse generation module 2 includes an acousto-optic modulator 30, a first erbium-doped fiber amplifier 40, a circulator 50, and a second erbium-doped fiber amplifier 70. The input end of the acousto-optic modulator 30 is connected to the coherent light source 1, and the output end is connected to the first erbium-doped fiber amplifier 40. The output end of the first erbium-doped fiber amplifier 40 is connected to the circulator 50. The circulator 50 is also connected to the sensing fiber 60 and the second erbium-doped fiber amplifier 70, respectively, for outputting the optical signal input to the circulator 50 to the sensing fiber 60, and for receiving Rayleigh backscattered light generated by the sensing fiber 60 and inputting it to the second erbium-doped fiber amplifier 70.

[0073] The signal acquisition and processing unit 100 also controls the acousto-optic modulator 30 to generate a pulse sequence to pulse modulate the continuous optical signal output by the coherent light source 1. The typical pulse width is 200 ns and the pulse repetition frequency is 1 kHz.

[0074] The operating frequency of the acousto-optic modulator 303 can be 200MHz; the amplification gain of the amplifier circuit 90 can be 0 to 30dB.

[0075] Example 2

[0076] This invention also discloses a method for eliminating polarization-dependent loss, applied in the phase-sensitive optical time-domain reflectometer of Embodiment 1 or Embodiment 2. When the signal acquisition and processing unit 100 is in the debugging state, the method for eliminating polarization-dependent loss includes the following steps:

[0077] S01, control the multi-channel optical switch 817 to work in the first state, and obtain the relative relationships of the first photodetector 803, the second photodetector 808, the third photodetector 811, the fourth photodetector 813 and the fifth photodetector 818 respectively;

[0078] S02, switch the multi-channel optical switch 817 to the second state, receive the X-state electropolarized signal and Y-state electropolarized signal output by the amplifier circuit 90, and adjust the gain ratio of the first transimpedance amplifier 806, the second transimpedance amplifier 816, and the amplifier circuit 90 so that the gain ratio of the X-state electropolarized signal and the Y-state electropolarized signal are consistent.

[0079] S03, using the relative relationship and the values ​​of the first photodetector 803, the second photodetector 808, the third photodetector 811, and the fourth photodetector 813 when the multi-channel optical switch 817 is switched to the second state, a polarization compensation coefficient is generated and sent to the signal acquisition and processing unit 100.

[0080] Specifically, in step S02, the controller receives the X-state and Y-state electrically polarized signals output by the amplifier circuit 90, and adjusts the gain ratios of the first transimpedance amplifier 806, the second transimpedance amplifier 816, and the amplifier circuit 90 to make the gain ratios of the X-state and Y-state electrically polarized signals consistent, including:

[0081] When the multi-channel optical switch 817 is in the first state, the first power value P1 and the second power value P2 of the fifth photodetector 818 are obtained when the fourth polarization-maintaining coupler 810 and the fifth polarization-maintaining coupler 812 are connected to the fifth photodetector 818 one by one.

[0082] When the multi-channel optical switch 817 is in the second state, the X-state electropolarized signal voltage value V1 and the Y-state electropolarized signal voltage value V2 output by the amplifier circuit 90 are acquired.

[0083] Adjust the gains of the first transimpedance amplifier 806, the second transimpedance amplifier 816, and the amplifier circuit 90 so that the first power value P1 and the second power value P2 satisfy: V1 / V2=P1 / P2.

[0084] Understandably, the amplifier circuit 90 may include a first amplifier circuit 90 and a second amplifier circuit 90 connected to the first transimpedance amplifier 806 and the second transimpedance amplifier 816, respectively. When adjusting the gain of the first transimpedance amplifier 806, the second transimpedance amplifier 816, and the amplifier circuit 90, the first transimpedance amplifier 806 and the second transimpedance amplifier 816 can be set to the same gain first, and the first amplifier circuit 90 and the second amplifier circuit 90 can also be set to the same gain. Then, the gain of each device can be gradually increased or decreased until V1 / V2 = P1 / P2, so that the total gain of the X-state electropolarized signal and the Y-state electropolarized signal output by the amplifier circuit 90 is consistent, thus overcoming the original problem of unbalanced output power from the perspective of ensuring responsivity and amplification factor.

[0085] Due to manufacturing processes, the loss of the same signal from different input ports to the output port of the multi-channel optical switch 817 may vary, thus introducing polarization-dependent losses. Therefore, the relative relationships between each input and output port can be pre-calibrated to identify the device characteristics and generate a polarization compensation coefficient to eliminate polarization-dependent losses. For example, when the multi-channel optical switch 817 is in its first operating state, the current values ​​I1, I2, I3, and I4 of the first photodetector 803, second photodetector 808, third photodetector 811, fourth photodetector 813, and fifth photodetector 818, and the corresponding power values ​​P1, P2, P3, and P4 of the fifth photodetector 818, are obtained. Assuming P1 = a*I1 + b, the signal power at input port 1 can be changed multiple times to determine the values ​​of parameters a and b, thus obtaining the relationship between the first photodetector 803 and the fifth detector. Similarly, the relationship between the second photodetector 808, the third photodetector 811, the fourth photodetector 813, and the fifth detector can be obtained. In practical applications, the output signals of each photodetector can be collected multiple times to improve the accuracy of the calibration of the relative relationships.

[0086] When the multi-channel optical switch 817 is in its second operating state, the output terminals of the second polarization-maintaining coupler 802 and the fourth polarization-maintaining coupler 810 are connected to the two input terminals of the first mixer 804; the output terminals of the third polarization-maintaining coupler 807 and the fifth polarization-maintaining coupler 812 are connected to the two input terminals of the second mixer 814. Understandably, due to manufacturing limitations, the beam splitting of the polarization beam splitter 801 and the first polarization-maintaining coupler 809 is generally not ideal. Therefore, polarization compensation coefficients can be generated by determining the relationship between the X-state and Y-state electrically polarized signals output by the amplifier circuit 90 and the input intrinsic signal and Rayleigh backscattered light. The output signals of the first photodetector 803, the second photodetector 808, the third photodetector 811, and the fourth photodetector 813 can be used to represent the intrinsic signal and Rayleigh backscattered light.

[0087] Due to the manufacturing process reasons mentioned above, the generation of the polarization compensation coefficient in step S03 includes the following steps:

[0088] When the multi-channel optical switch 817 is in the first state, it also acquires the output currents of the first photodetector 803, the second photodetector 808, the third photodetector 811, and the fourth photodetector 813, as well as the third power value P3 and the fourth power value P4 of the fifth photodetector 818 when the second polarization-maintaining coupler 802 and the third polarization-maintaining coupler 807 are connected to the fifth photodetector 818 one by one.

[0089] When the multi-channel optical switch 817 is in the second state, it also collects the output current of N first photodetectors 803, second photodetectors 808, third photodetectors 811, and fourth photodetectors 813 in real time according to a preset frequency.

[0090] The polarization compensation coefficients are generated according to the following formula:

[0091] α1=K1 / K2

[0092] α2=K2 / K1

[0093] in:

[0094]

[0095]

[0096] α1 is the polarization compensation coefficient corresponding to the X-state electropolarized signal, α2 is the polarization compensation coefficient corresponding to the Y-state electropolarized signal, I1, I2, I3, and I4 are the current values ​​when the first photodetector 803, the second photodetector 808, the third photodetector 811, and the fourth photodetector 813 are connected to the fifth photodetector 818 one by one, and P1, P2, P3, and P4 are the power values ​​of the corresponding fifth photodetector 818; I5 and I6 are the currents of the first photodetector 803 and the second photodetector 808 when the second polarization-maintaining coupler 802 is connected to the first mixer 804 and the third polarization-maintaining coupler 807 is connected to the second mixer 814; I7 and I8 are the currents of the third photodetector 811 and the fourth photodetector 813 when the fourth polarization-maintaining coupler 810 is connected to the first mixer 804 and the fifth polarization-maintaining coupler 812 is connected to the second mixer 814, and N is the current value for obtaining I5, I6, and I7. 6、 The number of times I7 and I8.

[0097] With this design, when the signal acquisition and processing unit 100 is in operation, the X-state electropolarized signal output by the amplification unit is multiplied by the polarization compensation coefficient α1, or the Y-state electropolarized signal is multiplied by the polarization compensation coefficient α2 to compensate for polarization correlation loss. Then, the intensity and phase information are demodulated according to the corresponding demodulation algorithm (such as I / Q quadrature phase demodulation). Since polarization correlation loss represents the inconsistency between the optical power and the total amplification of the receiving circuit between two orthogonal polarization states, compensating for either polarization state signal can achieve the effect of equalization between the two polarization states.

[0098] In the detailed description above, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features in a single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, with each claim representing a separate preferred embodiment of the invention.

[0099] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term “comprising” as used in the specification or claims is interpreted in a manner similar to the term “including,” just as “including,” is interpreted as a conjunction in the claims. Additionally, the use of any term “or” in the specification of the claims is intended to mean “non-exclusive or.”

Claims

1. A phase-sensitive optical time-domain reflectometer, characterized in that, It includes at least a polarization diversity receiver module, an amplifier circuit, and a signal acquisition and processing unit, wherein: The polarization diversity receiving module includes a polarization beam splitter, a first polarization-maintaining coupler, a second polarization-maintaining coupler, a third polarization-maintaining coupler, a fourth polarization-maintaining coupler, a fifth polarization-maintaining coupler, a first photodetector, a second photodetector, a third photodetector, a fourth photodetector, a fifth photodetector, a multi-channel optical switch, a first mixer, a second mixer, a first balanced receiver, a first transimpedance amplifier, a second balanced receiver, a second transimpedance amplifier, and a controller; The input end of the polarization beam splitter is used to receive Rayleigh backscattered light, and the output end is connected to the second polarization-maintaining coupler and the third polarization-maintaining coupler, respectively. The output of the second polarization-maintaining coupler is connected to the first photodetector and the multi-channel optical switch, respectively; the output of the third polarization-maintaining coupler is connected to the second photodetector and the multi-channel optical switch, respectively; the input of the first polarization-maintaining coupler is used to receive the intrinsic optical signal, and its output is connected to the fourth and fifth polarization-maintaining couplers, respectively; the output of the fourth polarization-maintaining coupler is connected to the third photodetector and the multi-channel optical switch, respectively; the output of the fifth polarization-maintaining coupler is connected to the fourth photodetector and the multi-channel optical switch, respectively. The control of the multi-channel optical switch receiver controller operates in a first state and a second state. In the first state, the first photodetector, the second photodetector, the third photodetector, and the fourth photodetector are connected to the fifth photodetector one by one. In the second state, the first photodetector, the second photodetector, the third photodetector, and the fourth photodetector are connected to the first mixer and the second mixer simultaneously. The output of the first mixer is connected to the input of the first balanced receiver, and the output of the second mixer is connected to the input of the second balanced receiver; the output of the first balanced receiver is connected to the first transimpedance amplifier, and the output of the second balanced receiver is connected to the second transimpedance amplifier; the first transimpedance amplifier circuit and the second transimpedance amplifier circuit are respectively used to output X-state electropolarized signal and Y-state electropolarized signal to the amplifier circuit. The signal acquisition and processing unit is connected to the first photodetector, the second photodetector, the third photodetector, the fourth photodetector, the fifth photodetector, the amplifier circuit, and the controller, respectively. In the debugging state, it acquires the output signals of the first, second, third, fourth, and fifth photodetectors, as well as the X-state and Y-state electropolarized signals output by the amplifier circuit, and sends them to the controller. In the working state, it multiplies the real-time acquired X-state or Y-state electropolarized signal by the polarization compensation coefficient fed back by the controller, and demodulates the intensity and phase information according to the corresponding demodulation algorithm. The controller is used to, when the signal acquisition and processing unit is in the debugging state, cause the multi-channel optical switch to first operate in the first state to obtain the relative relationship between the first, second, third, fourth, and fifth photodetectors. Then, it switches the multi-channel optical switch to the second state to receive the X-state and Y-state electropolarized signals output by the amplifier circuit. It adjusts the gain ratios of the first and second transimpedance amplifiers and the amplifier circuit to make the gain ratios of the X-state and Y-state electropolarized signals consistent. Then, it uses the relative relationship and the values ​​of the first, second, third, and fourth photodetectors when the multi-channel optical switch is in the second state to generate a polarization compensation coefficient and send it to the signal acquisition and processing unit. The controller is also used to, when the signal acquisition and processing unit is in the working state, cause the multi-channel optical switch to operate in the second state.

2. The phase-sensitive optical time-domain reflectometer as described in claim 1, characterized in that, When the multi-channel optical switch is in the second state, it is used to connect the output terminals of the second and fourth polarization-maintaining couplers to the two input terminals of the first mixer; and to connect the output terminals of the third and fifth polarization-maintaining couplers to the two input terminals of the second mixer.

3. The phase-sensitive optical time-domain reflectometer as described in claim 1, characterized in that, The polarization compensation coefficient is: α1=K1 / K2 α2=K2 / K1 in: α1 is the polarization compensation coefficient corresponding to the X-state electropolarized signal, α2 is the polarization compensation coefficient corresponding to the Y-state electropolarized signal, I1, I2, I3, and I4 are the current values ​​when the first, second, third, and fourth photodetectors are connected to the fifth photodetector one by one, respectively, and P1, P2, P3, and P4 are the power values ​​of the corresponding fifth photodetectors; I5 and I6 are the currents of the first and second photodetectors when the second polarization-maintaining coupler is connected to the first mixer, and the third polarization-maintaining coupler is connected to the second mixer, respectively; I7 and I8 are the currents of the third and fourth photodetectors when the fourth polarization-maintaining coupler is connected to the first mixer, and the fifth polarization-maintaining coupler is connected to the second mixer, respectively, and N is the current value for obtaining I5, I... 6、 The number of times I7 and I8.

4. The phase-sensitive optical time-domain reflectometer as described in claim 1, characterized in that, The phase-sensitive optical time-domain reflectometer further includes a coherent light source and a chirped light pulse generation module. The output of the coherent light source is connected to both the chirped light pulse generation module and the polarization diversity receiving module, respectively, to input the intrinsic light signal generated by the coherent light source into the polarization diversity receiving module. The input of the chirped light pulse generation module is connected to the coherent light source, and its output is connected to the polarization diversity receiving module, to input the Rayleigh backscattered light output by the chirped light pulse generation module into the polarization diversity receiving module.

5. The phase-sensitive optical time-domain reflectometer as described in claim 4, characterized in that, The coherent light source includes a narrow linewidth laser module and a sixth polarization-maintaining fiber coupler. The output end of the narrow linewidth laser module is connected to the sixth polarization-maintaining fiber coupler, and the output end of the sixth polarization-maintaining fiber coupler is connected to a polarization diversity receiving module and a chirped light pulse generating module, respectively.

6. The phase-sensitive optical time-domain reflectometer as described in claim 4, characterized in that, The chirped optical pulse generation module includes an acousto-optic modulator, a first erbium-doped fiber amplifier, a circulator, and a second erbium-doped fiber amplifier. The input end of the acousto-optic modulator is connected to a coherent light source, and the output end is connected to the first erbium-doped fiber amplifier. The output end of the first erbium-doped fiber amplifier is connected to the circulator. The circulator is also connected to the sensing fiber and the second erbium-doped fiber amplifier, respectively, for outputting the optical signal input to the circulator to the sensing fiber, and for receiving Rayleigh backscattered light generated by the sensing fiber and inputting it to the second erbium-doped fiber amplifier.

7. The phase-sensitive optical time-domain reflectometer as described in claim 1, characterized in that, The multi-channel optical switch includes four first multi-channel optical switches and one second multi-channel optical switch. Each first multi-channel optical switch includes one input terminal and two output terminals. The second multi-channel optical switch includes four input terminals and one output terminal. The input terminals of each first multi-channel optical switch are respectively used to connect to a second, third, fourth, and fifth polarization-maintaining coupler. One output terminal of each first multi-channel optical switch is used to connect to one input terminal of the second multi-channel optical switch, and the other output terminal is used to connect to a first mixer and a second mixer. The output terminal of the second multi-channel optical switch is used to connect to a fifth photodetector.

8. A method for eliminating polarization-dependent loss, applied to a phase-sensitive optical time-domain reflectometer as described in claim 1, characterized in that, When the signal acquisition and processing unit is in debugging mode, the method for eliminating polarization-dependent loss includes the following steps: By controlling the multi-channel optical switch to operate in the first state, the relative relationships of the first photodetector, the second photodetector, the third photodetector, the fourth photodetector, and the fifth photodetector are obtained respectively. Switch the multi-channel optical switch to the second state to receive the X-state and Y-state electrically polarized signals output by the amplifier circuit. Adjust the gain ratio of the first transimpedance amplifier, the second transimpedance amplifier, and the amplifier circuit to make the gain ratio of the X-state and Y-state electrically polarized signals the same. The polarization compensation coefficient is generated using the relative relationship and the values ​​of the first, second, third, and fourth photodetectors when the multi-channel optical switch is switched to the second state, and then sent to the signal acquisition and processing unit.

9. The method for eliminating polarization-dependent loss as described in claim 8, characterized in that, Receiving the X-state and Y-state electrically polarized signals output from the amplifier circuit, and adjusting the gain ratios of the first transimpedance amplifier, the second transimpedance amplifier, and the amplifier circuit to make the gain ratios of the X-state and Y-state electrically polarized signals identical includes: When the multi-channel optical switch is in the first state, the first power value P1 and the second power value P2 of the fifth photodetector are obtained when the fourth polarization-maintaining coupler and the fifth polarization-maintaining coupler are connected to the fifth photodetector one by one. When the multi-channel optical switch is in the second state, the X-state electropolarized signal voltage value V1 and the Y-state electropolarized signal voltage value V2 output by the amplifier circuit are obtained. Adjust the gain of the first transimpedance amplifier, the second transimpedance amplifier, and the amplifier circuit so that the first power value P1 and the second power value P2 satisfy: V1 / V2=P1 / P2.

10. The method for eliminating polarization-dependent loss as described in claim 9, characterized in that, Generating polarization compensation coefficients includes the following steps: When the multi-channel optical switch is in the first state, the output currents of the first photodetector, the second photodetector, the third photodetector, and the fourth photodetector are also acquired, as well as the third power value P3 and the fourth power value P4 of the fifth photodetector when the second and third polarization-maintaining couplers are connected to the fifth photodetector one by one. When the multi-channel optical switch is in the second state, the output currents of the first photodetector, the second photodetector, the third photodetector, and the fourth photodetector are also collected in real time at a preset frequency. The polarization compensation coefficients are generated according to the following formula: α1=K1 / K2 α2=K2 / K1 in: α1 is the polarization compensation coefficient corresponding to the X-state electropolarized signal, α2 is the polarization compensation coefficient corresponding to the Y-state electropolarized signal, I1, I2, I3, and I4 are the current values ​​when the first, second, third, and fourth photodetectors are connected to the fifth photodetector one by one, respectively, and P1, P2, P3, and P4 are the power values ​​of the corresponding fifth photodetectors; I5 and I6 are the currents of the first and second photodetectors when the second polarization-maintaining coupler is connected to the first mixer, and the third polarization-maintaining coupler is connected to the second mixer, respectively; I7 and I8 are the currents of the third and fourth photodetectors when the fourth polarization-maintaining coupler is connected to the first mixer, and the fifth polarization-maintaining coupler is connected to the second mixer, respectively, and N is the current value for obtaining I5, I... 6、 The number of times I7 and I8.

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