Optical CT sensing optical fiber state detection system and method

Abstract

The invention discloses an optical CT sensing optical fiber state detection system and method. The system comprises a tunable laser, a first 1 * 2 optical fiber beam splitter, a main interferometer module, an auxiliary interferometer module, a polarization generation and analysis unit and a signal processing control module, an optical signal emitted by the tunable laser is divided into two beams of optical signals through the first 1 * 2 optical fiber beam splitter, and the small-proportion optical signal enters the auxiliary interferometer module; a large-proportion optical signal enters the main interferometer module; an optical signal entering the main interferometer module is divided into two light beams, and one light beam is output into a polarization generation and analysis unit and then is output into an optical CT sensing optical fiber to be measured. The light scattered back by the optical CT sensing optical fiber to be measured is returned to the main interferometer module through the polarization generation and analysis unit, is subjected to interference beat frequency with the other light beam of the main interferometer module, and then enters the signal processing control module; the auxiliary interferometer module and the main interferometer module output electric signals which enter the signal processing control module to be processed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system measurement, and more particularly, to a kind of optical CT sensing optical fiber state detection system and method. BACKGROUND

[0002] The new power system action plan clearly coordinates the development of AC and DC grids, strengthens the digital transformation of the grid, and improves the level of operational safety and efficiency. As an important measuring device for DC grids, optical fiber current transformers (hereinafter referred to as optical CT) account for more than 50% of current measurement, and are a key link to improve the safe operation of DC grids. Optical fiber current transformers use optical fiber sensing technology to achieve non-contact measurement of current on high-voltage transmission lines, with advantages such as resistance to electromagnetic interference, good insulation performance, small size, and no need for grounding. Currently, optical fiber current transformers have been widely used in power systems for real-time monitoring, fault detection, and protection systems in smart grids.

[0003] Optical CT uses a preservation optical fiber as a sensing optical fiber, which is the core component of the optical CT. The birefringence characteristics of the preservation optical fiber are a key determinant of the performance of the optical fiber current sensor. Only when the preservation optical fiber has good circular polarization maintaining ability can the linear relationship between the Faraday rotation angle and the current be guaranteed, ensuring the high sensitivity and linearity of the sensor. However, the preservation optical fiber produced in actual production still has residual linear birefringence, which changes in size as affected by the environment, resulting in a large error in the system output, which cannot meet the technical requirements of high-precision applications.

[0004] During operation, the sensing optical fiber of the optical CT is subjected to twisting, bending, external pressure, and aging, which will cause the detection performance of the optical CT to decline. How to find these problems in daily inspection, locate the fault position and type is a major technical problem that cannot be solved at present. SUMMARY

[0005] To overcome the shortcomings of the prior art, the present application provides an optical CT sensing optical fiber state detection system and method.

[0006] According to one aspect of the present application, an optical CT sensing optical fiber state detection system is provided, comprising: a tunable laser, a first 1x2 optical fiber beam splitter, a main interferometer module, an auxiliary interferometer module, a polarization generation and analysis unit, and a signal processing control module, wherein,

[0007] The light signal emitted by the tunable laser is split into two light signals by the first 1x2 optical fiber beam splitter, and the small proportion light signal enters the auxiliary interferometer module, and the large proportion light signal enters the main interferometer module; the light signal entering the main interferometer module is split into two light beams, one of which is output into the polarization generation and analysis unit and enters the measured light CT sensing optical fiber, and the light scattered back by the measured light CT sensing optical fiber returns to the main interferometer module through the polarization generation and analysis unit, interferes with the other light beam of the main interferometer module, and then enters the signal processing control module; the electrical signals output by the auxiliary interferometer module and the main interferometer module enter the signal processing control module for processing.

[0008] Optionally, the splitting ratio of the first 1x2 optical fiber beam splitter is 1:99 to 5:95, and the small proportion light is divided into the auxiliary interferometer module, and the large proportion light is divided into the main interferometer module.

[0009] Optionally, the main interferometer module comprises a second 1x2 optical fiber beam splitter, an optical switch, a first 2x2 optical fiber coupler, and a first balanced photodetector, wherein

[0010] The second 1x2 optical fiber beam splitter is used to split the entering light signal into two light beams; one of which is used as a measurement reference light and enters the first 2x2 optical fiber coupler through the optical switch, and the light scattered back by the measured light CT sensing optical fiber enters the first balanced photodetector after the measurement reference light interferes with the other light beam in the first 2x2 optical fiber coupler, and the measurement electrical signal output by the first balanced photodetector is injected into the signal processing control module.

[0011] Optionally, the splitting ratio of the second 1x2 optical fiber beam splitter is 10:90, and 10% is used as the measurement reference light and 90% is used as the measurement light.

[0012] Optionally, the auxiliary interferometer module comprises a first optical fiber loop, a second 2x2 optical fiber coupler, a delay optical fiber, a first Faraday mirror, a second Faraday mirror, and a second balanced photodetector, wherein

[0013] The small proportion light signal enters the first optical fiber loop and then outputs light through the second port into the second 2x2 optical fiber coupler, and then is split into 50% and 50% through two output ends, one part is directly injected into the first Faraday mirror, and the other part is injected into the second Faraday mirror through the delay optical fiber, the light reflected by the first Faraday mirror and the second Faraday mirror interferes at the second 2x2 optical fiber coupler and is split into two paths, one of which is directly injected into the second balanced photodetector, and the other of which is injected into the second balanced photodetector through the second port to the third port of the first optical fiber loop, and the electrical signal output by the second balanced photodetector is injected into the signal processing control module.

[0014] Optionally, the polarization generation and analysis unit comprises a polarization generation module, a second fiber circulator and a polarization analysis module, wherein,

[0015] The measurement light output by the second 1x2 fiber beam splitter passes through the polarization generation module, sequentially generates light of four polarization states in time sequence, and then enters the first port of the second circulator, is injected into the measured optical CT sensing fiber through the second port, and the optical signal passes through the backscattering Rayleigh scattering generated by the measured optical CT sensing fiber or the reflected light at the rear end of the measured optical CT sensing fiber, and is output to the polarization analysis module through the third port of the device second circulator; the polarization analysis module sequentially analyzes the polarization of the measured signal of the optical CT sensing fiber corresponding to the light of the four polarization states, and outputs the light into the second 2x2 fiber coupler to interfere with the measurement reference light to generate beat frequency.

[0016] Optionally, the signal processing and control module comprises a signal processing unit, a polarization control circuit unit and a host computer, wherein,

[0017] The signal processing unit receives the measurement electrical signal output by the main interferometer module and the electrical signal output by the auxiliary interferometer module, performs unified signal processing, and sends the processed signal to the host computer;

[0018] The polarization control circuit unit is used to receive the instruction of the host computer to control the polarization generation of the polarization generation module and the synchronous analysis control of the polarization analysis module.

[0019] Optionally, the polarization generation module can generate horizontal linearly polarized light, +45° linearly polarized light, -45° linearly polarized light and right circularly polarized light in sequence under the control of the polarization control circuit unit.

[0020] According to another aspect of the present application, a method for detecting the state of an optical CT sensing fiber is provided, comprising:

[0021] S1: controlling the tunable laser to output linear sweep frequency laser and controlling the light switch to be closed by the host computer;

[0022] S2: controlling the polarization generation module and the polarization analysis module so that the light intensity received by the first balanced photodetector is maximum;

[0023] S3: collecting the signal of the first balanced photodetector and performing distributed fiber frequency domain reflection measurement signal processing;

[0024] S4: judging whether there is a reflection peak exceeding the preset threshold in the processing result; if there is, it is determined that the optical CT sensing fiber at the corresponding position has a breakpoint or damage.

[0025] Optionally, after step S4, a polarization state detection step is further included:

[0026] S5: control the tunable laser to output single-frequency laser, and control the optical switch to be off;

[0027] S6: control the polarization generation module to generate probe light of four different polarization states in sequence and control the polarization analysis module to analyze synchronously by the polarization control circuit unit;

[0028] S7: calculate the overall Mueller matrix of the measured optical CT sensing fiber according to the signals corresponding to the four polarization states collected by the first balanced photodetector;

[0029] S8: calculate the intrinsic circular birefringence and residual linear birefringence of the fiber based on the overall Mueller matrix, and compare them with the preset normal threshold to determine whether the overall polarization state of the fiber is normal.

[0030] Optionally, when it is determined in step S4 that the fiber has an abnormality or it is determined in step S8 that the polarization state is abnormal, perform the distributed polarization detection step:

[0031] S9: control the tunable laser to output linear sweep frequency laser, and control the optical switch to be on;

[0032] S10: control the polarization generation module to generate probe light of four different polarization states in sequence and control the polarization analysis module to analyze synchronously by the polarization control circuit unit during the sweep frequency process;

[0033] S11: calculate the distributed Mueller matrix of the measured optical CT sensing fiber along the length direction according to the distributed beat frequency signals corresponding to each polarization state collected by the first balanced photodetector;

[0034] S12: calculate the birefringence of each small length segment of the fiber based on the distributed Mueller matrix to obtain the birefringence distribution of the whole fiber;

[0035] S13: determine whether there is a birefringence peak exceeding the preset threshold in the birefringence distribution; if there is, it is determined that the optical CT sensing fiber at the corresponding position has an abnormality of being pressed or excessively bent.

[0036] Optionally, in step S11, the frequency modulation nonlinearity and phase noise of the linear sweep frequency laser are compensated in real time by using the equal optical frequency interval hardware trigger signal generated by the auxiliary interferometer module.

[0037] Optionally, by the automatic instruction of the upper computer or according to the user instruction, one or more detection modes of the distributed reflection detection of steps S1-S4, the overall polarization detection of steps S5-S8, or the distributed polarization detection of steps S9-S13 are selected to be executed.

[0038] According to still another aspect of the present application, there is provided a computer readable storage medium storing a computer program for performing the method according to any one of the preceding aspects of the present application.

[0039] According to still another aspect of the present application, there is provided an electronic device comprising: a processor; a memory for storing instructions executable by the processor; and the processor configured to read the executable instructions from the memory and execute the instructions to implement the method according to any one of the preceding aspects of the present application.

[0040] Therefore, the present application proposes a method combining the polarization analysis and the optical frequency domain reflectometry based on the polarization analysis, aiming at the problem that the sensing optical fiber is difficult to be detected and positioned in the fault such as the transverse pressure and the too small bending radius, and the state of the sensing optical fiber is detected and the fault is diagnosed through the polarization state analysis of the sensing optical fiber probe light and the distributed birefringence measurement. BRIEF DESCRIPTION OF DRAWINGS

[0041] The exemplary embodiments of the present application will be more fully understood from the following drawings, in which:

[0042] Figure 1 Fig. 1 is a structural schematic diagram of an optical CT sensing optical fiber state detection system according to an exemplary embodiment of the present application;

[0043] Figure 2 Fig. 2 is a flowchart of the optical CT sensing optical fiber state detection according to an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0044] Hereinafter, the exemplary embodiments according to the present application will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, and are not all the embodiments of the present application. It should be understood that the present application is not limited to the described exemplary embodiments.

[0045] It should be noted that: the relative arrangement, numerical expression and numerical value of the components and steps set forth in the embodiments are not limited to the scope of the present application, unless otherwise specified.

[0046] Those skilled in the art can understand that the terms "first", "second" and the like in the embodiments of the present application are only used to distinguish different steps, devices or modules, and do not represent any specific technical meaning, nor represent the inevitable logical sequence between them.

[0047] It should also be understood that in the embodiments of the present application, "a plurality of" can mean two or more, and "at least one" can mean one, two or more.

[0048] It should also be understood that, with respect to any part of the present application mentioned in the embodiments, one or more can be understood in general, without explicit limitation or in the context of the opposite implications.

[0049] In addition, the term "and / or" in the present application is only a description of the associated relationship between the associated objects, which means that there can be three relationships, for example, A and / or B can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in the present application generally represents that the front and rear associated objects are in an "or" relationship.

[0050] It should also be understood that the description of the present application for each embodiment emphasizes the differences between each embodiment, and the same or similar parts can be referred to each other, and for the sake of brevity, will not be repeated.

[0051] At the same time, it should be understood that, in order to facilitate the description, the size of each part shown in the drawings is not drawn according to the actual proportional relationship.

[0052] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the application or its application or use.

[0053] The techniques, methods, and devices known to those of ordinary skill in the relevant art can not be discussed in detail, but in appropriate cases, the techniques, methods, and devices should be considered as part of the specification.

[0054] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0055] Figure 1 The structure diagram of the optical CT sensing optical fiber state detection system provided by the first aspect of the embodiment of the present application is shown in Figure 1 The optical CT sensing optical fiber state detection system includes a tunable laser 1, a first 1x2 optical fiber beam splitter 2, a main interferometer module, an auxiliary interferometer module, a polarization generation and analysis unit, and a signal processing control module, wherein

[0056] The light signal emitted by the tunable laser 1 is divided into two light signals by the first 1*2 optical fiber beam splitter 2, and the light signal with a small proportion enters the auxiliary interferometer module, and the light signal with a large proportion enters the main interferometer module; the light signal entering the main interferometer module is divided into two light signals, one of which is output to enter the polarization generation and analysis unit and then enters the measured light CT sensing optical fiber, and the light scattered back by the measured light CT sensing optical fiber returns to the main interferometer module through the polarization generation and analysis unit, interferes with the other light signal of the main interferometer module, and then enters the signal processing control module; the electrical signals output by the auxiliary interferometer module and the main interferometer module enter the signal processing control module for processing.

[0057] Specifically, the application provides an optical CT sensing optical fiber state detection system suitable for fault diagnosis and detection of an optical CT sensing optical fiber, which can timely find the potential fault type and fault position of the sensing optical fiber during optical CT inspection, guide the repair and recovery of the sensing optical fiber to normal measurement performance, and guarantee the safe and stable operation of a direct current system.

[0058] To solve the above technical problems, the technical scheme adopted by the application is as follows: Figure 1 As shown in the figure, an optical CT sensing optical fiber state detection system includes a tunable laser 1, a first 1*2 optical fiber beam splitter 2, a second 1*2 optical fiber beam splitter 3, an optical switch 4, a first 2*2 optical fiber coupler 5, a first balanced photodetector 6, a first optical fiber ring 7, a second 2*2 optical fiber coupler 8, a delay optical fiber 9, a first Faraday mirror 10, a second Faraday mirror 11, a second photodetector module 12, a polarization generation module 13, a second optical fiber ring 14, a polarization analysis module 15, a signal processing unit 16, a polarization control circuit unit 17, and an upper computer 18.

[0059] The second 1*2 optical fiber beam splitter 3, the optical switch 4, the first 2*2 optical fiber coupler 5, and the first balanced photodetector 6 constitute the main interferometer module, the first optical fiber ring 7, the second 2*2 optical fiber coupler 8, the delay optical fiber 9, the first Faraday mirror 10, the second Faraday mirror 11, and the second balanced photodetector 12 constitute the auxiliary interferometer module; the signal processing unit 16, the polarization control circuit unit 17, and the upper computer constitute the signal processing module 18.

[0060] The further tunable laser emits a light signal, which is split into two light signals by a first 1x2 optical fiber beam splitter 2 at a splitting ratio of 1:99 to 5:95, and a small proportion enters an auxiliary interferometer module and a large proportion enters a main interferometer module. The light signal entering the main interferometer module is split into two beams at a 50:50 ratio by a second 1x2 optical fiber beam splitter 3, one of which is output into a polarization generation module and then output into a measured light CT sensing optical fiber through a second optical fiber loop. The light scattered back by the measured light CT sensing optical fiber is returned to the main interferometer module after passing through the second optical fiber loop, the polarization generation and analysis module. The auxiliary interferometer module and the main interferometer module output electrical signals into a signal processing control module for processing. The signal processing control module is connected to the polarization generation module 13 and the polarization analysis module 15 to jointly control the two modules.

[0061] The output light of the tunable laser 1 is split into two paths by the first 1x2 optical fiber beam splitter 2, one of which is 5% and used as the input light of the auxiliary interferometer and output to the first port of the first optical fiber loop 7, and the other of which is 95% and used as the probe light and output to the input end of the second 1x2 optical fiber beam splitter 3;

[0062] The second port of the first optical fiber loop 7 outputs light into the second 2x2 optical fiber coupler 8, which is then split into two parts of 50% and 50% through its two output ends, one part is directly injected into the first Faraday mirror 10, and the other part of light is injected into the second Faraday mirror 11 through the delay optical fiber 9. The reflected light of the first Faraday mirror 10 and the second Faraday mirror 11 interferes at the second 2x2 optical fiber coupler 8 and is split into two paths, one of which is directly injected into the second balanced photodetector 12, and the other of which is injected into the second balanced photodetector 12 through the second port to the third port of the first optical fiber loop 7.

[0063] Among them, the first optical fiber loop 7, the second 2x2 optical fiber coupler 8, the first Faraday mirror 10, the delay optical fiber 9, the second Faraday mirror 11, and the second balanced photodetector 12 constitute an auxiliary interferometer, and the electrical signal output by the auxiliary interferometer is injected into the signal processing unit 16.

[0064] The auxiliary interferometer is used to generate a hardware trigger signal with equal optical frequency intervals, and to compensate for the phase noise and frequency drift introduced by the laser frequency modulation nonlinearity in real time.

[0065] The 5% output light of the second 1x2 optical fiber beam splitter 3 is the measurement reference light, which enters the second 2x2 optical fiber coupler 5 through the optical switch 4. The 95% output light of the second 1x2 optical fiber beam splitter 3 is the measurement light, which first passes through the polarization generation module 13. The polarization generation module is controlled by the polarization generation and analysis control unit 17, and sequentially generates light of four polarization states in time sequence. The generated light then enters the first port of the second circulator 14, is injected into the measured optical CT sensing fiber through the second port, and the optical signal passes through the backscattering Rayleigh scattering generated by the measured optical CT sensing fiber or the reflected light at the rear end of the measured optical CT sensing fiber, and is output to the polarization analysis module through the third port of the second circulator 14.

[0066] The polarization generation module 13 controls the incident light and sequentially outputs horizontal linearly polarized light, +45° linearly polarized light, -45° linearly polarized light, and right circularly polarized light of four different known polarization states. The four different known polarization state probe lights return into the polarization analysis module through Rayleigh scattering in the measured CT sensing fiber, and the polarization analysis module sequentially analyzes the polarization of the four different known polarization state probe light return signals.

[0067] The polarization analysis module 15 analyzes the polarization of the measured signals of the optical CT sensing fiber corresponding to the light of the four sequentially generated polarization states one by one, and the synchronous analysis control is completed by the polarization generation and analysis control unit 17. Subsequently, the polarization analysis module 15 outputs the light into the second 2x2 optical fiber coupler 5, and the measurement reference light interferes and beats in the second 2x2 optical fiber coupler 5. Finally, the two output signals of the second 2x2 optical fiber coupler 5 after interference and beating enter the first balanced photodetector 6. The measurement electrical signal output by the first balanced photodetector 6 is injected into the signal processing unit 16, and the electrical signal generated by the auxiliary interferometer is uniformly processed.

[0068] The signal processing unit 16 processes the data and sends it to the host computer 18 for further operation and processing. At the same time, the host computer 18 controls the optical switch 4 and the polarization generation and analysis control unit 17 to set the test mode and complete the measurement of the set mode.

[0069] Figure 2 A flowchart of a light CT sensing fiber state detection method provided by the second aspect of the application is shown, and as shown in Figure 2 The light CT sensing fiber state detection method comprises:

[0070] S1: The host computer 18 controls the tunable laser 1 to output linear sweep frequency laser, and controls the optical switch 4 to be closed;

[0071] S2: The polarization generation module 13 and the polarization analysis module 15 are controlled so that the light intensity received by the first balanced photodetector (6) is maximum;

[0072] S3: Collecting the signal of the first balanced photodetector 6 and performing distributed fiber frequency domain reflection measurement signal processing;

[0073] S4: Determining whether there is a reflection peak exceeding the preset threshold in the processing result; if there is, it is determined that there is a breakpoint or damage in the optical CT sensing fiber at the corresponding position.

[0074] Specifically, the method for the host computer to cooperatively control the beat frequency signal obtained by the polarization generation module and the polarization analysis module to perform optical CT sensing fiber state detection is as follows:

[0075] Step 1: Set the tunable laser to output linear sweep frequency laser, and set the optical switch to the connected state;

[0076] Step 2: Set the polarization generation module and the polarization control module to maximize the light intensity received by the second balanced photodetector;

[0077] Step 3: The second balanced photodetector collects the light signal returned by the optical CT sensing fiber, and performs distributed fiber frequency domain reflection measurement signal processing on the measurement result;

[0078] Step 4: Determine whether there is an abnormality in the measurement result of the optical CT sensing distributed frequency domain reflection measurement, i.e., whether there is a reflection peak exceeding the set threshold; if there is a reflection peak exceeding the set threshold, it is determined that there is a breakpoint or damage in the optical CT sensing fiber at the position;

[0079] Step 5: Set the tunable laser to output single frequency laser, and set the optical switch to the disconnected state;

[0080] Step 6: The host computer generates four different polarized lights by setting the polarization generation module, controls the polarization analysis module at the same time, and the second balanced photodetector detects the returned light of the measured optical CT sensing fiber, and obtains the overall Mueller matrix of the measured optical CT sensing fiber through data processing and analysis;

[0081] Step 7: Based on the Mueller matrix of the measured optical CT sensing fiber, the intrinsic circular birefringence and the residual linear birefringence of the CT sensing fiber are calculated, and the obtained residual linear birefringence is compared with the reasonable residual linear birefringence to determine whether the working state of the optical CT sensing fiber is normal;

[0082] Step 8: If the CT sensing fiber is determined to be abnormal in step 3, set the tunable laser to output linear sweep frequency laser, and set the optical switch to the connected state. At this time, the diagnosis system works in the distributed fiber frequency domain reflection measurement mode which can perform polarization analysis.

[0083] Step 9: The host computer generates polarized light with four different polarization states by setting the polarization generation module, and at the same time controls the polarization analysis module and the second balanced photodetector to detect the return light of the optical CT sensing fiber under test. The distributed Mueller matrix of the optical CT sensing fiber under test is obtained through data processing and analysis.

[0084] Step 10: The host computer calculates the birefringence of the tiny length Δz fiber segment at each location of the optical CT sensing fiber, thus obtaining the birefringence distribution along the entire fiber.

[0085] Step 11: Determine if there is any abnormality in the birefringence distribution of the optical CT sensing fiber, that is, whether there is a birefringence peak exceeding the set threshold. If a birefringence peak exceeding the set threshold appears, it is determined that the optical CT sensing fiber at that location is under pressure or bent excessively, or there is an abnormality.

[0086] First, by setting the tunable laser 1 to output a linearly swept laser, and with the optical switch 4 in the connected state, the polarization generation module 13 and polarization control module 15 are configured to maximize the light intensity received by the second balanced photodetector 12, thus activating the optical CT sensing fiber optic status detection system in distributed optical frequency domain reflectance measurement mode. The second balanced photodetector 12 acquires the optical signal returned by the optical CT sensing fiber and performs distributed optical frequency domain reflectance measurement signal processing on the measurement results. Based on the measurement results of the distributed optical frequency domain reflectance measurement signal, it is determined whether there is an anomaly in the optical CT sensing fiber, i.e., whether there is a reflection peak in the distributed optical frequency domain reflectance measurement signal exceeding a set threshold. If a reflection peak exceeding the set threshold is found, it is determined that there is an anomaly such as a break or damage in the optical CT sensing fiber at that location.

[0087] Secondly, the tunable laser 1 is set to output a single-frequency laser, with the optical switch 4 in the off state; the tunable laser 1 outputs a linearly swept-frequency laser, with the optical switch 4 in the connected state, so that the optical CT sensing fiber status detection system operates in the polarization light generation, analysis, and measurement mode. The host computer 18 generates polarized light with four different polarization states by setting the polarization generation module 13, and simultaneously controls the polarization analysis module 15. The second balanced photodetector 12 detects the return light from the optical CT sensing fiber under test, and obtains the overall Mueller matrix of the optical CT sensing fiber under test through data processing and analysis. Based on the Mueller matrix of the optical CT sensing fiber under test, the intrinsic circular birefringence and residual linear birefringence of the CT sensing fiber are calculated, and the obtained residual linear birefringence is compared with the reasonable residual linear birefringence to determine whether the working state of the optical CT sensing fiber is normal.

[0088] Finally, the tunable laser 1 outputs a linear sweep laser, the optical switch 4 is in a connected state, and the optical CT sensing fiber state detection system works in a distributed optical frequency domain reflection measurement mode that can perform polarization analysis. The host computer 18 generates four different polarized lights through the polarization generation module 13, and controls the polarization analysis module 15 at the same time. The second balanced photodetector 12 detects the return light of the measured optical CT sensing fiber, and the distributed Mueller matrix of the measured optical CT sensing fiber is obtained through data processing analysis. The host computer 18 obtains the birefringence of the optical CT sensing fiber at each position through calculation, and thus obtains the birefringence distribution along the whole fiber. Based on the birefringence distribution of the optical CT sensing fiber, it is judged whether the optical CT sensing fiber is abnormal, that is, whether there is a birefringence peak exceeding the set threshold. If there is a birefringence peak exceeding the set threshold, it is determined that the optical CT sensing fiber at this position has abnormal conditions such as excessive pressure or bending.

[0089] Therefore, the optical CT sensing fiber state detection system effectively fuses polarization analysis technology and polarization analysis-based optical frequency domain reflection technology, solves the problem of online detection of the optical CT sensing fiber state, and has the following main effects:

[0090] 1. The application proposes a fusion technology of polarization analysis and polarization analysis-based optical frequency domain reflection, which can realize online detection of the optical CT sensing fiber state.

[0091] 2. The application proposes a detection system with polarization analysis and polarization analysis-based optical frequency domain reflection functions, which is used for realizing online detection of the optical CT sensing fiber state.

[0092] 3. The application can be widely used in the field of optical fiber sensing, and provides a reliable detection method for the state detection of the sensing fiber, and has good application prospect.

[0093] The above description has been given for the purpose of example and description. In addition, this description is not intended to limit the embodiments of the application to the forms disclosed herein. Although the above has discussed a plurality of example aspects and embodiments, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations.

Claims

1. A fiber optic condition detection system for optical CT sensing, characterized in that, include: The system comprises a tunable laser (1), a first 1×2 fiber beam splitter (2), a main interferometer module, an auxiliary interferometer module, a polarization generation and analysis unit, and a signal processing and control module, wherein... The optical signal emitted by the tunable laser (1) is split into two optical signals by the first 1×2 fiber beam splitter (2). The smaller proportion of the optical signal enters the auxiliary interferometer module, and the larger proportion of the optical signal enters the main interferometer module. The optical signal entering the main interferometer module is split into two beams. One beam is output into the polarization generation and analysis unit and then into the optical fiber of the optical CT sensor under test. The light scattered back from the optical CT sensor under test returns to the main interferometer module through the polarization generation and analysis unit and interferes with the other beam of the main interferometer module before entering the signal processing and control module. The electrical signals output by the auxiliary interferometer module and the main interferometer module are processed by the signal processing and control module.

2. The optical CT sensing fiber optic status detection system according to claim 1, characterized in that, The first 1×2 fiber beam splitter (2) has a splitting ratio of 1:99 to 5:95, splitting a small proportion of light into the auxiliary interferometer module and a large proportion of light into the main interferometer module.

3. The optical CT sensing fiber optic status detection system according to claim 1, characterized in that, The main interferometer module includes: a second 1×2 fiber optic beam splitter (3), an optical switch (4), a first 2×2 fiber optic coupler (5), and a first balanced photodetector (6), wherein... The second 1×2 fiber beam splitter (3) is used to split the incoming optical signal into two beams; one of the beams serves as the measurement reference light and enters the first 2×2 fiber coupler (5) through the optical switch (4). The light scattered back by the optical CT sensing fiber under test is subjected to interference beat frequency with the measurement reference light in the first 2×2 fiber coupler (5) by the polarization generation and analysis unit and then enters the measurement electrical signal output by the first balanced photodetector (6) and is injected into the signal processing and control module.

4. The optical CT sensing fiber optic status detection system according to claim 1 or 3, characterized in that, The splitting ratio of the second 1×2 fiber beam splitter (3) is 10:90, with 10% used as the measurement reference light and 90% used as the measurement light.

5. The optical CT sensing fiber optic status detection system according to claim 1, characterized in that, The auxiliary interferometer module includes: a first fiber optic circulator (7), a second 2×2 fiber optic coupler (8), a time-delay fiber (9), a first Faraday mirror (10), a second Faraday mirror (11), and a second balanced photodetector (12), wherein, After the small-scale optical signal enters the first fiber optic circulator (7), it outputs light through the second port and enters the second 2×2 fiber optic coupler (8). Then, it is divided into two parts of 50% and 50% through its two output ends. One part is directly injected into the first Faraday reflector (10), and the other part is injected into the second Faraday reflector (11) through the delay fiber (9). The light reflected by the first Faraday reflector (10) and the second Faraday reflector (11) interferes at the second 2×2 fiber optic coupler (8) and is divided into two paths. One path is directly injected into the second balanced photodetector (12), and the other path goes through the second port of the first fiber optic circulator (7) to the third port and is injected into the second balanced photodetector (12). The electrical signal output by the second balanced photodetector (12) is injected into the signal processing and control module.

6. The optical CT sensing fiber optic status detection system according to claim 2, characterized in that, The polarization generation and analysis unit includes: a polarization generation module (13), a second fiber optic circulator (14), and a polarization analysis module (15), wherein, The measurement light output from the second 1×2 fiber beam splitter (3) passes through the polarization generation module (13) and generates four polarization states in sequence according to time. Then, it enters the first port of the second circulator (14) and is injected into the optical CT sensing fiber under test through the second port. The optical signal is backscattered by Rayleigh or reflected from the rear end of the optical CT sensing fiber under test and output to the polarization analysis module (15) through the third port of the second circulator (14). The polarization analysis module (15) performs polarization analysis on the optical CT sensing fiber signal under test corresponding to the four polarization states generated in sequence and outputs the light into the second 2×2 fiber coupler (5) to interfere with the measurement reference light.

7. The optical CT sensing fiber optic status detection system according to claim 4, characterized in that, The signal processing control module includes: a signal processing unit (16), a polarization control circuit unit (17), and a host computer (18), wherein, The signal processing unit (16) receives the measurement electrical signal output by the main interferometer module and the electrical signal output by the auxiliary interferometer module, performs unified signal processing, and then sends it to the host computer (18). The polarization control circuit unit (17) is used to receive instructions from the host computer (18) to control the polarization generation module (13) and the synchronous analysis control of the polarization analysis module (15).

8. The optical CT sensing fiber optic status detection system according to claim 6, characterized in that, Under the control of the polarization control circuit unit (17), the polarization generation module (13) can sequentially generate four different known polarization states: horizontally linearly polarized light, +45° linearly polarized light, -45° linearly polarized light, and right-hand circularly polarized light.

9. A method for optical CT sensing fiber optic status detection based on the system described in any one of claims 1-8, characterized in that, include: S1: The host computer (18) controls the tunable laser (1) to output linear frequency sweep laser and controls the optical switch (4) to close. S2: Control the polarization generation module (13) and the polarization analysis module (15) to maximize the light intensity received by the first balanced photodetector (6); S3: Collect the signal from the first balanced photodetector (6) and perform distributed fiber frequency domain reflection measurement signal processing; S4: Determine whether there is a reflection peak in the processing result that exceeds the preset threshold; if so, determine that there is a break or damage in the optical CT sensing fiber at the corresponding location.

10. The method according to claim 9, characterized in that, Following step S4, a polarization state detection step is also included: S5: Control the tunable laser (1) to output a single-frequency laser and control the optical switch (4) to open; S6: The polarization control circuit unit (17) controls the polarization generation module (13) to generate four different polarization states of probe light in sequence, and simultaneously controls the polarization analysis module (15) to perform analysis. S7: Based on the signals corresponding to the four polarization states collected by the first balanced photodetector (6), the overall Mueller matrix of the optical CT sensing fiber under test is calculated. S8: Based on the overall Mueller matrix, calculate the intrinsic circular birefringence and residual linear birefringence of the optical fiber, and compare them with the preset normal threshold to determine whether the overall polarization state of the optical fiber is normal.

11. The method according to claim 10, characterized in that, When step S4 determines that there is an abnormality in the optical fiber or step S8 determines that the polarization state is abnormal, the distributed polarization detection step is executed: S9: Control the tunable laser (1) to output linear sweep laser and control the optical switch (4) to close; S10: During the frequency sweep process, the polarization control circuit unit (17) controls the polarization generation module (13) to generate four different polarization states of probe light in sequence, and simultaneously controls the polarization analysis module (15) to perform analysis. S11: Based on the distributed beat frequency signals corresponding to each polarization state collected by the first balanced photodetector (6), the distributed Mueller matrix along the length direction of the optical CT sensing fiber under test is calculated. S12: Based on the distributed Mueller matrix, calculate the birefringence of each small length segment of the optical fiber to obtain the birefringence distribution of the entire optical fiber. S13: Determine whether there is a birefringence peak value exceeding a preset threshold in the birefringence distribution; if so, determine that the optical CT sensing fiber at the corresponding position is abnormally compressed or bent.

12. The method according to claim 11, characterized in that, In step S11, the frequency modulation nonlinearity and phase noise of the linear sweep laser are compensated in real time using the equal optical frequency interval hardware trigger signal generated by the auxiliary interferometer module.

13. The method according to any one of claims 9-12, characterized in that, The host computer (18) automatically commands or according to user commands to select one or more detection modes among the distributed reflection detection in steps S1-S4, the overall polarization detection in steps S5-S8, or the distributed polarization detection in steps S9-S13.

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