Single-photon Raman temperature sensing system and sensing method thereof

Abstract

The invention discloses a single-photon Raman temperature sensing system and a sensing method thereof, solves the problem of photon counting curve jittering caused by Raman gain in an optical fiber and polarization sensitivity of a single-photon detector, and belongs to the technical field of distributed optical fiber sensing and single-photon detection. According to the distributed optical fiber temperature sensing system and method based on the dual-wavelength cross-polarization pulse pumping, Raman pumping and single photon detection are carried out by combining a dual-independent-wavelength pulse light source with a cross-polarization synthesis light path; and photon number jitter of the Raman gain and the single-photon detector in the optical fiber due to the change of the polarization state of the optical signal can be effectively solved. According to the invention, the problem that the temperature measurement curve in the traditional single-photon Raman temperature sensing system changes periodically is eliminated, and the temperature measurement accuracy and the temperature resolution are higher, so that the method can be conveniently applied to the high-precision single-photon Raman temperature sensing system.

Description

Technical Field

[0001] This invention relates to the fields of distributed optical fiber sensing and single-photon detection technology, and in particular to a single-photon Raman temperature sensing system and its sensing method. Background Technology

[0002] Distributed fiber optic sensing technology has long been the most widely used long-distance, large-area sensing technology, possessing advantages such as anti-interference and corrosion resistance not found in other sensing methods. Furthermore, in distributed fiber optic temperature sensing technology, light serves as both the transmission and sensing medium, allowing for the measurement of continuously distributed temperature fields via optical fiber, offering significant advantages such as low cost and no blind zones. However, at spatial resolutions on the order of meters per centimeter, polarization-dependent fluctuations in spontaneous Raman backscattered photons can be significantly observed, increasing the temperature measurement error of distributed Raman fiber optic temperature sensors. Orthogonally polarized double-pulse light can mitigate these fluctuations, but current solutions still require the use of delay fibers and single-pulse lasers to generate the orthogonally polarized double-pulse light, and the delay fiber length needs to be more than twice the length of the sensing fiber. This limits the sensing distance of distributed Raman fiber optic temperature sensors and increases system complexity.

[0003] Therefore, it is necessary to develop a single-photon Raman temperature sensing system and its sensing method to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to design a single-photon Raman temperature sensing system and its sensing method to solve the above-mentioned problems.

[0005] The present invention achieves the above objectives through the following technical solutions:

[0006] A single-photon Raman temperature sensing system includes a dual-wavelength orthogonal polarization pulse generation unit, a sensing unit, and a signal detection and demodulation unit. The dual-wavelength orthogonal polarization pulse generation unit is connected to the sensing unit. The dual-wavelength orthogonal polarization pulse generation unit includes an arbitrary waveform generator, a first pulse laser, a second pulse laser, a first fiber amplifier, a second fiber amplifier, a first polarization controller, a second polarization controller, a polarization combiner, and a tunable optical attenuator. The arbitrary waveform generator is connected to the first pulse laser and the second pulse laser, respectively. The output of the first pulse laser is connected to the polarization combiner sequentially through the first fiber amplifier and the first polarization controller. The output of the second pulse laser is connected to the polarization combiner sequentially through the second fiber amplifier and the second polarization controller, combining the two light streams into one output, which then enters the tunable optical attenuator.

[0007] The sensing unit includes a wavelength division multiplexer (WDM) and a single-mode fiber under test (SMD). The WDM has three ports: port 1, port 2, and port 3. Port 1 is the pump light input port, port 2 is the beam combining port, and port 3 is the spontaneous anti-Stokes Raman backscattered photon output port. Its output spectral bandwidth must be greater than the center wavelength difference between the first and second pulsed lasers. The pulsed light enters the WDM from port 1 and enters the SMD from port 2. The backscattered signal generated in the SMD returns to port 2 and the spontaneous anti-Stokes Raman backscattered photons are filtered out from port 3.

[0008] The signal detection and demodulation unit includes a single-photon detector, a time-to-digital converter, and a host computer. The single-photon detector is composed of an avalanche diode or a superconducting nanodevice. The time-to-digital converter is composed of any one of the following: a microcontroller, a programmable logic device, a digital signal processing chip, an embedded chip, or a delay device. The three ports of the wavelength division multiplexer are connected to the single-photon detector. The single-photon detector and the arbitrary waveform generator are both connected to the time-to-digital converter. The time-to-digital converter is connected to the host computer.

[0009] An arbitrary waveform generator is used to generate modulation pulses for a pulsed laser, and the time interval between two adjacent modulation pulses must be greater than the time required for the optical signal to travel over twice the length of the single-mode fiber under test.

[0010] Both the first pulse laser and the second pulse laser are semiconductor distributed feedback lasers, fiber lasers, or mode-locked lasers that employ internal or external modulation, and the center wavelength difference between the first pulse laser and the second pulse laser must be greater than 0 and less than the filtering bandwidth of the three ports of the wavelength division multiplexer.

[0011] The first polarization controller and the second polarization controller are used to control the light intensity and polarization state of the two pulsed lights;

[0012] A polarization beam combiner is used to combine two pulsed lights into a single dual-wavelength orthogonal polarization pulse pair.

[0013] A sensing method for a single-photon Raman temperature sensing system includes the following steps:

[0014] S1. The output of the dual-wavelength orthogonal polarization optical pulse generation unit includes a pair of optical pulses with independent wavelengths, mutually orthogonal polarization states, the same pulse width, time synchronization, and adjustable light intensity. This pair of optical pulses will be coupled into one port of the wavelength division multiplexer. The time interval between two adjacent optical pulse pairs in the time domain must be greater than the time required for the optical signal to transmit within twice the length of the single-mode optical fiber under test.

[0015] S2. The single-mode fiber under test is connected to port 2 of the wavelength division multiplexer. The spontaneous anti-Stokes Raman backscattered photons generated by it return to port 2 of the wavelength division multiplexer and are filtered out from port 3 of the wavelength division multiplexer.

[0016] S3. The filtered anti-Stokes Raman photons enter the single-photon detector, and then the number and time of photon arrival are recorded by the time-to-digital converter.

[0017] S4. The host computer analyzes and processes the count values ​​in the photon counting curve to obtain the temperature information of each point in the optical fiber. By analyzing the time coordinates corresponding to the photon count values ​​and using the time-of-flight positioning principle, high-precision positioning of different temperature points along the entire optical fiber can be achieved.

[0018] Furthermore, the Jones vector of the electric field vector of any polarized light in the fiber under test is expressed by Equation 1: (one)

[0019] in, and These represent the amplitude components of the probe light along the fast and slow axes, respectively. To detect the initial phase difference of the optical polarization components along the fast and slow axes;

[0020] The Jones matrix of the fiber under test with length z is represented by Formula 2: (two)

[0021] in, It is the phase difference of the probe light polarization component along the fast and slow axes of the fiber at the z-distance caused by PMD;

[0022] The Raman gain Jones matrix in optical fiber can be written as Equation 3:

[0023] (three)

[0024] in, and These are the Raman gain coefficients of the probe light along the fast and slow axes, respectively;

[0025] Spontaneous anti-Stokes Raman photon field This can be represented as Formula 4:

[0026] (Four).

[0027] Furthermore, after the dual-wavelength orthogonally polarized light pulses enter the fiber under test, the spontaneous anti-Stokes Raman backscattered photons generated by the pump light with different polarization directions interfere with each other. The number of Raman photons at the z-distance is expressed by Formula 5:

[0028] (five)

[0029] in, and The number of spontaneous anti-Stokes Raman backscattered photons generated at a distance z by the two-wavelength orthogonally polarized light pulse pairs propagating along the fast and slow axes of the optical fiber, respectively, can be eliminated by superimposing the number of spontaneous anti-Stokes Raman backscattered photons generated by the two-wavelength orthogonally polarized light pulse pairs in the optical fiber.

[0030] Furthermore, the number of spontaneous anti-Stokes Raman backscattered photons without polarization-dependent fluctuations is related to the temperature at a point z along the fiber, as given by Equation 6:

[0031] (six)

[0032] Where η is the SPD detection efficiency, P(z) is the peak power of the pump light at a distance z, and h is Planck's constant. The center frequency of anti-Stokes light, The center frequency of the input pulse light. Here, T is the Boltzmann constant, and T is the temperature at a distance z along the fiber. SPD dark count rate;

[0033] Analyzing the changes in the anti-Stokes Raman photon number allows for the demodulation of the temperature along the optical fiber; the demodulation formula is Equation Seven.

[0034] (seven)

[0035] in, It is the spontaneous anti-Stokes coefficient of Raman backscattering at the calibration temperature T0, and C is the temperature sensitivity coefficient;

[0036] Temperature information can be extracted from the above formula. Formula 8:

[0037] (eight)

[0038] Therefore, by recording the photon count of the non-polarization-dependent spontaneous anti-Stokes Raman backscattering signal, the temperature information at different locations of the fiber under test can be obtained with high precision.

[0039] The beneficial effects of this invention are as follows:

[0040] 1. The problem of photon counting curve jitter caused by Raman gain and the polarization sensitivity of single-photon detectors was solved by adopting a dual-wavelength orthogonal polarization pulse pumping method.

[0041] 2. Compared with the traditional method of using polarization diversity detection, the system structure of the present invention can reduce curve jitter caused by polarization by using a single-photon detector port, and avoid measurement errors caused by different dark counts and detection efficiencies of different ports.

[0042] 3. The present invention employs a polarization controller and a polarization beam combiner to control two orthogonally polarized double-pulse light, thereby improving the stability of the system. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort, wherein:

[0044] Figure 1 This is a schematic diagram of the system structure of the present invention;

[0045] The components in the diagram are labeled as follows: 1-Arbitrary wavefunction generator, 2-First pulse laser, 3-First fiber amplifier, 4-First polarization controller, 5-Polarization combiner, 6-Tuned optical attenuator, 7-Wavelength division multiplexer, 8-Single-mode fiber under test, 9-Second polarization controller, 10-Second fiber amplifier, 11-Second pulse laser, 12-Time-to-digital converter, 13-Single-photon detector, 14-Host computer. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0048] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0049] In the description of this invention, it should be understood that the terms "upper," "lower," "inner," "outer," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0050] Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0051] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, terms such as "set" and "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0052] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0053] like Figure 1 As shown, a single-photon Raman temperature sensing system includes a dual-wavelength orthogonal polarization pulse generation unit, a sensing unit, and a signal detection and demodulation unit. The dual-wavelength orthogonal polarization pulse generation unit is connected to the sensing unit. The dual-wavelength orthogonal polarization pulse generation unit includes an arbitrary waveform generator 1, a first pulse laser 2, a second pulse laser 11, a first fiber amplifier 3, a second fiber amplifier 10, a first polarization controller 4, a second polarization controller 9, a polarization combiner 5, and a tunable optical attenuator 6. The arbitrary waveform generator 1 is connected to the first pulse laser 2 and the second pulse laser 11 respectively. The output end of the first pulse laser 2 is connected to the polarization combiner 5 in sequence through the first fiber amplifier 3 and the first polarization controller 4. The output end of the second pulse laser 11 is connected to the polarization combiner 5 in sequence through the second fiber amplifier 10 and the second polarization controller 9, combining the two optical paths into one output, which then enters the tunable optical attenuator 6.

[0054] The sensing unit includes a wavelength division multiplexer 7 and a single-mode fiber under test 8. The wavelength division multiplexer 7 has three ports: a port 1, a port 2, and a port 3. The port 1 is the pump light input port, the port 2 is the beam combining port, and the port 3 is the spontaneous anti-Stokes Raman backscattered photon output port. Its output spectral bandwidth must be greater than the center wavelength difference between the first pulse laser 2 and the second pulse laser 11. The pulse light enters the wavelength division multiplexer 7 from the port 1 and enters the single-mode fiber under test 8 from the port 2. The backscattered signal generated in the single-mode fiber under test 8 returns to the port 2 and the spontaneous anti-Stokes Raman backscattered photons are filtered out from the port 3.

[0055] The signal detection and demodulation unit includes a single-photon detector 13, a time-to-digital converter 12, and a host computer 14. The single-photon detector 13 is composed of an avalanche diode or a superconducting nanodevice. The time-to-digital converter 12 is composed of any one of the following: a microcontroller, a programmable logic device, a digital signal processing chip, an embedded chip, or a delay device. The three ports of the wavelength division multiplexer 7 are connected to the single-photon detector 13. The single-photon detector 13 and the arbitrary waveform generator 1 are both connected to the time-to-digital converter 12. The time-to-digital converter 12 is connected to the host computer 14. The host computer contains signal demodulation and processing programs.

[0056] Arbitrary waveform generator 1 is used to generate modulation pulses for the pulsed laser, and the time interval between two adjacent modulation pulses must be greater than the time required for the optical signal to transmit over a range of twice the length of the single-mode fiber 8 under test.

[0057] Both the first pulse laser 2 and the second pulse laser 11 are semiconductor distributed feedback lasers, fiber lasers, or mode-locked lasers that use internal or external modulation, and the center wavelength difference between the first pulse laser 2 and the second pulse laser 11 must be greater than 0 and less than the filtering bandwidth of the three ports of the wavelength division multiplexer 7.

[0058] The first polarization controller 4 and the second polarization controller 9 are used to control the light intensity and polarization state of the two pulsed lights;

[0059] The polarization combiner 5 is used to combine two pulsed lights into a single dual-wavelength orthogonal polarization pulse pair.

[0060] A sensing method for a single-photon Raman temperature sensing system includes the following steps:

[0061] S1. The output of the dual-wavelength orthogonal polarization light pulse generation unit includes a pair of light pulses with independent wavelengths, mutually orthogonal polarization states, the same pulse width, time synchronization, and adjustable light intensity. This pair of light pulses will be coupled into one port of the wavelength division multiplexer 7. The time interval between two adjacent light pulse pairs in the time domain must be greater than the time required for the light signal to transmit within twice the length of the single-mode fiber 8 under test.

[0062] S2. The single-mode fiber 8 under test is connected to the two ports of the wavelength division multiplexer 7. The spontaneous anti-Stokes Raman backscattered photons generated by it return to the two ports of the wavelength division multiplexer 7 and are filtered out from the three ports of the wavelength division multiplexer 7. In step S3, the number of anti-Stokes Raman backscattered photons generated by the pulsed light varies with the magnitude of the external temperature, thereby realizing sensing.

[0063] S3. The filtered anti-Stokes Raman photons enter the single-photon detector 13, and then the number and time of photon arrival are recorded by the time-to-digital converter 12.

[0064] S4 and host computer 14 obtain temperature information of each point in the optical fiber by analyzing and processing the count values ​​in the photon counting curve; by analyzing the time coordinates corresponding to the photon symbol values ​​and using the time-of-flight positioning principle, high-precision positioning of different temperature points along the entire optical fiber can be achieved.

[0065] Furthermore, the Jones vector of the electric field vector of any polarized light in the fiber under test is expressed by Equation 1:

[0066] (one)

[0067] in, and These represent the amplitude components of the probe light along the fast and slow axes, respectively. To detect the initial phase difference of the optical polarization components along the fast and slow axes;

[0068] The Jones matrix of the fiber under test with length z is represented by Formula 2:

[0069] (two)

[0070] in, It is the phase difference of the probe light polarization component along the fast and slow axes of the fiber at a distance z caused by PMD (polarization mode dispersion);

[0071] The Raman gain Jones matrix in optical fiber can be written as Equation 3:

[0072] (three)

[0073] in, and These are the Raman gain coefficients of the probe light along the fast and slow axes, respectively;

[0074] Spontaneous anti-Stokes Raman photon field This can be represented as Formula 4:

[0075] (Four).

[0076] Furthermore, after the dual-wavelength orthogonally polarized light pulses enter the fiber under test, the spontaneous anti-Stokes Raman backscattered photons generated by the pump light with different polarization directions interfere with each other. The number of Raman photons at the z-distance is expressed by Formula 5:

[0077] (five)

[0078] in, and The number of spontaneous anti-Stokes Raman backscattered photons generated at a distance z by the two-wavelength orthogonally polarized light pulse pairs propagating along the fast and slow axes of the optical fiber, respectively, can be eliminated by superimposing the number of spontaneous anti-Stokes Raman backscattered photons generated by the two-wavelength orthogonally polarized light pulse pairs in the optical fiber.

[0079] Furthermore, the number of spontaneous anti-Stokes Raman backscattered photons without polarization-dependent fluctuations is related to the temperature at a point z along the fiber, as given by Equation 6:

[0080] (six)

[0081] Where η is the detection efficiency of the SPD (single-photon detector), P(z) is the peak power of the pump light at a distance z, and h is Planck's constant. The center frequency of anti-Stokes light, The center frequency of the input pulse light. Here, T is the Boltzmann constant, and T is the temperature at a distance z along the fiber. SPD dark count rate;

[0082] Analyzing the changes in the anti-Stokes Raman photon number allows for the demodulation of the temperature along the optical fiber; the demodulation formula is Equation Seven.

[0083] (seven)

[0084] in, It is the spontaneous anti-Stokes coefficient of Raman backscattering at the calibration temperature T0, and C is the temperature sensitivity coefficient;

[0085] Temperature information can be extracted from the above formula. Formula 8:

[0086] (eight)

[0087] Therefore, by recording the photon count of the non-polarization-dependent spontaneous anti-Stokes Raman backscattering signal, the temperature information at different locations of the fiber under test can be obtained with high precision.

[0088] In the system structure of this invention, adjusting two polarization controllers can change the polarization state of the pulsed light entering the polarization combiner, thereby adjusting the components in the two orthogonal polarization directions and ultimately changing the relative magnitude of the intensity of the two orthogonal polarized pulses. After passing through the polarization combiner, the two light pulses are combined into a pair of orthogonally polarized light pulses with dual wavelengths. This dual-wavelength orthogonally polarized light pulse superimposes the number of spontaneous anti-Stokes Raman backscattered photons generated in the single-mode fiber under test, eliminating photon count jitter caused by polarization state fluctuations of the single-wavelength pump light at different locations in the fiber. The superimposed spontaneous anti-Stokes Raman backscattered photons are filtered out by the three-port filter of the wavelength division multiplexer and then enter the signal detection and demodulation unit. Finally, a smooth spontaneous anti-Stokes Raman backscattered light curve can be obtained on the host computer, effectively reducing the polarization sensitivity of the system and thus improving the temperature detection accuracy of the system.

[0089] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A single-photon Raman temperature sensing system, characterized in that, It includes a dual-wavelength orthogonal polarization pulse generation unit, a sensing unit, and a signal detection and demodulation unit; the dual-wavelength orthogonal polarization pulse generation unit is connected to the sensing unit; the dual-wavelength orthogonal polarization pulse generation unit includes an arbitrary waveform generator (1), a first pulse laser (2), a second pulse laser (11), a first fiber amplifier (3), a second fiber amplifier (10), a first polarization controller (4), a second polarization controller (9), a polarization combiner (5), and a tunable optical attenuator (6); the arbitrary waveform generator (1) is connected to the first pulse laser (2) and the second pulse laser (11) respectively; the output end of the first pulse laser (2) is connected to the polarization combiner (5) in sequence through the first fiber amplifier (3) and the first polarization controller (4); the output end of the second pulse laser (11) is connected to the polarization combiner (5) in sequence through the second fiber amplifier (10) and the second polarization controller (9), combining the two beams into one output and entering the tunable optical attenuator (6); The sensing unit includes a wavelength division multiplexer (7) and a single-mode fiber under test (8); the wavelength division multiplexer (7) includes three ports, namely port one, port two and port three. Port one is the pump light input port, port two is the beam combining port, and port three is the spontaneous anti-Stokes Raman backscattered photon output port. Its output spectral bandwidth must be greater than the center wavelength difference between the first pulse laser (2) and the second pulse laser (11); the pulse light enters the wavelength division multiplexer (7) from port one and enters the single-mode fiber under test (8) from port two; the backscattered signal generated in the single-mode fiber under test (8) returns to port two and the spontaneous anti-Stokes Raman backscattered photons are filtered out from port three; The signal detection and demodulation unit includes a single-photon detector (13), a time-to-digital converter (12), and a host computer (14). The single-photon detector (13) is composed of an avalanche diode or a superconducting nanodevice. The time-to-digital converter (12) is composed of any one of the following: a microcontroller, a programmable logic device, a digital signal processing chip, an embedded chip, or a delay device. The three ports of the wavelength division multiplexer (7) are connected to the single-photon detector (13). The single-photon detector (13) and the arbitrary waveform generator (1) are both connected to the time-to-digital converter (12). The time-to-digital converter (12) is connected to the host computer (14). The arbitrary waveform generator (1) is used to generate the modulation pulse of the pulsed laser, and the time interval between two adjacent modulation pulses must be greater than the time required for the optical signal to be transmitted over a range of twice the length of the single-mode fiber under test (8). The first pulse laser (2) and the second pulse laser (11) are both semiconductor distributed feedback lasers, fiber lasers or mode-locked lasers with internal or external modulation, and the center wavelength difference between the first pulse laser (2) and the second pulse laser (11) must be greater than 0 and less than the three-port filtering bandwidth of the wavelength division multiplexer (7). The first polarization controller (4) and the second polarization controller (9) are used to control the light intensity and polarization state of the two pulsed lights; The polarization combiner (5) is used to combine two pulsed lights into a dual-wavelength orthogonal polarization pulse pair.

2. The sensing method of a single-photon Raman temperature sensing system according to claim 1, characterized in that, Includes the following steps: S1. The output of the dual-wavelength orthogonal polarization light pulse generation unit includes a pair of light pulses with independent wavelengths, mutually orthogonal polarization states, the same pulse width, time synchronization, and adjustable light intensity. This pair of light pulses will be coupled into one port of the wavelength division multiplexer (7). The time interval between two adjacent light pulse pairs in the time domain must be greater than the time required for the light signal to be transmitted within twice the length of the single-mode fiber under test (8). S2. The single-mode fiber (8) under test is connected to the two ports of the wavelength division multiplexer (7). The spontaneous anti-Stokes Raman backscattered photons generated by it return to the two ports of the wavelength division multiplexer (7) and are filtered out from the three ports of the wavelength division multiplexer (7). S3. The filtered anti-Stokes Raman photons enter the single-photon detector (13), and then the number and time of photon arrival are recorded by the time-to-digital converter (12). S4. The host computer (14) obtains the temperature information of each point in the optical fiber by analyzing and processing the count value in the photon counting curve; by analyzing the time coordinate corresponding to the photon count value, and using the time-of-flight positioning principle, it achieves high-precision positioning of different temperature points of the entire optical fiber.

3. The sensing method according to claim 2, characterized in that, The Jones vector of the electric field vector of any polarized light in the optical fiber under test is expressed by Equation 1: (one), in, and These represent the amplitude components of the probe light along the fast and slow axes, respectively. To detect the initial phase difference of the optical polarization components along the fast and slow axes; The Jones matrix of the fiber under test with length z is represented by Formula 2: (two), in, It is the phase difference of the probe light polarization component along the fast and slow axes of the fiber at the z-distance caused by PMD; The Raman gain Jones matrix in optical fiber can be written as Equation 3: (three), in, and These are the Raman gain coefficients of the probe light along the fast and slow axes, respectively; Spontaneous anti-Stokes Raman photon field This can be represented as Formula 4: (Four).

4. The sensing method according to claim 3, characterized in that, When a pair of orthogonally polarized light pulses of two wavelengths enters the optical fiber under test, the spontaneous anti-Stokes Raman backscattered photons generated by pump light with different polarization directions interfere with each other. The number of Raman photons at the z-distance is expressed by Formula 5: (five), in, and The number of spontaneous anti-Stokes Raman backscattered photons generated at a distance z by the two-wavelength orthogonally polarized light pulse pairs propagating along the fast and slow axes of the optical fiber, respectively, can be eliminated by superimposing the number of spontaneous anti-Stokes Raman backscattered photons generated by the two-wavelength orthogonally polarized light pulse pairs in the optical fiber.

5. The sensing method according to claim 4, characterized in that, The number of spontaneous anti-Stokes Raman backscattered photons without polarization-dependent fluctuations is related to the temperature at a point z along the fiber, as given by Equation 6: (six), Where η is the SPD detection efficiency, P(z) is the peak power of the pump light at a distance z, and h is Planck's constant. The center frequency of anti-Stokes light, The center frequency of the input pulse light. Here, T is the Boltzmann constant, and T is the temperature at a distance z along the fiber. SPD dark count rate; Analyzing the changes in the anti-Stokes Raman photon number allows for the demodulation of the temperature along the optical fiber; the demodulation formula is Equation Seven. (seven), in, It is the spontaneous anti-Stokes coefficient of Raman backscattering at the calibration temperature T0, and C is the temperature sensitivity coefficient; The temperature information T can be extracted from the above formula as shown in Formula 8: (eight), Therefore, by recording the photon count of the non-polarization-dependent spontaneous anti-Stokes Raman backscattering signal, the temperature information at different locations of the fiber under test can be obtained with high precision.

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