A method and system for improving the response frequency of OFDR based on time-frequency multiplexing

Abstract

The application provides a method and system for improving the response frequency of OFDR based on time-frequency multiplexing, comprising: transmitting continuous periodic swept light to an optical frequency domain reflectometer (OFDR) to obtain probe light; regarding each light signal segment corresponding to each period T in the probe light as a trace, uniformly dividing each trace into N segments along a time axis, regarding each M segment in the N segments as a combination, and regarding combinations with the same serial number in each trace as a multiplexing channel; for each multiplexing channel, respectively performing sliding average on each combination belonging to different traces in the multiplexing channel, respectively performing demodulation on each combination after the sliding average in the multiplexing channel, and obtaining a corresponding time-domain waveform; and rearranging the time-domain waveforms corresponding to each multiplexing channel in time sequence, and sampling the rearranged time-domain waveforms at a sampling frequency f s The application can adaptively and flexibly adjust the sampling frequency, realize high-frequency disturbance measurement, and ensure system performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical fiber sensing, and particularly relates to a method and system for improving the response frequency of OFDR based on time-frequency multiplexing. BACKGROUND

[0002] Optical frequency domain reflectometry (OFDR) is a quantitative measurement method that measures the shift of the local Rayleigh scattering spectrum of an optical fiber or the phase information of the scattered signal. Unlike optical time domain reflectometry, OFDR usually uses long pulses much longer than the round-trip time of the sensing optical fiber. The detection is severely restricted by the repetition frequency, and it is difficult to achieve high-frequency disturbance measurement, i.e., only low-frequency strain and temperature measurement can be achieved. In order to achieve high-frequency disturbance measurement, in 2012, researchers at the University of Ottawa in Canada used a time-resolved method to achieve 10 cm spatial resolution and 32 Hz frequency response on a 17 m optical line. However, the system performance (such as signal-to-noise ratio, signal crosstalk, etc.) is still poor. In 2020, researchers at Shanghai Jiaotong University proposed an IPD and RVS method based on the Hanning window, which achieved 1 kHz vibration measurement on a 950 m optical fiber. However, the repetition frequency is still restricted by the long pulse width of OFDR, and the system performance is difficult to further improve. Therefore, it is necessary to propose a new measurement method to make up for the poor performance of the existing OFDR in realizing high-frequency disturbance measurement. SUMMARY

[0003] The application provides a method for improving the response frequency of OFDR based on time-frequency multiplexing to solve the problem of poor performance of the existing OFDR in realizing high-frequency disturbance measurement.

[0004] According to a first aspect of the embodiments of the application, a method for improving the response frequency of OFDR based on time-frequency multiplexing is provided, comprising:

[0005] In step S110, a continuous periodic frequency-swept light is transmitted to an optical frequency domain reflectometer (OFDR) to obtain a probe light.

[0006] In step S120, each light signal segment corresponding to each period T in the probe light is taken as a trace, each trace is uniformly divided into N segments along the time axis, and each M segment in the N segments is taken as a combination. The combinations with the same serial number in each trace form a multiplexing channel. N and M are both integers greater than 0.

[0007] In step S130, for each multiplexing channel, the combinations belonging to different traces in the multiplexing channel are respectively subjected to sliding average.

[0008] In step S140, for each multiplexing channel, the combinations after sliding average in the multiplexing channel are respectively subjected to demodulation to obtain a corresponding time-domain waveform.

[0009] Step S150, rearranging the time domain waveforms corresponding to each multiplexing channel in time sequence, with a sampling frequency f s Sampling the rearranged time domain waveforms, wherein P=N / M, P is an integer greater than 0.

[0010] In an optional implementation, the signal-to-noise ratio is improved by increasing the moving average effect, thereby improving the fading suppression effect.

[0011] By increasing P=N / M, the probe light bandwidth of sampling is shortened, the perturbation modulation time is reduced, and the crosstalk suppression effect is improved.

[0012] By reducing N, the spatial resolution is improved.

[0013] By increasing P=N / M, the sampling frequency is improved, thereby realizing high-frequency sampling.

[0014] In another optional implementation, in the step S130, the frequency bandwidth of the optical signal segment in each section is Q1, and the frequency bandwidth Q2 of the optical signal segment in each combination is Q1*M; for each combination belonging to different traces in the multiplexing channel, a fixed width of the translation frame is Q1, and the translation frame is sequentially translated by a set width Q0 in the frequency band range of the combination. After each translation is completed, the frequency band of the combination in the translation frame is determined, the average value of the optical signal segment corresponding to the determined frequency band is calculated, thereby obtaining W average values, the set width Q0 is equal to R*Q1, R is a step rate, which is less than 1 and greater than 0, and W=(M-1) / R+1.

[0015] In another optional implementation, the moving average effect is improved by reducing the frequency width Q1 of the optical signal segment in each section, increasing the frequency width Q2 of the optical signal segment in each combination, and reducing the step rate R, thereby improving the fading suppression effect; wherein the frequency width Q1 of the optical signal segment in each section can be reduced by increasing N, and the frequency width Q2 of the optical signal segment in each combination can be increased by increasing M.

[0016] Thus, the moving average effect is improved by increasing N and M and reducing the step rate R, thereby improving the fading suppression effect.

[0017] In another optional implementation, in the step S120, for each trace, the overlap rate between every two adjacent combinations in the trace is L, L is greater than 0 and less than or equal to 1.

[0018] When the overlap rate L is equal to 1, the sampling frequency f

[0019] When the overlap rate L is less than 1, the sampling frequency fs increased by 1 / L times,

[0020] P=N / M.

[0021] In another optional implementation, N, M, R and L are set according to the following steps:

[0022] Step S210, determining N according to the set spatial resolution;

[0023] Step S220, determining P according to the set crosstalk suppression effect, so as to determine M according to the formula P=N / M;

[0024] Step S230, determining R according to the set fading suppression effect under the determined N and M;

[0025] Step S240, judging whether it is equal to the set sampling frequency f s , if yes, no processing is performed, otherwise, determining the overlap rate L between every two adjacent combinations in the trace according to the formula .

[0026] In another optional implementation, in the step S120, for each trace, Fourier transform is performed on each segment in the trace; the sliding average is the sum of the rotation vectors; and the demodulation mode in the step S140 includes one of phase demodulation, Rayleigh scattering pattern demodulation and local scattering spectrum shift amount demodulation.

[0027] For each trace, the time length corresponding to the frequency bandwidth of each combination in the trace is less than or equal to the corresponding round-trip time length of the optical signal on the sensing optical fiber.

[0028] In another optional implementation, before the step S120, the method further includes: eliminating the nonlinearity of the probe light.

[0029] According to a second aspect of the embodiment of the present application, a system for improving the response frequency of OFDR by using the above method is provided, which includes a narrow linewidth laser, a sweep frequency modulation module, a coupler, an optical circulator, a sensing optical fiber, a coherent detection module and a processor, wherein the narrow linewidth laser is connected to the input end of the coupler through the sweep frequency modulation module, the first output end of the coupler is connected to the first end of the optical circulator, the second output end is connected to the first input end of the coherent detection module, the second end of the optical circulator is connected to the sensing optical fiber, the third end is connected to the second input end of the coherent detection module, and the output end of the coherent detection module is connected to the processor.

[0030] The narrow linewidth laser provides continuous laser to the sweep frequency modulation module.

[0031] The sweep modulation module modulates the continuous laser into continuous periodic sweep light;

[0032] The coupler divides the continuous periodic sweep light into two paths, one of which is transmitted to the coherent detection module, and the other is transmitted to the sensing optical fiber through the optical circulator; the scattered light returned by the sensing optical fiber is transmitted to the coherent detection module through the optical circulator; the coherent detection module coherently detects the continuous periodic sweep light and the scattered light to obtain detection light;

[0033] The processor processes the detection light according to the method to improve the OFDR response frequency.

[0034] In an optional implementation, a nonlinear correction module is further included, an input end of the nonlinear correction module is connected to an output end of the sweep modulation module, and an output end of the nonlinear correction module is connected to the processor; the sweep modulation module provides the continuous periodic sweep light to the nonlinear correction module; and the nonlinear correction module is configured to acquire a feature of the continuous periodic sweep light and send the feature to the processor.

[0035] The processor eliminates the nonlinearity in the detection light by using the feature.

[0036] The present application has the following advantages:

[0037] 1. The present application takes each period T in the detection light as a trace, uniformly divides each trace into N segments, takes each M segment in the N segments as a combination, and forms a multiplexing channel by combining the combinations with the same serial number in each trace. The application performs sliding average on each combination of each multiplexing channel, fully utilizes the independence of noise between different frequency bands, and greatly improves the signal-to-noise ratio of the optical signal. The application demodulates each combination after sliding average in each multiplexing channel, obtains a time-domain waveform, and rearranges the time-domain waveform in time sequence, thereby increasing the sampling frequency by P times. By adjusting the size of P, the sampling frequency of OFDR can be increased to any value, realizing adaptive and flexible adjustment of the sampling frequency. By adjusting the sampling frequency, OFDR can realize high-frequency disturbance measurement and measure fast-changing temperature, strain and other disturbances. In addition, by adjusting N and P, the application can also adjust the signal-to-noise ratio, crosstalk degree and spatial resolution of the system, thereby realizing adaptive and flexible adjustment of the sampling frequency and high-frequency disturbance measurement while ensuring system performance.

[0038] 2. The present application introduces a step rate R when improving the sliding average effect. N, M and R can be adjusted to adjust the signal-to-noise ratio of the system. At this time, N, M and R can be adjusted to ensure that the sliding average effect, spatial resolution, crosstalk degree and sampling frequency meet the requirements at the same time.

[0039] 3、The application can also adjust the sampling frequency of the system by adjusting the overlap rate L between each adjacent combination in the trace, so that the system performance can be guaranteed when the sampling frequency is adjusted to any value.

[0040] 4、The application can guarantee the adjustability of the system performance by ensuring that the time length corresponding to the frequency bandwidth of each combination in each trace is less than or equal to the corresponding round-trip time length of the optical signal on the sensing optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is an embodiment flowchart of the method for improving the response frequency of OFDR based on time-frequency multiplexing of the application;

[0042] Figure 2 is a division schematic diagram of traces, segments, combinations and multiplexing channels of the application;

[0043] Figure 3 is a calculation principle schematic diagram of the moving average of the application;

[0044] Figure 4 is an embodiment structure block diagram of the system for improving the response frequency of OFDR of the application. DETAILED DESCRIPTION

[0045] In order to enable the personnel in the technical field to better understand the technical solutions in the embodiments of the application, and enable the above-mentioned purposes, features and advantages of the embodiments of the application to be more apparent and easy to understand, the technical solutions in the embodiments of the application will be further described in detail below with reference to the drawings.

[0046] In the description of the application, unless otherwise specified and limited, it should be understood that the term "connection" should be interpreted broadly, for example, it can be a mechanical connection or an electrical connection, or a communication between two elements, which can be directly connected or indirectly connected through an intermediate medium, and the specific meaning of the term can be understood by the person skilled in the art according to the specific situation.

[0047] Referring to Figure 1 is an embodiment flowchart of the method for improving the response frequency of OFDR based on time-frequency multiplexing of the application. The method for improving the response frequency of OFDR based on time-frequency multiplexing can include the following steps:

[0048] Step S110, transmitting continuous periodic swept light to an optical frequency domain reflectometer OFDR to obtain probe light. In this step, after the continuous periodic swept light is transmitted to the sensing optical fiber of the OFDR, the scattered light returned from the sensing optical fiber will be coherently detected with the continuous periodic swept light to obtain the probe light.

[0049] Step S120, combining Figure 2As shown, each light signal segment corresponding to each period T in the probe light is taken as a trace line, each trace line is uniformly divided into N segments along the time axis, and each M segment in the N segments is taken as a combination, the combinations with the same serial number in each trace line constitute a multiplexing channel, and N and M are both integers greater than 0.

[0050] Since the connected periodical swept light is chirped long pulse light, the scattered light returned by the sensing fiber is the response to the chirped long pulse light, and the probe light is the coherent probe light of the scattered light and the chirped long pulse light, therefore, signal extraction on the probe light along the time axis is equivalent to signal extraction on the probe light along the frequency axis, and after each trace line is uniformly divided into N segments along the time axis, the light signal segments in each segment correspond to different chirp frequencies, and thus this multiplexing technology can be called time-frequency multiplexing. The chirped long pulse light is continuously injected into the sensing fiber without interval, and therefore the scattered light and the chirped long pulse light as the local oscillator light are continuous in time during coherent detection. The number of combinations in each trace line and the number of multiplexing channels are both P, P = N / M, and P is an integer greater than 0.

[0051] In step S130, for each multiplexing channel, each combination belonging to different trace lines in the multiplexing channel is respectively subjected to sliding average.

[0052] In the step S130, the frequency band width of the light signal segment in each segment is Q1, and the frequency band width Q2 of the light signal segment in each combination is Q1*M; for each combination belonging to different trace lines in the multiplexing channel, a fixed width of the translation frame is Q1, within the frequency band range of the combination, the translation frame is sequentially translated by a set width Q0, after each translation period, the frequency band of the combination in the translation frame is determined, the average value of the light signal segment corresponding to the determined frequency band is calculated, and thus W average values are obtained, the set width Q0 is equal to R*Q1, R is a step rate, which is less than 1 and greater than 0, and W = (M-1) / R+1.

[0053] In combination Figure 3 As shown, each trace line is composed of 12 trace points, N = 6, M = 3, and there are 12 / 6 = 2 trace points in each segment, i.e. Q1 = 2 trace points; there are 2*3 = 6 trace points in each combination, i.e. Q2 = 6 trace points; when the sliding average is performed, the fixed width of the translation frame is 2 trace points, and if the step rate R = 50%, the set width Q0 = 2 trace points*50% = 1 trace point, within the frequency band range of the combination (i.e. the range of 6 trace points), the translation frame with the fixed width of 2 trace points is sequentially translated, and each translation period is 1 trace point. Figure 3 As can be seen from FIG. 5, after the translation frame is translated for 5 periods, the translation frame moves to the last trace point in the frequency band range of the combination, and since the average value of the light signal segment corresponding to the frequency band in the translation frame is calculated in each period, 5 average values can be obtained.

[0054] The present application carries out sliding average for each combination of different traces in each multiplexing channel, fully utilizes the independence of noise between different frequency bands, and greatly improves the signal-to-noise ratio of the optical signal. In addition, the more the number of shifts, the more the number of average values W obtained, the better the sliding average effect, and the higher the signal-to-noise ratio of the optical signal after sliding average, and the better the fading suppression effect. The present application can increase the number of average values W obtained by reducing the frequency width Q1 of the optical signal segment in each section, increasing the frequency width Q2 of the optical signal segment in each combination, and reducing the step rate R, thereby improving the sliding average effect; wherein by increasing N, the frequency width Q1 of the optical signal segment in each section can be reduced, and by increasing M, the frequency width Q2 of the optical signal segment in each combination can be increased. Thus, the sliding average effect can be improved by increasing N and M, and reducing the step rate R, thereby improving the fading suppression effect.

[0055] The system performance of the present application can include fading suppression effect, crosstalk suppression effect and spatial resolution. By improving the sliding average effect, the signal-to-noise ratio can be improved, thereby improving the fading suppression effect (the sliding average effect can be improved by increasing N and M, and reducing the step rate R); by increasing P=N / M, the sampling probe light width can be shortened, and the disturbance modulation time can be reduced, thereby improving the crosstalk suppression effect, wherein P is an integer greater than 0; by reducing N, the spatial resolution can be improved. In addition, by increasing P=N / M, the sampling frequency can be improved, thereby realizing high-frequency sampling. As described above, by adjusting N, M and R, the fading suppression effect, crosstalk suppression effect, spatial resolution and sampling frequency of the system can be adjusted.

[0056] In addition, in step S120, for each trace, the overlap rate between every two adjacent combinations in the trace is L, L is greater than 0 and less than or equal to 1;

[0057] When the overlap rate L is equal to 1, the sampling frequency f

[0058] When the overlap rate L is less than 1, the sampling frequency f s is increased by 1 / L times,

[0059] P=N / M.

[0060] As can be seen, by adjusting the overlap rate L between every two adjacent combinations in the trace, the sampling frequency of the system can be adjusted. In order to realize sampling at a set sampling frequency and ensure that the fading suppression effect, crosstalk suppression effect and spatial resolution of the system meet the requirements, N, M, R and L can be set according to the following steps:

[0061] Step S210, determining N according to the set spatial resolution;

[0062] Step S220, determining P according to the set crosstalk suppression effect, so as to determine M according to the formula P=N / M;

[0063] Step S230, determining R according to the set fading suppression effect under the determined N and M;

[0064] Step S240, judging whether it is equal to the set sampling frequency f s , if yes, no processing is performed, otherwise, determining the overlap rate L between every two adjacent combinations in the trace according to the formula .

[0065] Step S140, demodulating each combination after the sliding average in each multiplexing channel respectively to obtain the corresponding time-domain waveform.

[0066] In this step, the number of time-domain waveforms corresponding to each multiplexing channel is equal to the number of traces, and there are P time-domain waveforms in one trace, and P is the number of multiplexing channels. In the step S120, Fourier transform can be performed on each section in each trace; the sliding average can be the sum of the rotation vectors; and the demodulation mode in the step S140 can include one of phase demodulation, Rayleigh scattering pattern demodulation and local scattering spectrum shift amount demodulation. When the demodulation mode is phase demodulation, crosstalk will affect demodulation, and the crosstalk suppression effect needs to be considered; when the demodulation mode is Rayleigh scattering pattern demodulation, the influence of crosstalk can be ignored when the disturbance frequency is low, and the influence of crosstalk is small, and when the disturbance frequency is high, the local scattering pattern of the vibrating fiber section will be displaced, thereby causing demodulation error, so the influence of crosstalk on demodulation still needs to be considered, and the crosstalk suppression effect needs to be considered.

[0067] Step S150, rearranging the time-domain waveforms corresponding to each multiplexing channel in time sequence at the sampling frequency f s , and sampling the rearranged time-domain waveforms, wherein P=N / M, and P is an integer greater than 0.

[0068] In this step, if there are P multiplexing channels, s time-domain waveforms are obtained corresponding to the P multiplexing channels, s represents the number of traces, and s is an integer greater than 1. When the time-domain waveforms corresponding to each multiplexing channel are rearranged in time sequence, the first time-domain waveform of the P multiplexing channels is arranged in sequence, then the second time-domain waveform of the P multiplexing channels is arranged in sequence, and the s-th time-domain waveform of the P multiplexing channels is arranged in sequence.

[0069] When the time length of each light signal segment in each segment approaches the round-trip time length τ corresponding to the length of the sensing optical fiber r , the end signal-to-noise ratio approaches zero, and if M1, the performance limit of the system is reached, and the highest frequency response is , which is equal to the traditional frequency response, and at this time, even if N, M and R are adjusted, the system performance cannot be adjusted. In order to ensure that the system performance is adjustable, for each trace, the time length corresponding to the frequency bandwidth of each combination in the trace is less than or equal to the round-trip time length of the light signal on the sensing optical fiber. In addition, before the step S120, the nonlinearity of the probe light can also be eliminated.

[0070] As can be seen from the above embodiment, the present application takes each period T in the probe light as a trace, uniformly divides each trace into N segments, takes each M segment in the N segments as a combination, and forms a multiplexing channel with the combinations of the same number in each trace. The combinations of each multiplexing channel are respectively subjected to sliding average, the independence of the noise between different frequency bands is fully utilized, and thus the signal-to-noise ratio of the light signal is greatly improved. Each combination in each multiplexing channel after sliding average is respectively demodulated to obtain a time domain waveform, and the time domain waveform is rearranged in time sequence, and thus the sampling frequency can be increased by P times. By adjusting the size of P, the sampling frequency of the ODFR can be increased to any value, the sampling frequency is adaptively and flexibly adjusted, the ODFR can realize high-frequency disturbance measurement by adjusting the sampling frequency, and can measure fast-changing temperature, strain and other disturbances. In addition, by adjusting N and P, the signal-to-noise ratio, crosstalk degree and spatial resolution of the system can also be adjusted, so that the sampling frequency is adaptively and flexibly adjusted, high-frequency disturbance measurement is realized, and the system performance is also guaranteed.

[0071] Since N and M need to be increased to improve the sliding average effect, N needs to be reduced to improve the spatial resolution, and N needs to be increased and M needs to be reduced to reduce the crosstalk and improve the sampling frequency, there is a contradiction in the adjustment of N and M, and it is difficult to improve the signal-to-noise ratio and the spatial resolution while increasing the sampling frequency. Therefore, the present application introduces a step rate R when improving the sliding average effect, and the system signal-to-noise ratio can be adjusted by adjusting N, M and R, and at this time, the sliding average effect, the spatial resolution, the crosstalk degree and the sampling frequency can be simultaneously satisfied by adjusting N, M and R. In addition, the sampling frequency of the system can also be adjusted by adjusting the overlap rate L between each adjacent two combinations in the trace, so that the system performance can be guaranteed when the sampling frequency is adjusted to any value.

[0072] In addition, the present application also provides a system for improving the response frequency of the ODFR by using the above method, such as Figure 4As shown, the system can comprise a narrow linewidth laser, a sweep modulation module, a coupler, an optical circulator, a sensing fiber, a coherent detection module and a processor, wherein the narrow linewidth laser is connected to the input end of the coupler through the sweep modulation module, the first output end of the coupler is connected to the first end of the optical circulator, the second output end is connected to the first input end of the coherent detection module, the second end of the optical circulator is connected to the sensing fiber, the third end is connected to the second input end of the coherent detection module, and the output end of the coherent detection module is connected to the processor; the narrow linewidth laser provides continuous laser to the sweep modulation module; the sweep modulation module modulates the continuous laser into continuous periodic swept light; the coupler divides the continuous periodic swept light into two paths, one of which is transmitted to the coherent detection module, and the other is transmitted to the sensing fiber through the optical circulator; the scattered light returned by the sensing fiber is transmitted to the coherent detection module through the optical circulator; the coherent detection module coherently detects the continuous periodic swept light and the scattered light to obtain detection light; and the processor processes the detection light according to the method to improve the OFDR response frequency.

[0073] In addition, the system can further comprise a nonlinear correction module, the input end of which is connected to the output end of the sweep modulation module, and the output end is connected to the processor; the sweep modulation module provides the continuous periodic swept light to the nonlinear correction module; the nonlinear correction module is used to obtain the characteristics of the continuous periodic swept light, so as to send the characteristics to the processor; and the processor eliminates the nonlinearity in the detection light by using the characteristics. The nonlinear correction module can be composed of an auxiliary interferometer with a delay fiber and a photoelectric detection device.

[0074] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0075] It is to be understood that the application is not limited to the precise construction here described and as shown in the attached drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the application. The scope of the application is to be defined by the claims appended hereto.

Claims

1. A method for increasing the response frequency of OFDR based on time-frequency multiplexing, characterized in that, The method comprises the following steps: In step S110, the continuous periodic swept light is transmitted to an optical frequency domain reflectometer (OFDR) to obtain probe light; In step S120, each light signal segment corresponding to each period T in the probe light is taken as a trace, each trace is uniformly divided into N segments along a time axis, and each M segment in the N segments is taken as a combination, the combinations with the same serial number in each trace form a multiplexing channel, and N and M are both integers greater than 0; In step S130, for each multiplexing channel, the sliding average is performed on each combination belonging to different traces in the multiplexing channel; In step S140, for each multiplexing channel, the demodulation is performed on each combination after the sliding average in the multiplexing channel to obtain a corresponding time-domain waveform; Step S150, rearranging the time-domain waveforms corresponding to each multiplexing channel in time sequence, at a sampling frequency f s sampling the rearranged time-domain waveforms, wherein P=N / M, P is an integer greater than 0. In the step S130, the frequency bandwidth of the light signal segment in each segment is Q1, the frequency bandwidth Q2 of the light signal segment in each combination is Q1*M, for each combination belonging to different traces in the multiplexing channel, the fixed width of the translation frame is Q1, the translation frame is sequentially translated by a set width Q0 in the frequency band range of the combination, after the translation is completed in each period, the frequency band of the combination in the translation frame is determined, the average value of the light signal segment corresponding to the determined frequency band is calculated, and thus W average values are obtained, the set width Q0 is equal to R*Q1, R is a step rate, R is less than 1 and greater than 0, and W=(M-1) / R+1.

2. The method for increasing the response frequency of OFDR based on time-frequency multiplexing according to claim 1, characterized in that, By improving the sliding average effect, the signal-to-noise ratio is improved, and thus the fading suppression effect is improved; By increasing P=N / M, the sampling probe light frequency width is shortened, the disturbance modulation time is reduced, and thus the crosstalk suppression effect is improved; By reducing N, the spatial resolution is improved; By increasing P=N / M, the sampling frequency is improved, and thus high-frequency sampling is realized.

3. The method for increasing the response frequency of OFDR based on time-frequency multiplexing according to claim 1, characterized in that, By reducing the frequency width Q1 of the light signal segment in each segment, increasing the frequency width Q2 of the light signal segment in each combination, and reducing the step rate R, the number W of obtained average values is increased, and thus the sliding average effect is improved; wherein by increasing N, the frequency width Q1 of the light signal segment in each segment can be reduced, and by increasing M, the frequency width Q2 of the light signal segment in each combination can be increased; Therefore, by increasing N and M and reducing the step rate R, the sliding average effect is improved, and thus the fading suppression effect is improved.

4. The method for increasing the response frequency of OFDR based on time-frequency multiplexing according to any one of claims 1 to 3, characterized in that, In the step S120, for each trace, the overlap rate between each two adjacent combinations in the trace is L, L is greater than 0 and less than or equal to 1; When the overlap ratio L is equal to 1, the sampling frequency When the overlap ratio L is less than 1, the sampling frequency f s increased by 1 / L times, P=N / M.

5. The method for increasing the response frequency of OFDR based on time-frequency multiplexing according to claim 4, characterized in that, N, M, R and L are set according to the following steps: In step S210, N is determined according to a set spatial resolution; In step S220, P is determined according to a set crosstalk suppression effect, and thus M is determined according to the formula P=N / M; In step S230, R is determined according to a set fading suppression effect under the determined N and M; Step S240, judging whether it is equal to a set sampling frequency f s , if yes, no processing is done, otherwise, the overlap rate L between every two adjacent combinations in the trace is determined according to the formula .

6. The method for increasing the response frequency of OFDR based on time-frequency multiplexing according to claim 1, characterized in that, In the step S120, for each trace, Fourier transform is performed on each segment in the trace; the sliding average is a rotating vector summation; and the demodulation mode in the step S140 comprises one of phase demodulation, Rayleigh scattering pattern demodulation and local scattering spectrum shift demodulation. For each trace, the time length corresponding to the frequency bandwidth of each combination in the trace is less than or equal to the corresponding round-trip time length of the optical signal on the sensing fiber.

7. The method for increasing the response frequency of OFDR based on time-frequency multiplexing according to claim 1, characterized in that, Before the step S120, further comprising: eliminating the nonlinearity of the probe light.

8. A system for increasing the response frequency of OFDR using the method of any one of claims 1 to 7, characterized in that, The system comprises a narrow-linewidth laser, a sweep frequency modulation module, a coupler, an optical circulator, a sensing fiber, a coherent detection module and a processor, wherein the narrow-linewidth laser is connected to the input end of the coupler through the sweep frequency modulation module, the first output end of the coupler is connected to the first end of the optical circulator, the second output end is connected to the first input end of the coherent detection module, the second end of the optical circulator is connected to the sensing fiber, the third end is connected to the second input end of the coherent detection module, and the output end of the coherent detection module is connected to the processor. The narrow-linewidth laser provides continuous laser to the sweep frequency modulation module. The sweep frequency modulation module modulates the continuous laser into continuous periodic sweep light. The coupler divides the continuous periodic sweep light into two paths, one of which is transmitted to the coherent detection module, and the other of which is transmitted to the sensing fiber through the optical circulator; the scattered light returned by the sensing fiber is transmitted to the coherent detection module through the optical circulator; The coherent detection module coherently detects the continuous periodic sweep light and the scattered light to obtain probe light; The processor processes the probe light according to the method to improve the OFDR response frequency.

9. The system of claim 8, wherein, Further comprising a nonlinearity correction module, the input end of which is connected to the output end of the sweep frequency modulation module, and the output end of which is connected to the processor; the sweep frequency modulation module provides the continuous periodic sweep light to the nonlinearity correction module; The nonlinearity correction module is used to obtain the characteristics of the continuous periodic sweep light, and send the characteristics to the processor; The processor eliminates the nonlinearity in the probe light by using the characteristics.

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