CN114812855A - Brillouin optical time domain scattering system based on optical flight time and self-calibration method - Google Patents

Abstract

The invention relates to a Brillouin optical time domain scattering system based on optical flight time and a self-calibration method. The invention fully utilizes the measuring process by adding a small amount of hardware, corrects the corresponding relation between the propagation delay and the optical fiber space position, ensures that two subtracted values correspond to the same section of optical fiber when the maximum gain frequency deviation variation is calculated, avoids additional errors, and continuously corrects the problem of inconsistent delay between measured data and reference data by using a calibration means, thereby effectively reducing the reading error of the BOTDA system and the reading drift after long-term operation, and having important significance for the long-term operation stability of the long-distance BOTDA sensing system.

Description

A Brillouin Optical Time-Domain Scattering System and Self-Calibration Method Based on Optical Time-of-Flight

technical field

The invention belongs to the field of optical fiber sensing, in particular to a Brillouin optical time-domain scattering system and a self-calibration method based on the time-of-flight of light.

Background technique

Brillouin Optical Time Domain Analysis Distributed Optical Fiber Sensing System (BOTDA) is a widely used distributed optical fiber sensing system. The system injects pulsed pump light and continuous probe light at both ends of the fiber, respectively. When the frequency offset of the probe light relative to the pump light is in a specific range and the power is large enough, the stimulated Brillouin scattering effect in the fiber will transfer the energy of the pump light to the probe light, thereby amplifying the probe light. The probe light gain varies with frequency offset, where the point of maximum gain is affected by the temperature and strain of the fiber. BOTDA has a long detection distance and high sensitivity, and can realize fully distributed strain and temperature measurement.

In the prior art, Chinese invention patent 201811580430.X discloses a long gauge length distributed optical fiber Brillouin sensing-demodulation system and strain measurement method, involving high-precision, dynamic, non-uniform strain measurement for engineering measurement Measurement technology, but its existence will increase the number of steps of frequency sweep detection, resulting in an increase in the measurement time of the distributed optical fiber Brillouin sensing system, which cannot meet the requirements of dynamic measurement. At present, in order to track the frequency offset change, before the BOTDA system starts to measure, the maximum gain frequency offset under different delays after the pulsed pump light is emitted is read as the reference frequency offset, and then the pulsed pumping light is sent into the waiting time through the speed of light in the fiber. The delay after measuring the optical fiber is mapped to the spatial position, and the reference frequency offset at different positions is obtained. During the measurement, the measured maximum gain frequency offset under the same delay is directly compared with the reference frequency offset to obtain the frequency offset change. However, the speed of light in the optical fiber fluctuates due to the influence of environmental factors such as temperature. The measurement under the same delay and the reference frequency offset are measured at different times, which may correspond to the optical fibers in different positions. Due to the slight inconsistency of the optical fibers themselves, each The reference frequency offset value of the position is different. When calculating the frequency offset change, additional errors will be introduced, which will affect the measurement accuracy.

SUMMARY OF THE INVENTION

In view of the defects existing in the existing BOTDA system, the present invention provides a Brillouin optical time-domain scattering system based on the time-of-flight of light. The Brillouin optical time-domain scattering system based on the time-of-flight of the present invention should be able to make full use of the measurement process, correct the correspondence between the propagation delay and the optical fiber spatial position, and ensure that the measurement data is continuously corrected when calculating the maximum gain frequency offset variation. The problem of inconsistency between the delay and the benchmark data.

For realizing the above-mentioned purpose of the invention, the present invention adopts the technical scheme that the following steps are formed:

A Brillouin optical time-domain scattering system based on light time-of-flight, the system structure includes a laser light source, a first coupler, an electro-optical modulator, an acousto-optical modulator, a first fiber amplifier, a second fiber amplifier, and arbitrary waveform generation. a sensor fiber, a second coupler, a first photoelectric detection unit, a demodulation unit, a third coupler, a second photoelectric detection unit, the sensor fiber includes a first port of the sensor fiber and a first port of the sensor fiber two ports;

The laser light source emits laser light to the first coupler to split into probe light and pump light, the pump light is modulated by the acousto-optic modulator into pulsed pump light, and the pulsed pump light is passed through the fiber first amplifier After amplification, it reaches the first port of the sensing fiber through the second coupler, and the pulsed pump light enters the sensing fiber through the first port of the sensing fiber, and is transmitted to the first port of the sensing fiber in the sensing fiber. Two-port output, the output pulse pump light is received by the third coupler and then output to the second photodetection unit, and the second photodetection unit outputs a signal to the demodulation unit;

The detection light is frequency-shifted by the electro-optic modulator and modulated into continuous detection light, the continuous detection light is amplified by the second fiber amplifier, and then reaches the second port of the sensing fiber through the third coupler, and enters the continuous detection light in the sensing fiber. The detection light is transmitted to the first port of the sensing fiber for output, and the output continuous detection light is received by the second coupler and then output to the first photoelectric detection unit, and the first photoelectric detection unit outputs an electrical signal to the demodulation unit; the arbitrary waveform generator is respectively connected to the electro-optical modulator and the acousto-optical modulator, and the arbitrary waveform generator provides two-way electrical signal output, one output of a single-frequency rectangular signal to modulate In the electro-optical modulator, the other channel outputs a rectangular pulse signal to modulate the acousto-optical modulator.

The invention also relates to a self-calibration method of a Brillouin optical time-domain scattering system based on the time of flight of light. The method uses a third coupler and a second photoelectric detection unit to measure the light traversing the entire length of the fiber to be tested. Time-of-flight, realizes the delay of calibrating the maximum gain frequency offset, the corresponding data of the corrected current maximum gain frequency offset and the corrected reference maximum gain frequency offset correspond to the same fiber position, and realizes its automatic operation based on Brillouin optical time domain analysis. Calibration, the method includes the following steps:

Step 21: Before starting the measurement, obtain the maximum gain frequency offset in the Brillouin system of the probe light as the reference maximum gain frequency offset, and obtain the reference pulse pump light flight time of the optical fiber to be measured;

Step 22: During the measurement, obtain the current maximum gain frequency offset, and adjust the frequency of the modulation signal applied by the arbitrary waveform generator to the electro-optical modulator in steps of 1MHz between 9 and 13GHz. The frequency offset of the light, collect the Brillouin signals at each modulation frequency one by one, obtain the Brillouin gain spectrum of each position of the sensing fiber, and take the maximum gain point and record it as the maximum gain frequency offset;

Step 23: Measure the flight time of the current pulsed pump light, and record the delay of the pulsed pump light propagating through the entire fiber to reach the second photoelectric detection unit while measuring the frequency offset and transmitting the pulsed light, which is the current pulse pumping time of flight of light;

Step 24: Using the time-of-flight of the optical fiber to be tested, calibrate the delay of the maximum gain frequency offset;

Step 25: make the corresponding data of the corrected current maximum gain frequency offset and the corrected reference maximum gain frequency offset correspond to the same optical fiber position, and calculate the current maximum gain frequency offset change;

Step 26: Calculate the temperature measurement results of each position of the current optical fiber, demodulate the corrected signal, and finally obtain temperature information perceived by the optical fiber.

In the self-calibration method of the Brillouin optical time-domain scattering system based on the time of flight of the present invention, in the step 21, the reference maximum gain frequency offset and the time of flight of the pulse pump light are collected before the first measurement, The step of collecting the maximum gain frequency deviation of the reference is: between 9-13 GHz, adjust the frequency of the modulation signal applied by the arbitrary waveform generator to the electro-optical modulator with a step size of 1 MHz, and the frequency of the modulation signal is the detection light relative to the pump light. The Brillouin signal at each modulation frequency is collected one by one, and the Brillouin gain spectrum of each position of the sensing fiber is obtained, and the maximum gain point is recorded as the reference maximum gain frequency offset; the time of flight of the pulsed pump light The process is: while measuring the frequency offset and transmitting the pulsed light, record the delay of the pulsed pumping light propagating through the entire fiber to reach the second photoelectric detection unit, which is the flight time of the reference pulsed pumping light.

In a self-calibration method of the Brillouin optical time-domain scattering system based on the time of flight of the present invention, the delay after each pulse emission in the current measurement step 22 is collected and averaged to reduce errors.

In the self-calibration method of the Brillouin optical time-domain scattering system based on the time of flight of the present invention, for the step 24, the "DC" component of the time-of-flight variation is used to correct the delay, and the current measurement of a certain data point is recorded. The delay is t _N , then the delay of the corresponding reference data is:

That is to say, it is considered that the reference data acquisition time t ₀ and the current measurement time t _N correspond to the signal of the same segment of optical fiber.

In the self-calibration method of the Brillouin optical time-domain scattering system based on the time of flight of the present invention, for the step 25, the measured maximum gain frequency offset and the reference maximum gain frequency offset are subtracted to obtain the current maximum gain If the frequency offset changes, the time-domain sampling of the reference data is discrete, and there may be no delay corresponding to the sampling point, then two or more data points that are closest to this moment are selected and approximated by the interpolation method.

In a self-calibration method of the Brillouin optical time-domain scattering system based on the time of flight of the present invention, for the step 26, the temperature measurement result is set as ΔT _N (t), that is, the current measurement temperature is compared with the reference measurement time of the temperature change. Use the formula ΔT _N =Δf _N /A to obtain the current temperature measurement results of each position of the optical fiber. The proportional coefficient a is determined by the fiber material and is an invariant constant known before the measurement. For example, in the G652D standard single-mode fiber produced by Corning, A=1.05MHz/℃.

Based on the above technical solution, the long-distance Brillouin optical time-domain analysis distributed optical fiber sensing system of the present invention has the following technical advantages compared with the prior art:

1. The present invention makes full use of the measurement process by adding a small amount of hardware, corrects the correspondence between the propagation delay and the spatial position of the optical fiber, and ensures that when calculating the maximum gain frequency offset change, the two subtracted values correspond to the same segment of optical fiber, eliminating additional errors. , using calibration methods to continuously correct the delay inconsistency between the measured data and the reference data, so as to effectively reduce the reading error of the BOTDA system and the reading drift after long-term operation. important meaning.

2. The present invention continuously corrects the inconsistency of the delay between the measurement data and the reference data by using the means of self-calibration. While increasing the calibration function, the additional hardware of the system is minimized, thereby ensuring that the controllable cost significantly improves the performance and maintains a good performance. Competitiveness.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic structural diagram of the invention of a Brillouin optical time-domain scattering system based on the time of flight of light.

FIG. 2 is a measurement flow chart of the invention of a self-calibration method for a Brillouin optical time-domain scattering system based on the time of flight of light.

The symbols in the figure are:

1-laser light source, 2-first coupler, 3-electro-optical modulator, 4-first fiber amplifier, 5-acoustic-optical modulator, 6-second fiber amplifier, 7-arbitrary waveform generator, 8-sensing fiber , 9-second coupler, 10-first photoelectric detection unit, 11-third coupler, 12-second photoelectric detection unit, 13-demodulation unit, 101-sensing fiber first port 1, 102-transmission Sensor fiber second port

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in FIG. 1, the present invention is a Brillouin optical time-domain scattering system based on the time of flight of light, and the system structure includes a laser light source 1, a first coupler 2, an electro-optical modulator 3, an acousto-optical modulator 5, The first fiber amplifier 4, the second fiber amplifier 6, the arbitrary waveform generator 7, the sensing fiber 8, the second coupler 9, the first photoelectric detection unit 10, the demodulation unit 13, the third coupler 11, the second photoelectric The detection unit 12, the sensing fiber 8 includes a first port 101 of the sensing fiber and a second port 102 of the sensing fiber;

The laser light source 1 emits laser light to the first coupler 2 to split into a probe light and a pump light, the pump light is modulated into a pulsed pump light by the acousto-optic modulator 5, and the pulsed pump light is passed through an optical fiber. After being amplified by the first amplifier 6, it reaches the first port 101 of the sensing fiber through the second coupler 9. The pulsed pump light enters the sensing fiber 8 through the first port 101 of the sensing fiber, and the pulsed pump light is The sensing fiber 8 is transmitted to the second port 102 of the sensing fiber for output, and the output pulsed pump light is received by the third coupler 11 and then output to the second photoelectric detection unit 12. The second photoelectric detection The unit 12 outputs a signal to the demodulation unit 13 .

The detection light is frequency-shifted by the electro-optical modulator 3 and modulated into continuous detection light, and the continuous detection light is amplified by the second optical fiber amplifier 4, and then reaches the second port 102 of the sensing fiber through the third coupler 11, and enters the sensing fiber. The continuous detection light in 8 propagates to the first port 101 of the sensing fiber for output, and the output continuous detection light is received by the second coupler 9 and then output to the first photoelectric detection unit 10. The first photoelectric detection unit 10 outputs an electrical signal to the demodulation unit 13; the arbitrary waveform generator 7 is connected to the electro-optical modulator 3 and the acousto-optical modulator 5 respectively, and the arbitrary waveform generator 7 provides two-way electrical signal output , one channel outputs a single-frequency rectangular signal to modulate the electro-optical modulator 3 , and the other channel outputs a rectangular pulse signal to modulate the acousto-optical modulator 5 .

In the present invention as a Brillouin optical time-domain scattering system based on the time of flight of light, the laser light source 1 provides continuous signal light; the first coupler 2 splits the light of the laser light source 1 into the upper probe light and the lower pump The electro-optic modulator 3 shifts the frequency of the probe light by a certain value between 9-13 GHz; the first fiber amplifier 4 selects an erbium-doped fiber amplifier, whose function is to amplify the probe light after frequency shifting.

The acousto-optic modulator 5 generates pulsed pump light with a pulse width of 20-100ns, and the second fiber amplifier 6 amplifies the pulsed pump light; the arbitrary waveform generator 7 provides two electrical signal outputs, and the upper one is a single-frequency sinusoidal signal modulated electro-optical modulation Device 3, the next one is the rectangular pulse signal modulation acousto-optic modulator 5, and the repetition period of the rectangular pulse is determined by the user according to the applicable scene.

The total length of the sensing fiber 8 is 100km, and it has a first port 101 of the sensing fiber and a second port 102 of the sensing fiber, wherein the pulsed pump light enters from the first port 101 of the sensing fiber, and the continuous detection light enters from the sensing fiber. The second port 102 enters, and the pulsed pump light interacts with the continuous probe light to generate a Brillouin signal; the second coupler 9 couples the pulsed pump light into the first port 101 of the sensing fiber, and simultaneously couples the sensing fiber to the first port 101. The detection light and the Brillouin signal emitted from a port 101 are separated;

The first photoelectric detection unit 10 outputs an electrical signal whose voltage is proportional to the intensity of the detection light, and the third coupler 11 couples the continuous detection light into the second port 102 of the sensing fiber, and simultaneously receives and exits the continuous detection light. The second photodetection unit 12 outputs an electrical signal whose voltage is proportional to the intensity of the pump pulse light and the arrival time of the pulse. The demodulation unit 13 calculates the propagation delay of the pulsed light in the entire length of the optical fiber, and obtains the signal from the first photodetection unit 10 The voltage corresponding to the Brillouin signal is separated from the output of the optical fiber, the maximum gain frequency offset under each delay is analyzed and obtained, the delay self-correction is performed, and the change of the maximum gain frequency offset is calculated, and finally the temperature information of each part of the fiber is obtained.

For a section of optical fiber in space, first, the pulsed pump light propagates from the first port of the sensing fiber to this section of the sensing fiber 8, then, the pulsed pump light and the continuous probe light coincide in this section of the sensing fiber 8, and the excited distribution Brillouin scattering will amplify the intensity of the probe light, and finally, the probe light amplified on this section of the sensing fiber 8 propagates to the first port 101 of the sensing fiber and is received by the first photodetector 10 . The receiving delay is defined as the lag of the time when the first photodetection unit 10 or the second photodetection unit 12 receives the signal relative to the time when the pulsed pump light enters the first port 101 of the sensing fiber. According to the light propagation and interaction process, the Brillouin signals from different fiber positions can be distinguished by the reception delay.

Compared with the typical BOTDA system, the system of the present invention adds a coupler and a photodetector before injecting the probe light to receive the pulsed pump light propagating the entire length of the fiber to be tested. time-of-flight calibration. Usually, the BOTDA system quickly records signals with different delays, and converts the delays into distance information through the speed of light in the fiber; when calculating the change of the maximum gain frequency offset, the current maximum gain frequency offset of the same delay and the reference maximum gain frequency offset are directly subtract. However, because the physical quantities such as the speed of light in the fiber are also disturbed by the environment, under the same delay, the reference maximum gain frequency offset corresponds to fiber segment A, and the current maximum gain frequency offset corresponds to another fiber segment B. Since the BOTDA system usually has a long sensing distance of more than 10km, even if the relative change of the delay is small, it will produce a large absolute value change and positioning error at the far end, and the reference maximum gain frequency offset of A and B may be quite different. . In this way, when calculating the frequency offset change of the maximum gain, the error of the difference of the maximum gain of the reference between A and B is introduced. As far as the entire length of the fiber under test is concerned, the effect of delay can be divided into the average value of the delay change per unit length (that is, the "DC" component of the delay change), and the fluctuation of the delay change above and below this average value (that is, the "AC" component of the delay change. "weight), where the latter rises and falls in space. Because of the cumulative effect, the absolute value of the delay change at the far-end fiber will be larger, but the accumulation of the AC component over longer distances (or converted to time according to the speed of light propagation) tends to cancel each other out, contributing to the total delay change. The contribution is much smaller than the "DC" component. Therefore, it is possible to try to measure the overall delay change of the current entire length of fiber, calculate the "DC" component, and then largely correct the delay of each point currently measured, and minimize the error in calculating the maximum gain frequency offset.

Shown in FIG. 2 are the general steps of measurement and signal calibration in the Brillouin optical time-domain scattering system based on the optical time of flight of the present invention. Among them, "temperature measurement result" shows the difference between the temperature of each point of the fiber during the current measurement and the temperature of the reference measurement. Might as well set the "current measurement" as the Nth measurement.

Step 21: Before starting the measurement, obtain the maximum gain frequency deviation in the Brillouin system of the probe light as the reference maximum gain frequency deviation, and obtain the flight time of the reference pulse pump light of the optical fiber to be measured, where the two parameters are the reference The method for obtaining the time of flight of the pulsed pump light and the reference maximum gain frequency offset is the same as that in step 22 and step 23, but it needs to be collected before the first measurement starts.

Step 22: During measurement, obtain the current maximum gain frequency offset. The specific operation method is: between 9-13 GHz, adjust the frequency of the modulation signal applied by the arbitrary waveform generator 7 to the electro-optical modulator 3 at the first point (that is, the frequency offset of the probe light relative to the pump light) with a step size of 1 MHz, By collecting the Brillouin signals at each modulation frequency one by one, the Brillouin gain spectrum of each position of the sensing fiber 9 can be obtained. Take the maximum gain point and record it as f(t), and the maximum gain frequency offset of the fiber is f _N (t). In particular, before all measurements start, record the reference maximum gain frequency offset f ₀ (t), which should end with the reference fiber maximum gain frequency offset as one of the two parameter sources in step 21 .

Step 23: Perform frequency offset measurement according to Step 22, while transmitting pulse light, record the time delay of the pulse pump light propagating through the entire fiber to reach the second photoelectric detection unit 12, which is the current time of flight of the pulse pump light. In order to reduce the error, the delay after each pulse transmission in the current measurement step 22 can be collected and averaged. Assume that the measured delay of the pulsed light propagating the entire fiber is t _N,max . In particular, before all measurements are started, the time-of-flight t _0,max of the reference pulsed pump light is obtained in the same way as one of the two parameter sources in step 21 .

Step 24: Correct the delay using the "DC" component of the time-of-flight variation. Denote the delay of the current measurement of a certain data point as t _N , then the delay of the corresponding reference data is:

That is to say, it can be considered that t ₀ at the time of acquiring the reference data and t _N at the time of the current measurement correspond to the signal of the same segment of optical fiber.

相减，即得到当前最大增益频偏变化Δf_N(t_N)，也就是说

若基准数据时域采样离散，在没有采样点对应

延时，选取此时刻前后最邻近的两个或多个数据点，通过插值法，利用最邻近两点最大增益频偏的线性插值法，近似获取

Step 25: Compare the measured maximum gain frequency offset f _N (T _N ) with the reference maximum gain frequency offset

Subtraction, that is, the current maximum gain frequency offset change Δf _N (t _N ) is obtained, that is

If the time domain sampling of the reference data is discrete, if there is no sampling point corresponding to

Delay, select two or more adjacent data points before and after this time, through interpolation method, use the linear interpolation method of the maximum gain frequency offset of the nearest two points to obtain approximately

Step 26: The temperature measurement result is set as ΔT _N (t), that is, the change value of the current measured temperature compared with the reference temperature. According to the characteristics of Brillouin scattering, ΔT _N =Δf _N /A, according to which the temperature measurement result ΔT _N (t) of each position of the current optical fiber is obtained. The proportionality coefficient A is determined by the fiber material and is an invariant constant known before the measurement. For example, in the G652D standard single-mode fiber produced by Corning, a=1.05MHz/℃.

Although the embodiments have specifically described the present invention, it should be understood by those skilled in the art that modifications or improvements can be made based on the disclosure of the present invention without departing from the spirit and scope of the present invention. Modifications and improvements are within the spirit and scope of the present invention.

Claims (8)

1. A Brillouin optical time-domain scattering system based on light time-of-flight, characterized in that the system structure comprises a laser light source (1), a first coupler (2), an electro-optical modulator (3), an acousto-optical modulation (5), a first fiber amplifier (4), a second fiber amplifier (6), an arbitrary waveform generator (7), a sensing fiber (8), a second coupler (9), a first photoelectric detection unit ( 10), a demodulation unit (13), a third coupler (11), a second photoelectric detection unit (12), and the sensing fiber (8) includes a first port (101) of the sensing fiber and a first port (101) of the sensing fiber. Two ports (102); The laser light source (1) emits laser light to the first coupler (2) to split into probe light and pump light, the pump light is modulated into pulsed pump light by the acousto-optic modulator (5), the The pulsed pump light is amplified by the first optical fiber amplifier (6) and then reaches the first port (101) of the sensing optical fiber through the second coupler (9), and the pulsed pumping light passes through the first port of the sensing optical fiber. (101) Enter the sensing fiber (8), and transmit to the second port (102) of the sensing fiber for output, and the output pulsed pump light is received by the third coupler (11) and then output to the second In the photodetection unit (12), the second photodetection unit (12) outputs a signal to the demodulation unit (13); The probe light is frequency-shifted by the electro-optic modulator (3) and then modulated into continuous probe light, the continuous probe light is amplified by the second fiber amplifier (4), and then reaches the sensing fiber second through the third coupler (11). port (102), the continuous detection light entering the sensing fiber (8) is propagated to the first port (101) of the sensing fiber for output, and the output continuous detection light is received by the second coupler (9) and then output to the first photoelectric detection unit (10), the first photoelectric detection unit (10) outputs an electrical signal to the demodulation unit (13), and the arbitrary waveform generator (7) is respectively connected The electro-optical modulator (3) and the acousto-optical modulator (5), the arbitrary waveform generator (7) provides two-way electrical signal outputs, and one-way outputs a single-frequency rectangular signal to modulate the electro-optical modulator (3) ), the other channel outputs a rectangular pulse signal to modulate the acousto-optic modulator (5). 2. A self-calibration method for a Brillouin optical time-domain scattering system based on the time-of-flight of light, characterized in that, in the method, a third coupler (11) and a second coupler are arranged in the Brillouin optical time-domain scattering system The photoelectric detection unit (12) is used to measure the flight time of the light traversing the entire length of the optical fiber to be tested, so as to realize the delay of calibrating the maximum gain frequency offset, the corresponding data of the corrected current maximum gain frequency offset and the corrected reference maximum gain frequency offset Corresponding to the same fiber position, self-calibration is realized based on Brillouin optical time domain analysis, and the method includes the following steps: Step 21: Before starting the measurement, obtain the maximum gain frequency offset in the Brillouin system of the probe light as the reference maximum gain frequency offset, and obtain the reference pulse pump light flight time of the optical fiber to be measured; Step 22: During measurement, obtain the current maximum gain frequency offset; Step 23: Measure the flight time of the current pulsed pump light; Step 24: Using the time-of-flight of the optical fiber to be tested, calibrate the delay of the maximum gain frequency offset; Step 25: make the corresponding data of the corrected current maximum gain frequency offset and the corrected reference maximum gain frequency offset correspond to the same optical fiber position, and calculate the current maximum gain frequency offset change; Step 26: Calculate the temperature measurement results of each position of the current optical fiber, demodulate the corrected signal, and finally obtain temperature information perceived by the optical fiber. 3. The self-calibration method of a Brillouin optical time-domain scattering system based on the time-of-flight of light according to claim 2, wherein in the step 21, the reference maximum gain frequency is collected before the first measurement. offset and time-of-flight of the pulsed pump light, the step of collecting the reference maximum gain frequency offset is: between 9-13 GHz, adjust the modulation applied by the arbitrary waveform generator (7) to the electro-optical modulator (3) with a step size of 1 MHz Signal frequency, the frequency of the modulated signal is the frequency offset of the probe light relative to the pump light, collect the Brillouin signals at each modulation frequency one by one, and obtain the Brillouin gain spectrum at each position of the sensing fiber (8), and take the gain The maximum point record is used as the reference maximum gain frequency deviation; the process of the time-of-flight of the pulsed pump light is: while the frequency deviation measurement is performed and the pulsed light is emitted, the recorded pulsed pumping light propagates through the entire length of the fiber to reach the second photoelectric detection unit The delay of (12) is the flight time of the reference pulse pump light. 4. The self-calibration method of a Brillouin optical time-domain scattering system based on the time-of-flight of light according to claim 2, wherein in the step 23, the current measurement step 22 is collected after each pulse emission. Delay and average to reduce error. 5. The self-calibration method of a Brillouin optical time-domain scattering system based on the time of flight of light according to claim 2, wherein in the step 24, the time-of-flight variation "DC" component is used to correct the delay. When , record the delay of a certain data point currently measured as t _N , then the delay of the corresponding reference data is:

That is to say, it is considered that the reference data acquisition time t ₀ and the current measurement time t _N correspond to the signal of the same segment of optical fiber. 6. The self-calibration method of a Brillouin optical time-domain scattering system based on the time-of-flight of light according to claim 2, wherein in the step 25, the measured maximum gain frequency offset and the reference maximum gain frequency are Subtract the offset to obtain the current maximum gain frequency offset change Δf _N . 7. The self-calibration method of a Brillouin optical time-domain scattering system based on the time-of-flight of light according to claim 6, characterized in that, if the time-domain sampling of the reference data is discrete and there is no delay corresponding to the sampling point, then select The nearest two or more data points before and after this moment are approximated by interpolation. 8. The self-calibration method of a Brillouin optical time-domain scattering system based on the time-of-flight of light according to claim 2, wherein in the step 26, the temperature measurement result is set as ΔT _N (t), That is, the temperature change of the current measurement temperature compared with the reference measurement, the temperature measurement results of each position of the current optical fiber are obtained by the formula ΔT _N =Δf _N /A, where the proportional coefficient A is determined by the optical fiber material, which is known before the measurement. variable constant.

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