A phase-locked φ-otdr system with high operation efficiency

Abstract

The present application relates to a kind of high operation efficiency's phase-locked type φ-OTDR system, with brand-new hardware mode, the carrier signal in the coherent detection type φ-OTDR system in AOM drive source, the pulse modulation signal of acoustooptic modulator (AOM) drive source and the trigger signal of data acquisition card are all set as from same signal source, so that the initial phase of backscattering rayleigh scattering light collected is locked, then after phase-locked, the signal-to-noise ratio of frequency signal in φ-OTDR sensing system can be improved, higher sensitivity is obtained and the influence of non-zero problem is effectively inhibited;Further, the sampling data obtained in a clock cycle is divided into two ways with interval one sampling point, the IQ component in traditional IQ quadrature demodulation method can be obtained in the acquisition process, amplitude and phase information are directly realized by IQ demodulation, and the operation amount is greatly reduced.

Description

TECHNICAL FIELD

[0001] The application relates to a phase-locked phi-OTDR system with high operation efficiency, and belongs to the technical field of optical fiber sensing. BACKGROUND

[0002] As a technology capable of monitoring dynamic disturbance along an optical fiber, a phase-sensitive optical time domain reflectometer (phi-OTDR) has been widely applied in many fields, such as perimeter security, structure health monitoring, pipeline monitoring and earthquake wave monitoring, and has extremely high application value. A phi-OTDR system acquires dynamic disturbance information along an optical fiber by collecting Rayleigh backscattering light (RBS) in the optical fiber, but the intensity and phase of the RBS signal have certain randomness, which makes coherent fading noise inevitably appear in the superposition process of the RBS signal, and the signal-to-noise ratio of the system is sharply deteriorated due to the influence of the coherent fading noise, so that the reconstructed vibration signal is severely distorted. In order to suppress the influence of the noise, the signal-to-noise ratio can be improved by performing sliding average on the RBS signal in the time dimension.

[0003] In a traditional phi-OTDR system, there are generally three different clock sources, namely: ① a clock source for modulating a carrier signal in an Acoustic Optical Modulator (AOM) drive source in the AOM drive source; ② a clock source for a pulse modulation signal input to the AOM drive source in a pulse generator; and ③ a clock source for data acquisition in a data acquisition card. Since the three clock sources are independent of each other, the RBS signal cannot be directly averaged, otherwise the initial phase of each RBS signal curve collected by the phi-OTDR system will drift over time, and the correlation between the RBS signals at adjacent two time points will be poor, so the RBS signal cannot be directly averaged on the time axis, otherwise the signal-to-noise ratio of the signal will be reduced. Therefore, if the three clocks cannot be unified, it is difficult to eliminate the influence of the coherent fading noise; at the same time, since the phase is not locked, there is a significant non-zero problem in the system, that is, the phase of the RBS signal obtained in each period will gradually drift and be different, so it is not possible to directly superimpose adjacent RBS signals to improve the signal-to-noise ratio, and a phase signal will interfere with the normal disturbance signal. However, the prior art has a large amount of calculation and low practical application efficiency. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a phase-locked φ-OTDR system with high operation efficiency, which improves the signal-to-noise ratio of the frequency signal in the φ-OTDR sensing system, obtains higher sensitivity, effectively suppresses the influence of the non-zero problem, and simultaneously eliminates the multiplication operation in the IQ quadrature phase demodulation process, effectively reduces the operation amount, and improves the operation efficiency.

[0005] In order to solve the above technical problems, the present application adopts the following technical scheme: the present application designs a phase-locked φ-OTDR system with high operation efficiency, which is used for detecting the backscattered Rayleigh scattering light signal of a to-be-measured sensing optical fiber, and comprises a laser, a coupler A, a phase-locked module, an AOM acousto-optic crystal, an erbium-doped fiber amplifier, an optical fiber circulator, a sensing optical fiber, a coupler B, and a balanced detector.

[0006] The laser output end of the laser is connected with the input end of the coupler A, continuous narrow linewidth laser is output from the laser to the coupler A, and the received narrow linewidth laser is divided into initial detection light and local oscillator light according to a preset optical power ratio by the coupler A.

[0007] One of the output ends of the coupler A is connected with the input end of the AOM acousto-optic crystal, and is used for conveying the initial detection light to the AOM acousto-optic crystal; the other output end of the coupler A is connected with one of the input ends of the coupler B, and is used for conveying the local oscillator light to the coupler B; the AOM acousto-optic crystal receives the amplitude modulation radio frequency signal output by the phase-locked module, and modulates the received initial detection light into a pulsed detection light signal under the control of the amplitude modulation radio frequency signal.

[0008] The output end of the AOM acousto-optic crystal is connected with the input end of the erbium-doped fiber amplifier, and is used for conveying the pulsed detection light signal to the erbium-doped fiber amplifier; the erbium-doped fiber amplifier amplifies the pulsed detection light signal according to a preset ratio.

[0009] The output end of the erbium-doped fiber amplifier is connected with the input end of the optical fiber circulator, the pulsed detection light signal from the erbium-doped fiber amplifier is received by the optical fiber circulator, one end of the optical fiber circulator is connected with the to-be-measured sensing optical fiber, the pulsed detection light signal is conveyed to the to-be-measured sensing optical fiber, the backscattered Rayleigh scattering light signal from the to-be-measured sensing optical fiber is received by the end of the optical fiber circulator, and the output end of the optical fiber circulator is connected with the other input end of the coupler B, so as to convey the received backscattered Rayleigh scattering light signal to the coupler B.

[0010] The coupler B mixes the received local oscillator light and the back Rayleigh scattering light signal to form a coherent light signal, and divides the coherent light signal into two sub-coherent light signals according to 50% of the light intensity, the two output ends of the coupler B are connected to the two input ends of the balanced detector, and the two sub-coherent light signals are transmitted into the balanced detector, and the balanced detector converts the received two sub-coherent light signals into electrical signals;

[0011] The phase-locked module comprises a data acquisition card, a mixer, and a power amplifier, the receiving end of the data acquisition card is connected to the electrical signal output end of the balanced detector, the data acquisition card receives the electrical signal from the balanced detector, the data acquisition card internally has a low-frequency reference clock, the low-frequency reference clock is used to generate a sampling clock signal, a carrier signal, and a synthesized pulse modulation signal of the data acquisition card, so as to realize the synchronization phase-locked of the three signals; the data acquisition card is connected to the mixer, and the carrier signal and the pulse modulation signal are transmitted to the mixer, the mixer mixes the carrier signal and the pulse modulation signal to form a trigger modulation signal, the output end of the mixer is connected to the input end of the power amplifier, and the trigger modulation signal is transmitted to the power amplifier, and the power amplifier amplifies the trigger modulation signal to generate an amplitude modulation radio frequency signal.

[0012] As a preferred technical scheme of the present application: the repetition period of the pulse modulation signal generated by the data acquisition card is a positive integer multiple of the repetition period of the trigger modulation signal output by the mixer and the frequency shift of the AOM acousto-optic crystal.

[0013] As a preferred technical scheme of the present application: the sampling rate corresponding to the data acquisition card is 4 / 5 of the AOM acousto-optic crystal frequency shift.

[0014] As a preferred technical scheme of the present application: further comprising an upper computer connected to the data acquisition card, the data acquisition card uploads the electrical signal received from the balanced detector to the upper computer, the upper computer decomposes the electrical signal from the data acquisition card in a single clock cycle according to an interval of one sampling point, obtains odd sampling points and even sampling points, realizes IQ demodulation of the electrical signal, and obtains the amplitude information and phase information of the back Rayleigh scattering light signal corresponding to the to-be-measured sensing optical fiber.

[0015] As a preferred technical scheme of the present application: based on the sampling rate corresponding to the data acquisition card being 4 / 5 of the AOM acousto-optic crystal frequency shift, that is, the intermediate frequency signal frequency f m and the sampling rate f s , satisfy Then the electrical signal S(n) received by the data acquisition card from the balanced detector is as follows:

[0016]

[0017] wherein, n = 1, 2, 3…N, N is the total number of sampling points, S(n) represents the electrical signal of the balanced detector output corresponding to the nth sampling point, A(n) = 2E R (n)E L (n), E R (n) is the amplitude intensity of the backscattered Rayleigh scattering light signal corresponding to the nth sampling point, E L (n) is the amplitude intensity of the local light corresponding to the nth sampling point, and the phase represents the initial phase of the backscattered Rayleigh scattering light signal corresponding to the nth sampling point, represents the initial phase of the local light corresponding to the nth sampling point;

[0018] Further, the upper computer decomposes the electrical signal from the data acquisition card in a single clock cycle in an interval of one sampling point, and obtains odd sampling points and even sampling points as follows:

[0019]

[0020] The lock-in type φ-OTDR system with high operation efficiency has the following technical effects compared with the prior art by adopting the above technical scheme:

[0021] (1) The lock-in type φ-OTDR system with high operation efficiency is designed, the carrier signal inside the AOM driving source, the pulse modulation signal of the AOM driving source, and the trigger signal of the data acquisition card in the coherent detection type φ-OTDR system are all set to come from the same signal source in a brand-new hardware manner, so that the initial phase of the backscattered Rayleigh scattering light collected is locked, then the frequency signal signal-to-noise ratio in the φ-OTDR sensing system can be improved after phase locking, higher sensitivity is obtained, and the influence of the non-zero problem is effectively suppressed.

[0022] (2) The lock-in type φ-OTDR system with high operation efficiency is designed, the sampling rate corresponding to the data acquisition card is set to 4 / 5 of the AOM acoustooptic crystal frequency shift, that is, the sampling data collected in a clock cycle is divided into two data in an interval of one sampling point, the IQ component in the traditional IQ quadrature demodulation method can be obtained in the acquisition process, the IQ demodulation is directly realized, so that the amplitude and phase information is obtained, the operation of multiplying the sampling data with the signals with specific digital angular frequency of sine and cosine in the traditional IQ quadrature demodulation method is omitted, and the operation amount is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a system structure schematic diagram of the lock-in type φ-OTDR system with high operation efficiency designed by the application;

[0024] Figure 2 is a specific sampling rate IQ demodulation algorithm flow chart of the phase-locked φ-OTDR system designed by the application with high operation efficiency;

[0025] Figure 3 is a phase demodulation spectrum diagram when the traditional coherent detection type φ-OTDR system does not perform phase locking.

[0026] Figure 4 is a phase demodulation spectrum diagram when the traditional coherent detection type φ-OTDR system performs phase locking. DETAILED DESCRIPTION

[0027] The specific embodiments of the application will be further described in detail below in combination with the drawings of the specification.

[0028] The application designs a phase-locked φ-OTDR system with high operation efficiency, which is used for realizing detection of backscattered Rayleigh scattering light signals for a to-be-measured sensing optical fiber, as shown in the figure, including a laser, a coupler A, a phase locking module, an AOM acousto-optic crystal, an erbium-doped fiber amplifier, an optical fiber circulator, a sensing optical fiber, a coupler B, and a balanced detector. Figure 1

[0029] The laser output end of the laser is connected with the input end of the coupler A, and continuous narrow linewidth laser is output from the laser to the coupler A, and the coupler A divides the received narrow linewidth laser into initial detection light and local oscillator light according to a preset optical power ratio, and in actual application, the laser is specifically designed as a narrow linewidth laser.

[0030] One of the output ends of the coupler A is connected with the input end of the AOM acousto-optic crystal, for delivering the initial detection light to the AOM acousto-optic crystal, and the other output end of the coupler A is connected with one of the input ends of the coupler B, for delivering the local oscillator light to the coupler B; the AOM acousto-optic crystal receives the amplitude modulation radio frequency signal output by the phase locking module, and modulates the received initial detection light into a pulsed probe light signal under the control of the amplitude modulation radio frequency signal.

[0031] The output end of the AOM acousto-optic crystal is connected with the input end of the erbium-doped fiber amplifier, for delivering the pulsed probe light signal to the erbium-doped fiber amplifier, and the erbium-doped fiber amplifier amplifies the pulsed probe light signal according to a preset ratio.

[0032] ​The output end of the erbium-doped fiber amplifier is connected to the input end of the optical fiber circulator, the optical fiber circulator receives the pulse probe light signal from the erbium-doped fiber amplifier, one end of the optical fiber circulator is connected to the to-be-tested sensing optical fiber, the pulse probe light signal is transmitted to the to-be-tested sensing optical fiber, and the backscattering Rayleigh scattering light signal from the to-be-tested sensing optical fiber is received by the end of the optical fiber circulator, and the output end of the optical fiber circulator is connected to the other input end of the coupler B, and the received backscattering Rayleigh scattering light signal is transmitted to the coupler B.

[0033] The coupler B mixes the received local oscillator light and the backscattering Rayleigh scattering light signal to form a coherent light signal, and divides the coherent light signal into two sub-coherent light signals with an optical intensity of 50%. The two output ends of the coupler B are connected to the two input ends of the balanced detector, and the two sub-coherent light signals are transmitted to the balanced detector respectively. The balanced detector converts the received two sub-coherent light signals into electrical signals.

[0034] The phase-locked module includes a data acquisition card, a mixer, and a power amplifier. The receiving end of the data acquisition card is connected to the electrical signal output end of the balanced detector. The data acquisition card receives the electrical signal from the balanced detector. The data acquisition card has a low-frequency reference clock built-in. The low-frequency reference clock is used to generate a sampling clock signal, a carrier signal, and a synthesized pulse modulation signal of the data acquisition card, so as to realize the synchronization phase-locked of the three signals. In the application, the repetition period of the pulse modulation signal generated by the data acquisition card is set to be an integer multiple of the repetition period of the output trigger modulation signal of the mixer and the frequency shift of the AOM acousto-optic crystal.

[0035] The data acquisition card is connected to the mixer, and transmits the carrier signal and the pulse modulation signal to the mixer. The mixer mixes the carrier signal and the pulse modulation signal to form a trigger modulation signal. The output end of the mixer is connected to the input end of the power amplifier, and the trigger modulation signal is transmitted to the power amplifier. The power amplifier amplifies the trigger modulation signal to generate an amplitude modulation radio frequency signal.

[0036] In actual application, for the above-mentioned high-efficiency phase-locked φ-OTDR system, an upper computer connected to the data acquisition card is further designed. The data acquisition card uploads the received electrical signal from the balanced detector to the upper computer. The upper computer decomposes the electrical signal from the data acquisition card in a single clock cycle in an interval of one sampling point, obtains odd sampling points and even sampling points, realizes IQ demodulation of the electrical signal, and obtains the amplitude information and phase information of the backscattering Rayleigh scattering light signal corresponding to the to-be-tested sensing optical fiber.

[0037] The application designs a phase-locked phi-OTDR system with high operation efficiency, and in the specific actual implementation, a balanced detector is used to convert the coherent light signal input by the coupler B into an electrical signal and output to a data acquisition card, the back Rayleigh scattering light signal received by the data acquisition card is mixed with the local light in the coupler B to generate a beat signal, and the power of the beat signal output is:

[0038]

[0039] wherein E R (t) is the amplitude intensity of the back Rayleigh scattering light signal with time t, E L (t) is the amplitude intensity of the local light with time t, f m is the frequency of the intermediate frequency signal, is the initial phase of the back Rayleigh scattering light signal scattering light, is the initial phase of the local light.

[0040] The change of the light signal detected by the balanced detector with time t is finally collected in the form of discrete quantities by the data acquisition card, assuming that the corresponding sampling rate of the data acquisition card is f s , then the electrical signal S(n) received by the data acquisition card from the balanced detector is as follows:

[0041]

[0042] wherein S(n) represents the electrical signal output by the balanced detector corresponding to the nth sampling point, n = 1, 2, 3…N, and N is the total number of sampling points, E R (n) is the amplitude intensity of the back Rayleigh scattering light signal corresponding to the nth sampling point, E L (n) is the amplitude intensity of the local light corresponding to the nth sampling point, Δω n represents the digital angular frequency, and the phase represents the initial phase of the back Rayleigh scattering light signal corresponding to the nth sampling point, represents the initial phase of the local light corresponding to the nth sampling point.

[0043] In the application, the sampling rate corresponding to the data acquisition card is set to 4 / 5 of the frequency shift of the AOM acousto-optic crystal under the premise of phase locking, because the frequency shift frequency of the AOM acousto-optic crystal directly determines the heterodyne frequency, that is, 4 / 5 is used to collect all the signals; according to the Nyquist sampling rule, the sampling rate must be 200% of the collected signal, so the process is actually an under-sampling process. Because of under-sampling, the period is extended, that is, the original signal is extended by 4 / 5; therefore, the signal is changed to 1 / 5 of the original frequency, and the sampling result is: the sampling rate of 4 / 5 represents the frequency point of 1 / 5 of the original frequency, which exactly constitutes a 4:1 relationship, that is, The data acquisition card receives the electrical signal S(n) from the balance detector as follows:

[0044]

[0045] Wherein, A(n) = 2E R (n)E L (n)。

[0046] Further, the host computer decomposes the electrical signal from the data acquisition card in a single clock cycle in an interval of one sampling point, and obtains odd sampling points and even sampling points as follows:

[0047]

[0048] The high-efficiency phase-locked phi-OTDR system designed in the application is applied to practice, such as Figure 1 As shown in the figure, the NTK narrow linewidth laser is used to output continuous narrow linewidth laser with a wavelength of 1550 nm, a linewidth of 200 Hz and a power of 8.17 dBm to the coupler A; the coupler A is a 90:10 coupler, which is used to receive the narrow linewidth laser and divide it into two paths, one of which is used as the initial probe light input to the AOM acousto-optic crystal, which is 90% of the continuous narrow linewidth laser power; the other is used as the local oscillator light input to the coupler B, which is 10% of the continuous narrow linewidth laser power.

[0049] The phase-locked module comprises a data acquisition card, a mixer and a power amplifier, wherein the data acquisition card is used to collect data with a sampling rate of 160 MHz, and is used to output a 10 MHz reference clock signal as a carrier signal and a pulse modulation signal with a pulse width of 96 ns and a repetition period of 1 ms to the mixer for mixing, the carrier signal is obtained by frequency doubling the reference clock signal provided by the data acquisition card to 200 MHz, and the frequency of the carrier signal after frequency doubling is equal to the AOM frequency shift amount; the mixer is used to mix the reference clock provided by the data acquisition card as a carrier signal and a modulation signal to form a 200 MHz trigger modulation signal, which is output to the power amplifier; the power amplifier is used to amplify the trigger modulation signal to generate an amplitude modulation radio frequency signal for modulating the AOM acousto-optic crystal to modulate the initial probe light.

[0050] AOM acoustooptic crystal, used for modulating initial probe light into pulse probe light signal with frequency shift of 200MHz input to erbium-doped fiber amplifier (EDFA); erbium-doped fiber amplifier (EDFA) is used for amplifying pulse probe light signal to peak-peak value of -25.37Bm and then outputting to optical fiber circulator A port; the pulse probe light signal input to A port of optical fiber circulator is output to the to-be-measured sensing optical fiber by B port, and the backscattering Rayleigh scattering light signal generated by the to-be-measured sensing optical fiber is input to B port and output to coupler B by C port; wherein the to-be-measured sensing optical fiber is used for transmitting the pulse probe light signal input to B port of the optical fiber circulator and transmitting the backscattering light signal generated to B port of the optical fiber circulator; the coupler B is a 50:50 coupler, used for mixing the backscattering Rayleigh scattering light signal input to C port of the optical fiber circulator and the intrinsic light signal input to the coupler A to form coherent light signal and output to the balanced detector; the balanced detector is used for converting the coherent light signal input to the coupler B into an electrical signal and outputting to the data acquisition card; and the host computer is used for IQ demodulating the digital signal collected by the data acquisition card.

[0051] As shown in Figure 2 the present application sets the sampling rate to 4 / 5 of the frequency shift of the AOM acoustooptic crystal under the premise of phase locking: the sampling rate is 160MHz, and the frequency shift of the AOM acoustooptic crystal is 200MHz. The data acquisition card collects the digital signal S(n), and the host computer divides S(n) into two data by an interval of one sampling point, that is, one is data 1 for the odd sampling points of the collected data, and the other is data 2 for the even sampling points of the collected data. In the process of collecting, the IQ components in the traditional IQ quadrature demodulation method are obtained, and the IQ demodulation can be directly realized, so that the amplitude and phase information are obtained.

[0052] In order to verify the influence of phase locking and non-phase locking on the phase demodulation result, in the specific embodiment, data collection is carried out in a quiet environment, and the background noise brought by the two to the system is analyzed.

[0053] As shown in Figure 3 the present application sets the sampling rate to 4 / 5 of the frequency shift of the AOM acoustooptic crystal under the premise of phase locking: the sampling rate is 160MHz, and the frequency shift of the AOM acoustooptic crystal is 200MHz. The data acquisition card collects the digital signal S(n), and the host computer divides S(n) into two data by an interval of one sampling point, that is, one is data 1 for the odd sampling points of the collected data, and the other is data 2 for the even sampling points of the collected data. In the process of collecting, the IQ components in the traditional IQ quadrature demodulation method are obtained, and the IQ demodulation can be directly realized, so that the amplitude and phase information are obtained.

[0054] AsFigure 4 As shown, it is a phase demodulation spectrum diagram when a traditional coherent detection type phi-OTDR system is phase-locked. When the clock sources of a carrier signal inside an acousto-optic modulator (AOM) drive source, a pulse modulation signal for input to the AOM drive source and a trigger signal for a data acquisition card are phase-locked, the intermediate frequency signal waveforms detected by the balance detector at different times are subjected to the specific sampling rate demodulation method of the application to obtain a background noise spectrum diagram. Since phase locking is performed, adjacent RBS signals are directly superimposed and do not produce noise of a specific frequency, and low-frequency disturbances also do not produce noise.

[0055] By comparison of the prior art and the application, it can be shown that the method of the application makes the carrier signal inside the AOM drive source, the pulse modulation signal of the acousto-optic modulator (AOM) drive source and the trigger signal of the data acquisition card come from the same signal source, so that the initial phase of the collected backscattered Rayleigh scattering light is locked. The signal-to-noise ratio of the obtained intermediate frequency signal is significantly improved, the non-zero problem after phase demodulation is greatly improved, it is suitable for observing low-frequency vibration signals, thereby obtaining higher sensitivity and effectively suppressing the influence of the non-zero problem. Figure 3 Figure 4 The above describes the embodiments of the application in detail in combination with the drawings, but the application is not limited to the above-described embodiments, and various changes can be made within the knowledge possessed by those skilled in the art without departing from the purpose of the application.

[0056] The above describes the embodiments of the application in detail in combination with the drawings, but the application is not limited to the above-described embodiments, and various changes can be made within the knowledge possessed by those skilled in the art without departing from the purpose of the application.​

Claims

1. A phase-locked φ-OTDR system with high operation efficiency, for realizing detection of back Rayleigh scattering light signals for a to-be-measured sensing optical fiber, characterized in that: The laser, the coupler A, the phase locking module, the AOM acousto-optic crystal, the erbium-doped fiber amplifier, the fiber ring, the sensing fiber, the coupler B and the balanced detector are connected in series. The laser output end of the laser is connected with the input end of the coupler A, continuous narrow linewidth laser is output from the laser to the coupler A, and the coupler A divides the received narrow linewidth laser into initial detection light and local oscillator light according to a preset optical power ratio. One output end of the coupler A is connected with the input end of the AOM acousto-optic crystal, and the initial detection light is transmitted to the AOM acousto-optic crystal, and the other output end of the coupler A is connected with one input end of the coupler B, and the local oscillator light is transmitted to the coupler B; the AOM acousto-optic crystal receives the amplitude modulation radio frequency signal output by the phase locking module, and modulates the received initial detection light into pulsed detection light signal under the control of the amplitude modulation radio frequency signal. The output end of the AOM acousto-optic crystal is connected with the input end of the erbium-doped fiber amplifier, and the pulsed detection light signal is transmitted to the erbium-doped fiber amplifier, and the erbium-doped fiber amplifier amplifies the pulsed detection light signal according to a preset ratio. The output end of the erbium-doped fiber amplifier is connected with the input end of the fiber ring, the fiber ring receives the pulsed detection light signal from the erbium-doped fiber amplifier, one end of the fiber ring is connected with the sensing fiber to be tested, the pulsed detection light signal is transmitted to the sensing fiber to be tested, and the backscattering Rayleigh scattering light signal from the sensing fiber to be tested is received by the end of the fiber ring, and the output end of the fiber ring is connected with the other input end of the coupler B, and the received backscattering Rayleigh scattering light signal is transmitted to the coupler B. The coupler B mixes the received local oscillator light and backscattering Rayleigh scattering light signal to form coherent light signal, and divides the coherent light signal into two sub-coherent light signals according to 50% optical intensity, and the two output ends of the coupler B are connected with the two input ends of the balanced detector to transmit the two sub-coherent light signals to the balanced detector, and the balanced detector converts the received two sub-coherent light signals into electrical signals. The phase locking module includes a data acquisition card, a mixer and a power amplifier, the receiving end of the data acquisition card is connected with the electrical signal output end of the balanced detector, the data acquisition card receives the electrical signal from the balanced detector, the data acquisition card has a low frequency reference clock inside, which is used to generate a sampling clock signal, a carrier signal and a synthesized pulse modulation signal of the data acquisition card, so as to realize the synchronization phase locking of the three signals; the data acquisition card is connected with the mixer, and transmits the carrier signal and the pulse modulation signal to the mixer, the mixer mixes the carrier signal and the pulse modulation signal to form a trigger modulation signal, the output end of the mixer is connected with the input end of the power amplifier, and the trigger modulation signal is transmitted to the power amplifier, and the power amplifier amplifies the trigger modulation signal to generate an amplitude modulation radio frequency signal.

2. The phase-locked φ-OTDR system with high operation efficiency according to claim 1, characterized in that: The repetition period of the pulse modulation signal generated by the data acquisition card is a positive integer multiple of the repetition period of the trigger modulation signal output by the mixer and the frequency shift of the AOM acousto-optic crystal.

3. The phase-locked φ-OTDR system with high operation efficiency according to claim 2, characterized in that: The sampling rate corresponding to the data acquisition card is 4 / 5 of the AOM acousto-optic crystal frequency shift.

4. The phase-locked φ-OTDR system with high operation efficiency according to claim 3, characterized in that: Further comprising a host computer connected with the data acquisition card, the electrical signal received from the balanced detector is uploaded to the host computer by the data acquisition card, the host computer decomposes the electrical signal from the data acquisition card in a single clock cycle in a manner of interval one sampling point, obtains odd sampling points and even sampling points, realizes IQ demodulation for the electrical signal, and obtains the amplitude information and phase information of the backscattering Rayleigh scattering light signal corresponding to the to-be-measured sensing optical fiber.

5. The phase-locked φ-OTDR system with high operation efficiency according to claim 4, characterized in that: Based on the sampling rate corresponding to the data acquisition card is the AOM acoustooptic crystal frequency shift 4 / 5, namely intermediate frequency signal frequency f m With the data acquisition card corresponding sampling rate f s , satisfy Then the data acquisition card receives the electrical signal S(n) from the balanced detector as follows: wherein, n = 1, 2, 3...N, N is the total number of sampling points, S(n) represents the electrical signal of the balanced detector output corresponding to the nth sampling point, A(n) = 2E R (n)E L (n)E R (n) is the amplitude intensity of the backscattering Rayleigh scattering light signal corresponding to the nth sampling point, E L (n) is the amplitude intensity of the local light corresponding to the nth sampling point, and the phase represents the initial phase of the backscattering Rayleigh scattering light signal corresponding to the nth sampling point, represents the initial phase of the local light corresponding to the nth sampling point; Further, the host computer decomposes the electrical signal from the data acquisition card in a single clock cycle in a manner of interval one sampling point, obtains odd sampling points and even sampling points as follows:

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