A single-ended distributed fiber optic vibration sensor system and signal processing method

Abstract

The application discloses a single-end distributed optical fiber vibration sensor system and a signal processing method, and relates to the technical field of optical fiber vibration sensors. The system comprises a laser source, an electro-optical modulator, a to-be-measured optical fiber, a piezoelectric ceramic, a 1*2 coupler, a frequency mixer, an oscilloscope and a PC end. The laser source transmits laser to the to-be-measured optical fiber after the laser is loaded with a carrier frequency by the electro-optical modulator. The to-be-measured optical fiber changes the phase of the light conducted in the optical fiber after being affected by external environmental vibration. The piezoelectric ceramic generates a vibration signal to modulate the phase information of the to-be-measured optical fiber, and then transmits the vibration signal to the 1*2 coupler. The 1*2 coupler divides the vibration signal into signal light and local oscillator light, and then transmits the signal light and the local oscillator light to the frequency mixer for coherent mixing. The frequency mixer demodulates the phase change. The PC end demodulates and processes the phase change collected by the oscilloscope to obtain vibration information of the external environment. The single-end distributed optical fiber vibration sensor system has a large dynamic range, a long measurement distance, low cost and measurement stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology, and particularly relates to a single-end distributed optical fiber vibration sensor system and a signal processing method. BACKGROUND

[0002] Large-area remote monitoring of the seabed using distributed optical fiber vibration sensors can provide real-time feedback on changes in the local environment of the seabed caused by marine earthquakes or hydrate exploitation, thereby making more informed decisions, better safety, and maximum production. More than 1.2 million km of optical cables crisscross the seabed, which is the hidden infrastructure that enables the Internet. If the optical fibers in these optical cables can also become distributed seismic sensors in addition to their normal functions, it will be a major breakthrough.

[0003] Current distributed vibration technology is mainly divided into two categories: OFDR (Optical Frequency Domain Reflection) and OTDR (Optical Time-Domain Reflectometer). The OTDR has a simple basic structure, relatively good dynamic response capability, and a detection range of tens of kilometers, and can respond to vibration information in real time. However, the OTDR system also has the disadvantages of low signal-to-noise ratio, difficulty in achieving full-range sensitivity, difficulty in balancing resolution and dynamic range, and the like. OFDR can meet these requirements, as it has the advantages of high sensitivity and high spatial resolution. However, the OFDR system has two limitations: the limitations of light source phase noise and coherence, and the limitations of light source sweep nonlinearity. Both of these technologies are based on backscattering, and the scattered light is very weak. Therefore, in order to improve the signal-to-noise ratio and the detection range, the power of the light source must be increased, which will introduce significant nonlinear effects. In addition, in order to achieve long-distance sensing, an optical amplifier is added, which increases the complexity of the actual system. Moreover, high-power, ultra-narrow linewidth lasers greatly increase the cost of the distributed system, making the long-distance distributed system costly and causing serious nonlinear effects.

[0004] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0005] The main purpose of the present application is to provide a single-end distributed optical fiber vibration sensor system and a signal processing method, which aims to solve the problems of small measurement range, short sensing distance, complex equipment, and high cost of the prior art distributed vibration sensor.

[0006] To achieve the above purpose, the present application provides a single-end distributed optical fiber vibration sensor system, which comprises:

[0007] The laser source, the electro-optical modulator, the to-be-measured optical fiber, the piezoelectric ceramic, the 1*2 coupler, the frequency mixer, the oscilloscope and the PC end are sequentially connected.

[0008] The laser source is used for emitting laser, which is transmitted to the to-be-measured optical fiber after being loaded with a carrier frequency by the electro-optical modulator.

[0009] The to-be-measured optical fiber changes the phase of the light conducted in the optical fiber after being affected by external environmental vibration, and the piezoelectric ceramic generates a vibration signal to modulate the phase information of the to-be-measured optical fiber and then transmits the vibration signal to the 1*2 coupler.

[0010] The 1*2 coupler is used for dividing the phase information into signal light and local oscillator light and then transmitting the signal light and the local oscillator light to the frequency mixer, respectively.

[0011] The oscilloscope is used for collecting the phase change obtained by the frequency mixer, and the PC end is used for demodulating the phase change collected by the oscilloscope to obtain vibration information of the external environment.

[0012] The single-end distributed optical fiber vibration sensor system, wherein the frequency mixer is a port 90° optical frequency mixer.

[0013] The port 90° optical frequency mixer is used for coherently mixing the local oscillator light and the signal light, so that the relative phase difference of the four output ports is 0°, 90°, 180° and 270°, respectively.

[0014] The single-end distributed optical fiber vibration sensor system, wherein the port 90° optical frequency mixer comprises a quarter-wave plate, two half-wave plates and three polarization beam splitting prisms.

[0015] The single-end distributed optical fiber vibration sensor system, wherein the to-be-measured optical fiber is composed of a single-mode optical fiber.

[0016] The single-end distributed optical fiber vibration sensor system, wherein the local oscillator light and the signal light have the same wavelength.

[0017] The single-end distributed optical fiber vibration sensor system, wherein the laser source is a semiconductor laser.

[0018] The single-end distributed optical fiber vibration sensor system, wherein the line width of the semiconductor laser is 50 kHz.

[0019] In addition, in order to achieve the above object, the application further provides a signal processing method based on the single-end distributed optical fiber vibration sensor system, wherein the signal processing method comprises the following steps:

[0020] The laser source emits laser, which is transmitted to the optical fiber to be measured after being loaded with a carrier frequency by the electro-optical modulator;

[0021] The optical fiber to be measured changes the phase of the light conducted in the optical fiber after being affected by the external environment vibration, and the phase information of the optical fiber to be measured is modulated by the vibration signal generated by the piezoelectric ceramic and then transmitted to the 1*2 coupler;

[0022] The 1*2 coupler transmits the phase information to the frequency mixer after dividing the phase information into signal light and local oscillator light, the frequency mixer coherently mixes the local oscillator light and the signal light, and the phase change is obtained by demodulation;

[0023] The oscilloscope collects the phase change obtained by the frequency mixer, and the PC end demodulates and processes the phase change collected by the oscilloscope to obtain the vibration information of the external environment.

[0024] The signal processing method further comprises the following steps:

[0025] When the phase changes due to the influence of vibration on the optical fiber to be measured, the time delay of the two-phase time delay relationship is used to solve the time delay by cross-correlation to determine the position of the external event.

[0026] The signal processing method further comprises the following steps:

[0027] The intensity and frequency information of the external event are obtained by analyzing the phase change.

[0028] In the present application, the single-end distributed optical fiber vibration sensor system comprises: a laser source, an electro-optical modulator, a fiber to be measured, a piezoelectric ceramic, a 1*2 coupler, a frequency mixer, an oscilloscope and a PC end; the laser source, the electro-optical modulator, the fiber to be measured, the piezoelectric ceramic, the 1*2 coupler, the frequency mixer, the oscilloscope and the PC end are connected in sequence; the laser source is used for emitting laser, which is transmitted to the fiber to be measured after being loaded with a carrier frequency by the electro-optical modulator; the fiber to be measured changes the phase of the light conducted inside the fiber after being affected by external environmental vibration, the piezoelectric ceramic generates a vibration signal to modulate the phase information of the fiber to be measured and then transmits it to the 1*2 coupler; the 1*2 coupler is used for dividing the phase information into signal light and local oscillator light and then transmitting them to the frequency mixer, the frequency mixer is used for coherently mixing the local oscillator light and the signal light and demodulating to obtain the phase change; the oscilloscope is used for collecting the phase change obtained by the frequency mixer, and the PC end is used for demodulating and processing the phase change collected by the oscilloscope to obtain the vibration information of the external environment. The single-end distributed optical fiber vibration sensor system of the present application has a large dynamic range, a long measurement distance, a low cost and a stable measurement, can well detect the vibration signal and can efficiently measure the high-frequency vibration. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a principle schematic diagram of a preferred embodiment of the single-end distributed optical fiber vibration sensor system of the present application;

[0030] Figure 2 is a function schematic diagram of the frequency mixer in the preferred embodiment of the single-end distributed optical fiber vibration sensor system of the present application;

[0031] Figure 3 is a structure schematic diagram of the frequency mixer in the preferred embodiment of the single-end distributed optical fiber vibration sensor system of the present application;

[0032] Figure 4 is an output schematic diagram of the frequency mixer in the preferred embodiment of the single-end distributed optical fiber vibration sensor system of the present application;

[0033] Figure 5 is a structure schematic diagram of the distributed vibration sensing system based on forward transmission of the present application;

[0034] Figure 6 is a schematic diagram for solving the time delay by cross-correlation when the phase is changed due to the vibration affecting the optical fiber in the present application;

[0035] Figure 7 is a flowchart of a preferred embodiment of the signal processing method based on the single-end distributed optical fiber vibration sensor system of the present application. DETAILED DESCRIPTION

[0036] In order to make the objects, technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not intended to limit the present application.

[0037] The present application first introduces the phase shift of light in an optical fiber caused by a disturbance signal. When a pre-buried sensing optical fiber is subjected to pressure, heat transfer or bending of a disturbance source, due to the photoelastic effect and thermal strain effect of the optical fiber, the physical parameters such as the refractive index, length and diameter of the optical fiber will change, thereby causing the transmission light in the fiber core to produce a phase shift containing disturbance information, i.e. to realize the modulation of the transmission light phase by the external disturbance. If the total length of the sensing optical fiber is L, the refractive index is n, and the optical wavelength is λ, the phase shift of a certain fixed frequency optical wave through the sensing optical fiber is represented as:

[0038]

[0039] wherein β is the propagation constant, which is directly affected by the effective refractive index of the optical fiber;

[0040] When there is an external disturbance, the phase shift amount is represented as:

[0041]

[0042] wherein and respectively represent the phase shift caused by the change of the sensing optical fiber length due to elastic deformation, the phase shift caused by the change of the refractive index of the optical fiber due to the photoelastic effect, and the phase shift caused by the change of the fiber core diameter of the optical fiber due to the Poisson effect, ΔL, Δβ, Δn and ΔD respectively represent the length change amount of the optical fiber, the propagation constant change amount, the refractive index change amount, and the fiber core diameter change amount of the optical fiber.

[0043] Since is and small by more than two orders of magnitude, they are ignored, i.e. the phase shift amount is approximately represented as:

[0044]

[0045] wherein and respectively represent the phase shift caused by the change of the sensing optical fiber length due to elastic deformation and the phase shift caused by the change of the refractive index of the optical fiber due to the photoelastic effect.

[0046] For the phase shift caused by the change of the sensing optical fiber length due to elastic deformation According to the strain theory, the strain amount ε iThe description, let ε be the normal strain vector of the sensing fiber, when the sensing fiber is disturbed by the longitudinal pressure P, has:

[0047]

[0048] Wherein, ε x , ε y , ε z are the strain of the sensing fiber in X, Y, Z three directions respectively, E is the Young's modulus of the sensing fiber, μ is the Poisson ratio of the fiber, the phase change caused by the length change in Z direction is:

[0049]

[0050] For the phase shift caused by the change of the refractive index of the fiber due to the photoelastic effect According to the principle of elasticity, the relationship between the refractive index change and the strain ε i suffered by the quartz fiber from the photoelastic tensor and the principal strain tensor is:

[0051]

[0052] Wherein, P m = (P 11 -P 12 ) / 2, ΔB i = -2Δn i / n i 3 , the fourth order photoelastic tensor P ij is a constant.

[0053] For the quartz fiber, ε x = ε y , n i = n, so the refractive index change of the sensing fiber in X, Y, Z three directions is:

[0054]

[0055] Therefore, the phase shift caused by the change of the refractive index of the fiber due to the photoelastic effect is:

[0056]

[0057] Therefore, the phase shift caused by the external disturbance is:

[0058]

[0059] ​It can be seen from the above formula that the transmission light phase shift is proportional to the fiber strain caused by the disturbance. In practice, the dynamic external disturbance can be regarded as a function of time t. If the phase change function can be obtained by combining the demodulation means during post-processing The type of external disturbance can be easily distinguished, and the sensing system with the fiber itself as the sensitive element is realized.

[0060] The single-end distributed optical fiber vibration sensor system described in the preferred embodiment of the present application, as shown in Figure 1 The single-end distributed optical fiber vibration sensor system comprises a laser source, an electro-optical modulator, a to-be-measured optical fiber, a piezoelectric ceramic, a 1*2 coupler, a frequency mixer, an oscilloscope and a PC end. The laser source, the electro-optical modulator, the to-be-measured optical fiber, the piezoelectric ceramic, the 1*2 coupler, the frequency mixer, the oscilloscope and the PC end are connected in sequence.

[0061] Specifically, the laser source is used to emit laser, which is transmitted to the to-be-measured optical fiber after being loaded with a carrier frequency (so that the signal frequency band is moved to a high frequency) by the electro-optical modulator; the to-be-measured optical fiber changes the phase of the light conducted in the optical fiber after being affected by the external environment vibration; the piezoelectric ceramic generates a vibration signal to modulate the phase information of the to-be-measured optical fiber and then transmits it to the 1*2 coupler; the 1*2 coupler is used to divide the phase information into signal light and local oscillator light and then transmit them to the frequency mixer, respectively; the frequency mixer is used to coherently mix the local oscillator light and the signal light and demodulate the phase change; the oscilloscope is used to collect the phase change obtained by the frequency mixer; and the PC end is used to demodulate and process the phase change collected by the oscilloscope to obtain the vibration information of the external environment.

[0062] The to-be-measured optical fiber is also called a sensing unit, and the sensing unit is composed of a single-mode optical fiber (SMF) with a length of tens of kilometers; the 1*2 coupler and the frequency mixer form a demodulation unit; the sensing unit will be affected by the external environment vibration, thereby changing the phase of the light conducted in the optical fiber, so that the demodulation unit demodulates the phase change to obtain the vibration information of the external environment. The present application has a large dynamic range, a long measurement distance, a low cost and a stable measurement.

[0063] The frequency mixer is a port 90° optical frequency mixer; the port 90° optical frequency mixer coherently mixes the local oscillator light and the signal light, so that the relative phase difference of the four output ports is 0°, 90°, 180° and 270°, respectively. The direct current components of the photocurrents obtained by the 0° and 180° and 90° and 270° port balanced detectors are equal, respectively, so that two coherent signals can be obtained by subtracting each other, and the relative phase difference of the two signals is 90°, and the relative intensity is K1K2 / K3K4, K1, K2, K3 and K4 represent intensity coefficients, as shown in Figure 2 S ​E LO E E

[0064] As shown in Fig. 1, the port 90° optical hybrid consists of a quarter wave plate, two half wave plates and three polarizing beam splitters. Figure 3 As shown in Fig. 1, the port 90° optical hybrid consists of a quarter wave plate, two half wave plates and three polarizing beam splitters. Figure 3 i LO The signal light P i and the local light P LO have the same wavelength (1064nm) and enter the port 90° optical hybrid as linearly polarized light through a polarizer. 1 is a quarter wave plate, whose fast (slow) axis is at 45° to the polarization direction of the local light, so that the local light becomes circularly polarized light after passing through 1. 2, 4 and 6 are polarizing beam splitters (PBS), so that P light components can only be transmitted and S light components can only be reflected (P light components and S light components can be understood as the decomposition of plane light vectors into two mutually perpendicular directions). 3 and 5 are half wave plates, whose fast (slow) axis is at 22.5° to the S (P) light direction, so that the linearly polarized light on the two branches after passing through 2 becomes linearly polarized light with a polarization direction at 45° to the P light after passing through 3. The light on the last two branches is split by PBS to obtain four output lights with relative phase differences of 0°, 90°, 180° and 270° respectively. The polarizing beam splitter is an optical element obtained by coating a multi-layer film structure on the hypotenuse of a right-angle prism and then cementing it into a cube structure, which uses the property that the transmission rate of P polarized light is 1 and the transmission rate of S polarized light is less than 1 when light is incident at the Brewster angle, and after the light passes through the multi-layer film structure at the Brewster angle for many times, the P polarized component is completely transmitted and most of the S polarized component is reflected (at least 90% or more). The incident interference light intensity can be shown in Fig. 2, and the difference between the output light intensities at both ends only leaves the alternating component, so that the actual phase can be calculated by using the tangent calculation method. Figure 4

[0065] Further, the structure of the distributed vibration sensing system based on forward transmission is shown in Fig. 5, PMM represents a plane mirror, TDF represents a time delay fiber, FTU represents a fiber test unit, Mixer represents a mixer, PC represents a computer, and LD represents a laser diode (i.e., a laser source). The semiconductor laser is the light source (i.e., the laser source) of the system, and the line width of the semiconductor laser is 50 kHz. The light emitted by the narrow line width laser first enters the circulator (CIR), and the phase change of the sensing fiber is carried by the optical signal. The end passes through the 50:50 beam splitter, and the two light paths are respectively in the electro-optic modulator (EOM). The electro-optic modulator needs a signal generator to drive it, and the driving frequency is several tens of MHz, and the peak-to-peak voltage (Vpp) is 3.5 V. The acousto-optic modulator modulates the continuous light and generates a several tens of MHz signal frequency shift. After being reflected by the circulator and entering the 50:50 beam splitter, the optical signal is divided into two paths and coherently superimposed in the mixer. The optical signal is converted into an electrical signal by the balanced photodiode (BPD), and the bandwidth of the balanced photodiode is 500 MHz. The output signal is finally collected by the data acquisition card (DAQ).

[0066] The principle of distributed vibration sensing is described below. When light passes through the optical fiber, the phase of the light is accumulated in different places. Therefore, the two paths are:

[0067] P1: a→b→c→d→c→b→a; P2: a→b→c→f→c→b→a;

[0068] The phases generated by different paths can be expressed as:

[0069] Phase 1:

[0070] Phase 2:

[0071] where t1 = nL bcdcb / c is the delay time at the d end, t2 = nL bcfcb / c is the delay time at the f end, ω1 is the operating frequency of the d end EOM, and ω2 is the operating frequency of the f end EOM.

[0072] The phase obtained by self-coherence through time delay is:

[0073]

[0074]

[0075] wherein, and represents the delayed fiber output light of the receiving end;

[0076] tdelay=nL delay / c , respectively, the phase difference is derived:

[0077]

[0078]

[0079] wherein, Δt=t2-t1, by simple derivation:

[0080]

[0081] From the above formula, when the optical fiber is affected by vibration, the phase changes, and the time delay relationship of the two phases is utilized, the time delay can be solved by cross-correlation as shown in formula (1): Figure 6 Thus, the position L of the external event is determined bcfcb =t 2cn . At the same time, the intensity and frequency information of the external event are obtained by analyzing the phase changes and .

[0082] The application provides a single-end distributed optical fiber vibration sensor system, and experimental results show that the system has a large frequency range, a long sensing distance, low cost and good stability, and can well detect vibration signals; the distributed vibration optical fiber sensor can efficiently measure high-frequency vibration.

[0083] Further, as shown in formula (2), a signal processing method based on the single-end distributed optical fiber vibration sensor system comprises the following steps: Figure 7 S10, the laser source emits laser, which is transmitted to the to-be-measured optical fiber after being loaded with a carrier frequency by the electro-optical modulator;

[0084] S20, the to-be-measured optical fiber changes the phase of light conducted in the optical fiber after being affected by external environmental vibration, and the phase information of the to-be-measured optical fiber is modulated by a vibration signal generated by the piezoelectric ceramic and then transmitted to the 1*2 coupler;

[0085] S30, the 1*2 coupler transmits the phase information to the frequency mixer after dividing the phase information into signal light and local oscillator light, the frequency mixer coherently mixes the local oscillator light and the signal light, and demodulates to obtain the phase change;

[0086]

[0087] ​S40, the oscilloscope collects the phase change obtained by the frequency mixer, and the PC end demodulates the phase change collected by the oscilloscope to obtain vibration information of an external environment.

[0088] In addition, the detection frequency range of the distributed vibration optical fiber sensor can be changed, the detection distance can be changed, and the type of the optical fiber can be changed, such as being replaced by a special vibration-sensitive optical fiber or being replaced by another type of optical fiber, for example, a multi-core optical fiber or a polarization maintaining optical fiber.

[0089] To sum up, the single-end distributed optical fiber vibration sensor system and the signal processing method provided by the application, the single-end distributed optical fiber vibration sensor system comprises a laser source, an electro-optical modulator, a to-be-measured optical fiber, a piezoelectric ceramic, a 1*2 coupler, a frequency mixer, an oscilloscope and a PC end; the laser source, the electro-optical modulator, the to-be-measured optical fiber, the piezoelectric ceramic, the 1*2 coupler, the frequency mixer, the oscilloscope and the PC end are connected in sequence; the laser source is used to emit laser, which is transmitted to the to-be-measured optical fiber after being loaded with a carrier frequency by the electro-optical modulator; the to-be-measured optical fiber changes the phase of the light conducted in the optical fiber after being affected by the vibration of the external environment, the piezoelectric ceramic generates a vibration signal to modulate the phase information of the to-be-measured optical fiber and then transmits the vibration signal to the 1*2 coupler; the 1*2 coupler is used to divide the phase information into signal light and local oscillator light and then transmit the signal light and the local oscillator light to the frequency mixer, the frequency mixer is used to coherently mix the local oscillator light and the signal light and demodulate the phase change; the oscilloscope is used to collect the phase change obtained by the frequency mixer, and the PC end is used to demodulate the phase change collected by the oscilloscope to obtain vibration information of an external environment. The single-end distributed optical fiber vibration sensor system has a large dynamic range, a long measurement distance, a low cost and a stable measurement, can well detect the vibration signal and can efficiently measure high-frequency vibration.

[0090] Of course, those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by a computer program instructing related hardware (such as a processor, a controller, etc.) to complete, and the program can be stored in a computer readable storage medium readable by a computer, and the program can include the processes of the above-mentioned method embodiments when executed. The computer readable storage medium can be a memory, a disk, an optical disk, etc.

[0091] It should be understood that the application of the application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the claims of the application.

Claims

1. A single-ended distributed optical fiber vibration sensor system, the distributed optical fiber vibration sensor system comprising: The laser source, the electro-optical modulator, the optical fiber to be measured, the piezoelectric ceramic, the 1*2 coupler, the frequency mixer, the oscilloscope and the PC end are sequentially connected. The laser source, the electro-optical modulator, the optical fiber to be measured, the piezoelectric ceramic, the 1*2 coupler, the frequency mixer, the oscilloscope and the PC end are sequentially connected. The laser source is used for emitting laser, which is transmitted to the optical fiber to be measured after being loaded with a carrier frequency by the electro-optical modulator. The optical fiber to be measured changes the phase of the light conducted in the optical fiber after being affected by the vibration of the external environment, and the piezoelectric ceramic generates a vibration signal to modulate the phase information of the optical fiber to be measured and then transmits the signal to the 1*2 coupler. The 1*2 coupler is used for dividing the phase information into signal light and local oscillator light and then transmitting the two kinds of light to the frequency mixer, respectively. The frequency mixer is used for coherently mixing the local oscillator light and the signal light and demodulating the phase change. The oscilloscope is used for collecting the phase change obtained by the frequency mixer, and the PC end is used for demodulating and processing the phase change collected by the oscilloscope to obtain the vibration information of the external environment. When the phase of the optical fiber to be measured changes due to the vibration, the time delay of the two-phase is solved by cross-correlation to determine the position of the external event. ； ； By analyzing the phase change and the strength and frequency information of the external event is obtained: ； ； wherein is the delay time at the d end, is the delay time at the f end, ω1is the operating frequency of the EOM at the d end, and ω2is the operating frequency of the EOM at the f end; When the light passes through the optical fiber, the phase of the light is the sum of different places, so the two paths are: ； ； wherein and represents the delayed fiber output light at the receiving end; respectively, and the phase difference is derived as: ； ； wherein By simple derivation, it can be obtained that: 。 2. The single-ended distributed optical fibre vibration sensor system of claim 1, wherein, The phase obtained by self-coherence is realized by time delay. The frequency mixer is a port 90° optical frequency mixer.

3. The single-ended distributed optical fibre vibration sensor system of claim 2, wherein, The port 90° optical frequency mixer is used for coherently mixing the local oscillator light and the signal light, so that the relative phase difference of the four output ports is 0°, 90°, 180° and 270°, respectively.

4. The single-ended distributed optical fibre vibration sensor system of claim 1, wherein, The port 90° optical frequency mixer comprises a quarter-wave plate, two half-wave plates and three polarization beam splitting prisms.

5. The single-ended distributed optical fibre vibration sensor system of claim 1, wherein, The optical fiber to be measured is composed of a single-mode optical fiber.

6. The single-ended distributed optical fibre vibration sensor system of claim 1, wherein, The wavelength of the local oscillator light is the same as that of the signal light.

7. The single-ended distributed optical fibre vibration sensor system of claim 6, wherein, The laser source is a semiconductor laser.

8. A signal processing method for a single-ended distributed fibre optic vibration sensor system according to any one of claims 1 to 7, characterised in that, The line width of the semiconductor laser is 50 kHz. The signal processing method comprises: The laser source emits laser, which is transmitted to the optical fiber to be measured after being loaded with a carrier frequency by the electro-optical modulator. The optical fiber to be measured changes the phase of the light conducted in the optical fiber after being affected by the vibration of the external environment, and the piezoelectric ceramic generates a vibration signal to modulate the phase information of the optical fiber to be measured and then transmits the signal to the 1*2 coupler. The 1*2 coupler is used for dividing the phase information into signal light and local oscillator light and then transmitting the two kinds of light to the frequency mixer, respectively. The frequency mixer is used for coherently mixing the local oscillator light and the signal light and demodulating the phase change. The oscilloscope is used for collecting the phase change obtained by the frequency mixer, and the PC end is used for demodulating and processing the phase change collected by the oscilloscope to obtain the vibration information of the external environment. ； ； By analyzing the phase changes and the strength and frequency information of the external event is obtained: ； ； wherein is the delay time at the d end, is the delay time at the f end, ω1is the operating frequency of the EOM at the d end, and ω2is the operating frequency of the EOM at the f end; When the phase of the optical fiber to be measured changes due to the vibration, the time delay of the two-phase is solved by cross-correlation to determine the position of the external event. When the light passes through the optical fiber, the phase of the light is the sum of different places, so the two paths are: The phase obtained by self-coherence is realized by time delay. ； ； wherein and represents the delayed fiber output light at the receiving end; respectively, and the phase difference is derived as: ； ； wherein By simple derivation, it can be obtained that: 。

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