A method for optical frequency precision measurement of optical fiber vibration sensing for simultaneous identification of multiple disturbances

Abstract

The invention proposes an optical frequency precision measurement optical fiber vibration sensing method for simultaneously identifying multi-point disturbances, which relates to the technical field of optical fiber vibration sensing. A plurality of relay units are arranged in a sensing system of an optical fiber link, and the plurality of relay units divide the sensing system into a plurality of sensing subsystems. Inside each relay unit, an optical signal is frequency-shifted by an acousto-optic modulator, and the frequency-shifted optical signal is divided into two beams by a beam splitter, one optical signal continues to be transmitted forward along the optical fiber link, and the other optical signal is looped back and transmitted backward along the optical fiber link through an isolator and a beam combiner. Each relay unit transmits the backward-transmitted optical signal back to a source end to beat with a light source, extracts corresponding phase variation amounts for optical signals with different carrier frequencies, and simultaneously identifies the positions of a plurality of disturbance points along the optical fiber link in combination with the cross-correlation calculation results of detection signals at both ends of the optical fiber link.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber vibration sensing technology, and in particular to an optical fiber vibration sensing method for simultaneously identifying multi-point disturbances based on TF-QKD. Background Art

[0002] Fiber optic vibration sensing technology uses optical fiber as a signal transmission medium and sensing element, and uses the characteristic changes of light in the optical fiber (such as phase, polarization, etc.) to sense external vibration disturbances along the optical fiber link. Compared with traditional point-type vibration monitors, fiber optic vibration sensing technology has high-density, high-resolution vibration monitoring capabilities, and has many advantages such as real-time, permanent and low-cost. This technology provides a revolutionary technical means for earthquake monitoring and underground space detection. The widely used fiber optic sensing technology at present is distributed optical fiber sensing (DAS). DAS uses the characteristic changes of backscattered light signals for sensing. However, due to the limitation of the system signal-to-noise ratio, its sensing distance is usually no more than 100 kilometers. In contrast, the frequency metrology fiber optic vibration sensing technology developed in recent years uses the characteristic changes of transmitted light signals for vibration disturbance sensing. Its sensing distance can easily exceed hundreds of kilometers, with the advantages of wide coverage, low monitoring cost and high real-time performance.

[0003] Optical frequency precision measurement fiber optic vibration sensing uses the phase coherent evolution control technology of long-distance light fields to analyze the acoustic signals caused by external vibrations along the optical cable in a large range and in quasi-real time. The entire system is similar to using two large-scale unequal-arm optical interferometers, two long-distance, high-coherence lasers, which keep part of the laser locally as local oscillator light and send the other part as signal light to the other end for interference. Because external disturbances such as sound and temperature fluctuations along the optical fiber link will cause strain in the optical fiber link, the characteristics of the transmitted laser (such as phase, polarization, etc.) will change. The changed signal light is transmitted to both ends to interfere with the local oscillator light. The vibration disturbance along the optical fiber link can be interpreted based on the relative phase change recovered by interference. However, since the interpreted signal is the sum of the disturbance information accumulated along the optical fiber link, that is, the spatial resolution of the sensor is the entire optical fiber link, it is difficult to simultaneously identify multi-point disturbance signals distributed along the optical fiber. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes an optical frequency precision measurement optical fiber vibration sensing method for simultaneously identifying multi-point disturbances, comprising the following steps:

[0005] A plurality of relay units are arranged in the sensing system of the optical fiber link, wherein the plurality of relay units divide the sensing system into a plurality of sensing subsystems;

[0006] Inside each relay unit, the optical signal is frequency-shifted by an acousto-optic modulator. The frequency-shifted optical signal is then split into two beams by a beam splitter. One beam of optical signal continues to be transmitted forward along the optical fiber link, while the other beam of optical signal is looped back and transmitted backward along the optical fiber link through an isolator and a beam combiner.

[0007] Each relay unit transmits the reverse-transmitted optical signal back to the source end to beat the light source, extracts the corresponding phase change of the optical signals with different carrier frequencies, combines the cross-correlation calculation results of the detection signals at both ends of the optical fiber link, and simultaneously identifies the locations of multiple disturbance points along the optical fiber link.

[0008] Furthermore, is the carrier frequency of the optical signal emitted by the light source; are the frequency shifts of the acousto-optic modulators in the 1st, 2nd, ..., Nth relay units respectively; are the phase changes caused by the jitter of the optical fiber links of the 1st, 2nd, ..., Nth sensor subsystems respectively; the phase change of the forward transmitted optical signal after passing through the Nth relay unit to the other end is ;

[0009] The optical signal transmitted in the reverse direction is frequency-shifted again by the acousto-optic modulator in the Nth relay unit. The carrier frequency after frequency shift is , the phase is .

[0010] Furthermore, when the sensing system of the optical fiber link is divided into two sensing subsystems through a relay unit to achieve simultaneous positioning of two-point disturbances, when the optical signal returns in the relay unit, the two source ends simultaneously receive the carrier frequency and The optical signal, where the carrier frequency received by the two source ends is The phase changes of the optical signals are respectively given by and Indicates that the carrier frequency is The phase change of the optical signal is .

[0011] Furthermore, the carrier frequency received by the two source ends at the same time is and The optical signal is cross-correlated:

[0012] ;

[0013] ;

[0014] in, and is the carrier frequency received by the two source ends The optical signal is used to recover the phase disturbance signal. and The carrier frequency received by the two source ends is The phase disturbance signal recovered from the optical signal, the maximum value of the cross-correlation corresponds to and They are the time differences between the optical signals of two frequencies arriving at the source end of each sensing subsystem.

[0015] Furthermore, both source ends include: a laser light source, a circulator, a beam splitter / combiner and a photoelectric detector. The photoelectric detector uses part of the light signal emitted by the laser light source as reference light. The reference light and the detection signal reflected back from the circulator are combined by the beam splitter / combiner and converted into an electrical signal by the photoelectric detector.

[0016] Furthermore, the speeds at which the disturbance signal reaches the two source ends are and , the distance difference between the two source ends of the disturbance distance fiber is:

[0017] ;

[0018] Among them, the time difference between the optical signal reaching the two ends of the optical fiber link of each sensing subsystem is ,

[0019] According to the total length of each optical fiber link, the precise location of the disturbance source can be obtained.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] Since the traditional optical frequency precision measurement type fiber optic vibration sensing technology is based on the phase jitter detected at the end of the entire optical fiber for sensing, the phase change information caused by multi-point disturbances will gradually accumulate and superimpose as the signal is transmitted in the optical fiber link. Therefore, the spatial resolution of the sensing is the entire optical fiber link, and it is impossible to effectively detect vibration signals at multiple locations along the optical fiber link at the same time. The present invention decomposes the optical fiber link used for sensing into segments to form multiple sensing units connected in series, thereby improving the spatial resolution of the sensing and realizing the simultaneous identification of "multi-point" vibration disturbances.

[0022] The spatial resolution of conventional technology is the entire optical fiber link, which is usually several hundred kilometers. The present invention can achieve a spatial resolution better than 50 kilometers.

[0023] It is difficult for traditional technology to identify "multi-point" vibration sources at the same time. The present invention divides the sensing unit and can detect "multi-point" disturbance information at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0025] Figure 1 It is a structural schematic diagram of an optical frequency precision measurement optical fiber vibration sensing system in the prior art;

[0026] Figure 2 This is a schematic diagram of the optical frequency precision measurement optical fiber vibration sensor for simultaneously identifying multiple disturbances of the present invention;

[0027] Figure 3 This is the schematic diagram of multi-point vibration signal decomposition;

[0028] Figure 4 Schematic diagram for simultaneous identification of two-point vibration signals. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0030] In the drawings of the specific embodiments of the present invention, in order to better and more clearly describe the working principles of the various components in the system, the connection relationship of the various parts in the device is shown, which only clearly distinguishes the relative position relationship between the various components, and cannot constitute a limitation on the signal transmission direction, connection sequence and size, dimensions and shape of the components or structures.

[0031] like Figure 1 As shown, it is a schematic diagram of the structure of an optical frequency precision measurement optical fiber vibration sensing system in the prior art.

[0032] The optical frequency precision measurement optical fiber vibration sensing system consists of two optical fiber links. One link is used to synchronize the frequency / phase of the optical signals emitted by the two light sources Laser1 and Laser2, as well as the time of the two devices. The other optical fiber is used as a sensing system to sense vibration disturbances along the link. A relay station is set up every 70 to 80 kilometers, and a relay unit is inserted for signal relay.

[0033] The sensing system includes: a light source locking unit, an optical fiber, an optical fiber link, a beam splitter, a circulator, a photoelectric detector PD, a relay unit and a data processing and vibration waveform interpretation unit.

[0034] In order to overcome the challenge that the optical frequency precision measurement fiber optic vibration sensing system in the prior art is difficult to simultaneously identify multi-point disturbance signals, the present invention segmentally decomposes the optical fiber link used as the sensing system to form multiple series-connected sensing subsystems from a whole sensing system, thereby improving the disturbance recognition rate of the sensing space and realizing the simultaneous recognition of "multi-point" vibration disturbances.

[0035] like Figure 2 The figure shows the principle diagram of the optical frequency precision measurement optical fiber vibration sensor for simultaneously identifying multiple disturbances of the present invention. Both source ends (Alice and Bob) include: a laser light source, a circulator, a beam splitter / combiner and a photoelectric detector.

[0036] Figure 2 In the figure, Laser1 and Laser2 are laser light sources; bi-EDFA is a bidirectional erbium-doped fiber amplifier; AOM is an acousto-optic modulator; ISO is an isolator; BS is a beam splitter / combiner; CIR is a circulator; and PD is a photodetector.

[0037] In each relay unit of the sensing optical fiber link, the optical signal is first amplified by a bidirectional erbium-doped fiber amplifier (bi-EDFA) and then frequency-shifted by an acousto-optic modulator (AOM). The frequency shift of the optical signal after passing through the Nth relay unit is Then the optical signal is split into two beams by the beam splitter, one beam continues to be transmitted forward along the link, and the other beam is looped back through the isolator ISO and the beam combiner BS and transmitted backward along the link. The photodetector PD uses part of the optical signal emitted by the laser as reference light and the detection signal reflected back by the circulator CIR to convert it into an electrical signal.

[0038] like Figure 3 As shown in the figure, it is a schematic diagram of the decomposition principle of the "multi-point" vibration signal, showing the frequency shift effect of the acousto-optic modulator AOM, where: is the carrier frequency of the optical signal emitted by the light source; are the frequency shifts of the acousto-optic modulators at the 1st, 2nd, ..., Nth relay units respectively; are the phase changes caused by the jitter of the optical fiber link between relay units 1 to 2, 2 to 3, ..., and N-1 to N respectively; then the optical signal transmitted backward by the N-th relay unit will pass through the N-1, N-2 and N-3 relay units twice. 1 The AOM of the relay unit shifts the frequency, so the carrier frequency is ; Since the optical fiber passes through the transmitter to the Nth relay unit twice, the phase of the optical signal transmitted backward after passing through the Nth relay unit is .

[0039] Correspondingly, the phase change of the forward transmission optical signal after passing through N relay units to the other end is .

[0040] Figure 3 (a) shows the frequency shift effect of the backward and forward transmitted optical signals of each relay unit. The laser transmitted backward from each relay unit to the source end and the laser sent from the other end will experience different frequency shifts. Therefore, after beating with the local laser, the optical signals returned from each relay unit and the optical signals sent from the other end can be effectively identified based on the carrier frequencies of different optical signals. Then, the phase jitter of each optical signal is extracted separately, and all vibration disturbances detected based on the backward returned optical signal and the optical signal transmitted from the other end can be obtained.

[0041] Figure 3 (b) in the figure shows the phase change effect of the back-transmitted and forward-transmitted optical signals of each relay unit. By combining and decomposing each disturbance signal based on the back-transmitted optical signal detection with the disturbance signal based on the transmitted optical signal detection, the disturbance signal between any two relay units can be obtained.

[0042] Through the above process, multiple relay units are inserted into the sensing system of the entire phase-locked optical fiber link. The multiple relay units divide the sensing system into multiple sensing subsystems with shorter lengths, thereby converting the disturbance recognition rate of the entire sensing space from the entire optical fiber link to the disturbance recognition rate of the space between two relay units, thereby improving the disturbance recognition accuracy.

[0043] In addition, when signal detection is performed at Alice and Bob's ends at the same time, and the detection results of each sensor unit at Alice and Bob's ends are cross-correlated and analyzed, the distance between the vibration disturbance point and Alice and Bob's ends can be accurately calculated based on the time difference between the disturbance signal of the sensor unit reaching Alice and Bob's ends, as well as the optical fiber length of the sensor unit and the propagation speed of light in the optical fiber, thereby determining the specific position where the disturbance occurs in the sensor unit.

[0044] Therefore, by segmenting and decomposing the sensing unit of the TF-QKD phase-locked optical fiber link, part of the optical signal is transmitted back to the source end at each relay unit to beat the light source for phase jitter detection, and all the detection signals are decomposed in the frequency domain. Combined with the results of the cross-correlation analysis of the detection signals on both sides, "multi-point" vibration disturbances along the optical fiber link can be identified simultaneously.

[0045] In one embodiment, if Figure 4As shown in the figure, a relay unit is set in the sensing optical fiber link, and the sensing system of the entire optical fiber link is divided into two sensing subsystems through a relay unit to achieve simultaneous positioning of the "two points" of vibration disturbance. When the optical signal returns from the relay unit, Alice and Bob can receive the carrier frequency at the same time. and The optical carrier frequency signal, where the carrier frequency The phase disturbance information carried by the optical signal is the phase change of the local optical fiber link from the relay unit to the two detection ends, which is twice the phase change. and Indicates that the carrier frequency is The phase disturbance information carried by the optical carrier signal is the phase change of the local to the opposite end optical fiber link, which is given by In this way, the entire optical fiber link (the phase change is ) and each small segment of optical fiber link (the phase changes are and ) of the disturbance information.

[0046] Alice sets the carrier frequency and The phase disturbance signals of the segmented optical fiber are calculated from the optical carrier signal. and , accordingly, the carrier frequency is set at Bob's end and The phase disturbance signals of the segmented optical fiber are calculated from the optical carrier signal. and .

[0047] Perform cross-correlation operation on two signals:

[0048] ;

[0049] ;

[0050] in, and The wavelength is the carrier frequency is The phase disturbance signal of the signal light is recovered, and The carrier frequency is The phase disturbance signal recovered from the signal light, the time parameter corresponding to the maximum value of the cross-correlation and It is the time difference between the two signals arriving at the two ends of the optical fiber link of each sensing subsystem (the two optical fibers are composed of and According to the total length of each fiber link (The two optical fibers are respectively and ), and the speed of light in the optical fiber , the precise positions of the two disturbance points in each sensing subsystem can be calculated.

[0051] For example, in the first section of optical fiber, the speeds at which the disturbance signal reaches the two source ends of the optical fiber can be and , then the distance difference between the two source ends of the disturbance distance fiber is: , according to the total length of the first optical fiber , the precise location of the disturbance source can be obtained.

[0052] In the second section of optical fiber, the distance difference between the two ends of the disturbance distance optical fiber can be obtained by the same logic:

[0053] ;

[0054] According to the total length of the second optical fiber , the precise location of the disturbance source can be obtained.

[0055] Therefore, by segmenting and decomposing the sensing optical fiber link, part of the optical signal is transmitted back to the local site at each site for phase jitter detection with the light source beat frequency, and all the detection signals are decomposed in the frequency domain. Combined with the results of the cross-correlation analysis of the detection signals on both sides, "multi-point" vibration disturbances along the optical fiber link can be identified simultaneously.

[0056] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted through the computer-readable storage medium. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or a data center that includes one or more available media integrated. The available medium may be a magnetic medium, (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid state disk (SSD)), etc.

[0057] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for optical frequency precision measurement optical fiber vibration sensing for simultaneously identifying multi-point disturbances, characterized in that: The steps include: Setting at least one relay unit in the sensing system of the optical fiber link, wherein the at least one relay unit divides the sensing system into a plurality of sensing subsystems; Both source ends include: a laser light source, a circulator, a beam splitter / combiner and a photoelectric detector. The photoelectric detector uses part of the optical signal emitted by the laser light source as reference light. The reference light and the detection signal reflected by the circulator are combined by the beam splitter / combiner and converted into an electrical signal by the photoelectric detector. Inside each relay unit, the optical signal is frequency-shifted by an acousto-optic modulator. The frequency-shifted optical signal is then split into two beams by a beam splitter. One beam of optical signal continues to be transmitted forward along the optical fiber link, while the other beam of optical signal is looped back and transmitted backward along the optical fiber link through an isolator and a beam combiner. Each relay unit transmits the reversely transmitted optical signal back to the source end to beat the light source, extracts the corresponding phase change of the optical signal with different carrier frequencies, combines the cross-correlation calculation results of the detection signals at both ends of the optical fiber link, and simultaneously identifies the positions of multiple disturbance points along the optical fiber link; set up is the carrier frequency of the optical signal emitted by the light source; are the frequency shifts of the acousto-optic modulators in the 1st, 2nd, ..., Nth relay units respectively; are the phase changes caused by the jitter of the optical fiber links of the 1st, 2nd, ..., Nth sensor subsystems respectively; the phase change of the forward transmitted optical signal after passing through the Nth relay unit to the other end is ; The optical signal transmitted in the reverse direction is frequency-shifted again by the acousto-optic modulator in the Nth relay unit. The carrier frequency after frequency shift is , the phase is ; When the sensing system of the optical fiber link is divided into two sensing subsystems through a relay unit to achieve simultaneous positioning of two-point disturbances, when the optical signal returns in the relay unit, the two source ends simultaneously receive the carrier frequency and The optical signal, where the carrier frequency received by the two source ends is The phase changes of the optical signals are respectively given by and Indicates that the carrier frequency is The phase change of the optical signal is ; The carrier frequency received by both sources at the same time is and The optical signal is cross-correlated: ； ； in, and is the carrier frequency received by the two source ends The optical signal is used to recover the phase disturbance signal. and The carrier frequency received by the two source ends is The phase disturbance signal recovered from the optical signal, the maximum value of the cross-correlation corresponds to and are the time differences between the optical signals of two frequencies arriving at the source end of each sensing subsystem; The speeds at which the disturbance signal reaches the two source ends are and , the distance difference between the two source ends of the disturbance distance fiber is: ； Among them, the time difference between the optical signal reaching the two ends of the optical fiber link of each sensing subsystem is , According to the total length of each optical fiber link, the precise location of the disturbance source can be obtained.

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