A method for locating vibration signals in a transmission-type optical fiber sensing system

Abstract

The present invention proposes a method for locating vibration signals in a transmission-type optical fiber sensing system, which relates to the field of optical fiber sensing technology. A dual-wavelength ultra-stable laser is used to emit two continuous laser beams, which are combined by a first dense wavelength division multiplexer and then split into two beams by a first beam splitter. One beam is used as signal light, which is frequency-shifted by an optical fiber circulator and an acousto-optic modulator to enter an optical fiber link, and after reaching the far end, it is looped back by a second beam splitter and returned along the original optical fiber link. The other beam is used as reference light, which is combined and frequency-beaten with the signal light by a second dense wavelength division multiplexer and then split in wavelength, and photoelectrically detected by a photoelectric detector. A data acquisition system collects vibration disturbance signals of the two photoelectrically detected signal lights passing through a long optical fiber link, and the position of the vibration signal can be accurately located by cross-correlating the two signals.

Description

Technical Field

[0001] The present application relates to the technical field of vibration source positioning in a transmission-type optical fiber sensing system, and in particular to a method for positioning a vibration signal in a transmission-type optical fiber sensing system. Background Art

[0002] Fiber-optic sensing technology has rapidly developed alongside the advancement of optical fiber and fiber-optic communications. It uses light waves as a carrier and optical fiber as a medium to sense and transmit external signals. Since its inception, fiber-optic sensing technology has been widely used in various fields due to its high sensitivity, small size and light weight, flexible form factor, and strong resistance to electromagnetic interference and corrosion.

[0003] Fiber optic sensing encompasses two functions: sensing and transmitting external signals (the measured quantity). Perception refers to the fact that the external signal, in accordance with its changing patterns, causes changes in the physical characteristic parameters of the lightwave transmitted through the optical fiber, such as intensity (power), wavelength, frequency, phase, and polarization state. Measuring these changes in optical parameters is the process of "sensing" changes in the external signal. Transmission involves the optical fiber transmitting the lightwave modulated by the external signal to a photodetector for detection, extracting the external signal from the lightwave, and performing data processing as needed—this is known as demodulation. Therefore, fiber optic sensing technology encompasses both modulation (or loading) techniques for modulating the lightwave parameters in the optical fiber with the external signal (the measured quantity), and demodulation (or detection) techniques for extracting the external signal (the measured quantity) from the modulated lightwave. Depending on the changes in the physical characteristic parameters of the lightwave modulated by the external signal, lightwave modulation can be categorized as intensity modulation, wavelength modulation, phase modulation, and polarization modulation.

[0004] Reflective fiber optic sensing (such as DAS) uses Rayleigh scattered light as a detection signal. Due to the different arrival times of light signals reflected at different locations along the fiber optic link, it can simultaneously locate vibration signals at multiple points with high resolution. However, reflective fiber optic sensing is limited by the signal-to-noise ratio at long distances, and its sensing range typically does not exceed 50 kilometers. Transmission-type fiber optic sensing uses transmitted laser light as a detection signal and has a wide sensing range, typically reaching hundreds or even thousands of kilometers. However, the vibration signal detected by transmission-type fiber optic sensing is the accumulation of the entire fiber optic link, making it impossible to directly locate the vibration signal. The distances between major cities are typically hundreds of kilometers. Transmission-type fiber optic sensing is crucial for monitoring inter-city natural disasters such as earthquakes, debris flows, and landslides. Therefore, accurate positioning of vibration signals over a large range is crucial.

[0005] For large-scale transmission-type fiber optic sensing systems, two parallel optical fiber pairs are currently usually used as sensor devices. The detection laser is split into two and injected into two optical fibers respectively. The two optical fibers are directly connected at the far end to form a loop. The two laser beams return to the local area after each circulation. They then interfere with the local oscillator light for detection. The position of the vibration signal can be located based on the time difference between the two laser beams detecting the signal, combined with the total length of the optical fiber and the propagation speed of light in the optical fiber. However, in actual applications, optical fiber resources are scarce and expensive. It is more desirable to use only one optical fiber to realize the positioning of the vibration signal in the transmission-type fiber optic vibration sensing system. Summary of the Invention

[0006] Based on this, the present invention utilizes the dispersion of optical fiber and simultaneously injects two lasers of different wavelengths into a single optical fiber. Since lasers of different wavelengths have different transmission speeds in the optical fiber, the position of the vibration signal can be accurately located based on the time difference between the two wavelength lasers detecting the signal, combined with the speed difference of the two lasers in the optical fiber and the total length of the optical fiber.

[0007] A method for locating vibration signals in a transmission-type optical fiber sensing system comprises the following steps:

[0008] A dual-wavelength ultra-stable laser is used to emit two continuous laser beams with wavelengths of λ1 and λ2, which are combined by a first dense wavelength division multiplexer and then split into two beams by a first beam splitter;

[0009] One of the beams is used as the signal light, which is frequency-shifted by the fiber circulator and the acousto-optic modulator and enters the fiber link. After reaching the far end, it is looped back by the second beam splitter and returns along the original fiber link.

[0010] The other beam is used as a reference light. The reference light and the signal light are combined and beat by a second dense wavelength division multiplexer and then split in wavelength, and then photoelectrically detected by a photodetector.

[0011] The data acquisition system collects the vibration disturbance signals of two signal lights with wavelengths of λ1 and λ2 detected by photoelectric detection through the long optical fiber link, and calculates the position of the disturbance point by cross-correlating the two signals.

[0012] Furthermore, the two signals are cross-correlated by the following formula:

[0013]

[0014] in, is the disturbance signal recovered from the signal light with wavelength λ1 at time t, The disturbance signal is recovered from the signal light with a wavelength of λ2 at time t+τ. The time parameter τ corresponding to the maximum cross-correlation value is the arrival time difference ΔT of the two signals. The position of the disturbance point is calculated based on ΔT.

[0015] Furthermore, let the total length of the long optical fiber link be L, the distance between the light source and the disturbance point be L1, the distance from the disturbance point to the detector through the remote loop be L2+L, the speed of the detection light with a wavelength of λ1 be c1, and the time it takes for the light to reach the photodetector from the disturbance point be t1, and the speed of the detection light with a wavelength of λ2 be c2, and the time it takes for the light to reach the photodetector from the disturbance point be t2;

[0016] The time difference ΔT between the self-disturbance points of the two detection light with different wavelengths reaching the photodetector through the far-end loop is:

[0017]

[0018]

[0019] Where C is a constant, we can get:

[0020]

[0021] The distance between the light source and the disturbance point:

[0022] L1=2L-L2;

[0023] This allows the specific location of the disturbance point in the link to be located.

[0024] Furthermore, the distance L2+L from the disturbance point to the photodetector through the far-end loop is:

[0025] L2+L=c1t1=c2t2;

[0026] From this we can conclude that:

[0027] Where C is a constant;

[0028]

[0029] Compared with the prior art, the present invention has the following beneficial technical effects:

[0030] The present invention utilizes the dispersion of optical fibers and simultaneously injects two lasers of different wavelengths into a single optical fiber. Since lasers of different wavelengths have different transmission speeds in the optical fiber, the position of the vibration signal can be accurately located based on the time difference between the two wavelength lasers detecting the signal, combined with the speed difference of the two lasers in the optical fiber and the total length of the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the structure principle of the optical fiber sensing system of the present invention;

[0032] Figure 2 Schematic diagram of the structure of the optical fiber sensing system according to the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0034] 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 does not constitute a limitation on the signal transmission direction, connection sequence and size, dimension and shape of the components or structures.

[0035] like Figure 1 FIG. 1 is a schematic diagram showing the structural principle of the optical fiber sensing system of the present invention.

[0036] Assume the total length of the link is L, the distance between the light source and the perturbation point is L1, and the distance between the perturbation point and the detector is L2. The light source emits two signal lights with wavelengths λ1 and λ2. The detection light with wavelength λ1 has a speed of c1 and arrives at the detector from the perturbation point in t1. The detection light with wavelength λ2 has a speed of c2 and arrives at the detector from the perturbation point in t2.

[0037] The distance L2 between the disturbance point and the detector:

[0038] L2=c1t1=c2t2;

[0039] From this we can conclude that:

[0040]

[0041] Where C is a constant.

[0042]

[0043] The time difference ΔT between the self-disturbance points of the two detection light with different wavelengths reaching the detector is:

[0044]

[0045]

[0046] From this we can conclude that:

[0047]

[0048] The distance L1 between the light source and the disturbance point:

[0049] L1=L-L2;

[0050] This can help locate the specific location of the disturbance point in the link.

[0051] like Figure 2 FIG. 1 is a schematic diagram of the structure of an optical fiber sensing system according to a preferred embodiment of the present invention.

[0052] In a preferred embodiment, a dual-wavelength PDH-locked ultrastable laser FP emits two continuous laser beams with wavelengths of 1520 nm and 1620 nm. These beams are combined by a first dense wavelength division multiplexer (DWDM1) and then split into two beams by a first beam splitter (BS1). One beam serves as the signal beam, which is frequency-shifted by a fiber circulator (C) and an acousto-optic modulator (AOM) into the optical fiber link. After reaching the remote end, it is combined and looped back by BS2 and returned along the original optical fiber link. The other beam serves as the reference beam. After the reference beam and the 1520 nm and 1620 nm laser beams in the signal beam are combined and beat by a second dense wavelength division multiplexer (DWDM2), the reference beam is split in wavelength. The reference beam is then photoelectrically detected by a first photodetector (PD1) and a second photodetector (PD2), respectively. Finally, the data acquisition system acquires the vibration disturbance signals of the 1520 nm and 1620 nm signal beams passing through the long optical fiber link. The two signals are then cross-correlated to obtain the following:

[0053]

[0054] in, is the disturbance signal recovered from the 1520nm signal light at time t, is the disturbance signal recovered from the 1620nm signal light at time t+τ. The time parameter τ corresponding to the maximum cross-correlation value is the arrival time difference ΔT of the two signals. The position of the disturbance point can be calculated based on ΔT.

[0055] Assume the total length of the link is L, the distance between the light source and the perturbation point is L1, and the distance from the perturbation point to the detector via the remote loopback is L2 + L. The light source emits two signal lights, one at 1520 nm and the other at 1620 nm. The 1520 nm probe light has a speed of c1 and takes t1 to reach the detector from the perturbation point. The 1620 nm probe light has a speed of c2 and takes t2 to reach the detector from the perturbation point.

[0056] The distance from the disturbance point to the detector through the far loop:

[0057] L2+L=c1t1=c2t2;

[0058] From this we can conclude that:

[0059] Where C is a constant;

[0060]

[0061] The time difference ΔT between the self-disturbance points of the two detection light with different wavelengths reaching the detector through the far-end loop is:

[0062]

[0063]

[0064] From this we can conclude that:

[0065]

[0066] The distance between the light source and the disturbance point:

[0067] L1=2L-L2;

[0068] This can help locate the specific location of the disturbance point in the link.

[0069] The present invention utilizes the dispersion of optical fibers and simultaneously injects two lasers of different wavelengths into a single optical fiber. Since lasers of different wavelengths have different transmission speeds in the optical fiber, the position of the vibration signal can be accurately located based on the time difference between the two wavelength lasers detecting the signal, combined with the speed difference of the two lasers in the optical fiber and the total length of the optical fiber.

[0070] 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 can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted via the computer-readable storage medium. The computer-readable storage medium can 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 integrations. The available medium can 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 drive (SSD)).

[0071] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for locating vibration signals in a transmission-type optical fiber sensing system, characterized in that: The steps include: A dual-wavelength ultra-stable laser is used to emit two continuous laser beams with wavelengths of λ1 and λ2, which are combined by a first dense wavelength division multiplexer and then split into two beams by a first beam splitter; One of the beams is used as the signal light, which is frequency-shifted by the fiber circulator and the acousto-optic modulator and enters the fiber link. After reaching the far end, it is looped back by the second beam splitter and returns along the original fiber link. The other beam is used as a reference light. The reference light and the signal light are combined and beat by a second dense wavelength division multiplexer and then split in wavelength, and then photoelectrically detected by a photodetector. The data acquisition system collects the vibration disturbance signals of two signal lights with wavelengths of λ1 and λ2 detected by the photoelectric detection through the long optical fiber link, and calculates the position of the disturbance point by cross-correlating the two signals; Cross-correlate the two signals using the following formula: ； in, is the disturbance signal recovered from the signal light with wavelength λ1 at time t, for The time parameter corresponding to the maximum value of the cross-correlation is the disturbance signal restored by the signal light with a wavelength of λ2 at the moment The arrival time difference between the two signals ,according to Calculate the position of the disturbance point; Assume that the total length of the long optical fiber link is L, the distance between the light source and the disturbance point is L1, the distance from the disturbance point to the detector through the remote loop is L2+L, the speed of the detection light with a wavelength of λ1 is c1, and the time it takes for the light to reach the photodetector from the disturbance point is t1, and the speed of the detection light with a wavelength of λ2 is c2, and the time it takes for the light to reach the photodetector from the disturbance point is t2; The time difference between the self-disturbance points of two different wavelengths of detection light reaching the photodetector through the far-end loop : ； ； Where C is a constant, we can get: ； The distance between the light source and the disturbance point: ； This will locate the specific location of the disturbance point in the link; The distance L2+L from the disturbance point to the photodetector through the far-end loop is: ； From this we can conclude that: , where C is a constant; 。

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