A time-frequency distribution based distributed optical fiber vibration sensing method and system

Abstract

The application provides a kind of distributed optical fiber vibration sensing method and system based on time-frequency distribution, related to high-precision time-frequency synchronization and optical fiber sensing multi-network fusion field, time-frequency reference network distributes the ultra-stable optical frequency signal of source end node and time synchronization signal to all receiving nodes through time-frequency distribution link;And ensure the synchronization of the optical signal frequency, phase and time of all nodes;Vibration sensing network sends the optical signal of adjacent node to the opposite end through sensing optical fiber link to beat frequency detection, and obtains the vibration disturbance signal along the sensing optical fiber link, determines the position of vibration disturbance, breaks through the bottleneck of traditional forward transmission distributed optical fiber sensing system in monitoring mode and spatial resolution.

Description

Technical Field

[0001] The present invention proposes a distributed optical fiber vibration sensing method and system based on time-frequency distribution, which relates to the technical field of high-precision time-frequency synchronization and optical fiber sensing multi-network fusion. Background Art

[0002] Fiber optic sensing technology is gaining increasing attention due to its significant advantages over traditional electrical sensors. These sensors offer exceptional sensitivity, significantly improving measurement accuracy, while also exhibiting excellent resistance to electromagnetic interference, ensuring stable measurement performance even in high-noise environments. Furthermore, fiber optic sensors are able to operate stably under extreme temperature conditions, enabling them to function effectively in harsh environments where electrical sensors would otherwise struggle. When integrated into optical cables as a distributed system, fiber optic sensors can efficiently collect and integrate data from multiple monitoring points. Properly configured, fiber optic sensors can monitor key parameters such as vibration, pressure, and temperature in real time, providing crucial data on dynamic geological changes and marine activity. Consequently, fiber optic sensing technology is widely regarded as a highly effective solution for monitoring high-risk and remote environments.

[0003] Traditional distributed fiber-optic vibration sensing technologies, such as DAS (distributed acoustic sensing) and DVS (distributed vibration sensing), based on backscattered light detection, achieve monitoring by capturing Rayleigh backscattering signals in optical fibers. However, their sensing distance is limited by the exponential decay of scattered signal intensity with distance, and their effective coverage typically does not exceed 50 kilometers (typical value at 1550nm). Recent advances in forward-propagating distributed fiber-optic vibration sensing technology have overcome this bottleneck. For example, the phase-sensitive forward-propagating optical distributed vibration sensing system (POD) extends the sensing distance to hundreds to thousands of kilometers by detecting phase perturbations in the forward-propagating optical signal. This has been applied to transoceanic submarine cable monitoring, providing innovative solutions for scenarios such as global-scale earthquake monitoring and ultra-long-haul oil and gas pipeline safety monitoring.

[0004] However, conventional forward-distributed fiber-optic vibration sensing technology can only monitor a single line along the fiber, failing to achieve large-scale, surface-level monitoring. Furthermore, because the transmitted signal reflects the cumulative phase perturbations along the entire fiber link, the spatial resolution is proportional to the total fiber length, making it incapable of meeting high-precision monitoring requirements. Summary of the Invention

[0005] The present invention proposes a distributed optical fiber vibration sensing system based on time-frequency distribution, comprising: a time-frequency reference network and a vibration sensing network;

[0006] The time-frequency reference network distributes the ultra-stable optical frequency signal and time synchronization signal of the source node to all receiving nodes through the time-frequency distribution link; and ensures the synchronization of the optical signal frequency, phase and time of all nodes;

[0007] The vibration sensing network sends the optical signals of adjacent nodes to the other end through the sensing optical fiber link for beat frequency detection, and obtains the vibration disturbance signal along the sensing optical fiber link to determine the location of the vibration disturbance.

[0008] In a preferred embodiment, the source node uses a highly coherent ultra-stable laser as a light source and utilizes ultra-stable optical frequency distribution technology. The optical signal is stably distributed from the source node to each receiving node through a time-frequency distribution link; each receiving node uses optical phase-locking technology to perform local ultra-stable optical frequency regeneration on the optical signal.

[0009] In a preferred embodiment, after ultra-stable optical frequency regeneration is achieved in all receiving nodes, the optical signals they output are transmitted to adjacent nodes through a sensing fiber link, and at each adjacent node, heterodyne interferometry technology is used for detection. By analyzing the phase fluctuations of the interference signal, the time-frequency characteristics of the disturbance source are interpreted.

[0010] In a preferred embodiment, the time-frequency reference network utilizes wavelength division multiplexing technology to load the time synchronization signal onto an optical carrier at the source node, and utilizes a dense wavelength division multiplexer to multiplex the optical carrier with an ultra-stable optical frequency signal and transmit it to the receiving node via a time-frequency distribution link. High-precision two-way time comparison is performed between the source node and the receiving node, and time synchronization between the nodes is achieved based on the received optical carrier.

[0011] In a preferred embodiment, the receiving node that has been synchronized with the time base of the source node is used as a new secondary time source, and the time synchronization signal is further distributed to the downstream receiving node through a dense wavelength division multiplexer; the downstream receiving node performs a two-way time comparison with the receiving node that serves as the new secondary time source to achieve time synchronization between the two nodes, and ultimately achieve high-precision synchronization of multiple nodes based on the same time base.

[0012] In a preferred embodiment, in the source node, an ultra-stable laser source distributes the ultra-stable optical frequency signal to the next node B through an unequal-arm Michelson fiber interferometer. The short arm is connected to a Faraday reflector, which serves as a local oscillator light source. The long arm is composed of a time-frequency distribution link between the two nodes, which transmits the optical signal to node B. When the signal reaches node B, it is first amplified by a bidirectional fiber amplifier and then frequency-shifted by an acousto-optic modulator to distinguish the parasitic reflection noise of the fiber link. Then, part of the signal is reflected back to the source node through a semi-transparent and semi-reflective Faraday reflector for beat frequency detection together with the local oscillator light.

[0013] In a preferred embodiment, a servo controller drives a local acousto-optic modulator to adjust the carrier frequency in real time to compensate for phase noise in the time-frequency distribution link, ensuring that the signal received by the remote node B is consistent with the optical signal of the source node in frequency and phase. The optical signal of node B is then used as an optical frequency reference signal, and the laser is locked to the optical frequency reference signal using optical phase-locked loop technology to achieve high-precision regeneration of the local signal of node B. The regenerated optical signal will then be distributed to other nodes.

[0014] The present invention also proposes a distributed optical fiber vibration sensing method based on time-frequency distribution, which is implemented by the above-mentioned distributed optical fiber vibration sensing system based on time-frequency distribution, including:

[0015] Distribute the ultra-stable optical frequency signal and time synchronization signal of the source node to all receiving nodes through the time-frequency distribution link, ensuring the synchronization of the optical signal frequency, phase and time of all nodes;

[0016] The optical signals of the adjacent nodes are sent to the other end through the sensing fiber link for beat frequency detection;

[0017] The vibration disturbance signal along the sensing optical fiber link is obtained to determine the location of the vibration disturbance.

[0018] In a preferred embodiment, when the optical fiber is not disturbed by the outside world, the phase difference detected on both sides is 、 They are:

[0019] ;

[0020] ;

[0021] in, and is the phase of the laser at both nodes; Represents the phase difference of optical fiber transmission;

[0022] When the fiber is at a distance from node A At the outside world The phase difference between the two detections when the disturbance 、 They are:

[0023] ;

[0024] ;

[0025] Where T is the transmission time of the optical signal from the disturbance to node A, The speed at which light signals are transmitted in optical fibers. is the coupling coefficient between the optical fiber and the noise signal, and L is the total length of the optical fiber between nodes A and B.

[0026] Compared with the prior art, the present invention has the following beneficial technical effects:

[0027] The present invention achieves high-precision coherent optical frequency / phase signal distribution through a frequency distribution link, supports any topological network structure, and uses a sensor array to sense vibration disturbances along the network topology. It can cover a detection range of thousands or even tens of thousands of kilometers, and the sensor array has a spatial resolution of node spacing. Through signal cross-correlation technology, it can achieve precise positioning of kilometer-level vibration sources. Compared with the traditional single-point detection mode, the present invention expands the detection method from linear detection to planar array detection, significantly improving the performance and flexibility of the system, and breaking through the bottleneck of traditional forward transmission distributed fiber optic sensing systems in monitoring methods and spatial resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 Schematic diagram of the distributed optical fiber vibration sensor array with forward transmission architecture;

[0030] Figure 2 This is the principle diagram of two-node forward-fractionated optical fiber vibration sensing. DETAILED DESCRIPTION

[0031] 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.

[0032] 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 structural size, size and shape of each part within the component or structure.

[0033] Example 1

[0034] The distributed optical fiber vibration sensing system based on time-frequency distribution includes: a time-frequency reference network and a vibration sensing network.

[0035] The time-frequency reference network is used to establish a high-precision coherent optical signal network and a unified system time reference. Figure 1 As shown, the time signal from the source node (node ​​A) and the ultra-stable optical frequency signal emitted by the ultra-stable light source are distributed to all receiving nodes (nodes B, C, D, E, N, etc.) through a high-precision time-frequency distribution link. Fiber Doppler noise suppression technology is used to compensate for the coherent evolution of the ultra-stable optical frequency signal during transmission, while bidirectional time comparison technology is used to suppress time drift during transmission.

[0036] All nodes are synchronized according to the received time signal and lock the local seed laser through an optical phase-locked loop to complete the regeneration of the ultra-stable optical frequency signal, ensuring the precise synchronization of the optical signal frequency, phase and system time of all nodes.

[0037] The vibration sensing network, a sensor array, is responsible for detecting vibration disturbances within the link. In the coherent optical signal network, every two adjacent nodes transmit optical signals to the other end via a sensing fiber link for beat frequency detection. This detects the vibration disturbance signals along the sensing fiber link. Cross-correlation analysis of the signals from adjacent nodes can pinpoint the location of the vibration disturbance.

[0038] An ultra-stable light source serves as the system's optical frequency reference, transmitting a highly stable, ultra-stable optical frequency signal as a coherent optical signal to each node via a time-frequency distribution link, providing a synchronized frequency and phase reference for remote nodes. The terminal node utilizes optical phase-locked loop technology to phase-lock the local seed laser to the received coherent optical signal, achieving high-fidelity regeneration of the source's ultra-stable optical frequency signal.

[0039] The distributed fiber-optic vibration sensing system based on time-frequency distribution (TFD) uses phase-coherent transmission and regeneration technology to establish a traceable optical frequency reference system within a distributed network. This ensures that each node accurately replicates the ultrastable frequency characteristics of the source and maintains phase synchronization. Furthermore, based on dense wavelength division multiplexing (DWDM), the TFD link transmits time synchronization signals to each node, providing a time reference for remote nodes.

[0040] Example 2

[0041] like Figure 2 As shown in the figure, it is the principle diagram of two-node forward split optical fiber vibration sensing.

[0042] The optical signal replicated and phase-synchronized at each node is split into two beams by a beam splitter. One beam serves as the local oscillator (LO) light for demodulation of the vibration signal, while the other serves as the probe light. This light is sent to adjacent nodes via the sensing fiber link to detect vibration disturbances along the link. Simultaneously, all nodes also receive the probe light from their neighbors.

[0043] Each node performs heterodyne interference between the detection light from the adjacent node and the local LO light. By interpreting the phase changes of the heterodyne signal, the vibration disturbance information of the connected node is obtained. By cross-correlation analysis of the disturbance information of adjacent nodes, combined with the fiber length and light speed between nodes, the location of the disturbance signal can be accurately calculated. The specific steps are as follows:

[0044] 1. Optical frequency reference signal distribution.

[0045] To achieve ultra-long-distance sensing, the source node (node ​​A) uses a highly coherent, ultra-stable laser (SLS) as its light source. Ultra-stable optical frequency distribution technology enables the stable distribution of optical signals from the source node to each node via a time-frequency distribution link. At each node, optical phase locking technology is used to regenerate the optical signal locally, ensuring that the optical frequency and phase of each node remain synchronized with those of the source node.

[0046] like Figure 2 As shown in the figure, in node A, the source node, an ultrastable laser source (SLS) distributes the optical signal to the next node, B, via a 2×2 Michelson fiber interferometer with unequal arms. The short arm is connected to a Faraday reflector (FR), whose length and phase variations are negligible, and serves as the local oscillator (LO) light source. The long arm, consisting of the time-frequency distribution link between nodes A and B, transmits the optical signal to node B. When the signal reaches node B, it is first amplified by a bidirectional fiber amplifier (Bi-EDFA) and then frequency-shifted by an acousto-optic modulator (AOM2) to distinguish parasitic reflection noise from the fiber link. A portion of the signal is then reflected back to node A by a semi-transparent, semi-reflective Faraday reflector (HFR) for beat frequency detection along with the LO light. This process effectively captures phase noise in the time-frequency distribution link.

[0047] Subsequently, the servo controller drives the local acousto-optic modulator (AOM1) to adjust its carrier frequency in real time to compensate for the phase noise in the time-frequency distribution link, thereby ensuring that the signal received by the remote node B is consistent with the optical signal of the source node A in frequency and phase.

[0048] Next, the signal from node B is used as the optical frequency reference signal, and the optical phase-locked loop (OPLL) technology is used to lock the laser SL1 to the optical frequency reference signal, thereby achieving high-precision regeneration of the local signal of node B; the regenerated signal will continue to be distributed to other nodes such as C, D, etc., and the above frequency synchronization process from node A to node B will be repeated.

[0049] 2. Time synchronization signal distribution.

[0050] While distributing the optical frequency signal, Node A, acting as the source node, uses wavelength division multiplexing (WDM) to load the time synchronization signal onto a specific optical carrier. This optical carrier is then multiplexed with the optical frequency signal and transmitted to Node B via a time-frequency distribution link using a dense wavelength division multiplexer (DWDM). High-precision two-way time transfer (TWTT) is performed between Nodes A and B based on the received optical carrier signal, eliminating the effects of link asymmetry and achieving time synchronization between Nodes A and B.

[0051] Repeat the above process with Node B, which is synchronized to Node A's time base, as the new secondary time source:

[0052] 1) Distribute the time synchronization signal to downstream nodes, such as node C, through dense wavelength division multiplexing (DWDM).

[0053] 2) Node B and node C perform two-way time comparison to achieve time synchronization between nodes B and C.

[0054] This cascade distribution and two-way comparison process can be sequentially extended to more nodes, such as node D, and ultimately achieve high-precision synchronization of multiple nodes in the entire network based on the same time reference.

[0055] 3. Interpretation of disturbance signals

[0056] After all nodes achieve high-precision optical frequency signal regeneration, their output optical signals are transmitted to adjacent nodes via a sensing fiber link. Within each node, heterodyne interferometry is used for detection. Because the frequency and phase of the light sources between nodes are synchronized, the phase information obtained from interferometric detection directly reflects the extent of environmental noise perturbations on the link. By analyzing the phase fluctuations of the interference signal at each node, the time-frequency characteristics of the disturbance source can be effectively deciphered.

[0057] Taking nodes A and B as an example, when the optical fiber is not disturbed by the outside world, the phase difference detected on both sides is and They are:

[0058] ;

[0059] ;

[0060] in, Represents the phase difference of optical fiber transmission; and is the phase of the lasers at both nodes. Since the light source frequency / phase of all nodes are synchronized, , (C is a constant), when no disturbance occurs, the transmission phase of the optical fiber remains constant, that is, , when the fiber is at a distance from node A At the external noise source When the disturbance occurs (T is the transmission time of the optical signal from the disturbance point to node A, is the speed of light signal transmission in the optical fiber), the phase differences detected on both sides are:

[0061] ;

[0062] ;

[0063] in, is the coupling coefficient between the optical fiber and the noise signal, and L is the total length of the optical fiber between nodes A and B.

[0064] 4. Disturbance source location

[0065] Adjacent nodes transmit detected optical information to each other via optical fiber links and perform cross-correlation analysis. Combining the fiber length between nodes and the speed of light propagation in the fiber, the system can accurately calculate and locate the source of the disturbance.

[0066] Perform cross-correlation operation on the two optical signals:

[0067] ;

[0068] The time corresponding to the maximum value of the cross-correlation That is the time difference between the signal arriving at nodes A and B , based on the total length L of the optical fiber link between A and B, and the speed of light in the optical fiber , the precise position of the disturbance point can be calculated. For example, the speed at which the disturbance signal reaches the two ends of the optical fiber can be and , then the distance between the disturbance position and the two ends of the optical fiber is: , according to the total length L of this optical fiber, the precise location of the disturbance source can be obtained.

[0069] 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 distributed optical fiber vibration sensing system based on time-frequency distribution, characterized in that: include: Time-frequency reference network and vibration sensing network; The time-frequency reference network distributes the ultra-stable optical frequency signal and time synchronization signal of the source node to all receiving nodes through the time-frequency distribution link; and ensures the synchronization of the optical signal frequency, phase and time of all nodes; The source node uses a highly coherent ultra-stable laser as its light source. Utilizing ultra-stable optical frequency distribution technology, the optical signal is stably distributed from the source node to each receiving node via a time-frequency distribution link. Each receiving node uses optical phase-locking technology to perform local ultra-stable optical frequency regeneration of the optical signal. The time-frequency reference network uses wavelength division multiplexing technology to load the time synchronization signal onto an optical carrier at the source node. Using a dense wavelength division multiplexer, the optical carrier is multiplexed with an ultra-stable optical frequency signal and transmitted to the receiving node via a time-frequency distribution link. High-precision two-way time comparison is performed between the source node and the receiving node, and time synchronization between the nodes is achieved based on the received optical carrier. The receiving node that has been synchronized to the source node time base is used as the new secondary time source, and the time synchronization signal is further distributed to the downstream receiving nodes through the dense wavelength division multiplexing; The downstream receiving node performs a two-way time comparison with the receiving node serving as the new secondary time source to achieve time synchronization between the two nodes, ultimately achieving high-precision synchronization of multiple nodes based on the same time reference; At the source node, an ultra-stable laser source distributes the ultra-stable optical frequency signal to the next node, B, via an unequal-arm Michelson fiber interferometer. The short arm is connected to a Faraday reflector, serving as a local oscillator light source. The long arm, consisting of a time-frequency distribution link between the two nodes, transmits the optical signal to node B. When the signal arrives at node B, it is first amplified by a bidirectional fiber amplifier and then frequency-shifted by an acousto-optic modulator to distinguish it from parasitic reflection noise in the fiber link. Then, a part of the signal is reflected back to the source node through a semi-transparent and semi-reflective Faraday reflector, and is used together with the local oscillator light for beat frequency detection. The servo controller drives the local acousto-optic modulator to adjust the carrier frequency in real time to compensate for phase noise in the time-frequency distribution link, ensuring that the signal received by the remote node B is consistent with the optical signal of the source node in frequency and phase. The optical signal of node B is then used as an optical frequency reference signal, and the laser is locked to the optical frequency reference signal using optical phase-locked loop technology to achieve high-precision regeneration of the local signal of node B. The regenerated optical signal will continue to be distributed to other nodes; The vibration sensing network sends the optical signals of adjacent nodes to the other end through the sensing optical fiber link for beat frequency detection, and obtains the vibration disturbance signal along the sensing optical fiber link to determine the location of the vibration disturbance.

2. The distributed optical fiber vibration sensing system based on time-frequency distribution according to claim 1, characterized in that: After ultra-stable optical frequency regeneration is achieved at all receiving nodes, the output optical signal is transmitted to the adjacent nodes through the sensing fiber link. At each adjacent node, heterodyne interferometry technology is used for detection. By analyzing the phase fluctuations of the interference signal, the time-frequency characteristics of the disturbance source are interpreted.

3. A distributed optical fiber vibration sensing method based on time-frequency distribution, characterized in that: The method is implemented by the distributed optical fiber vibration sensing system based on time-frequency distribution according to any one of claims 1 to 2, comprising: Distribute the ultra-stable optical frequency signal and time synchronization signal of the source node to all receiving nodes through the time-frequency distribution link, ensuring the synchronization of the optical signal frequency, phase and time of all nodes; The optical signals of the adjacent nodes are sent to the other end through the sensing fiber link for beat frequency detection; The vibration disturbance signal along the sensing optical fiber link is obtained to determine the location of the vibration disturbance.

4. The distributed optical fiber vibration sensing method based on time-frequency distribution according to claim 3, characterized in that: When the optical fiber is not disturbed by the outside world, the phase difference detected on both sides is 、 They are: ； ； in, and is the phase of the laser at both nodes; Represents the phase difference of optical fiber transmission; When the fiber is at a distance from node A At the outside world The phase difference between the two detections when the disturbance 、 They are: ； ； Where T is the transmission time of the optical signal from the disturbance to node A, The speed at which light signals are transmitted in optical fibers. is the coupling coefficient between the optical fiber and the noise signal, and L is the total length of the optical fiber between nodes A and B.

Images