An adjustable distributed fiber sensing performance enhancement device, sensing system and method

Abstract

The application discloses a kind of adjustable distributed optical fiber sensing performance promotion device, sensing system and method, device includes: narrow linewidth laser, acoustooptic modulator, first signal generator and frequency shift ring;Narrow linewidth laser is configured to output narrow linewidth laser to acoustooptic modulator;First signal generator is configured to generate pulse function signal, function signal controls acoustooptic modulator, and single-frequency laser is modulated into pulsed light;Acoustooptic modulator is configured to modulate single-frequency laser into corresponding pulsed light in acoustooptic modulator according to the pulse function signal generated by first signal generator;Frequency shift ring is configured to multiple cyclic frequency shifts of pulsed light into it, and generate broadband multi-frequency light output.The device generates MHz-level pulsed light by acoustooptic modulator modulation, and generates GHz-level broadband multi-frequency light by multiple cyclic frequency shifts of frequency shift ring, which is applied to sensing system, and the response bandwidth of sensing system can be improved, and the flexibility of sensing test is improved.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to an adjustable distributed fiber optic sensing performance enhancement device, sensing system, and method. Background Technology

[0002] Distributed optical fiber acoustic sensing (DAS) is a novel sensing technology that utilizes the Rayleigh scattering interference effect in optical fibers to detect sound waves. Besides sharing the common advantages of fiber optic sensing systems (such as being inherently passive and capable of operating in harsh environments with strong electromagnetic interference, high temperature and pressure, and strong chemical corrosion), DAS technology can also effectively achieve long-distance distributed detection of strain (vibration, sound waves, etc.) along the optical fiber. Its basic principle is as follows: When light propagates in an optical fiber, because the fiber cannot be made completely homogeneous during manufacturing, the incident light wave undergoes elastic scattering within the fiber, producing Rayleigh scattered light. When the fiber is subjected to external physical forces such as sound waves or pressure, the phase of the Rayleigh scattered light in the fiber is affected accordingly. By demodulating the phase information of the Rayleigh scattered light, sound wave information can be obtained, thus achieving distributed sensing of sound wave information.

[0003] Traditional DAS systems use single-frequency pulsed light as the probe light to traverse the fiber optic cable, establishing a one-to-one mapping between the spatial and temporal domains. After the probe pulse is injected into the fiber, it propagates at a speed of c / n (c is the speed of light in vacuum, n is the refractive index of the fiber), thus traversing the fiber. Each time the probe pulse reaches a region on the fiber, it senses the environmental disturbance information experienced at that moment. This information is then transmitted back to the front end for analysis using Rayleigh scattering. By utilizing the time difference between the Rayleigh scattering signals returning to the probe end from different locations on the fiber, a one-to-one mapping between the spatial and temporal domains is established, enabling the sensing and localization of disturbance information at every point on the fiber. However, for any point z on the fiber, the system only performs discrete sampling of the disturbance information at that point with a period of T (T being the round-trip time of the light pulse traversing the entire fiber segment), leaving a significant portion of the time in an information blind zone. For long-distance sensing, this severely limits the system's response bandwidth. Meanwhile, the spatial resolution of the system is limited by the pulse width of the pulsed light. To achieve high spatial resolution, narrow pulse width light needs to be injected. However, the narrower the pulse width, the lower the average power of the light pulse and the worse the signal-to-noise ratio of the system. To ensure that the system signal-to-noise ratio does not deteriorate too much, pulsed light with a pulse width on the order of tens of nanoseconds is generally required, which can only achieve a spatial resolution on the order of several meters.

[0004] To address the limitations of traditional single-frequency pulse-type DAS systems in terms of response bandwidth and spatial resolution due to the sensing principle, existing solutions include injecting multi-frequency light as the probe light. Based on the frequency division multiplexing principle, this breaks through the theoretical frequency response limit of single-frequency light source systems. Alternatively, based on the pulse compression principle, spatial resolution can be improved, such as generating broadband chirped continuous light to replace traditional single-frequency light pulses, enabling time-slot-free continuous information sensing of the entire fiber optic cable. For example, Jialin Jiang et al. implemented an OFDR-type DAS system based on the optical heterodyne coherence principle in Continuous chirped-wave phase-sensitive optical time domain reflectometry. Optics Letters, 2021, 46, 928-928. This system uses a broadband continuous function signal generator (GHz level) to control an IQ electro-optic modulator to modulate a narrow-linewidth laser source, generating broadband chirped continuous light (GHz level) as the probe light. Using single-frequency light as the local oscillator, the Rayleigh scattering light field at any frequency and any time is reconstructed through coherent detection. For any point z on the optical fiber, it is constantly probed by chirped continuous light, generating a Rayleigh scattering signal. Loading the perturbation information at this point onto the scattered signal and transmitting it back to the receiver can greatly improve the response bandwidth of the sensing system. However, this system requires wide-bandwidth continuous modulation of the sensing light, thus necessitating the use of an IQ electro-optic modulator and a wide-bandwidth function signal generator. While IQ electro-optic modulation can achieve wide-bandwidth modulation, its modulation performance is often inferior to that of acousto-optic modulators when used for narrow-bandwidth modulation. Wide-bandwidth function signal generators are not only extremely expensive but also bulky and difficult to integrate and implement practically.

[0005] refer to Figure 9-11 The IQ electro-optic modulator integrates an electro-optic Mach-Zehnder modulator (MEM) and a phase modulator. The phase modulator works by applying an external electric field to the electro-optic material, which generates a linear photoelectric effect that causes a change in the material's refractive index. This results in a phase change in the optical signal input to the waveguide region, thus loading the radio frequency signal information onto the optical carrier and achieving phase modulation. However, its output spectrum, in addition to the optical carrier, also produces frequencies including f0±f... S The first-order sideband. MEM consists of two phase modulators connected in parallel. By adjusting the DC bias voltage, a suitable bias point can be selected, allowing the modulators to operate in different modulation regions. To achieve carrier-suppressed single-sideband modulation, the DC bias voltages of its I and Q paths should be equal and both should operate at the minimum operating point of the transfer function, i.e., satisfying... Furthermore, the phase difference of the Q-channel phase modulator must be fixed at 90 degrees. Even if the IQ electro-optic modulator is controlled to operate in single-sideband modulation mode, sidebands will still exist after frequency shifting. Its modulation effect is referenced... Figure 12 .

[0006] Chinese invention patent CN 114337808 A discloses a broadband high-speed optical vector analyzer based on a cyclic frequency shifter. In this patent, an electro-optic modulator and a wide-bandwidth signal generator are still used in front of the loop to generate GHz-level chirped light. Moreover, the frequency shifting loop structure cannot select delay optical fibers of different lengths, the system is fixed, and it is impossible to achieve flexible adjustment of chirp parameters. Summary of the Invention

[0007] One of the objectives of this invention is, at least, to address the problems existing in the prior art by providing an adjustable distributed optical fiber sensing performance enhancement device, sensing system, and method. This device can modulate a single-frequency laser into MHz-level narrowband linear chirped pulses using an acousto-optic modulator and a first signal generator. Multiple narrowband chirped pulses are generated through cyclic frequency shifting via a frequency shifting loop. These multiple narrowband chirped pulses are then spliced ​​together in the time domain to form GHz-level broadband chirped continuous light or chirped pulse light. By selecting delay fibers of different lengths through an optical switch within the frequency shifting loop, the chirping rate, bandwidth, and other parameters of the output broadband chirped continuous light or chirped pulse light can be flexibly adjusted, resulting in high-modulation-quality, low-cost, and highly integrated broadband chirped continuous light or chirped pulse light.

[0008] The device can also modulate a single-frequency laser into a MHz-level single-frequency pulse through an acousto-optic modulator and a first signal generator, and generate a GHz-level wide-bandwidth multi-frequency pulse with a certain time-domain interval through a frequency-shifting loop. By flexibly adjusting the time-domain interval of the output wide-bandwidth multi-frequency pulse light through an optical switch in the frequency-shifting loop, different response bandwidth or spatial resolution improvement effects can be achieved.

[0009] Injecting the aforementioned broadband multi-frequency light into the sensing fiber enables high-bandwidth or high-spatial-resolution sensing and detection in the DAS system.

[0010] To achieve the above objectives, the technical solution adopted by the present invention includes the following aspects.

[0011] An adjustable distributed fiber optic sensing performance enhancement device includes: a narrow linewidth laser, an acousto-optic modulator, a first signal generator, and a frequency shift loop;

[0012] The narrow linewidth laser is configured to output narrow linewidth laser light to an acousto-optic modulator;

[0013] The first signal generator is configured to generate a pulse function signal, which controls an acousto-optic modulator to modulate a single-frequency laser into pulsed light.

[0014] The acousto-optic modulator is configured to modulate the single-frequency laser entering the acousto-optic modulator into corresponding pulsed light according to the pulse function signal generated by the first signal generator;

[0015] The frequency shift loop is configured to perform multiple cyclic frequency shifts on the pulse light entering it, thereby generating a wide-bandwidth multi-frequency optical output.

[0016] Preferably, the frequency shift loop includes a coupler, a low-noise optical amplifier, at least two optical switches, multiple delay fibers of different lengths, an acousto-optic frequency shifter, a second signal generator, and a third signal generator;

[0017] The pulsed light generated by the acousto-optic modulator before the frequency shift loop enters the frequency shift loop through the coupler;

[0018] The low-noise optical amplifier is configured to compensate for cyclic frequency shift loss;

[0019] The third signal generator is configured to generate a second electrical signal to turn different switching channels of each optical switch on or off.

[0020] Each optical switch is configured to open or close the corresponding switch channel connected to delay optical fibers of different lengths under the action of the second electrical signal according to the test requirements, so that the delay optical fiber of the corresponding length is connected to the frequency shift loop and the appropriate length of delay optical fiber is selected.

[0021] The second signal generator is configured to generate a first electrical signal to control the acousto-optic frequency shifter, thereby controlling the number of frequency shifts of the pulsed light within the frequency shift loop;

[0022] The acousto-optic frequency shifter is configured to shift the frequency of the pulsed light entering the acousto-optic frequency shifter according to the first electrical signal generated by the second signal generator;

[0023] The pulsed light is cyclically shifted multiple times within the frequency shift loop to generate wide-bandwidth multi-frequency light, which is then output via a coupler.

[0024] Preferably, the first signal generator is configured to generate a narrowband linear chirped function signal, and the function signal controls an acousto-optic modulator to modulate a single-frequency laser into a narrowband linear chirped pulse light;

[0025] The acousto-optic modulator is configured to modulate a single-frequency laser entering the acousto-optic modulator into a narrowband linear chirped pulse light based on a narrowband linear chirped function signal generated by a first signal generator.

[0026] The narrowband linear chirped pulse light enters the frequency shift loop through the coupler and undergoes multiple cyclic frequency shifts to generate multiple narrowband chirped pulses. These multiple narrowband chirped pulses are seamlessly spliced ​​in the time domain into broadband chirped continuous light or into broadband chirped pulse light, and then output through the coupler.

[0027] Preferably, the first signal generator is configured to generate a pulse function signal, which controls an acousto-optic modulator to modulate a single-frequency laser into a single-frequency pulse light.

[0028] The acousto-optic modulator is configured to modulate the single-frequency laser entering the acousto-optic modulator into a single-frequency pulse light according to the pulse function signal generated by the first signal generator;

[0029] The single-frequency pulse light enters the frequency shifting loop through the coupler and undergoes multiple cyclic frequency shifts to generate a wide-bandwidth multi-frequency pulse light with a certain time-domain interval or no time-domain interval, which is then output through the coupler.

[0030] A sensing system based on an adjustable distributed optical fiber sensing performance enhancement device, wherein the system adopts any of the aforementioned adjustable distributed optical fiber sensing performance enhancement devices, and the system further includes a splitter, a circulator, a sensing optical fiber, and a detection demodulation module.

[0031] The splitter is configured to split the narrow-linewidth laser generated by the narrow-linewidth laser into two paths. The first path enters the detection and demodulation module, and the second path is used to generate wide-bandwidth multi-frequency light.

[0032] Wideband multi-frequency light enters the sensing fiber through the circulator, undergoes Rayleigh scattering in the sensing fiber, and generates back Rayleigh scattered light. The back Rayleigh scattered light returns to the circulator and enters the detection demodulation module through the circulator, where it interferes with the first laser.

[0033] The detection and demodulation module is configured to demodulate the vibration information of the sensing fiber based on the interference light.

[0034] A method for improving the sensing performance of a sensing system based on an adjustable distributed optical fiber sensing performance enhancement device includes the following steps:

[0035] The narrow-linewidth laser is turned on and split into two paths by a splitter. The first path enters the detection and demodulation module, and the second path enters the acousto-optic modulator. The first signal generator produces a pulse function signal to control the acousto-optic modulator, modulating the single-frequency laser into corresponding pulsed light. The pulsed light enters the frequency shift loop through a coupler, where it undergoes multiple cyclic frequency shifts to generate wide-bandwidth multi-frequency light. This wide-bandwidth multi-frequency light is output through a coupler and injected into the sensing fiber. The wide-bandwidth multi-frequency light undergoes Rayleigh scattering in the sensing fiber, generating backscattered Rayleigh light. This backscattered light returns to the circulator and enters the detection and demodulation module, where it interferes with the first laser path. The interference light is detected and demodulated by the detection and demodulation module, thereby obtaining the fiber vibration information.

[0036] Using the above method, GHz-level wide-bandwidth chirped continuous light or GHz-level wide-bandwidth multi-frequency pulsed light with a certain time-domain interval can be injected into the sensing fiber of a sensing system based on an adjustable distributed optical fiber sensing performance enhancement device, thereby improving the response bandwidth of the sensing system and enabling the sensing system to be flexibly applied to occasions with different testing requirements. Preferably, the sensing system response bandwidth improvement factor is 1 to 1000 times, the total bandwidth of the wide-bandwidth multi-frequency pulsed light (wide-bandwidth chirped continuous light and wide-bandwidth multi-frequency pulsed light) is 0.1 to 10 GHz, and the pulse time-domain interval of each frequency component in the wide-bandwidth multi-frequency pulsed light is 0.1 to 48.67 μs.

[0037] Using the above method, chirped pulse light or pulse light without time domain interval (ideally without time domain interval, but in reality there will be a narrow time domain interval) can also be injected into the sensing fiber of the sensing system, thereby improving the spatial resolution performance of the sensing system and making the sensing system flexibly applicable to different testing needs.

[0038] In summary, by adopting the above technical solution, the present invention has at least the following beneficial effects:

[0039] By configuring an acousto-optic modulator, a first signal generator, and a frequency shift loop, the acousto-optic modulator and the first signal generator modulate a single-frequency laser generated by a narrow-linewidth laser into MHz-level narrowband linearly chirped pulses. These linearly chirped pulses are then cyclically shifted within the frequency shift loop to generate multiple narrowband chirped pulses. These multiple narrowband chirped pulses are then spliced ​​in the time domain to form GHz-level broadband chirped continuous light or chirped pulsed light, which is then injected into the sensing fiber. The frequency shift loop includes a coupler, a low-noise optical amplifier, multiple optical switches, multiple delay fibers of different lengths, an acousto-optic frequency shifter, and a second signal generator. The multiple optical switches allow selection of delay fiber lengths, controlling the fiber length of the frequency shift loop and enabling flexible adjustment of parameters such as the chirped rate and bandwidth of the chirped continuous light or pulsed light. Applying this chirped continuous light or pulsed light to a DAS system can improve the system's bandwidth response or spatial resolution performance according to testing requirements, making it flexible for various testing scenarios.

[0040] A single-frequency laser generated by a narrow-linewidth laser is modulated into MHz-level single-frequency pulses using an acousto-optic modulator and a first signal generator. These pulses are then cyclically shifted within a frequency-shifting loop to generate GHz-level wide-bandwidth multi-frequency pulses, which are then injected into the sensing fiber. The frequency-shifting loop includes a coupler, a low-noise optical amplifier, multiple optical switches, multiple delay fibers of varying lengths, an acousto-optic frequency shifter, and a second signal generator. The multiple optical switches allow for selection of different delay fiber lengths, controlling the fiber length of the frequency-shifting loop and enabling flexible adjustment of the output pulse time-domain interval. Applying this wide-bandwidth multi-frequency light to a DAS system can improve the system's response bandwidth or spatial resolution performance according to testing requirements, making it flexible for various testing scenarios. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of a distributed optical fiber acoustic wave sensing system based on an adjustable distributed optical fiber sensing performance enhancement device, which is an exemplary embodiment of the present invention.

[0042] Figure 2 This is a schematic diagram of the structure of a distributed optical fiber acoustic wave sensing system based on an adjustable distributed optical fiber sensing performance enhancement device, which is another exemplary embodiment of the present invention.

[0043] Figure 3 This is a schematic diagram of narrowband linear chirped pulse light generated by a narrow-linewidth laser modulated by an acousto-optic modulator according to an exemplary embodiment of the present invention.

[0044] Figure 4 yes Figure 3 A schematic diagram of the chirped continuous light generated by cyclic frequency shifting of a narrowband linear chirped pulse light through a frequency shifter loop.

[0045] Figure 5 yes Figure 3 A schematic diagram of the chirped pulse light generated after the narrowband linear chirped pulse light is cyclically frequency-shifted by a frequency-shifting loop.

[0046] Figure 6 This is a schematic diagram of a single-frequency pulsed light generated by a narrow-linewidth laser modulated by an acousto-optic modulator, according to an exemplary embodiment of the present invention.

[0047] Figure 7 yes Figure 6 A schematic diagram of multi-frequency pulse light generated after single-frequency pulse light is cyclically shifted by a frequency shifter.

[0048] Figure 8 yes Figure 6 A schematic diagram of a time-space-free multi-frequency pulse light generated by cyclically shifting the frequency of a single-frequency pulse light through a frequency shifting loop.

[0049] Figure 9 This is a schematic diagram of an existing electro-optic phase modulator.

[0050] Figure 10 This is a schematic diagram of an existing electro-optic Mach-Zehnder modulator (MEM).

[0051] Figure 11 This is a schematic diagram of an existing IQ electro-optic modulator.

[0052] Figure 12 This is a schematic diagram of the modulation effect of the IQ electro-optic modulator. Detailed Implementation

[0053] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, so that the objectives, technical solutions, and advantages of the present invention will be clearer. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0054] An exemplary embodiment of the present invention provides an adjustable distributed fiber optic sensing performance enhancement device comprising a narrow linewidth laser, an acousto-optic modulator, a first signal generator (signal generator 1), and a frequency shift loop.

[0055] A narrow-linewidth laser (single-frequency) generated by a narrow-linewidth laser enters an acousto-optic modulator, which modulates it to form a narrowband linearly chirped pulse. A first signal generator is configured to generate a narrowband linearly chirped function signal, which controls the acousto-optic modulator to modulate the single-frequency laser into a narrowband linearly chirped pulse. The linearly chirped pulse enters a frequency-shifting loop, where it undergoes multiple cyclic frequency shifts to generate multiple narrowband chirped pulses. These multiple narrowband chirped pulses are seamlessly spliced ​​together in the time domain to form a broadband chirped continuous light or a chirped pulse output.

[0056] This invention modulates a single-frequency laser generated by a narrow-linewidth laser into a MHz-level narrowband linear chirped pulse light using an acousto-optic modulator. The narrowband linear chirped pulse light is then cyclically shifted through a frequency-shifting loop to generate multiple narrowband chirped pulses. These multiple narrowband chirped pulses are then spliced ​​together in the time domain to form a GHz-level broadband chirped continuous light or chirped pulse light. This improves modulation quality and enables the low-cost, high-integration output of broadband chirped continuous light or chirped pulse light.

[0057] refer to Figure 1 The frequency shifting loop includes a coupler, a low-noise optical amplifier, a first optical switch, multiple delay fibers of different lengths, a second optical switch, an acousto-optic frequency shifter, a second signal generator (signal generator 2), and a third signal generator (signal generator 3). The coupler, low-noise optical amplifier, first optical switch, multiple delay fibers of different lengths (each delay fiber's two ends are connected to the corresponding switching channels of the first and second optical switches), the second optical switch, and the acousto-optic frequency shifter are sequentially connected to form a loop structure. The second signal generator is configured to generate a first electrical signal to control the acousto-optic frequency shifter, thereby controlling the number of frequency shifts of the linearly chirped pulse light in the frequency shifting loop. The low-noise optical amplifier is configured to compensate for cyclic frequency shifting loss. The third signal generator is configured to generate a second electrical signal to open or close different switching channels of the first and second optical switches. The first and second optical switches are configured to open or close the corresponding switching channels connected to delay fibers of different lengths under the action of the second electrical signal, according to test requirements, and to select a suitable length of delay fiber.

[0058] The linearly chirped pulse light modulated by the acousto-optic modulator enters the frequency shift loop via a coupler. After multiple cyclic frequency shifts via a low-noise optical amplifier, a first optical switch, a delay fiber, a second optical switch, and an acousto-optic frequency shifter, multiple narrowband chirped pulses are generated. These narrowband chirped pulses are seamlessly spliced ​​in the time domain into a broadband chirped continuous light or a chirped pulse light, which is then output via a coupler. The chirped bandwidth of the linearly chirped pulse light is the same as the fixed frequency shift amount of the acousto-optic frequency shifter within the frequency shift loop. The linearly chirped pulse light and the seamlessly spliced ​​broadband chirped continuous light and chirped pulse light are respectively referenced to... Figure 3 , Figure 4 and Figure 5 .

[0059] For different testing requirements, the length of the delayed optical fiber that meets the testing requirements can be selected by using the first optical switch and the second optical switch, thereby controlling the length of the optical fiber in the frequency shift loop and flexibly changing the chirping rate, bandwidth and other parameters of the output chirped continuous light or chirped pulse light. When the chirped continuous light or chirped pulse light is applied to the distributed sensing system, the system response bandwidth or spatial resolution performance can be improved according to the testing requirements.

[0060] During use, two or more optical switches and delay fibers of different lengths can be set within the frequency shift loop according to testing requirements (see reference). Figure 2 By controlling the access of delayed optical fibers of different lengths to the frequency shift ring through multiple optical switches, the equivalent delayed optical fibers of different lengths can be flexibly realized, thereby changing the length of the optical fiber within the frequency shift ring.

[0061] use Figure 1 or Figure 2 The adjustable distributed sensing performance enhancement device can also generate wide-bandwidth multi-frequency pulsed light with a certain time-domain interval, the time-domain interval of which is flexibly adjustable. When applied to a distributed sensing system, it can improve the system's response bandwidth or spatial resolution performance according to testing requirements. The generation process of this wide-bandwidth multi-frequency pulsed light is as follows: a narrow-linewidth laser (single-frequency) generated by a narrow-linewidth laser enters an acousto-optic modulator. A first signal generator generates a pulse function signal, which controls the acousto-optic modulator to modulate the single-frequency laser into a single-frequency pulsed light. The single-frequency pulsed light enters a frequency-shifting loop via a coupler. After multiple cyclic frequency shifts in the frequency-shifting loop, wide-bandwidth multi-frequency pulsed light with a certain time-domain interval is generated and output via a coupler. Single-frequency pulsed light and wide-bandwidth multi-frequency pulsed light with and without a certain time-domain interval are respectively referenced. Figure 6 , Figure 7 and Figure 8 .

[0062] The basic working principle of an acousto-optic frequency shifter is based on acousto-optic interaction, which refers to the phenomenon of light waves being diffracted or scattered by an ultrasonic field when propagating in a medium. When a light wave propagates in a medium, diffraction occurs, and the intensity, frequency, and direction of the diffracted light change with the ultrasonic field. When the acoustic frequency is high, the acousto-optic interaction length is large, and the beam is obliquely incident at a certain angle to the acoustic wavefront, the light wave passes through multiple acoustic wavefronts in the medium, thus the medium possesses the property of a "volume grating." When certain conditions are met between the incident light and the acoustic wavefronts, the diffracted light of each order in the medium will interfere with each other, and the higher-order diffracted light will cancel each other out, resulting in only the 0th and +1st order (or -1st order, depending on the direction of the incident light) diffracted light, i.e., Bragg diffraction. Let the diffraction efficiency of the +1st order diffracted light (frequency-shifted light) be:

[0063]

[0064] Where I1 is the intensity of the first-order diffraction light, I in The intensity of the incident light. The phase shift is caused by the acoustic-optic interaction, and it reflects the strength of the acoustic-optic interaction. As shown in the following formula:

[0065]

[0066] in, The momentum mismatch is represented by the first-order diffraction, and L is the width of the acousto-optic interaction region.

[0067] When the incident light is incident at the Bragg angle, that is... At that time, there were:

[0068]

[0069] when hour, All the energy of the incident light is converted into frequency-shifted light, and its energy can be fully utilized.

[0070] This invention also provides a distributed fiber optic acoustic wave sensing system based on an adjustable distributed fiber optic sensing performance enhancement device. This sensing system can be applied to various testing applications. (Continue to refer to...) Figure 1 The sensing system includes a narrow linewidth laser, a splitter, an acousto-optic modulator, a first signal generator, a coupler, a low-noise optical amplifier, a first optical switch, multiple delay fibers of different lengths, a second optical switch, an acousto-optic frequency shifter, a second signal generator, a third signal generator, a circulator, sensing fibers, and a detection and demodulation module.

[0071] A single-frequency laser generated by a narrow-linewidth laser is split into two paths by a splitter. The first path enters the detection and demodulation module, while the second path is modulated by an acousto-optic modulator to form a narrowband linearly chirped pulse. A first signal generator generates a narrowband linearly chirped function signal, which controls the acousto-optic modulator to modulate the single-frequency laser into a narrowband linearly chirped pulse. The chirped pulse then enters a frequency shift loop (coupler, low-noise optical amplifier, first optical switch, delay fiber, second optical switch, acousto-optic frequency shifter, second signal generator, and third signal generator) for frequency shifting. The second signal generator generates a first electrical signal to control the acousto-optic frequency shifter, thereby controlling the number of cyclic frequency shifts. The third signal generator generates a second electrical signal. The first and second electrical signals control the first and second optical switches to open or close the corresponding switch channels connected to multiple delay optical fibers of different lengths, selecting the appropriate length of delay optical fiber; a low-noise optical amplifier is used to compensate for cyclic loss; after multiple cyclic frequency shifts, the chirped pulse light generates multiple narrowband chirped pulses, which are seamlessly spliced ​​in the time domain and finally output as chirped continuous light through a coupler. The chirped continuous light enters the sensing fiber through a circulator, where Rayleigh scattering occurs, generating backscattered Rayleigh light. The backscattered Rayleigh light returns to the circulator and enters the detection and demodulation module, interfering with the first laser. The interference light is detected and demodulated by the detection and demodulation module, thereby obtaining the fiber vibration information.

[0072] By setting optical switches (first optical switch and second optical switch) and delay fibers of different lengths within the frequency shift loop, different lengths of delay fibers can be flexibly selected through the optical switches to change the fiber length within the frequency shift loop according to different testing requirements of the sensing system. This allows for flexible adjustment of parameters such as the chirping rate and bandwidth of the chirped continuous light, thereby improving the response bandwidth of the sensing system and making it suitable for various testing needs.

[0073] The process of the first optical switch and the second optical switch selecting delay fibers of different lengths is as follows:

[0074] According to the testing requirements of the sensing system, a second electrical signal is generated by a third signal generator to control the corresponding switching channels of the first optical switch, the second optical switch and the delay fiber; the second electrical signal causes the corresponding switching channels of the first optical switch and the second optical switch to open and close simultaneously.

[0075] When delay fiber 1 is a delay fiber of suitable length, the electrical signal output by signal generator 3 controls the simultaneous opening of the first optical switch channel 1 and the second optical switch channel 1, and delay fiber 1 is connected to the frequency shift loop, while the remaining delay fibers are disconnected from the loop; when delay fiber 2 is a delay fiber of suitable length, the electrical signal output by signal generator 3 controls the simultaneous opening of the first optical switch channel 2 and the second optical switch channel 2, and delay fiber 2 is connected to the frequency shift loop, while the remaining delay fibers are disconnected from the loop; ..., when delay fiber n is a delay fiber of suitable length, the electrical signal output by signal generator 3 controls the simultaneous opening of the first optical switch channel n and the second optical switch channel n, and delay fiber n is connected to the frequency shift loop, while the remaining delay fibers are disconnected from the loop.

[0076] The principle for setting the length of the delay fiber in the frequency shift loop is as follows:

[0077] Chirped continuous optical cycle It should meet the following requirements:

[0078]

[0079] Where n is the refractive index of the optical fiber, and L is the length of the sensing optical fiber. Let c be the system spatial resolution and c be the speed of light in a vacuum.

[0080] Let the pulse width of the chirped pulse generated by the single-frequency laser before the frequency shift loop after modulation by the acousto-optic modulator be... The cycle is Then, optical switches (first optical switch and second optical switch) are needed to select the length of the delay fiber, so that the time for the light to travel one cycle through the frequency shift loop is... satisfy:

[0081]

[0082] Among them, L c L is the total length of all optical fibers in the frequency shift loop except for the delay fiber. d This represents the length of the delay fiber.

[0083] Let the frequency shift step size of the acousto-optic frequency shifter in the frequency shift loop be B = 50 MHz, and the number of cyclic frequency shifts be m = 39. Then the total frequency shift bandwidth is B. a =(m+1)*B=2GHz.

[0084] Chirped continuous optical cycle Chirped pulse width Chirped pulse period The cyclic frequency shift number m satisfies the following relationship:

[0085]

[0086] Therefore, the length of the delay fiber and the length of the sensing fiber satisfy the following relationship:

[0087]

[0088] Assume the system spatial resolution is The frequency shift cycle has m=39 times, and the total length L of all optical fibers in the frequency shift loop except for the delay fiber is... c =20m.

[0089] Based on the above principles, different lengths of delay fibers can be pre-configured for common application scenarios of sensing fibers. For example, the corresponding configuration of sensing fibers and delay fibers is shown in Table 1:

[0090] Table 1. Correspondence between sensing fiber and delay fiber settings

[0091] Length of sensing fiber (km) Delay fiber length (km) 100 4.991 70 3.481 50 2.481 20 0.981 10 0.481 5 0.231 3 0.131 2 0.081 1 0.031

[0092] Assuming the length of the sensing fiber is 1~100km, after selecting different lengths of delay fiber through an optical switch, the total bandwidth of the chirped continuous light injected into the sensing fiber of the sensing system is 0.1~10GHz. According to the setting principle of the delay fiber length in the frequency shift loop, the chirping period of the chirped continuous light is 9.77~973us.

[0093] Continue to refer to Figure 1 Furthermore, wide-bandwidth multi-frequency pulsed light with a certain time interval can be injected into the sensing fiber in this sensing system. The wide-bandwidth multi-frequency pulsed light can be used to improve the response bandwidth of the sensing system, making the sensing system flexibly applicable to different testing needs.

[0094] The specific process is as follows:

[0095] The laser light generated by the narrow linewidth laser is split into two paths by a splitter. The first path enters the detection and demodulation module, and the second path is modulated by an acousto-optic modulator to form a single-frequency pulse light. A signal generator generates a pulse function signal, which controls the acousto-optic modulator to modulate the single-frequency laser light into a single-frequency pulse light. The single-frequency pulse light enters a frequency shift loop (coupler, low-noise optical amplifier, first optical switch, delay fiber, second optical switch, acousto-optic frequency shifter, second signal generator, and third signal generator) for multiple cyclic frequency shifts. The second signal generator generates a first electrical signal to control the acousto-optic frequency shifter, thereby controlling the number of cyclic frequency shifts. The third signal generator is used to generate a first electrical signal to control the acousto-optic frequency shifter, thereby controlling the number of cyclic frequency shifts. A second electrical signal is generated, which controls the first and second optical switches to open or close the corresponding switch channels connected to multiple delay optical fibers of different lengths, and selects a suitable length of delay optical fiber. A low-noise optical amplifier is used to compensate for cycle loss. After multiple cyclic frequency shifts, the single-frequency pulse light generates broadband multi-frequency pulses with equal time intervals. The broadband multi-frequency pulses enter the sensing optical fiber through a circulator, where Rayleigh scattering occurs, generating backscattered Rayleigh light. The backscattered Rayleigh light returns to the circulator and enters the detection and demodulation module, where it interferes with the first laser. The interference light is detected and demodulated by the detection and demodulation module, thereby obtaining the fiber vibration information.

[0096] The process of selecting different lengths of delay fiber for the first and second optical switches has been described in detail previously and will not be repeated here.

[0097] In this sensing system, the time-domain interval t1 between any two pulses within a single cycle is determined by the length of the delay fiber within the frequency shift loop. With the delay fiber length fixed, the pulse time-domain interval within a single cycle is fixed. The time-domain interval t2 between the last pulse of the nth cycle and the first pulse of the (n+1)th cycle is determined by the cycle duration, the number of cycles, and the length of the delay fiber. When the system operates in response bandwidth enhancement mode, it generates... Figure 7 The multi-frequency pulses used to enhance system response bandwidth require control of various parameters to ensure that the time interval between the last pulse generated in each cycle and the initial pulse of the next cycle is the same as the time interval between any two pulses within the cycle. The improvement in system response bandwidth is determined by the number of pulses in a single cycle.

[0098] When broadband multi-frequency pulses with equal time-domain intervals are injected into the sensing fiber, the principle for setting the length of the delay fiber is as follows:

[0099] Suppose that, according to the testing requirements, after injecting wide-bandwidth multi-frequency pulses into the sensing fiber, the response bandwidth of the sensing system is increased by a factor of k compared to injecting single-frequency pulses into the sensing fiber. Then the number of cyclic frequency shifts should be m = k-1 times.

[0100] The multi-frequency pulse period used in the sensing system is It should meet the following requirements:

[0101]

[0102] Where n is the refractive index of the optical fiber, and L is the length of the sensing optical fiber. Let c be the system spatial resolution and c be the speed of light in a vacuum.

[0103] Let the time-domain interval of each frequency component pulse in the multi-frequency pulse be . Then we have:

[0104]

[0105] Among them, L c L is the total length of all optical fibers in the frequency shift loop except for the delay fiber. d This represents the length of the delay fiber.

[0106] Then the multi-frequency pulse period The time-domain interval of each frequency component in a multi-frequency pulse The cyclic frequency shift number m satisfies the following relationship

[0107]

[0108] Therefore, the lengths of the delay fiber and the sensing fiber, along with the target bandwidth enhancement factor, satisfy the following relationship:

[0109]

[0110] Based on the above principles, different lengths of delay fibers can be pre-configured for common application scenarios of sensing fibers. For example, the corresponding configuration of sensing fibers and delay fibers is shown in Table 2:

[0111] Table 2 Correspondence between Sensing Fiber and Delay Fiber

[0112] Length of sensing fiber (km) Delay fiber length (km) 100 4.981 70 3.481 50 2.481 20 0.981 10 0.481 5 0.231 3 0.131 2 0.081 1 0.031

[0113] Assuming the sensing fiber length is fixed at 50km and the system spatial resolution is... The total length L of all optical fibers in the frequency shift loop except for the delay fiber is... c =20m. The corresponding relationship between the target bandwidth enhancement factor and the delay fiber settings is shown in Table 3:

[0114] Table 3. Corresponding relationship between target bandwidth enhancement factor and delay fiber settings

[0115] Target bandwidth increase factor Delay fiber length (km) 10 9.981 20 4.981 30 3.314 40 2.481 50 1.981 100 0.981 1000 0.081

[0116] The total bandwidth of the wideband multi-frequency pulsed light injected into the sensing fiber in this sensing system with a certain time-domain interval is 0.1~10GHz, and the time-domain interval of each frequency component pulse of the wideband multi-frequency pulsed light is 0.1~48.67us. The response bandwidth of the sensing system can be increased by 1~1000 times.

[0117] Continue to refer to Figure 1 Furthermore, wide-bandwidth chirped pulse light can be injected into the sensing fiber in this sensing system to improve the spatial resolution of the sensing system, enabling the sensing system to be flexibly applied to different testing needs.

[0118] The generation process of wideband chirped pulse light is roughly the same as that of wideband chirped continuous light. The difference is that multiple narrowband chirped pulses generated by the frequency shifting loop after multiple cyclic frequency shifts are seamlessly spliced ​​in the time domain and then output as chirped pulse light through a coupler.

[0119] When a wide-bandwidth chirped pulse light is injected into the sensing fiber, the principle for setting the length of the delay fiber is to select the shortest possible delay fiber.

[0120] The process of selecting different lengths of delay fiber for the first and second optical switches has been described in detail previously and will not be repeated here.

[0121] Continue to refer to Figure 1 Furthermore, the sensing fiber in this sensing system can also be injected with wide-bandwidth multi-frequency pulse light without time interval. The spatial resolution of the sensing system can be improved by using wide-bandwidth multi-frequency pulse light, making the sensing system flexibly applicable to different testing needs.

[0122] When the sensing system operates in spatial resolution mode, it generates Figure 8 In this process, broadband multi-frequency pulses are used to improve the spatial resolution of the system. An optical switch within the frequency shift loop selects the delay fiber to adapt to the set pulse width, minimizing the time-domain interval between pulses, or ideally, eliminating it entirely (though in practice, a narrow time-domain interval is possible). The improvement in system spatial resolution is determined by the frequency domain bandwidth of the generated multi-frequency pulses.

[0123] When broadband multi-frequency pulse light without time-domain intervals is injected into the sensing fiber, the principle for setting the length of the delay fiber is to select the shortest length delay fiber.

[0124] The process of selecting different lengths of delay fiber for the first and second optical switches has been described in detail previously and will not be repeated here.

[0125] This invention also provides another distributed fiber optic acoustic wave sensing system based on an adjustable distributed fiber optic sensing performance enhancement device. This sensing system can be applied to various testing scenarios. (See reference...) Figure 2The sensing system includes a narrow linewidth laser, a splitter, an acousto-optic modulator, a first signal generator, a coupler, a low-noise optical amplifier, a first optical switch, a second optical switch, ... an nth optical switch (n>2), delay fibers of different lengths, an acousto-optic frequency shifter, a second signal generator, a third signal generator, a circulator, sensing fibers, and a detection and demodulation module.

[0126] A single-frequency laser generated by a narrow-linewidth laser is split into two paths by a splitter. The first path enters the detection and demodulation module, while the second path is modulated by an acousto-optic modulator to form narrowband linear chirped pulses. A first signal generator generates a narrowband linear chirped function signal, which controls the acousto-optic modulator to modulate the single-frequency laser into narrowband linear chirped pulses. The chirped pulses then enter a frequency shift loop (coupler, low-noise optical amplifier, first optical switch, second optical switch...nth optical switch, delay fiber, acousto-optic frequency shifter, second signal generator, third signal generator) for frequency shifting. The second signal generator generates a first electrical signal to control the acousto-optic frequency shifter, thereby controlling the number of cyclic frequency shifts. The third signal generator generates a second electrical signal, which controls the first optical switch to open channel 1 (close channel 2) or open channel 2 (close channel 1). The second electrical signal also controls the second optical switch to open channels 1 and 3 (close channels 2 and 4), or open channels 2 and 3 (close channels 1 and 4), or open channel 1. 4 (Close channels 2 and 3) or open channels 2 and 4 (close channels 1 and 3); the second electrical signal controls the third optical switch to open channels 1 and 3 (close channels 2 and 4) or open channels 2 and 3 (close channels 1 and 4) or open channels 1 and 4 (close channels 2 and 3) or open channels 2 and 4 (close channels 1 and 3)... The second electrical signal controls the nth optical switch to open channel 1 (close channel 2) or open channel 2 (close channel 1), selecting a suitable length of delay fiber; low-noise optical amplifier is used. To compensate for cyclic loss, the chirped pulse light undergoes multiple cyclic frequency shifts to generate multiple narrowband chirped pulses. These multiple narrowband chirped pulses are seamlessly spliced ​​in the time domain and finally output as chirped continuous light through a coupler. The chirped continuous light enters the sensing fiber through a circulator and undergoes Rayleigh scattering in the sensing fiber, generating backscattered Rayleigh light. The backscattered Rayleigh light returns to the circulator and enters the detection and demodulation module, where it interferes with the first laser. The interference light is detected and demodulated by the detection and demodulation module, thereby obtaining the fiber vibration information.

[0127] By setting optical switches (first optical switch, second optical switch...nth optical switch) and delay fibers of different lengths within the frequency shift ring, it is possible to control the access of delay fibers of different lengths into the frequency shift ring through multiple optical switches according to different testing requirements of the sensing system. This allows for flexible implementation of equivalent delay fibers of different lengths, changing the fiber length within the frequency shift ring, thereby flexibly adjusting parameters such as the chirping rate and bandwidth of the chirped continuous light, improving the response bandwidth of the sensing system, and making the sensing system suitable for occasions with different testing requirements.

[0128] The process of selecting different equivalent delay fiber lengths for the first optical switch, the second optical switch, ... the nth optical switch is as follows:

[0129] According to the testing requirements of the sensing system, the third signal generator generates a second electrical signal, which controls the first optical switch to open channel 1 (close channel 2) or open channel 2 (close channel 1); the second electrical signal controls the second optical switch to open channels 1 and 3 (close channels 2 and 4), or open channels 2 and 3 (close channels 1 and 4), or open channels 1 and 4 (close channels 2 and 3), or open channels 2 and 4 (close channels 1 and 3); the second electrical signal controls the third optical switch to open channels 1 and 3 (close channels 2 and 4), or open channels 2 and 3 (close channels 1 and 4), or open channels 1 and 4 (close channels 2 and 3), or open channels 2 and 4 (close channels 1 and 3)... the second electrical signal controls the nth optical switch to open channel 1 (close channel 2) or open channel 2 (close channel 1).

[0130] Delay fiber 1 has a length of L1; delay fiber 2 has a length of L2; delay fiber 3 has a length of L3... delay fiber n-1 has a length of L... n-1 .

[0131] When L1 is a delay fiber of suitable length, the electrical signal output by the signal generator 3 controls the first optical switch channel 1 to open, the second optical switch channels 1 and 4 to open, the third optical switch channels 2 and 4 to open, ... the nth optical switch channel 2 to open. At this time, the delay fiber 1 is connected to the loop, and the remaining delay fibers are disconnected from the loop.

[0132] When L1+L3 is a suitable length of delay fiber, the electrical signal output by the signal generator 3 controls the first optical switch channel 1 to open, the second optical switch channels 1 and 4 to open, the third optical switch channels 3 and 4 to open, the fourth optical switch channels 1 and 4 to open... and the nth optical switch channel 2 to open. At this time, delay fiber 1 and delay fiber 3 are connected to the loop, and the remaining delay fibers are disconnected from the loop.

[0133] ...

[0134] When L1+L2+L3+……L n-1 When the length of the delay fiber is appropriate, the electrical signal output by the signal generator 3 controls the first optical switch channel 1 to open, the second optical switch channels 1 and 3 to open, the third optical switch channels 1 and 3 to open, the fourth optical switch channels 1 and 3 to open, ... the nth optical switch channel 1 to open. At this time, the delay fiber 1, delay fiber 2, delay fiber 3 ... delay fiber n are connected to the loop, and the remaining delay fibers are disconnected from the loop.

[0135] Compared to the aforementioned embodiments, shorter delay fibers can be used to achieve a greater equivalent length of delay fiber.

[0136] The principles for setting the length of the delay fiber in the frequency shift loop have been described in detail above and will not be repeated here.

[0137] Continue to refer to Figure 2 Furthermore, wide-bandwidth multi-frequency pulsed light with a certain time interval can be injected into the sensing fiber in this sensing system. The wide-bandwidth multi-frequency pulsed light can be used to improve the response bandwidth of the sensing system, making the sensing system flexibly applicable to different testing needs.

[0138] The specific process is as follows:

[0139] The laser light generated by the narrow linewidth laser is split into two paths by a splitter. The first path enters the detection and demodulation module, and the second path is modulated by an acousto-optic modulator to form a single-frequency pulse light. A signal generator generates a pulse function signal, which controls the acousto-optic modulator to modulate the single-frequency laser light into a single-frequency pulse light. The single-frequency pulse light enters a frequency shift loop (coupler, low-noise optical amplifier, first optical switch, second optical switch...nth optical switch, delay fibers of different lengths, acousto-optic frequency shifter, second signal generator, and third signal generator) for multiple cyclic frequency shifts. The second signal generator generates a first electrical signal to control the acousto-optic frequency shifter, thereby controlling the number of cyclic frequency shifts. The third signal generator generates... The device generates a second electrical signal, which controls the first optical switch, the second optical switch, ... the nth optical switch to open or close the corresponding switch channels connected to multiple delay optical fibers of different lengths, and selects a suitable length of delay optical fiber; the low-noise optical amplifier is used to compensate for cycle loss; after multiple cyclic frequency shifts, the single-frequency pulse light generates broadband multi-frequency pulses with equal time intervals. The broadband multi-frequency pulses enter the sensing optical fiber through the circulator, where Rayleigh scattering occurs, generating backscattered Rayleigh light. The backscattered Rayleigh light returns to the circulator and enters the detection and demodulation module, where it interferes with the first laser. The interference light is detected and demodulated by the detection and demodulation module, thereby obtaining the fiber vibration information.

[0140] The process of selecting different lengths of delay fiber for the first optical switch, the second optical switch, ... the nth optical switch has been described in detail above and will not be repeated here.

[0141] Continue to refer to Figure 2 Furthermore, wide-bandwidth chirped pulse light can be injected into the sensing fiber in this sensing system to improve the spatial resolution of the sensing system, enabling the sensing system to be flexibly applied to different testing needs.

[0142] The generation process of wideband chirped pulse light in this sensing system is roughly the same as that of wideband chirped continuous light. The difference is that multiple narrowband chirped pulses generated by the frequency shifting loop after multiple cyclic frequency shifts are seamlessly spliced ​​in the time domain and then output as chirped pulse light through a coupler.

[0143] When a wide-bandwidth chirped pulse light is injected into the sensing fiber, the principle for setting the length of the delay fiber is to select the shortest possible delay fiber.

[0144] The process of selecting different lengths of delay fiber for the first optical switch, the second optical switch, ... the nth optical switch has been described in detail above and will not be repeated here.

[0145] Continue to refer to Figure 2 Furthermore, the sensing fiber in this sensing system can also be injected with wide-bandwidth multi-frequency pulse light without time interval. The spatial resolution of the sensing system can be improved by using wide-bandwidth multi-frequency pulse light, making the sensing system flexibly applicable to different testing needs.

[0146] When the sensing system operates in spatial resolution mode, it generates Figure 8 In this process, broadband multi-frequency pulses are used to improve the spatial resolution of the system. An optical switch within the frequency shift loop selects the delay fiber to adapt to the set pulse width, minimizing the time-domain interval between pulses, or ideally, eliminating it entirely (though in practice, a narrow time-domain interval is possible). The improvement in system spatial resolution is determined by the frequency domain bandwidth of the generated multi-frequency pulses.

[0147] When broadband multi-frequency pulse light without time-domain intervals is injected into the sensing fiber, the principle for setting the length of the delay fiber is to select the shortest length delay fiber.

[0148] The process of selecting different lengths of delay fiber for the first optical switch, the second optical switch, ... the nth optical switch has been described in detail above and will not be repeated here.

[0149] The above description is merely a detailed illustration of specific embodiments of the present invention and is not intended to limit the invention. Various substitutions, modifications, and improvements made by those skilled in the art without departing from the principles and scope of the present invention should be included within the protection scope of the present invention.

Claims

1. An adjustable distributed optical fiber sensing performance enhancement device, characterized in that, include: Narrow linewidth laser, acousto-optic modulator, first signal generator, and frequency shift loop; The narrow linewidth laser is configured to output narrow linewidth laser light to an acousto-optic modulator; The first signal generator is configured to generate a pulse function signal, which controls an acousto-optic modulator to modulate a single-frequency laser into pulsed light. The acousto-optic modulator is configured to modulate the single-frequency laser entering the acousto-optic modulator into corresponding pulsed light according to the pulse function signal generated by the first signal generator; The frequency shift loop is configured to perform multiple cyclic frequency shifts on the pulse light entering it, thereby generating a wide-bandwidth multi-frequency optical output; The frequency shift loop includes a coupler, a low-noise optical amplifier, at least two optical switches, multiple delay fibers of different lengths, an acousto-optic frequency shifter, a second signal generator, and a third signal generator; The pulsed light generated by the acousto-optic modulator before the frequency shift loop enters the frequency shift loop through the coupler; The low-noise optical amplifier is configured to compensate for cyclic frequency shift loss; The third signal generator is configured to generate a second electrical signal to turn different switching channels of each optical switch on or off. Each optical switch is configured to open or close the corresponding switch channel connected to delay optical fibers of different lengths under the action of the second electrical signal according to the test requirements, so that the delay optical fiber of the corresponding length is connected to the frequency shift loop and the appropriate length of delay optical fiber is selected. The second signal generator is configured to generate a first electrical signal to control the acousto-optic frequency shifter, thereby controlling the number of frequency shifts of the pulsed light within the frequency shift loop; The acousto-optic frequency shifter is configured to shift the frequency of the pulsed light entering the acousto-optic frequency shifter according to the first electrical signal generated by the second signal generator; The pulsed light is cyclically shifted multiple times within the frequency shift loop to generate wide-bandwidth multi-frequency light, which is then output via a coupler.

2. The adjustable distributed optical fiber sensing performance enhancement device according to claim 1, characterized in that, The first signal generator is configured to generate a narrowband linear chirped function signal, which controls an acousto-optic modulator to modulate a single-frequency laser into a narrowband linear chirped pulse light. The acousto-optic modulator is configured to modulate a single-frequency laser entering the acousto-optic modulator into a narrowband linear chirped pulse light based on a narrowband linear chirped function signal generated by a first signal generator. The narrowband linear chirped pulse light enters the frequency shift loop through the coupler and is cyclically shifted multiple times to generate multiple narrowband chirped pulses. The multiple narrowband chirped pulses are seamlessly spliced ​​in the time domain to form broadband chirped continuous light or broadband chirped pulse light, which is then output through the coupler.

3. The adjustable distributed optical fiber sensing performance enhancement device according to claim 1, characterized in that, The first signal generator is configured to generate a pulse function signal, which controls an acousto-optic modulator to modulate a single-frequency laser into a single-frequency pulse light. The acousto-optic modulator is configured to modulate the single-frequency laser entering the acousto-optic modulator into a single-frequency pulse light according to the pulse function signal generated by the first signal generator; The single-frequency pulse light enters the frequency shifting loop through the coupler and undergoes multiple cyclic frequency shifts to generate a wide-bandwidth multi-frequency pulse light with a certain time-domain interval or no time-domain interval, which is then output through the coupler.

4. A sensing system based on an adjustable distributed optical fiber sensing performance enhancement device, characterized in that, The device includes the adjustable distributed optical fiber sensing performance enhancement device, splitter, circulator, sensing optical fiber, and detection demodulation module as described in any one of claims 1 to 3. The splitter is configured to split the narrow-linewidth laser generated by the narrow-linewidth laser into two paths. The first path enters the detection and demodulation module, and the second path is used to generate wide-bandwidth multi-frequency light. Wideband multi-frequency light enters the sensing fiber through the circulator, undergoes Rayleigh scattering in the sensing fiber, and generates back Rayleigh scattered light. The back Rayleigh scattered light returns to the circulator and enters the detection demodulation module through the circulator, where it interferes with the first laser. The detection and demodulation module is configured to demodulate the vibration information of the sensing fiber based on the interference light.

5. A method for improving the sensing performance of a sensing system based on an adjustable distributed optical fiber sensing performance enhancement device, characterized in that, The adjustable distributed fiber optic sensing performance enhancement device according to any one of claims 1 to 3 includes the following steps: The narrow-linewidth laser is turned on and split into two paths by a splitter. The first path enters the detection and demodulation module, and the second path enters the acousto-optic modulator. The first signal generator produces a pulse function signal to control the acousto-optic modulator, modulating the single-frequency laser into corresponding pulsed light. The pulsed light enters the frequency shift loop through a coupler, where it undergoes multiple cyclic frequency shifts to generate wide-bandwidth multi-frequency light. This wide-bandwidth multi-frequency light is output through a coupler and injected into the sensing fiber. The wide-bandwidth multi-frequency light undergoes Rayleigh scattering in the sensing fiber, generating backscattered Rayleigh light. This backscattered light returns to the circulator and enters the detection and demodulation module, where it interferes with the first laser path. The interference light is detected and demodulated by the detection and demodulation module, thereby obtaining the fiber vibration information.

6. The method according to claim 5, characterized in that, When broadband chirped continuous light is injected into the sensing fiber, the method for setting the length of the delay fiber within the frequency shift loop is as follows: Chirped continuous optical cycle It should meet the following requirements: ,in, n The refractive index of the optical fiber. L The length of the sensing fiber. For system spatial resolution, c The speed of light in a vacuum; Let the pulse width of the chirped pulse generated by the single-frequency laser before the frequency shift loop after modulation by the acousto-optic modulator be... The cycle is The length of the delay fiber is selected by the first optical switch and the second optical switch, which determines the duration of one cycle of the frequency shift loop for the light. satisfy: ,in, L c This represents the total length of all optical fibers in the frequency shift loop, excluding the delay fiber. L d This refers to the length of the delay fiber. Let the frequency shift step size of the acousto-optic frequency shifter within the frequency shift loop be B, and the number of cyclic frequency shifts be m. Then the total frequency shift bandwidth is B. a =(m+1)*B; Chirped continuous optical cycle Chirped pulse width Chirped pulse period The cyclic frequency shift number m satisfies the following relationship: Therefore, the length of the delay fiber and the length of the sensing fiber satisfy the following relationship: 。 7. The method according to claim 5, characterized in that, When a wide-bandwidth multi-frequency pulse light with a certain time-domain interval is injected into the sensing fiber, the method for setting the length of the delay fiber in the frequency shift loop is as follows: Suppose that, according to the test requirements, after injecting wide-bandwidth multi-frequency pulse light into the sensing fiber, the response bandwidth of the sensing system is increased by a factor of k compared to injecting a single-frequency pulse into the sensing fiber. Then the number of cyclic frequency shifts should be m = k-1 times. The multi-frequency pulse period used in the sensing system is It should meet the following requirements: ； Where n is the refractive index of the optical fiber. L The length of the sensing fiber. For system spatial resolution, c The speed of light in a vacuum; Let the time-domain interval of each frequency component pulse in the multi-frequency pulse be . Then we have: ； in, L c This represents the total length of all optical fibers in the frequency shift loop, excluding the delay fiber. L d This refers to the length of the delay fiber. Then the multi-frequency pulse period The time-domain interval of each frequency component in a multi-frequency pulse The cyclic frequency shift number m satisfies the following relationship: ； Therefore, the lengths of the delay fiber and the sensing fiber, along with the target bandwidth enhancement factor, satisfy the following relationship: 。 8. The method according to claim 5, characterized in that, When the frequency shifting loop includes a first optical switch and a second optical switch, during the cyclic frequency shifting process, the first optical switch and the corresponding switch channels connected to the second optical switch and different length delay fibers are opened or closed according to the second electrical signal generated by the third signal generator, and different length delay fibers are selected. When the frequency shift loop includes two or more optical switches, during the cyclic frequency shifting process, the corresponding switch channel connected to each optical switch and the delay fiber of different length is opened or closed according to the second electrical signal generated by the third signal generator, and the equivalent delay fiber of different length is selected.

9. The method according to claim 7, characterized in that, The adjustable distributed optical fiber sensing performance enhancement device improves the sensing system response bandwidth by 1 to 1000 times, the total bandwidth of the wide bandwidth multi-frequency pulse light is 0.1 to 10 GHz, and the pulse time-domain interval of each frequency component in the wide bandwidth multi-frequency pulse light is 0.1 to 48.67 μs.

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