DAS gas detection system based on quantum weak measurement

Abstract

This invention relates to the fields of quantum precision measurement and distributed fiber optic sensing technology, and discloses a DAS gas detection system based on quantum weak measurement, including a DAS device, a pre-selection module, a weak coupling module, a post-selection module, and a measurement module. The post-selection module includes a half-wave plate and a polarization beam splitter. The DAS device outputs a backscattered Rayleigh signal carrying coal and rock deformation signals. After polarization control by the pre-selection module, the backscattered Rayleigh signal is coupled with the local oscillator light through the weak coupling module and sent to the half-wave plate for polarization adjustment. The light field of the half-wave plate is output by the polarization beam splitter and sent to the measurement module for detection and demodulation to obtain the coal and rock deformation signal, thereby realizing the monitoring of gas outburst conditions. This invention has high detection sensitivity and can be widely used in real-time monitoring and early warning of coal and gas outbursts.

Description

Technical Field

[0001] This invention relates to the fields of quantum precision measurement and distributed optical fiber sensing technology, and in particular to a DAS gas detection system based on quantum weak measurement. Background Technology

[0002] Coal and gas outbursts and other dynamic disasters during coal mining pose significant hazards, necessitating real-time monitoring. Current coal mine outburst prediction relies primarily on conventional indicators such as drill cuttings volume, initial gas emission velocity from boreholes, and borehole desorption indices, as well as geophysical methods like electromagnetic radiation and acoustic emission. These methods are essentially point-based detection, deploying a limited number of measuring points on the roadway or coal face to infer the critical state of the entire geological body ahead of the mining face using local information. However, coal and gas outbursts are nonlinear abrupt changes involving the coupling of three fields: geostress, gas pressure, and coal strength, exhibiting a high degree of spatial heterogeneity in their development and evolution. Covering the entire geological body ahead of the working face with sparse point monitoring inevitably creates numerous spatiotemporal blind spots, making it difficult to capture the formation and evolution of outburst sources. In contrast, fiber optic sensing technology offers advantages in coal and gas monitoring, including ease of installation, long-distance transmission capability, comprehensive coverage without blind spots, distributed sensing of stress changes, and immunity to environmental factors such as light. Overcoming the limitations of point-based monitoring, continuous monitoring along roadways for tens of kilometers can be achieved, constructing a comprehensive sensing network covering the area in front of the mining face. However, coal and gas outbursts are often accompanied by extremely weak subsonic infrasound waves, micro-fracture signals, and electromagnetic radiation. The sensitivity of existing sensors and signal processing algorithms are insufficient to reliably extract these precursory information from strong noise backgrounds, leading to a large number of outburst accidents occurring without warning.

[0003] Chinese patent document CN120667205A discloses a method for monitoring the regional fracturing influence range based on distributed fiber optic acoustic sensing. This method uses a DAS (distributed fiber optic acoustic sensing) system to acquire raw signals, identify microseismic events and P-wave arrival times, and combines this with MCMC (Markov Chain Monte Carlo) algorithm to determine the distribution location of microseismic events, thus achieving accurate characterization of the fracturing influence range. However, this method suffers from time-consuming large-scale iterative calculations in the MCMC algorithm, resulting in poor real-time performance. It is also susceptible to environmental noise from downhole pumps, drilling sites, etc., leading to insufficient signal-to-noise ratio, weak anti-interference ability, and the easy submersion of weak fracturing signals by noise. Chinese patent document CN117706625A discloses a DAS-based method for monitoring microseismic events in coal seam fracturing. This method utilizes a DAS system deployed along the fracturing monitoring well to collect data, identifies microseismic events through wavelet transform denoising and waveform cross-correlation, and combines constrained location methods and travel-time difference methods to locate the seismic source, improving the signal-to-noise ratio and location accuracy of the monitoring data. However, this method involves a cumbersome denoising process and relies on manual parameter tuning. It also suffers from insufficient signal fidelity in noisy downhole environments, low sensitivity in identifying microseismic signals, and an inability to effectively capture low-amplitude microseismic signals, making it difficult to meet the high-precision monitoring requirements under complex geological conditions. Overall, current research primarily focuses on improving signal processing methods, which requires sacrificing signal measurement or processing time to compensate for the sensitivity reduction caused by large noise tolerance. This results in time delays in accident monitoring, a critical issue for gas early warning systems.

[0004] Therefore, there is an urgent need for a high-sensitivity detection system that can achieve weak signal detection through experimental devices during the detection process, so as to reduce the signal processing time of the back-end system and thus improve the reliability of gas early warning. Summary of the Invention

[0005] To address the issue of low sensitivity in traditional DAS sensing technology, this invention proposes a gas detection system and method based on quantum weak measurement DAS technology to achieve real-time monitoring and early warning of coal and gas outburst problems.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a DAS gas detection system based on quantum weak measurement, comprising: a DAS device, a pre-selection module, a weak coupling module, a post-selection module, and a measurement module; the post-selection module includes a half-wave plate and a polarization beam splitter; The DAS device is used to output a backscattered Rayleigh signal carrying coal and rock deformation signals from the sensing fiber. The preselection module is used to perform polarization and polarization control on the backscattered Rayleigh signal before sending it to the weak coupling module. The preselection module is configured to make the polarization direction of the backscattered Rayleigh signal without deformation signals parallel to the polarization corresponding to the output end of the polarization beam splitter. The weak coupling module is used to couple it with the local oscillator of the DAS device and then send it to the half-wave plate. The half-wave plate is used to rotate the polarization of the beat frequency signal output by the weakly coupled module by °; the beat frequency signal after polarization adjustment by the half-wave plate is incident on the polarization beam splitter, and after being output by the polarization beam splitter, it is sent to the measurement module for detection and demodulation to obtain the coal and rock deformation signal, thereby realizing the monitoring of gas outburst status.

[0007] The pre-selection module includes: an optical fiber polarizer and a first polarization controller. The optical fiber polarizer is located at the output end of the DAS device and is used to polarize the backscattered Rayleigh light output by the DAS device. The first polarization controller is located at the output end of the optical fiber polarizer and is used to adjust the polarization of the polarized backscattered Rayleigh light so that its polarization direction is parallel to the polarization corresponding to the output end of the polarization beam splitter.

[0008] The DAS device includes a first polarization-maintaining coupler and a second polarization controller, and the weak coupling module includes a second polarization-maintaining coupler. The first polarization-maintaining coupler is used to separate a portion of the laser output from the laser in the DAS device as the local oscillator light. The second polarization controller is used to adjust the polarization of the local oscillator light so that it is parallel to the polarization of the output terminal of the post-selection module. The second polarization-maintaining coupler is used to couple the back Rayleigh scattering signal output from the pre-selection module after polarization and polarization control with the local oscillator light and then send it to the post-selection module.

[0009] The measurement module includes a photodetector, a data acquisition card, and a data processor. The backscattered Rayleigh light and the local oscillator light after passing through the selection module are detected by the photodetector and converted into photoelectric signals. The acquisition card then collects the beat frequency signal and sends it to the data processor for demodulation to obtain the coal and rock deformation signal.

[0010] The DAS device includes a laser, an acousto-optic modulator, a first erbium-doped fiber amplifier, an optical circulator, and a sensing fiber. The continuous light output from the laser is modulated into pulsed light by an acousto-optic modulator, and then injected into the sensing fiber through an optical circulator after passing through the first erbium-doped fiber amplifier. The backscattered Rayleigh light generated in the sensing fiber returns to the optical circulator and is then output through the optical circulator.

[0011] The DAS device also includes a second erbium-doped fiber amplifier. The backscattered Rayleigh light generated in the sensing fiber is output by the optical circulator, amplified by the second erbium-doped fiber amplifier, and then sent to the preselection module.

[0012] The DAS gas detection system based on quantum weak measurement also includes a signal generator, which drives an acousto-optic modulator to modulate the continuous light output by the laser into pulsed light.

[0013] The sensing optical fiber is a polarization-maintaining fiber, which is laid in the underground mining face and key sections of the roadway.

[0014] The DAS gas detection system based on quantum weak measurement further includes a first filter and a second filter; The first filter is disposed at the output end of the DAS device to filter out back Rayleigh scattered light; The second filter is located at the output end of the polarization beam splitter and is used to filter out stray light.

[0015] Compared with the prior art, the present invention has the following advantages: (1) This invention utilizes the high sensitivity of quantum weak measurement to minute differences in quantum states and the weak value amplification effect to amplify the weak phase shift signal caused by weak deformation of optical fiber at the quantum level, thereby realizing the effective extraction of nano-strain level sub-audio frequency precursor signals, breaking through the traditional DAS detection limit, significantly improving the detection sensitivity of weak signals, and being able to detect weak coal and gas outburst precursor signals.

[0016] (2) This invention achieves the screening of specific physical fields by introducing a pre-selection module and a post-selection module, which can separate the real geomechanical signal from the background of strong industrial noise, suppress environmental noise interference, improve the signal-to-noise ratio, and thus significantly improve the detection capability of the system. At the same time, by using the pre-selection module and the post-selection module to achieve the orthogonality of the polarization final state and the initial state, weak value amplification can be achieved, which can reduce the phase drift caused by slowly varying interferences such as temperature and stress, reduce the system background noise, and improve the measurement stability in complex environments.

[0017] (3) The present invention uses a weak coupling mechanism between quantum weak measurement and local oscillator light as a pointer. The measurement process hardly interferes with the quantum state of the propagating light field in the optical fiber. It can completely preserve the phase, amplitude and frequency information of weak vibration signal, reduce measurement disturbance and signal distortion, improve dynamic signal fidelity, obtain more real and complete weak vibration waveform information, and improve the anti-interference ability of the system.

[0018] In summary, this invention, based on quantum weak measurement and DAS for gas detection, has high detection sensitivity and can effectively capture subsonic infrasound and micro-rupture signals preceding a gas outburst, thus enabling early warning of disasters. Attached Figure Description

[0019] Figure 1 A structural block diagram of a gas detection system based on quantum weak measurement DAS technology provided in an embodiment of the present invention; Figure 2 A schematic diagram of a gas detection system based on quantum weak measurement DAS technology provided in an embodiment of the present invention; In the diagram: 1 is a narrow linewidth laser, 2 is the first polarization-maintaining coupler, 3 is an acousto-optic modulator, 4 is a signal generator, 5 is the first erbium-doped fiber amplifier, 6 is an optical circulator, 7 is a sensing fiber, 8 is the second erbium-doped fiber amplifier, 9 is the first polarization controller, 10 is the first filter, 11 is the polarization-maintaining fiber polarizer, 12 is the second polarization controller, 13 is the second polarization-maintaining coupler, 14 is a half-wave plate, 15 is a polarization beam splitter, 16 is the second filter, 17 is a photodetector, 18 is a data acquisition card, and 19 is a data processor. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, this embodiment of the invention provides a DAS gas detection system based on quantum weak measurement, including: a DAS device, a pre-selection module, a weak coupling module, a post-selection module, and a measurement module.

[0022] Specifically, in this embodiment, the post-selection module includes a half-wave plate 14 and a polarization beam splitter 15. The DAS device outputs a backscattered Rayleigh signal carrying coal and rock deformation signals from the sensing fiber 7. The pre-selection module performs polarization control on the backscattered Rayleigh signal before sending it to the weak coupling module. The pre-selection module is configured to make the polarization direction of the backscattered Rayleigh signal without deformation signals parallel to the polarization corresponding to the output of the polarization beam splitter 15. The weak coupling module couples the signal with the local oscillator of the DAS device and sends it to the half-wave plate 14 of the post-selection module. The half-wave plate 14 adjusts the polarization of the beat frequency signal output by the weak coupling module, rotating it by 90°. The beat frequency signal, after polarization adjustment by the half-wave plate 14, is incident on the polarization beam splitter 15. After being output by the polarization beam splitter 15, it is sent to the measurement module for detection and demodulation to obtain the coal and rock deformation signal, thereby realizing gas outburst monitoring.

[0023] Specifically, for the back Rayleigh scattering signal without any variable signal, after the polarization is adjusted by the half-wave plate 14 and rotated by 90°, its polarization direction is orthogonal to the polarization corresponding to the output end of the polarization beam splitter 15.

[0024] In this embodiment, the output end of the polarization beam splitter 15 is the transmission end, and its corresponding polarization is horizontally polarized light, with the transmission axis direction being horizontal. When the sensing fiber 7 is not strained, the polarization of the backscattered Rayleigh signal output by the pre-selection module is the same as that of the polarization beam splitter 15. After being polarized and rotated by the half-wave plate 14, it becomes vertically polarized light, which is orthogonal to the horizontal polarization of the output end of the polarization beam splitter 15 and cannot be output from the output end of the polarization beam splitter 15. When strain changes occur in the sensing fiber 7, the phase of the backscattered Rayleigh signal shifts, and the polarization angle changes. After passing through the half-wave plate 14, the photons carrying weak signals in the backscattered Rayleigh signal rotate from the current polarization state. Some of the rotated photons can be output from the output end of the polarization beam splitter 15 and then enter the photodetector 17, while the remaining photons are reflected and discarded by the polarization beam splitter 15.

[0025] Malus's law describes the relationship between the intensity of linearly polarized light transmitted through a polarizing beam splitter and the square of the polarization angle. When linearly polarized light is incident on polarizing beam splitter 15, the intensity of the transmitted light satisfies: ; (1) in, Indicates the intensity of incident ray-polarized light. This indicates the output light intensity at the transmission end of the polarization beam splitter. This represents the angle between the polarization direction of the incident light and the transmission axis of the polarization beam splitter 15. The polarization state of the linearly polarized light is nearly orthogonal to the transmission axis of the polarization beam splitter 15. In the near-orthogonal polarization operating range, the slope of the Malus's law response curve is extremely large. Through Malus's law, the minute polarization angle changes caused by gas and coal rock disturbances in the optical fiber are converted into light intensity changes that can be collected by the photodetector 17.

[0026] In the measurement module of this embodiment, the coupling degree between the signal light and the reference light can be determined by the weak amplification factor. To describe. Weak value amplification factor. The calculation formula is: ; (2) In the formula, Indicates the initial state of the system. The final state after selection is represented by A, which represents the Pauli operator. The formula for calculating the weak value amplification factor reveals that the measurement results can be significantly amplified through the pre-selection and post-selection modules in this invention. Specifically, by precisely adjusting the direction of the final state, when the final state is nearly orthogonal to the initial state, that is... →0, weak values ​​can be much larger than the system's eigenvalue range.

[0027] Furthermore, such as Figure 2 As shown, in this embodiment, the pre-selection module includes: an optical fiber polarizer 11 and a first polarization controller 12. The optical fiber polarizer 11 is disposed at the output end of the DAS device and is used to polarize the backscattered Rayleigh light output by the DAS device. The first polarization controller 12 is disposed at the output end of the optical fiber polarizer 11 and is used to adjust the polarization of the polarized backscattered Rayleigh light so that its polarization direction is parallel to the polarization corresponding to the output end of the polarization beam splitter 15. In this embodiment, the optical fiber polarizer 11 is a high-precision optical fiber polarizer with an extinction ratio greater than 30dB. It prepares the backscattered Rayleigh light returned from the sensing fiber into linearly polarized light, and then controls the polarization direction through the first polarization controller 12. The polarization state of the light output by the first polarization controller 12 is the initial state |ψi>.

[0028] Furthermore, such as Figure 2 As shown, in this embodiment, the DAS device includes a first polarization-maintaining coupler 2 and a second polarization controller 9, and the weak coupling module includes a second polarization-maintaining coupler 13. The first polarization-maintaining coupler 2 is used to separate a portion of the laser output from the laser 1 in the DAS device as the local oscillator light. The second polarization controller 9 is used to adjust the polarization of the local oscillator light so that it is parallel to the polarization of the output terminal of the post-selection module. The second polarization-maintaining coupler 13 is used to couple the backscattered Rayleigh scattering signal output from the pre-selection module after polarization and polarization control with the local oscillator light and then send it to the post-selection module.

[0029] Specifically, in this embodiment, the second polarization-maintaining coupler 13 is an ultra-low loss polarization-maintaining fiber coupler. The reference light serves as the measurement pointer, and the phase shift of the back Rayleigh scattered light relative to the reference light is proportional to the external strain information to be measured. The splitting ratio of the second polarization-maintaining coupler 13 is set to 1:99, with 1% of the port connected to the output of the second polarization controller 9 to ensure that the interaction intensity is kept at a low level.

[0030] Furthermore, such as Figure 2 As shown, in this embodiment, the measurement module includes a photodetector 17, a data acquisition card 18, and a data processor 19. The backscattered Rayleigh light and the local oscillator light after passing through the post-selection module are detected by the photodetector 17 and converted into photoelectric signals. The acquisition card 18 then acquires the beat frequency signal and sends it to the data processor 19 for demodulation to obtain the coal and rock deformation signal.

[0031] Specifically, in this embodiment, the photodetector 17 is an MPPC single-photon detector module.

[0032] Specifically, in this embodiment, the data processor 19 is equipped with signal processing algorithm software based on the weak value amplification effect to perform weak value calculation and signal reconstruction on the beat frequency signal output by the acquisition card 18, so as to realize the real-time extraction and feature recognition of subsonic frequency infrasound and micro-fracture signals, thereby monitoring the coal and gas outburst state.

[0033] During stress accumulation, crack propagation, and gas migration, coal and rock masses undergo slight deformation. This deformation, when applied to the sensing fiber, induces dynamic phase perturbations in the backscattered Rayleigh light. When the post-selected polarization state is nearly orthogonal to the pre-selected polarization state, the system exhibits a weak amplification effect, causing the original weak phase perturbation to... Enlarged to: ; (3) in, This represents the equivalent phase response after weak-value amplification. This represents the weak-value amplification factor.

[0034] The backscattered signal, after weak amplification, interferes with the local oscillator light at the detector end. The beat frequency signal output by photodetector 17 can be expressed as: ; (4) Where A(t) is the amplitude of the beat frequency signal. The frequency difference between the local oscillator light and the signal light. This is the dynamic phase information after weak amplification.

[0035] Data processor 19 employs a digital down-conversion (DDC) method to perform quadrature demodulation on the beat frequency signal. Data processor 19 first mixes the original beat frequency signal with a local reference cosine signal and a sine signal, respectively, and then performs a low-pass filter to obtain the in-phase component. Orthogonal components , in-phase component Orthogonal components It can be represented as: ; (5) ; (6) Further utilizing the arctangent operation, the dynamic phase information after weak amplification can be obtained. The calculation formula is as follows: ; (7) Since the phase may jump by 2π during dynamic vibration, a phase expansion algorithm is needed to recover the continuous phase sequence in order to obtain the complete weakly amplified post-dynamic phase information. .

[0036] To recover the true vibration information of coal and rock, the amplified phase can be inverted based on the weak amplification factor Aw to obtain the original dynamic phase disturbance. : ; (8) Furthermore, the vibration and strain information of coal and rock are recovered based on the DAS phase-strain conversion relationship.

[0037] For the recovered vibration signal, in this embodiment, the data processor 19 further employs a continuous time-domain analysis method based on a sliding time window to continuously analyze the vibration signal. First, the continuous vibration signal is segmented into windows of fixed time length, and continuous time-domain tracking is achieved through a sliding update method. To improve the detection stability of weak vibration signals, the vibration energy within adjacent time windows is cumulatively enhanced, thereby improving the detectability of weak events under low signal-to-noise ratio conditions. Since the propagation of microcracks in coal and rock typically manifests as high-frequency pulse vibrations, while gas migration generates low-frequency continuous infrasound, different frequency bands are used for analysis. Within each time window, wavelet threshold denoising is first used to suppress random shot noise and environmental noise, and then an adaptive bandpass filter is used to separate vibrations in different frequency bands. Specifically, the 0.01–20 Hz band is used to extract subsonic and infrasound signals generated by gas migration; the 20–500 Hz band is used to extract vibration signals from the propagation and microfracture of microcracks in coal and rock.

[0038] To achieve early warning identification of coal and gas outbursts, in this embodiment, the data processor 19 further employs Short-Time Fourier Transform (STFT) to perform time-frequency analysis on the vibration signal and extracts characteristic parameters such as vibration energy, dominant frequency drift, spectral entropy, pulse count rate, and phase abrupt change rate. When a continuous increase in low-frequency infrasound energy is detected, coupled with a significant increase in high-frequency micro-fracture events, the system determines that the coal and rock mass is in a state of stress instability and gas outburst risk, and outputs early warning information to the monitoring platform.

[0039] Furthermore, such as Figure 2 As shown, in this embodiment, the DAS device includes a laser 1, an acousto-optic modulator 3, a first erbium-doped fiber amplifier 5, an optical circulator 6, and a sensing fiber 7. The continuous light output from the laser 1 is modulated into pulsed light by the acousto-optic modulator 3, and then injected into the sensing fiber 7 through the first erbium-doped fiber amplifier 5 and the optical circulator 6. The backscattered Rayleigh light generated in the sensing fiber 7 returns to the optical circulator 6 and is output through the optical circulator 6.

[0040] Furthermore, such as Figure 2 As shown, in this embodiment, the DAS device further includes a second erbium-doped fiber amplifier 8. The backscattered Rayleigh light generated in the sensing fiber 7 is output through the optical circulator 6, amplified by the second erbium-doped fiber amplifier 8, and then sent to the pre-selection module. The first port of the optical circulator 6 is connected to the output of the first erbium-doped fiber amplifier 5, the second port is connected to one end of the sensing fiber 7, and the third port is connected to the input of the second erbium-doped fiber amplifier 8.

[0041] Furthermore, the DAS gas detection system based on quantum weak measurement in this embodiment also includes a signal generator 4, which is used to drive the acousto-optic modulator 3 to modulate the continuous light output by the laser 1 into pulsed light.

[0042] Furthermore, in this embodiment, the sensing optical fiber 7 is a polarization-maintaining fiber to ensure polarization stability, and it is laid in the underground mining face and key sections of the roadway. Its total scale is 20 kilometers, including 10 kilometers in the coal mining face roadway, 6 kilometers in the tunneling face, and 4 kilometers in the main roadway and key structural areas.

[0043] Furthermore, such as Figure 2 As shown, a DAS gas detection system based on quantum weak measurement in this embodiment further includes a first filter 10 and a second filter 16; the first filter 10 is disposed at the output end of the DAS device and is used to filter out back Rayleigh scattered light; the second filter 16 is disposed at the output end of the polarization beam splitter 15 and is used to filter out stray light.

[0044] Furthermore, in this embodiment, laser 1 is a narrow linewidth laser with an output laser center wavelength of 1550.12 nm and a linewidth of less than 0.1 kHz. After being modulated by acousto-optic modulator 3, it generates a single-frequency pulse with a pulse width of 5 ns and a repetition period of 300 μs.

[0045] like Figure 2 As shown, the optical path transmission process in this embodiment of the invention is as follows: The continuous laser output from laser 1 is split into two beams after passing through the first polarization-maintaining coupler 2, with 90% of the light used as probe light and 10% used as local oscillator light; the probe light enters the acousto-optic modulator 3, and the signal generator 4 drives the acousto-optic modulator 3 to modulate it into pulse light. The pulse light is amplified by the first erbium-doped fiber amplifier 5 and then injected into the sensing fiber 7 through the optical circulator 6 for transmission. The backscattered Rayleigh light generated in the sensing fiber 7 returns to the optical circulator 6 and is output from the third port. After being amplified by the second erbium-doped fiber amplifier 8, the amplified backscattered Rayleigh light signal is sequentially filtered by the first filter. After passing through the fiber polarizer 11 and the first polarization controller 12, the light is incident on the second polarization-maintaining coupler 13. The local oscillator light is polarized by the second polarization controller 9 and then incident on the second polarization-maintaining coupler 13. The back Rayleigh scattered light signal and the local oscillator light beat at the second polarization-maintaining coupler 13. The signal after beating is polarized by the half-wave plate 14 and then incident on the polarization beam splitter 15. After passing through the polarization beam splitter 15, a portion of the photons parallel to the transmission axis of the polarization beam splitter 15 are output from the transmission end and enter the photodetector 17. Then, the beat signal is acquired by the acquisition card 18 and sent to the data processor 19 for demodulation to obtain the coal and rock deformation signal.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A DAS gas detection system based on quantum weak measurement, characterized in that, include: The device comprises a DAS device, a pre-selection module, a weakly coupled module, a post-selection module, and a measurement module; the post-selection module includes a half-wave plate (14) and a polarization beam splitter (15). The DAS device is used to output a backscattered Rayleigh signal carrying coal and rock deformation signals from the sensing fiber (7). The preselection module is used to perform polarization and polarization control on the backscattered Rayleigh signal and then send it to the weak coupling module. The preselection module is set to make the polarization direction of the backscattered Rayleigh signal without deformation signals parallel to the polarization corresponding to the output end of the polarization beam splitter (15). The weak coupling module is used to couple it with the local oscillator of the DAS device and then send it to the half-wave plate (14). The half-wave plate (14) is used to rotate the polarization of the beat frequency signal output by the weak coupling module by 90°. The beat frequency signal after polarization adjustment by the half-wave plate (14) is incident on the polarization beam splitter (15), and after being output by the polarization beam splitter (15), it is sent to the measurement module for detection and demodulation to obtain the coal and rock deformation signal, thereby realizing the monitoring of gas outburst status.

2. The DAS gas detection system based on quantum weak measurement according to claim 1, characterized in that, The pre-selection module includes: an optical fiber polarizer (11) and a first polarization controller (12). The optical fiber polarizer (11) is located at the output end of the DAS device and is used to polarize the back Rayleigh scattered light output by the DAS device. The first polarization controller (12) is located at the output end of the optical fiber polarizer (11) and is used to adjust the polarization of the back Rayleigh scattered light after polarization so that its polarization direction is parallel to the polarization corresponding to the output end of the polarization beam splitter (15).

3. The DAS gas detection system based on quantum weak measurement according to claim 1, characterized in that, The DAS device includes a first polarization-maintaining coupler (2) and a second polarization controller (9), and the weak coupling module includes a second polarization-maintaining coupler (13). The first polarization-maintaining coupler (2) is used to separate a portion of the laser output from the laser (1) in the DAS device as the local oscillator light. The second polarization controller (9) is used to adjust the polarization of the local oscillator light so that it is parallel to the polarization of the output terminal of the post-selection module. The second polarization-maintaining coupler (13) is used to couple the back Rayleigh scattering signal output from the pre-selection module after polarization and polarization control with the local oscillator light and send it to the post-selection module.

4. The DAS gas detection system based on quantum weak measurement according to claim 1, characterized in that, The measurement module includes a photodetector (17), a data acquisition card (18), and a data processor (19). The back Rayleigh scattering light and the local oscillator light after passing through the back selection module are detected by the photodetector (17) and converted by photoelectric conversion. The beat frequency signal is then acquired by the data acquisition card (18) and sent to the data processor (19) for demodulation to obtain the coal and rock deformation signal.

5. The DAS gas detection system based on quantum weak measurement according to claim 1, characterized in that, The DAS device includes a laser (1), an acousto-optic modulator (3), a first erbium-doped fiber amplifier (5), an optical circulator (6), and a sensing fiber (7). The continuous light output by the laser (1) is modulated into pulsed light by the acousto-optic modulator (3), and then injected into the sensing fiber (7) through the first erbium-doped fiber amplifier (5) and the optical circulator (6). The backscattered Rayleigh light generated in the sensing fiber (7) returns to the optical circulator (6) and is output through the optical circulator (6).

6. The DAS gas detection system based on quantum weak measurement according to claim 5, characterized in that, The DAS device also includes a second erbium-doped fiber amplifier (8). The backscattered Rayleigh light generated in the sensing fiber (7) is output by the optical circulator (6), amplified by the second erbium-doped fiber amplifier (8), and then sent to the preselection module.

7. The DAS gas detection system based on quantum weak measurement according to claim 5, characterized in that, It also includes a signal generator (4) for driving an acousto-optic modulator (3) to modulate the continuous light output from the laser (1) into pulsed light.

8. The DAS gas detection system based on quantum weak measurement according to claim 5, characterized in that, The sensing fiber (7) is a polarization-maintaining fiber, which is laid in the underground mining face and key sections of the roadway in the coal mine.

9. The DAS gas detection system based on quantum weak measurement according to claim 1, characterized in that, It also includes a first filter (10) and a second filter (16); The first filter (10) is disposed at the output end of the DAS device to filter out back Rayleigh scattered light; The second filter (16) is set at the output end of the polarization beam splitter (15) to filter out stray light.

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