Distributed optical fiber sound wave sensing system

Abstract

The utility model relates to a distributed optical fiber sound wave sensing system. The system comprises a narrow linewidth laser, a first coupler, an acousto-optic modulation circuit, a circulator, a second coupler, a balance detector, a first signal converter, a dynamic gain control circuit, a signal acquisition circuit and a signal control circuit. The narrow linewidth laser is connected with the input end of the first coupler, the first output end of the first coupler is connected with the first input end of the acousto-optic modulation circuit, the acousto-optic modulation circuit, the circulator and a tested optical fiber are sequentially connected, and the circulator is further connected with the first input end of the second coupler. The second output end of the first coupler is connected with the second input end of the second coupler, and the second coupler, the balance detector, the first signal converter, the dynamic gain control circuit, the signal acquisition circuit, the signal control circuit and the acousto-optic modulation circuit are sequentially connected. According to the utility model, the size of signals entering the signal acquisition circuit can be dynamically adjusted through the dynamic gain control circuit.

Description

Technical Field

[0001] This utility model relates to the field of fiber optic sensing technology, and more specifically, to a distributed fiber optic acoustic wave sensing system. Background Technology

[0002] A distributed fiber optic acoustic sensor (DAS) is an advanced device that reconstructs external vibration signals by measuring the phase difference of the signal under test. Utilizing optical fiber as the sensing medium, it detects external vibrations or acoustic signals by detecting phase changes in the optical signal within the fiber. Traditional DAS systems typically employ fixed-gain receiving circuits to process the optical signal. While simple and easy to implement, this approach has significant limitations in practical applications. For example, when the intensity of the measured optical signal is high, the fixed-gain circuit may cause the analog-to-digital converter (ADC) to saturate, affecting accurate signal acquisition and potentially causing permanent damage to the ADC. Conversely, when the measured signal is weak, the fixed-gain circuit cannot effectively amplify the signal, resulting in an insufficient signal amplitude entering the ADC, reducing the signal-to-noise ratio and affecting measurement accuracy; it may even prevent the detection of a valid signal. These limitations severely restrict the adaptability and reliability of DAS systems in various application scenarios. Utility Model Content

[0003] The present invention aims to overcome at least one of the defects (deficiencies) of the prior art and provide a distributed fiber optic acoustic wave sensing system to improve the reliability of the system.

[0004] The technical solution adopted by this utility model is to propose a distributed optical fiber acoustic wave sensing system, which includes a narrow linewidth laser, a first coupler, an acousto-optic modulation circuit, a circulator, an optical fiber under test, a second coupler, a balanced detector, a first signal converter, a dynamic gain control circuit, a signal acquisition circuit, and a signal control circuit.

[0005] The output of the narrow linewidth laser is connected to the input of the first coupler, the first output of the first coupler is connected to the first input of the acousto-optic modulation circuit, the output of the acousto-optic modulation circuit is connected to the first transmission end of the circulator, the second transmission end of the circulator is used to connect to the optical fiber under test, and the third transmission end of the circulator is connected to the first input of the second coupler.

[0006] The second output terminal of the first coupler is connected to the second input terminal of the second coupler, the first output terminal of the second coupler is connected to the first input terminal of the balanced detector, and the second output terminal of the second coupler is connected to the second input terminal of the balanced detector.

[0007] The first output terminal of the balanced detector is connected to the first input terminal of the first signal converter, the second output terminal of the balanced detector is connected to the second input terminal of the first signal converter, the output terminal of the first signal converter is connected to the input terminal of the dynamic gain control circuit, the output terminal of the dynamic gain control circuit is connected to the input terminal of the signal acquisition circuit, the output terminal of the signal acquisition circuit is connected to the input terminal of the signal control circuit, and the output terminal of the signal control circuit is connected to the second input terminal of the acousto-optic modulation circuit.

[0008] In this solution, a dynamic gain control circuit is added to the distributed fiber optic acoustic wave sensing system, breaking away from the traditional fixed gain concept, thereby improving the performance of the sensing system and enhancing the reliability of detection.

[0009] Furthermore, the dynamic gain control circuit includes a power divider, a detector circuit, a variable gain amplifier, and a second signal converter;

[0010] The output terminal of the first signal converter is connected to the input terminal of the power divider. The first output terminal of the power divider is connected to the input terminal of the detector circuit. The second output terminal of the power divider is connected to the first input terminal of the variable gain amplifier. The output terminal of the detector circuit is connected to the second input terminal of the variable gain amplifier. The output terminal of the variable gain amplifier is connected to the input terminal of the second signal converter. The first and second output terminals of the second signal converter are respectively connected to the first and second input terminals of the signal acquisition circuit.

[0011] In this scheme, the dynamic gain control circuit includes a power divider, a detector circuit, a variable gain amplifier, and a second signal converter. The power divider splits the input optical signal into two or more paths, one of which is used for subsequent signal processing, and the other optical signal enters the detector circuit. The output voltage of the detector circuit is used to control the gain of the variable gain amplifier. The variable gain amplifier dynamically adjusts the amplification factor according to the strength of the output voltage of the detector circuit to ensure that the signal has sufficient amplitude in subsequent processing. The amplified electrical signal enters the second signal converter for further processing or conversion.

[0012] Furthermore, the dynamic gain control circuit also includes an amplifier; the first output terminal of the power divider is connected to the input terminal of the amplifier, and the output terminal of the amplifier is connected to the input terminal of the detector circuit.

[0013] In this scheme, the amplifier is used to amplify the signal entering the detector circuit, thereby making it more suitable for the detector circuit to process the signal.

[0014] Furthermore, the first signal converter is a differential-to-single-ended amplifier;

[0015] And / or, the signal acquisition circuit is an analog-to-digital conversion circuit;

[0016] And / or, the signal control circuit is an FPGA chip circuit.

[0017] In this scheme, the differential-to-single-ended amplifier converts the two signals output from the balanced detector into single-ended signals, and simultaneously amplifies and processes these single-ended signals. Additionally, the analog-to-digital converter circuit converts the electrical signals into digital signals, and the FPGA chip circuit acquires these digital signals for logic control, ultimately outputting control commands.

[0018] Furthermore, the system also includes a first optical signal processing circuit;

[0019] The output terminal of the acousto-optic modulation circuit is connected to the input terminal of the first optical signal processing circuit, and the output terminal of the first optical signal processing circuit is connected to the first transmission terminal of the circulator.

[0020] And / or,

[0021] The system also includes a second optical signal processing circuit;

[0022] The third transmission terminal of the circulator is connected to the input terminal of the second optical signal processing circuit, and the output terminal of the second optical signal processing circuit is connected to the first input terminal of the second coupler.

[0023] In this scheme, the first optical signal processing circuit and the second optical signal processing circuit are used to process optical signals, including amplifying the optical signals, preventing reflected light from adversely affecting the light source or optical path system, and selectively transmitting or blocking optical signals of specific wavelengths.

[0024] Furthermore, the first optical signal processing circuit includes a first optical isolator and a first optical filter;

[0025] The output terminal of the acousto-optic modulation circuit is connected to the input terminal of the first optical isolator, the output terminal of the first optical isolator is connected to the input terminal of the first optical filter, and the output terminal of the first optical filter is connected to the first transmission terminal of the circulator.

[0026] In this scheme, the first optical isolator of the first optical signal processing circuit is used to prevent reflected light from having an adverse effect on the light source or optical path system, and the first optical filter is used to selectively transmit or block optical signals of a specific wavelength.

[0027] Furthermore, the first optical signal processing circuit also includes a first erbium-doped amplifier;

[0028] The output of the first optical isolator is connected to the input of the first erbium-doped amplifier, and the output of the first erbium-doped amplifier is connected to the input of the first optical filter.

[0029] In this scheme, the first erbium-doped amplifier is used to amplify the incoming signal.

[0030] Furthermore, the second optical signal processing circuit includes a second optical isolator and a second optical filter;

[0031] The third transmission terminal of the circulator is connected to the input terminal of the second optical filter, the output terminal of the second optical filter is connected to the input terminal of the second optical isolator, and the output terminal of the second optical isolator is connected to the first input terminal of the second coupler.

[0032] In this scheme, the second optical isolator of the second optical signal processing circuit is used to prevent reflected light from having an adverse effect on the light source or optical path system, and the second optical filter is used to selectively transmit or block optical signals of specific wavelengths, etc.

[0033] Furthermore, the second optical signal processing circuit also includes a second erbium-doped amplifier;

[0034] The third transmission terminal of the circulator is connected to the input terminal of the second erbium-doped amplifier, and the output terminal of the second erbium-doped amplifier is connected to the input terminal of the second optical filter.

[0035] In this scheme, the first erbium-doped amplifier is used to amplify the signal.

[0036] Furthermore, the acousto-optic modulation circuit includes an acousto-optic modulator and an acousto-optic modulator driving circuit;

[0037] The first output terminal of the first coupler is connected to the first input terminal of the acousto-optic modulator, and the output terminal of the acousto-optic modulator is connected to the first transmission terminal of the circulator.

[0038] The output terminal of the signal control circuit is connected to the input terminal of the acoustic-optic modulator driving circuit, and the output terminal of the acoustic-optic modulator driving circuit is connected to the second input terminal of the acoustic-optic modulator.

[0039] In this scheme, the acousto-optic modulator can modulate the intensity, frequency, and phase of the optical signal. By changing the frequency and amplitude of the sound wave, it can achieve precise control of the optical signal, and modulate the laser emitted by the narrow linewidth laser into pulsed light for optical fiber sensing.

[0040] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0041] This invention dynamically adjusts the signal gain by adding a dynamic gain control circuit, thereby ensuring that the signal acquisition circuit can acquire the signal stably and accurately, thus improving the system's adaptability and reliability.

[0042] Furthermore, this invention's fiber optic sensing system, based on an FPGA-controlled AOM (acousto-optic modulator) driver circuit, optimizes fiber optic sensing performance by dynamically adjusting pulse width and gain control. The FPGA emits pulses of different widths to control the AOM's on and off states. A wider pulse width results in greater optical power transmitted to the fiber under test, leading to stronger scattered light. After photoelectric conversion by a balanced detector, the resulting electrical signal is also stronger, increasing the sensing distance. However, if the pulse width or laser emission power continues to increase, the scattered light signal from the near-distance fiber may become too strong, potentially causing ADC (analog-to-digital converter) saturation and preventing demodulation of sensing information. This invention addresses this by automatically reducing the gain of the variable gain amplifier near the sensing fiber when the signal is strong, preventing ADC saturation; and automatically increasing the gain of the variable gain amplifier at the far end of the sensing fiber when the signal is weak, ensuring the signal can be recognized and converted by the ADC. Through this dynamic gain control mechanism, the system effectively avoids ADC saturation while enhancing the detection capability of weak signals, significantly increasing the system's dynamic range, extending the sensing distance, and improving overall system performance. Attached Figure Description

[0043] Figure 1 This is a structural diagram of the present invention.

[0044] 1. Narrow linewidth laser; 2. First coupler; 3. Circulator; 4. Fiber under test; 5. Second coupler; 6. Balanced detector; 7. First signal converter; 8. Dynamic gain control circuit; 9. Signal acquisition circuit; 10. Signal control circuit; 20. Acousto-optic modulation circuit; 21. Acousto-optic modulator driver circuit; 22. Acousto-optic modulator; 80. Power divider; 81. Amplifier; 82. Detector circuit; 83. Variable gain amplifier; 84. Second signal converter; 11. First signal processing circuit; 111. First isolator; 112. First erbium-doped amplifier; 113. First optical filter; 12. Second signal processing circuit; 121. Second isolator; 122. Second optical filter; 123. Second erbium-doped amplifier. Detailed Implementation

[0045] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this invention. To better illustrate the following embodiments, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0046] Example 1

[0047] like Figure 1 As shown, this embodiment proposes a distributed fiber optic acoustic wave sensing system, which includes a narrow linewidth laser 1, a first coupler 2, an acousto-optic modulation circuit 20, a circulator 3, a fiber under test 4, a second coupler 5, a balanced detector 6, a first signal converter 7, a dynamic gain control circuit 8, a signal acquisition circuit 9, and a signal control circuit 10.

[0048] The output end of the narrow linewidth laser 1 is connected to the input end of the first coupler 2, the first output end of the first coupler 2 is connected to the first input end of the acousto-optic modulation circuit 20, the output end of the acousto-optic modulation circuit 20 is connected to the first transmission end of the circulator 3, the second transmission end of the circulator 3 is used to connect to the optical fiber 4 under test, and the third transmission end of the circulator 3 is connected to the first input end of the second coupler 5.

[0049] The second output terminal of the first coupler 2 is connected to the second input terminal of the second coupler 5, the first output terminal of the second coupler 5 is connected to the first input terminal of the balance detector 6, and the second output terminal of the second coupler 5 is connected to the second input terminal of the balance detector 6.

[0050] The first output terminal of the balanced detector 6 is connected to the first input terminal of the first signal converter 7, the second output terminal of the balanced detector 6 is connected to the second input terminal of the first signal converter 7, the output terminal of the first signal converter 7 is connected to the input terminal of the dynamic gain control circuit 8, the output terminal of the dynamic gain control circuit 8 is connected to the input terminal of the signal acquisition circuit 9, the output terminal of the signal acquisition circuit 9 is connected to the input terminal of the signal control circuit 10, and the output terminal of the signal control circuit 10 is connected to the second input terminal of the acousto-optic modulation circuit 20.

[0051] In specific implementation, the laser emitted by the narrow linewidth laser 1 passes through the first coupler 2, which splits the incoming laser beam into two beams: a local oscillator beam and a sensing beam. The local oscillator beam directly enters the second coupler 5, while the sensing beam enters the acousto-optic modulation circuit 20 for modulation into pulsed light. The pulsed light then passes through the first transmission end of the circulator 3 and finally reaches the fiber under test 4. After Rayleigh scattering occurs in the fiber under test 4, the light is fed back to the second coupler 5. The local oscillator beam and the sensing beam undergo coherent interference at the second coupler 5. The balanced detector 6 detects the interference result to obtain a detection result, which is then converted into an electrical signal by the first signal converter 7. This electrical signal is transmitted to the dynamic gain control circuit 8, which dynamically adjusts the gain of the input electrical signal. The signal then reaches the signal acquisition circuit 9 and the signal control circuit 10. The signal control circuit 10 executes a judgment command based on the logical judgment of the detection result, controlling the acousto-optic modulation circuit 20 to modulate the incoming laser, thereby improving the sensing performance of the entire system.

[0052] It is understood that the narrow linewidth laser 1 and the first coupler 2, the first coupler 2 and the acousto-optic modulation circuit 20, the acousto-optic modulation circuit 20 and the circulator 3, and the circulator 3 and the second coupler 5 are all optical path connections.

[0053] The first coupler 2 and the second coupler 5, the second coupler 5 and the balanced detector 6, and the second coupler 5 and the balanced detector 6 are all optical path connections;

[0054] The balance detector 6 is electrically connected to the first signal converter 7, the first signal converter 7 is electrically connected to the dynamic gain control circuit 8, the dynamic gain control circuit 8 is electrically connected to the signal acquisition circuit 9, the signal acquisition circuit 9 is electrically connected to the signal control circuit 10, and the signal control circuit 10 is electrically connected to the acousto-optic modulation circuit 20.

[0055] Optionally, the first signal converter 7 may be a differential-to-single-ended amplifier; the differential-to-single-ended amplifier converts the two signals output by the balanced detector 6 into single-ended signals, and simultaneously amplifies and processes the single-ended signals so that the subsequent dynamic gain control circuit 8 can adjust the gain of the amplified signals.

[0056] Optionally, the dynamic gain control circuit 8 includes a power divider 80, a detector circuit 82, a variable gain amplifier 83, and a second signal converter 84;

[0057] The output terminal of the first signal converter 7 is connected to the input terminal of the power divider 80. The first output terminal of the power divider 80 is connected to the input terminal of the detector circuit 82. The second output terminal of the power divider 80 is connected to the first input terminal of the variable gain amplifier 83. The output terminal of the detector circuit 82 is connected to the second input terminal of the variable gain amplifier 83. The output terminal of the variable gain amplifier 83 is connected to the input terminal of the second signal converter 84. The first and second output terminals of the second signal converter 84 are respectively connected to the first and second input terminals of the signal acquisition circuit 9.

[0058] It is understood that the first signal converter 7 is electrically connected to the power divider 80, the power divider 80 is electrically connected to the detector circuit 82, the power divider 80 is electrically connected to the variable gain amplifier 83, the detector circuit 82 is electrically connected to the variable gain amplifier 83, the variable gain amplifier 83 is electrically connected to the second signal converter 84, and the second signal converter 84 is electrically connected to the signal acquisition circuit 9.

[0059] Optionally, the second signal converter 84 is a single-ended to differential amplifier, which can convert a single-ended signal into a differential signal so that the signal acquisition circuit 9 can receive and process the differential signal.

[0060] In a specific implementation, the power divider 80 splits the input signal into two signals. One signal is transmitted to the detection circuit 82, and the other signal is transmitted to the variable gain amplifier 83. The detection circuit 82 detects the input signal and feeds back the detection result to the variable gain amplifier 83. The variable gain amplifier 83 improves the detection performance by adjusting the gain. In specific implementation, the gain of the variable gain amplifier 83 is controlled by the voltage output of the detection circuit 82. Specifically, a chip whose gain is inversely proportional to the output voltage of the detection circuit 82 can be selected as the variable gain amplifier 83: when the light signal under test in the optical fiber 4 increases, the voltage output of the detection circuit 82 increases, and the gain of the variable gain amplifier 83 decreases, resulting in a corresponding decrease in the signal input to the signal acquisition circuit 9; when the light signal under test in the optical fiber 4 decreases, the voltage output of the detection circuit 82 decreases, and the gain of the variable gain amplifier 83 increases, resulting in a corresponding increase in the amplitude of the signal input to the signal acquisition circuit 9. This avoids the problem of a low signal-to-noise ratio caused by an excessively small signal amplitude in the signal acquisition circuit 9. Based on this, this invention improves the reliability of the distributed optical fiber acoustic wave sensing system (DAS) by adding a dynamic gain control circuit 8.

[0061] Optionally, the dynamic gain control circuit 8 further includes an amplifier 81; the first output terminal of the power divider 80 is connected to the input terminal of the amplifier 81, and the output terminal of the amplifier 81 is connected to the input terminal of the detector circuit 82.

[0062] In specific implementation, the amplifier 81 includes, but is not limited to, amplifying the amplitude, power or other parameters of the input signal, so as to make it more suitable for subsequent processing, transmission or driving load.

[0063] In specific implementation, the signal acquisition circuit 9 can be an analog-to-digital conversion circuit to acquire the signal output by the dynamic gain control circuit 80 and perform analog-to-digital conversion to obtain a digital signal for subsequent signal control circuit 10 to process and control.

[0064] It is understood that the power divider 80 and the amplifier 81, as well as the amplifier 81 and the detector circuit 82, are electrically connected.

[0065] Optionally, the signal control circuit 10 may employ an FPGA chip circuit.

[0066] In practical implementation, the FPGA chip circuit can control the acousto-optic modulation circuit 20 by emitting pulses of different pulse widths and durations. A larger pulse width results in greater optical power transmitted to the fiber optic cable 4 under test, leading to a larger scattered sensing light. After photoelectric conversion by the balanced detector 6 and the first signal converter 7, the resulting electrical signal is also stronger, extending the sensing distance. However, if the pulse width or laser emission power is further increased, the signal may become too strong at close range, causing the signal acquisition circuit 9 to saturate and preventing demodulation of the sensing information. Therefore, a dynamic gain control circuit 8 is added. Near the fiber optic cable 4, when the signal is relatively strong, the gain of the variable gain amplifier 83 decreases, preventing saturation of the signal acquisition circuit 9. Conversely, at the far end of the fiber optic cable 4, when the signal is relatively weak, the gain of the variable gain amplifier 83 increases, allowing the signal to be recognized and converted by the signal acquisition circuit 9. This increases the dynamic range, extends the sensing distance, and improves system performance.

[0067] Optionally, the system further includes a first optical signal processing circuit 11;

[0068] The output terminal of the acousto-optic modulation circuit 20 is connected to the input terminal of the first optical signal processing circuit 11, and the output terminal of the first optical signal processing circuit 11 is connected to the first transmission terminal of the circulator 3.

[0069] The first optical signal processing circuit 11 is used to process optical signals, including amplifying the optical signals, preventing reflected light from adversely affecting the light source or optical path system, and selectively transmitting or blocking optical signals of specific wavelengths.

[0070] It is understood that the acousto-optic modulation circuit 20 and the first optical signal processing circuit 11, as well as the first optical signal processing circuit 11 and the circulator 3, are all optical path connections.

[0071] In a preferred embodiment, the first optical signal processing circuit 11 includes a first optical isolator 111 and a first optical filter 113;

[0072] The output terminal of the acousto-optic modulation circuit 20 is connected to the input terminal of the first optical isolator 111, the output terminal of the first optical isolator 111 is connected to the input terminal of the first optical filter 113, and the output terminal of the first optical filter 113 is connected to the first transmission terminal of the circulator 3.

[0073] In specific implementation, the first optical isolator 111 of the first optical signal processing circuit 11 is used to prevent reflected light from having an adverse effect on the light source or optical path system, and the first optical filter 113 is used to selectively transmit or block optical signals of a specific wavelength.

[0074] It is understood that the acousto-optic modulation circuit 20 is optically connected to the first optical isolator 111, the first optical isolator 111 is optically connected to the first optical filter 113, and the first optical filter 113 is optically connected to the circulator 3.

[0075] Furthermore, the first optical signal processing circuit 11 also includes a first erbium-doped amplifier 112;

[0076] The output terminal of the first optical isolator 111 is connected to the input terminal of the first erbium-doped amplifier 112, and the output terminal of the first erbium-doped amplifier 112 is connected to the input terminal of the first optical filter 113.

[0077] In specific implementation, the first erbium-doped amplifier 112 is used to amplify the incoming laser signal.

[0078] It is understandable that the first optical isolator 111 and the first erbium-doped amplifier 112, and the first erbium-doped amplifier 112 and the first optical filter 113 are all optical path connections.

[0079] Optionally, the system further includes a second optical signal processing circuit 12;

[0080] The third transmission terminal of the circulator 3 is connected to the input terminal of the second optical signal processing circuit 12, and the output terminal of the second optical signal processing circuit 12 is connected to the first input terminal of the second coupler 5.

[0081] In specific implementation, the second optical signal processing circuit 12 is used to process optical signals, including amplifying optical signals, preventing reflected light from having an adverse effect on the light source or optical path system, and selectively transmitting or blocking optical signals of specific wavelengths.

[0082] It is understood that the circulator 3 and the second optical signal processing circuit 12, and the second optical signal processing circuit 12 and the second coupler 5 are both optical path connections.

[0083] In a preferred embodiment, the second optical signal processing circuit 12 includes a second optical isolator 121 and a second optical filter 122;

[0084] The third transmission terminal of the circulator 3 is connected to the input terminal of the second optical filter 122, the output terminal of the second optical filter 122 is connected to the input terminal of the second optical isolator 121, and the output terminal of the second optical isolator 121 is connected to the first input terminal of the second coupler 5.

[0085] In specific implementation, the second optical isolator 121 of the second optical signal processing circuit 12 is used to prevent reflected light from having an adverse effect on the light source or optical path system, and the second optical filter 122 is used to selectively transmit or block optical signals of a specific wavelength.

[0086] It is understood that the circulator 3 and the second optical filter 122, the second optical filter 122 and the second optical isolator 121, and the second optical isolator 121 and the second coupler 5 are all optical path connections.

[0087] Furthermore, the second optical signal processing circuit 12 also includes a second erbium-doped amplifier 123;

[0088] The third transmission terminal of the circulator 3 is connected to the input terminal of the second erbium-doped amplifier 123, and the output terminal of the second erbium-doped amplifier 123 is connected to the input terminal of the second optical filter 122.

[0089] In practice, the second erbium-doped amplifier 123 is used to amplify the incoming signal.

[0090] It is understood that the circulator 3 and the second erbium-doped amplifier 123, and the second erbium-doped amplifier 123 and the second optical filter 122 are all optical path connections.

[0091] Optionally, the acousto-optic modulation circuit 20 includes an acousto-optic modulator 22 and an acousto-optic modulator driving circuit 21;

[0092] The first output terminal of the first coupler 2 is connected to the first input terminal of the acousto-optic modulator 22, and the output terminal of the acousto-optic modulator 22 is connected to the first transmission terminal of the circulator 3.

[0093] The output terminal of the signal control circuit 10 is connected to the input terminal of the acoustic-optic modulator driving circuit 21, and the output terminal of the acoustic-optic modulator driving circuit 21 is connected to the second input terminal of the acoustic-optic modulator 22.

[0094] In a specific implementation, the output terminal of the signal control circuit 10 is connected to the acousto-optic modulator driving circuit 21. The signal control circuit 10 sends a driving signal to the acousto-optic modulator driving circuit 21. The acousto-optic modulator driving circuit 21 drives the acousto-optic modulator 22 according to the driving signal, so that the acousto-optic modulator 22 modulates the incoming laser and then reaches the first transmission terminal of the circulator 3.

[0095] It is understandable that the first coupler 2 and the acousto-optic modulator 22, and the acousto-optic modulator 22 and the circulator 3 are both optical path connections;

[0096] The signal control circuit 10 and the acousto-optic modulator driving circuit 21, as well as the acousto-optic modulator driving circuit 21 and the acousto-optic modulator 22, are electrically connected.

[0097] Further explanation of the present invention: This invention provides a scheme for dynamically adjusting the gain of the DAS receiving circuit. It adds a power divider 80, an amplifier 81, a detector circuit 82, a variable gain amplifier 83, and a second signal converter 84. The gain of the variable gain amplifier 83 is controlled by the voltage output of the detector circuit 82. When the measured optical signal increases, the voltage output of the detector circuit 82 increases. A chip whose gain is inversely proportional to the control voltage is selected to implement the variable gain amplifier 83. Therefore, the gain of the variable gain amplifier 83 decreases, and the signal input to the signal acquisition circuit 9 decreases accordingly. When the measured optical signal decreases, the voltage output of the detector circuit 82 decreases, and the gain of the variable gain amplifier 83 increases. This prevents the signal amplitude input to the signal acquisition circuit 9 from being too small, thus avoiding a low signal-to-noise ratio. The signal control circuit 10 receives the signal acquired by the signal acquisition circuit 9. The signal control circuit 10 has a built-in FPGA chip for logical judgment, thereby controlling the system and improving the effectiveness of the gain.

[0098] Obviously, the above embodiments of this utility model are merely examples for clearly illustrating the technical solution of this utility model, and are not intended to limit the specific implementation of this utility model. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of this utility model should be included within the protection scope of the claims of this utility model.

Claims

1. A distributed fiber optic acoustic sensing system, comprising: The system comprises a narrow linewidth laser, a first coupler, an acousto-optic modulation circuit, a circulator, a second coupler, a balanced detector, a first signal converter, a dynamic gain control circuit, a signal acquisition circuit and a signal control circuit; The output end of the narrow linewidth laser is connected to the input end of the first coupler, the first output end of the first coupler is connected to the first input end of the acousto-optic modulation circuit, the output end of the acousto-optic modulation circuit is connected to the first transmission end of the circulator, the second transmission end of the circulator is used for connecting a measured optical fiber, and the third transmission end of the circulator is connected to the first input end of the second coupler; The second output end of the first coupler is connected to the second input end of the second coupler, the first output end of the second coupler is connected to the first input end of the balanced detector, and the second output end of the second coupler is connected to the second input end of the balanced detector; The first output end of the balanced detector is connected to the first input end of the first signal converter, the second output end of the balanced detector is connected to the second input end of the first signal converter, the output end of the first signal converter is connected to the input end of the dynamic gain control circuit, the output end of the dynamic gain control circuit is connected to the input end of the signal acquisition circuit, the output end of the signal acquisition circuit is connected to the input end of the signal control circuit, and the output end of the signal control circuit is connected to the second input end of the acousto-optic modulation circuit.

2. A distributed optical fibre acoustic wave sensing system according to claim 1, characterised in that, The dynamic gain control circuit comprises a power divider, a detection circuit, a variable gain amplifier and a second signal converter; The output end of the first signal converter is connected to the input end of the power divider, the first output end of the power divider is connected to the input end of the detection circuit, the second output end of the power divider is connected to the first input end of the variable gain amplifier, the output end of the detection circuit is connected to the second input end of the variable gain amplifier, the output end of the variable gain amplifier is connected to the input end of the second signal converter, and the first output end and the second output end of the second signal converter are connected to the first input end and the second input end of the signal acquisition circuit respectively.

3. A distributed optical fibre acoustic wave sensing system according to claim 2, wherein, The dynamic gain control circuit further comprises an amplifier, the first output end of the power divider is connected to the input end of the amplifier, and the output end of the amplifier is connected to the input end of the detection circuit.

4. A distributed optical fibre acoustic wave sensing system according to any one of claims 1 to 3, wherein, The first signal converter is a differential-to-single-ended amplifier. And / or, the signal acquisition circuit is an analog-to-digital conversion circuit. And / or, the signal control circuit is an FPGA chip circuit.

5. A distributed optical fibre acoustic wave sensing system according to any one of claims 1 to 3, wherein, The system further comprises a first optical signal processing circuit; The output end of the acousto-optic modulation circuit is connected to the input end of the first optical signal processing circuit, and the output end of the first optical signal processing circuit is connected to the first transmission end of the circulator. And / or, The system further comprises a second optical signal processing circuit; The third transmission end of the circulator is connected to the input end of the second optical signal processing circuit, and the output end of the second optical signal processing circuit is connected to the first input end of the second coupler.

6. A distributed optical fibre acoustic wave sensing system according to claim 5, wherein, The first optical signal processing circuit comprises a first optical isolator and a first optical filter; An output end of the acousto-optic modulation circuit is connected to an input end of the first optical isolator, an output end of the first optical isolator is connected to an input end of the first optical filter, and an output end of the first optical filter is connected to the first transmission end of the circulator.

7. A distributed optical fibre acoustic wave sensing system according to claim 6, wherein, The first optical signal processing circuit further comprises a first erbium-doped amplifier; An output end of the first optical isolator is connected to an input end of the first erbium-doped amplifier, and an output end of the first erbium-doped amplifier is connected to an input end of the first optical filter.

8. A distributed optical fibre acoustic wave sensing system according to claim 5, wherein, The second optical signal processing circuit comprises a second optical isolator and a second optical filter; The third transmission end of the circulator is connected to an input end of the second optical filter, an output end of the second optical filter is connected to an input end of the second optical isolator, and an output end of the second optical isolator is connected to the first input end of the second coupler.

9. A distributed optical fibre acoustic wave sensing system according to claim 8, wherein, The second optical signal processing circuit further comprises a second erbium-doped amplifier; The third transmission end of the circulator is connected to an input end of the second erbium-doped amplifier, and an output end of the second erbium-doped amplifier is connected to an input end of the second optical filter.

10. A distributed optical fibre acoustic wave sensing system according to any one of claims 1 to 3, wherein, The acousto-optic modulation circuit comprises an acousto-optic modulator and an acousto-optic modulator driving circuit; The first output end of the first coupler is connected to the first input end of the acousto-optic modulator, and an output end of the acousto-optic modulator is connected to the first transmission end of the circulator; An output end of the signal control circuit is connected to an input end of the acousto-optic modulator driving circuit, and an output end of the acousto-optic modulator driving circuit is connected to the second input end of the acousto-optic modulator.

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