Remote interferometric fiber-optic sensing system and method for suppressing spontaneous modulation instability thereof

Abstract

In view of the problem that the spontaneous modulation instability of the current remote interferometric fiber sensing system has not been solved sufficiently, resulting in the limited system detection performance, the application provides a remote interferometric fiber sensing system and a spontaneous modulation instability suppression method thereof, which comprises a single-frequency laser, a pulse generation module, a sideband generation module, a programmable filter, a fiber amplifier, a narrowband filter, a transmission fiber, an interferometric fiber sensor array module and a spontaneous modulation instability monitoring and control device; the spontaneous modulation instability of the remote interferometric fiber sensing system and the phase noise thereof can be effectively suppressed by controlling the phase difference between the single-frequency laser and each order sideband, so as to realize a low-noise remote interferometric fiber sensing system and improve the detection performance of the system.

Description

Technical Field

[0001] This invention relates to the field of interferometric fiber optic sensing technology, and in particular to a remote interferometric fiber optic sensing system and a method for suppressing spontaneous modulation instability. Background Technology

[0002] In long-range interferometric fiber optic sensing systems, when high-power optical pulses propagate through the fiber, spontaneous modulation instability (MI) is triggered by amplified spontaneous emission (ASE) noise. This causes the high-power optical pulse to amplify the ASE noise and form symmetrical sidelobes. The sidelobes generated by MI inherit the incoherence of the ASE noise, resulting in severe phase noise in the system and degrading its detection performance.

[0003] To suppress spontaneous modulation instability in optical fibers, various suppression schemes have been proposed, including optical narrowband filtering, orthogonal polarization pulse method, time and frequency pump-probe multiplexing method, and dual-wavelength laser, etc. However, the above methods have limitations in interferometric fiber optic sensing systems. Summary of the Invention

[0004] To address the problem that the severe phase noise caused by spontaneous modulation instability in current remote interferometric fiber optic sensing systems has not yet been effectively suppressed, this invention proposes a remote interferometric fiber optic sensing system and a method for suppressing spontaneous modulation instability.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: On the one hand, a remote interferometric fiber optic sensing system is provided, including a single-frequency laser, a pulse generation module, a sideband generation module, a programmable filter, a fiber amplifier, a narrowband filter, a transmission fiber, an interferometric fiber optic sensor array module, and a spontaneous modulation instability monitoring and control device. The single-frequency laser, pulse generation module, sideband generation module, programmable filter, fiber amplifier, narrowband filter, and transmission fiber are connected in sequence. The output port of the transmission fiber is connected to the input port of the interferometric fiber optic sensor array module, and the output port of the interferometric fiber optic sensor array module is connected to the spontaneous modulation instability monitoring and control device. The spontaneous modulation instability monitoring and control device collects and extracts the optical interference signal generated by the interferometric fiber optic sensor array module, thereby monitoring the phase noise caused by spontaneous modulation instability in the system. After applying phase modulation of different frequencies to the sideband generation module, it observes the changes in the resulting phase noise and determines the frequency corresponding to the lowest phase noise value, i.e., the spontaneous modulation instability. The optimal gain frequency for stability is determined by applying a weak coherent sideband at this frequency. This suppresses spontaneous modulation instability by stimulating induced spontaneous modulation instability. Simultaneously, the spontaneous modulation instability monitoring and control device outputs a control signal for a programmable filter based on real-time phase noise monitoring results. This signal is used to set the phase difference and the order of the symmetrical frequency sidebands of the programmable filter. The bandpass filtering function of the programmable filter is used to filter out the single-frequency laser and the required symmetrical frequency sideband signals. Based on the currently set phase difference of the programmable filter, the filtered single-frequency laser and the symmetrical frequency sideband signals are phase-modulated until the phase noise dominated by spontaneous modulation instability is fully suppressed.

[0006] Preferably, the spontaneous modulation instability monitoring and control device includes a photodetector and a signal acquisition and processing module, wherein the output port of the interferometric fiber optic sensor array module is connected to the input port of the photodetector, and the output port of the photodetector is connected to the signal acquisition and processing module.

[0007] The present invention has the following beneficial effects: This invention effectively suppresses spontaneous modulation instability (MI) and phase noise in remote interferometric fiber optic sensing systems by controlling the phase difference between single-frequency lasers and sidebands of each order, thereby realizing a low-noise remote interferometric fiber optic sensing system and improving the system's detection performance. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0009] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2This is a test result diagram of a specific embodiment of the present invention. Detailed Implementation

[0010] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0011] In one embodiment, the present invention provides a remote interferometric fiber optic sensing system, including a single-frequency laser 1, a pulse generation module 2, a sideband generation module 3, a programmable filter 4, a fiber amplifier 5, a narrowband filter 6, a transmission fiber 7, an interferometric fiber optic sensor array module, and a spontaneous modulation instability monitoring and control device. The single-frequency laser 1, pulse generation module 2, sideband generation module 3, programmable filter 4, fiber amplifier 5, narrowband filter 6, and transmission fiber 7 are connected in sequence. The output port of transmission fiber 7 is connected to the input port of the interferometric fiber optic sensor array module, and the output port of the interferometric fiber optic sensor array module is connected to the spontaneous modulation instability monitoring and control device. The spontaneous modulation instability monitoring and control device collects and extracts the optical interference signal generated by the interferometric fiber optic sensor array module, thereby monitoring the phase noise caused by spontaneous modulation instability in the system. After applying phase modulation of different frequencies to the sideband generation module, it observes the changes in phase noise caused by it and determines the frequency corresponding to the lowest value of phase noise, i.e., the spontaneous modulation frequency. The optimal gain frequency for instability is determined by applying a weak coherent sideband at this frequency. This induces spontaneous modulation instability and suppresses it. Simultaneously, the spontaneous modulation instability monitoring and control device outputs a control signal for the programmable filter 4 based on real-time phase noise monitoring results. This signal is used to set the phase difference and the order of the symmetrical frequency sidebands of the programmable filter 4. The bandpass filtering function of the programmable filter 4 is used to filter out the single-frequency laser and the required symmetrical frequency sideband signals. Based on the currently set phase difference of the programmable filter 4, the filtered single-frequency laser and the symmetrical frequency sideband signals are phase-modulated until the phase noise dominated by spontaneous modulation instability is fully suppressed.

[0012] First, phase modulation at different frequencies is applied, and the changes in phase noise of the remote interferometric fiber optic sensing system are observed. The frequency corresponding to the lowest phase noise value is then determined, which is the optimal gain frequency for spontaneous modulation instability. At the optimal gain frequency of spontaneous modulation instability A weak coherent sideband is applied to suppress spontaneous modulation instability by stimulating induced spontaneous modulation instability. Then, the phase difference between the weak coherent sideband and the single-frequency laser is controlled, thereby altering the competitive relationship between spontaneous modulation instability and induced spontaneous modulation instability. Under a specific phase difference, induced spontaneous modulation instability dominates the competition, thus effectively suppressing the phase noise caused by spontaneous modulation instability within the system.

[0013] See Figure 1 In one embodiment, a remote interferometric fiber optic sensing system is provided, including a single-frequency laser 1, a pulse generation module 2, a sideband generation module 3, a programmable filter 4, a fiber optic amplifier 5, a narrowband filter 6, a transmission fiber optic cable 7, an interferometric fiber optic sensor array module, a photodetector 9, and a signal acquisition and processing module 10.

[0014] The single-frequency laser 1, pulse generation module 2, sideband generation module 3, programmable filter 4, fiber amplifier 5, narrowband filter 6, and transmission fiber 7 are connected in sequence. Specifically, the output port 11 of the single-frequency laser 1 is connected to the input port 21 of the pulse generation module 2, the output port 22 of the pulse generation module 2 is connected to the input port 31 of the sideband generation module 3, the output port 32 of the sideband generation module 3 is connected to the input port 41 of the programmable filter 4, the output port 42 of the programmable filter 4 is connected to the input port 51 of the fiber amplifier 5, the output port 52 of the fiber amplifier 5 is connected to the input port 61 of the narrowband filter 6, and the output port 62 of the narrowband filter 6 is connected to the input port 71 of the transmission fiber 7.

[0015] The output port 72 of the transmission optical fiber 7 is connected to the input port 81 of the interferometric fiber optic sensor array module. The output port 82 of the interferometric fiber optic sensor array module is connected to the input port 91 of the photodetector 9. The output port 92 of the photodetector 9 is connected to the input port 101 of the signal acquisition and processing module 10. The signal acquisition and processing module 10 outputs a control signal for the programmable filter 4, which is used to set the phase difference of the programmable filter 4 and the order of the symmetrical frequency sidebands to be screened. The single-frequency laser and the required symmetrical frequency sideband signals are screened through the bandpass filtering of the programmable filter 4. Based on the phase difference currently set by the programmable filter 4, the filtered single-frequency laser and the symmetrical frequency sideband signals are phase-modulated until the phase noise dominated by spontaneous modulation instability is fully suppressed.

[0016] The pulse generation module 2 is used to generate a pulse with a frequency of 100 Hz from the single-frequency laser. The single-frequency continuous laser is modulated into a single-frequency pulsed laser. The implementation of the pulse generation module 2 is not limited, and it can be a combination of a signal source and an acousto-optic modulator, an electro-optic forced modulator, a semiconductor amplifier, or an optical switch.

[0017] The sideband generation module 3 is used to generate symmetrical frequency sideband signals on both sides of the single-frequency pulsed laser output by the pulse generation module. The implementation of the sideband generation module is not limited, and it can be a combination of a signal source and an electro-optic phase modulator or an electro-optic intensity modulator.

[0018] The aforementioned interferometric fiber optic sensor array module includes multiple interferometric fiber optic sensors, with adjacent sensors connected by delay modules, each consisting of a delay fiber of a certain length. The interferometric fiber optic sensors are non-equilateral fiber optic interferometers, such as Michelson interferometers, Sagnac interferometers, or Mach-Zehnder interferometers.

[0019] The method for suppressing spontaneous modulation instability in the aforementioned remote interferometric fiber optic sensing system includes: (1) Set the initial phase difference of the programmable filter and the order of the symmetrical frequency sidebands to be screened; (2) The single-frequency laser generates and outputs a frequency of: The single-frequency continuous laser, after passing through the pulse generation module, is modulated into a pulse width of... The single-frequency pulsed light, the sideband generation module passes through a frequency of ( The phase modulation of the optimal gain frequency (i.e., the frequency corresponding to the lowest phase noise) on both sides of a single-frequency pulse light produces a relative intensity of... Symmetrical frequency sideband signals, the symmetric frequency sideband signals include A symmetrical frequency sideband signal with different frequencies, the first The frequencies of the first-order symmetric frequency sideband signals are respectively , , For positive integers; after the symmetrical frequency sideband signal passes through the programmable filter, the frequencies set by the programmable filter are respectively The filter passband is bandpass filtered to select the single-frequency laser and the required symmetrical frequency sideband signals. The bandwidth of each filter passband is less than 10 GHz. Based on the phase difference currently set by the programmable filter, the filtered single-frequency laser and the symmetrical frequency sideband signals are phase-modulated. The optical signal output from the programmable filter is then amplified by an optical fiber amplifier, and then further filtered by a narrowband filter to remove excess spontaneous emission noise before being injected into the transmission optical fiber. The optical signal after passing through the transmission optical fiber is injected into the interferometric fiber optic sensor array module to generate an optical interference signal. In the interferometric fiber optic sensor array module, a delay module is used between two adjacent interferometric fiber optic sensors to ensure that the time interval between the reflected light pulses is greater than the pulse width. The optical interference signal is injected into the photodetector signal, the photodetector converts the optical signal into an electrical signal, and the electrical signal is finally uploaded to the signal acquisition and processing module for demodulation to measure the current phase noise of the system. (3) Compare the current phase noise of the system with the phase noise of the initial state of the system. If it is higher than the phase noise of the initial state, update the phase difference and the order of the symmetrical frequency sideband to be screened in the current setting of the programmable filter, and go to step (2). Repeat this process until the current phase noise of the system reaches the lowest level compared with the phase noise of the initial state, thereby fully suppressing the phase noise dominated by spontaneous modulation instability.

[0020] In step (3), the method for updating the current phase difference of the programmable filter is as follows: the update is performed within the set phase difference range with a set step size. The set phase difference range is 0 rad to 6.28 rad, and the set step size is 0.05 rad. If the initial phase difference of the programmable filter is set to 0 rad, then the phase difference of the programmable filter will be 0.05 rad in the next update, that is, each update increases by 0.05 rad based on the previous one.

[0021] Without loss of generality, a typical embodiment of the present invention is as follows: (1) Set the initial phase difference of the programmable filter to 0 rad; (2) The single-frequency laser 1 generates an output frequency of Single-frequency laser, The typical value is 193.15 THz. After passing through pulse generation module 2, the continuous light is modulated into a pulse width of... Pulsed light, The typical value is 110 ns; Sideband generation module 3 passes through a frequency of Phase modulation produces a relative intensity of on both sides of a single-frequency laser. Symmetrical frequency sideband signal, The typical value is 23 GHz. The typical value is -20dB. The symmetrical frequency sideband signal includes... The sideband signals with different frequencies, the first The frequencies of the step sideband signals are respectively , , It is a positive integer.

[0022] After the symmetrical frequency sideband signal passes through programmable filter 4, the frequencies set by the programmable filter are respectively... The filter passband is bandpass filtered to select single-frequency laser and the required symmetrical frequency sideband signals. The bandwidth of each filter passband is less than 10 GHz. Based on the phase difference currently set by the programmable filter, the filtered single-frequency laser and the symmetrical frequency sideband signals are phase difference modulated. The optical signal output from the programmable filter 4 is then amplified by the fiber amplifier 5. The typical peak power after amplification is 744 mW. After filtering out excess ASE noise by the narrowband filter 6, it is injected into the transmission fiber 7. The typical length of the transmission fiber 7 is 50 km. The optical signal will generate spontaneous modulation instability in the transmission fiber 7. The combined effect of ASE noise and sidebands will generate both spontaneous modulation instability and induced spontaneous modulation instability, which compete with each other during transmission. The competition characteristics are determined by the phase difference set by the programmable filter 4 and affect the phase noise of the system.

[0023] After passing through optical fiber 7, the optical signal is injected into the interferometric fiber optic sensor array module to generate an optical interference signal. The typical value of the arm difference of the interferometric fiber optic sensor is 0.5m. A delay module is used between the two sensors to ensure that the time interval between the reflected light pulses is greater than the pulse width. Its typical value is 200 ns.

[0024] The optical interference signal is injected into the photodetector 9, which converts the optical signal into an electrical signal. The electrical signal is then uploaded to the signal acquisition and processing module 10 for demodulation, measuring the current phase noise of the system. The signal acquisition and processing module 10 employs well-established and widely used technologies in the field for demodulation, such as phase generation carrier-PGC demodulation, 3×3 demodulation, and heterodyne demodulation.

[0025] (3) Compare the current phase noise of the system with the initial phase noise (0 rad). If it is higher than the initial phase noise, update the current phase difference and the required symmetric frequency sideband order of the programmable filter, and go to step (2). Repeat this process until the current phase noise of the system reaches its lowest value compared to the initial state, thereby fully suppressing the phase noise dominated by spontaneous modulation instability. The method for updating the current phase difference of the programmable filter is as follows: update the phase difference within the set phase difference range with a set step size. The set phase difference range is 0 rad - 6.28 rad, and the set step size is 0.05 rad.

[0026] Reference Figure 2 , Figure 2 The figure shows the test results of the specific embodiment described above. With a peak input light power of 744mW, a first-order symmetric frequency sideband signal with a frequency of 23GHz relative to the center light, and a relative intensity of -20dB, the phase noise between the single-frequency laser and the first-order symmetric frequency sideband signal is 0rad and 2.0rad, respectively. Compared to 0rad (no phase difference modulation), modulating the phase difference to 2.0rad further reduces the system's phase noise by -3dB. This is because spontaneous modulation instability is extremely sensitive to phase difference, exhibiting significant differences in phase noise under different phase differences. Spontaneous modulation instability originates from ASE noise, and its incoherence deteriorates the system's phase noise. Induced spontaneous modulation instability originates from various sidebands, maintaining a certain degree of coherence with the single-frequency laser. Therefore, by changing the phase difference to make the induced spontaneous modulation instability competitively dominant, the phase noise of the long-range interferometric fiber optic sensing system can be effectively suppressed.

[0027] To address the problem that the spontaneous modulation instability of current remote interferometric fiber optic sensing systems has not been adequately resolved, thus limiting the system's detection performance, this invention effectively suppresses the spontaneous modulation instability and phase noise of remote interferometric fiber optic sensing systems by controlling the phase difference between single-frequency lasers and each order sideband. This results in a low-noise remote interferometric fiber optic sensing system and improves the system's detection performance.

[0028] Matters not covered in this invention are common knowledge.

[0029] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0030] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application.

[0031] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A remote interferometric fiber optic sensing system, characterized in that, It includes a single-frequency laser, a pulse generation module, a sideband generation module, a programmable filter, an optical fiber amplifier, a narrowband filter, and a transmission optical fiber, connected in sequence. The output port of the transmission optical fiber is connected to the input port of the interferometric fiber optic sensor array module, and the output port of the interferometric fiber optic sensor array module is connected to the spontaneous modulation instability monitoring and control device. The spontaneous modulation instability monitoring and control device collects and extracts the optical interference signal generated by the interferometric fiber optic sensor array module, thereby monitoring the phase noise caused by spontaneous modulation instability in the system. It also applies phase modulation of different frequencies to the sideband generation module, observes the resulting changes in phase noise, and determines the frequency corresponding to the lowest phase noise value. In frequency A weak coherent sideband is applied to suppress spontaneous modulation instability by stimulating induced spontaneous modulation instability. Simultaneously, the spontaneous modulation instability monitoring and control device outputs a control signal for a programmable filter based on real-time phase noise monitoring results. This signal is used to set the phase difference and the order of the symmetrical frequency sideband of the programmable filter. The bandpass filtering function of the programmable filter is used to filter out the single-frequency laser and the required symmetrical frequency sideband signals. Based on the phase difference currently set by the programmable filter, the filtered single-frequency laser and the symmetrical frequency sideband signals are phase-modulated until the phase noise dominated by spontaneous modulation instability is fully suppressed.

2. The remote interferometric fiber optic sensing system according to claim 1, characterized in that, The spontaneous modulation instability monitoring and control device includes a photodetector and a signal acquisition and processing module. The output port of the interferometric fiber optic sensor array module is connected to the input port of the photodetector, and the output port of the photodetector is connected to the signal acquisition and processing module.

3. The remote interferometric fiber optic sensing system according to claim 1 or 2, characterized in that, The pulse generation module is used to generate a pulse with a frequency of 100 Hz from the single-frequency laser. The single-frequency continuous laser is modulated into a single-frequency pulsed laser, and the pulse generation module is a combination of a signal source and an acousto-optic modulator, an electro-optic forced modulator, a semiconductor amplifier, or an optical switch.

4. The remote interferometric fiber optic sensing system according to claim 3, characterized in that, The sideband generation module is used to generate symmetrical frequency sideband signals on both sides of the single-frequency pulse laser output by the pulse generation module. The sideband generation module is a combination of a signal source and an electro-optic phase modulator or an electro-optic intensity modulator.

5. The remote interferometric fiber optic sensing system according to claim 3, characterized in that, The aforementioned interferometric fiber optic sensor array module includes multiple interferometric fiber optic sensors, and adjacent interferometric fiber optic sensors are connected by a delay module, which is a delay fiber.

6. The remote interferometric fiber optic sensing system according to claim 5, characterized in that, The interferometric fiber optic sensor is a Michelson interferometer, a Sagnac interferometer, or a Mach-Zehnder interferometer.

7. The method for suppressing spontaneous modulation instability in a remote interferometric fiber optic sensing system as described in claim 1, characterized in that, The spontaneous modulation instability monitoring and control device includes a photodetector and a signal acquisition and processing module, and the spontaneous modulation instability suppression method includes: (1) Set the initial phase difference of the programmable filter and the order of the symmetrical frequency sidebands to be screened; (2) The single-frequency laser generates and outputs a frequency of: The single-frequency continuous laser, after passing through the pulse generation module, is modulated into a pulse width of... The single-frequency pulsed light, the sideband generation module through a frequency of Phase modulation produces a relative intensity of on both sides of a single-frequency pulse light. The symmetrical frequency sideband signal includes... A symmetrical frequency sideband signal with different frequencies, the first The frequencies of the first-order symmetric frequency sideband signals are respectively , , For positive integers; after the symmetrical frequency sideband signal passes through the programmable filter, the frequencies set by the programmable filter are respectively The filter passband is bandpass filtered to select the single-frequency laser and the required symmetrical frequency sideband signals. The bandwidth of each filter passband is less than 10 GHz. Based on the phase difference currently set by the programmable filter, the filtered single-frequency laser and the symmetrical frequency sideband signals are phase-modulated. The optical signal output from the programmable filter is then amplified by an optical fiber amplifier, and after filtering out excess spontaneous emission noise by a narrowband filter, it is injected into the transmission optical fiber. The optical signal after passing through the transmission optical fiber is injected into the interferometric fiber optic sensor array module to generate an optical interference signal. In the interferometric fiber optic sensor array module, a delay module is used between two adjacent interferometric fiber optic sensors to ensure that the time interval between the reflected light pulses is greater than the pulse width. The optical interference signal is injected into the photodetector signal, the photodetector converts the optical signal into an electrical signal, and the electrical signal is finally uploaded to the signal acquisition and processing module for demodulation to measure the current phase noise of the system. (3) Compare the current phase noise of the system with the phase noise of the initial state of the system. If it is higher than the phase noise of the initial state, update the phase difference and the order of the symmetrical frequency sideband to be screened in the current setting of the programmable filter, and go to step (2). Repeat this process until the current phase noise of the system reaches the lowest level compared with the phase noise of the initial state, thereby fully suppressing the phase noise dominated by spontaneous modulation instability.

8. The method for suppressing spontaneous modulation instability in a remote interferometric fiber optic sensing system according to claim 7, characterized in that, In step (3), the method for updating the current phase difference of the programmable filter is as follows: update the phase difference within the set phase difference range with a set step size. The set phase difference range is 0 rad - 6.28 rad, and the set step size is 0.05 rad.

9. The method for suppressing spontaneous modulation instability in a remote interferometric fiber optic sensing system according to claim 7, characterized in that, In step (1), the initial phase difference is 0 rad.

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