A method and system for common mode noise rejection in a PGC fiber optic hydrophone system

Abstract

The application relates to a PGC optical fiber hydrophone system common mode noise suppression method and system, and belongs to the optical fiber sensing technical field. In the PGC-based optical fiber hydrophone system, a 3*3 reference interferometer is introduced, two reference interference signal linear combinations with fixed phase difference of the 3*3 reference interferometer are used to form a reference signal, the relationship between the initial phases of the sensing interference signal and the reference signal satisfies a pre-derived photoelectric common mode noise strong suppression effect initial phase condition, that is, the initial phases of the two kinds of interferometers only need to be different by an integer multiple to realize the strong suppression effect of the photoelectric common mode noise; in the noise suppression process, the light intensity compensation method is introduced, the intensity of the interference pulse is divided by the intensity of the associated amplitude modulation pulse to eliminate the associated amplitude modulation influence, improve the reference signal phase locking capability, and finally improve the common mode noise suppression effect.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing technology, and in particular to a common-mode noise suppression method and system for a PGC fiber optic hydrophone system. Background Technology

[0002] In deep-sea fiber optic hydrophone systems, photoelectric noise is a key factor affecting the system's detection performance. These noise sources include light source noise, optical amplifier noise, acousto-optic modulator noise, photodetector noise, analog-to-digital converter noise, optical cable transmission noise, and additional noise introduced by signal detection methods. As fiber optic hydrophone systems are increasingly used in deep-sea applications, the system's photoelectric noise is gradually exceeding environmental noise. Therefore, there is an urgent need to comprehensively suppress the phase noise converted from various photoelectric noise sources to meet the requirements of deep-sea applications.

[0003] In existing technologies, an acoustically insensitive interferometer is typically introduced into the system as a reference interferometer. This reference interferometer picks up the phase noise generated by the aforementioned noise sources, which can then be considered as common-mode noise between the reference and sensing interferometers. This noise can then be suppressed using direct subtraction, cross-multiplication-subtraction, or adaptive filtering methods. However, practical experience shows that in Phase Generated Carrier (PGC) signal detection systems, the noise suppression effects of these methods are not stable. Direct subtraction cannot suppress both high-frequency phase noise sources and intensity noise sources. While cross-multiplication-subtraction can suppress phase common-mode noise sources, it cannot suppress the phase noise generated by intensity noise sources through signal detection because the PGC method is ultimately used to detect the phase signal. Adaptive filtering completely delegates the initial phase matching process to the program, inevitably leading to occasional mismatches, which is unacceptable for a fully autonomous deep-sea fiber optic vector hydrophone vertical array system. Summary of the Invention

[0004] Based on this, it is necessary to provide a common-mode noise suppression method and system for PGC fiber optic hydrophone systems to address the above-mentioned technical problems. This method and system can comprehensively suppress common-mode noise from optoelectronic devices, optical cable transmission, and additional noise introduced by optoelectronic signal detection, thereby achieving effective suppression of optoelectronic common-mode noise in deep-sea fiber optic hydrophone systems.

[0005] A common-mode noise suppression system for a PGC fiber optic hydrophone system includes a PGC pulse generator, an arbitrary waveform generator, a 1×2 coupler, two delay fibers, a sensing interferometer, a 3×3 reference interferometer, three attenuators, a detection system, and a demodulation system.

[0006] The PGC pulse generator is used to receive signals from an arbitrary waveform generator, modulate and generate carrier pulses, and send them to a 1×2 coupler. The carrier pulses are input to a sensing interferometer and a 3×3 reference interferometer via the 1×2 coupler to generate sensing interference pulses and two reference interference pulses. The sensing interference pulses are input to the detection system via a first attenuator and a first delay fiber. The first reference interference pulses are input to the detection system via a second attenuator and a second delay fiber, and the second reference interference pulses are input to the detection system via a third attenuator.

[0007] The detection system is used to convert each interference pulse into an electrical signal and then into a digital-to-analog signal, outputting the sensing interference signal. and two reference interference signals and The system simultaneously receives two accompanying amplitude modulation pulses generated by the carrier pulse transmission and inputs them into the demodulation system. The intensity of the interference pulse is divided by the intensity of the accompanying amplitude modulation pulse using the light intensity compensation method to eliminate the influence of the accompanying amplitude modulation.

[0008] After demodulating each interfering signal using PGC, the demodulation system first uses an ellipse fitting method to eliminate the influence of accompanying amplitude modulation. and Perform calibration and combine into a reference signal , making Initial phase and The initial phase satisfies the pre-derived initial phase condition for strong suppression of optoelectronic common-mode noise, that is, the two initial phases differ by a certain amount. Integer multiples of;

[0009] Again and Subtract the time-domain outputs obtained from PGC detection to obtain the time-domain output after photoelectric common-mode noise suppression.

[0010] In one embodiment, the PGC pulse generating device includes a laser, an optical isolator, and an acousto-optic modulator connected in sequence; wherein the modulation interfaces of the laser and the acousto-optic modulator are both connected to the output terminal of an arbitrary waveform generator.

[0011] The laser is used to perform optical frequency modulation based on the sinusoidal signal input from the arbitrary waveform generator and output a PGC continuous optical signal to the optical isolator;

[0012] Optical isolators are used to ensure unidirectional transmission of PGC continuous optical signals from the laser to the acousto-optic modulator.

[0013] An acousto-optic modulator is used to intensity modulate a received PGC continuous optical signal based on a pulse signal input from an arbitrary waveform generator, ultimately generating a carrier pulse.

[0014] In one embodiment, the sensing interferometer includes a 2×2 coupler, a first sensing fiber, a second sensing fiber, a first Faraday rotator, and a second Faraday rotator; wherein, the first port of the 2×2 coupler is used to receive carrier pulses, the second port of the 2×2 coupler is used to output sensing interference pulses generated by the sensing interferometer, the third port of the 2×2 coupler is connected to the first Faraday rotator via the first sensing fiber, and the fourth port of the 2×2 coupler is connected to the second Faraday rotator via the second sensing fiber.

[0015] In one embodiment, the 3×3 reference interferometer includes a 3×3 coupler, a first reference fiber, a second reference fiber, a third delay fiber, a third Faraday rotator, a fourth Faraday rotator, and a fifth Faraday rotator. The first port of the 3×3 coupler is used to receive a carrier pulse; the second port of the 3×3 coupler is used to output a second reference interference pulse generated by the 3×3 reference interferometer; the third port of the 3×3 coupler is used to output a first reference interference pulse generated by the 3×3 reference interferometer; the fourth port of the 3×3 coupler is connected to the third Faraday rotator via the first reference fiber; the fifth port of the 3×3 coupler is connected to the fourth Faraday rotator via the third delay fiber; and the sixth port of the 3×3 coupler is connected to the fifth Faraday rotator via the second reference fiber.

[0016] In one embodiment, the detection system includes a 1×3 coupler, a photodetector, and a digital-to-analog converter connected in sequence;

[0017] The 1×3 coupler is used to receive the sensing interference pulse, the first reference interference pulse, the second reference interference pulse, and two accompanying amplitude modulation pulses generated during the carrier pulse transmission. The sensing interference pulse is input to the detection system via a first attenuator and a first delay fiber; the first reference interference pulse is input to the detection system via a second attenuator and a second delay fiber; and the second reference interference pulse is input to the detection system via a third attenuator. The first accompanying amplitude modulation pulse is generated by reflecting the carrier pulse emitted by the PGC pulse generator after being reflected by a fourth Faraday rotator, and then passing through a third delay fiber and a third attenuator. The second accompanying amplitude modulation pulse is generated by reflecting the carrier pulse emitted by the PGC pulse generator after being reflected by a fourth Faraday rotator, and then passing through a third delay fiber, a second attenuator, and a second delay fiber.

[0018] The photodetector is used to convert the received interference pulses into electrical signals;

[0019] The input of the digital-to-analog converter is connected to the output of the arbitrary waveform generator. Based on the synchronization signal and acquisition trigger signal provided by the arbitrary waveform generator, it performs digital-to-analog conversion on the electrical signals converted from each interference pulse, outputting the sensing interference signal. First reference interferometry signal Second reference interference signal .

[0020] In one embodiment, the time division of each pulse received in the detection system is controlled by the length of each delay fiber. The five pulses received by the detection system in a single repetition cycle have a certain time delay and do not affect each other. The five pulses are the first reference interference pulse, the second reference interference pulse, the sensing interference pulse, the first accompanying amplitude modulation pulse, and the second accompanying amplitude modulation pulse.

[0021] The arrival time interval between the first reference interference pulse and the second reference interference pulse is controlled by the second delay fiber, the arrival time interval between the second reference interference pulse and the sensing interference pulse is controlled by the first delay fiber, the arrival time interval between the sensing interference pulse and the first accompanying amplitude modulation pulse is controlled by the third delay fiber in the 3×3 reference interferometer, and the arrival time interval between the first accompanying amplitude modulation pulse and the second accompanying amplitude modulation pulse is controlled by the second delay fiber.

[0022] In one embodiment, three attenuators are used to adjust the peak values ​​of each interference pulse input to the photodetector in the detection system, ensuring that the peak values ​​of the sensing interference pulse, the first reference interference pulse, and the second reference interference pulse are basically balanced and at their highest values ​​when the photodetector is not saturated, thereby reducing the influence of non-common-mode additive noise sources.

[0023] In one embodiment, the initial phase condition for strong suppression of optoelectronic common-mode noise is derived from the PGC noise model, obtaining the theoretical formula for the PSD value. Using the PSD minimum value as a constraint, the initial phase condition that achieves the optimal overall suppression effect of optoelectronic common-mode noise is obtained. The derivation process includes:

[0024] Assuming a sensing interferometer The initial phase of the obtained sensing interference signal is Reference interferometer The initial phase of the obtained reference interferometric signal is The phase noise source and multiplicative noise source picked up by the two interferometers are the same, that is , However, additive noise sources are different, namely This is because the interference signals obtained by the two interferometers need to be detected and acquired at different times by the same photodetector and analog-to-digital converter in the detection system, but the PSD values ​​of the two interferometers are consistent, that is... Considering only noise, the time-domain output expression of the phase signal of the interference signals from the two interferometers after PGC detection is:

[0025] ;

[0026] in, The output phase noise of the sensing interferometer As a reference, the output phase noise of the interferometer For the time domain output of the sensor, For reference time domain output, As a phase noise source for the sensing interferometer, As a reference interferometer, the phase noise source As a source of phase noise, As a multiplicative noise source for the sensing interferometer, As a reference interferometer, the multiplicative noise source As a multiplicative noise source, As an additive noise source for the sensing interferometer, As a reference interferometer, the additive noise source The output phase noise PSD value of the additive noise source of the sensing interferometer. The output phase noise PSD value of the additive noise source of the reference interferometer;

[0027] After PGC signal detection and The time-domain signal obtained by subtraction for:

[0028] ;

[0029] in, and The phase noise source superposition coefficients are respectively in and The value at that location, and The superposition coefficients of the multiplicative noise sources are respectively in and The value at that location, and The superposition coefficients of additive noise sources are respectively in and The value at that location, Represents convolution operation. Let be the unit impulse response function of the low-pass filter. and These are first-order and second-order Bessel functions, respectively. For order, For PGC carrier frequency, For time, The amplitude of the DC voltage of the interference signal. The visibility of the interference signal fringes;

[0030] right Its spectrum is obtained by high-pass filtering and Fourier transform. for:

[0031] ;

[0032] in, Let be the transfer function of the low-pass filter. Angular frequency, The spectral amplitude of the phase noise source. The spectral amplitude of the multiplicative noise source. The spectral amplitude of the additive noise source in the sensing interferometer. The spectral amplitude of the additive noise source of the reference interferometer;

[0033] Then, based on the Wiener-Khinchin theorem and the white noise approximation condition, the time-domain signal obtained by subtraction is obtained. The PSD file is:

[0034] ;

[0035] in, The power spectral density of the phase noise source. The power spectral density of the multiplicative noise source. The power spectral density of the additive noise source in the sensing interferometer. The power spectral density of the additive noise source of the reference interferometer;

[0036] To reduce direct time domain signal The output phase noise, expressed in PSD value Using the minimum value as a constraint, the initial phase condition that achieves the optimal overall suppression effect of optoelectronic common-mode noise is obtained as follows: ,in, If the value is an integer, then the effects of phase noise sources and multiplicative noise sources will be completely eliminated, i.e.:

[0037] .

[0038] A common-mode noise suppression method for a PGC fiber optic hydrophone system, the method being implemented based on the aforementioned common-mode noise suppression system for a PGC fiber optic hydrophone system, the method comprising:

[0039] Step 1: Acquire the sensing interference signal output by the sensing interferometer. The first reference interference signal output by the 3×3 reference interferometer Second reference interference signal ;

[0040] Step 2: The two reference interferometric signals are calibrated using the ellipse fitting method after eliminating the influence of accompanying amplitude modulation, obtaining the DC bias voltage and AC amplitude coefficient of the two reference interferometric signals, and then the DC bias voltage of the two reference interferometric signals is removed respectively; wherein, and They are represented as follows:

[0041] ;

[0042] in, and They are respectively and DC bias voltage. and They are respectively and AC amplitude coefficient; The phase term is generated by integrating the signal frequency. and They are respectively and The initial phase parameters;

[0043] Step 3, respectively, the sensing interference signals PGC signal detection is performed on the two reference interference signals after removing the DC bias voltage to obtain the sensing time-domain output, the first reference time-domain output, and the second time-domain output. The average of these outputs is then calculated to obtain the initial phase parameters of the sensing interference signal, the first reference interference signal, and the second reference interference signal, which are expressed as follows: , and ;

[0044] Step 4, using , , , and Calculations were performed to obtain two superposition coefficients. and , respectively represented as:

[0045] ;

[0046] Step 5, according to and right and A linear combination is performed to obtain the reference signal. This causes the sensing interference signal initial phase With reference signal initial phase The relationship between them satisfies the pre-derived initial phase condition for strong suppression of photoelectric common-mode noise, that is, the initial phase difference between the initial phase of the sensing interference signal and the initial phase of the reference signal is satisfied. Integer multiples of;

[0047] Step 6, for the reference signal Perform PGC signal detection to obtain the reference time domain output;

[0048] Step 7: Subtract the sensor time-domain output from the reference time-domain output to obtain the time-domain output after photoelectric common-mode noise suppression.

[0049] In one embodiment, an elliptic fitting method, after eliminating the influence of accompanying amplitude modulation, is used to calibrate the two reference interferometric signals to obtain the DC bias voltage and AC amplitude coefficients of the two reference interferometric signals, including:

[0050] After using the intensity compensation method to divide the intensity of the interference pulse by the intensity of the accompanying amplitude-modulated pulse to eliminate the influence of the accompanying amplitude modulation, the DC bias voltage and AC amplitude coefficients of the two reference interference signals are obtained using the elliptic fitting method; the elliptic fitting method includes:

[0051] Acquire reference interferometric signal pair over a period of time And draw it as a Lissajous figure;

[0052] The ellipse that best approximates the Lissajous figure is fitted using the least squares method. The equation of the ellipse is:

[0053] ;

[0054] in, These are the coefficients obtained after fitting;

[0055] Based on the fitting coefficients, the DC bias voltage is calculated as follows:

[0056] ; ;

[0057] Based on the fitting coefficients and the calculated DC bias voltage, the AC amplitude coefficients are calculated as follows:

[0058] ;

[0059] .

[0060] The above-mentioned common-mode noise suppression method and system for PGC fiber optic hydrophone system has the following beneficial effects:

[0061] 1. Within the system and method, a reference signal is formed by linearly combining two reference interference signals with a fixed phase difference using a 3×3 reference interferometer. This ensures that the relationship between the initial phase of the sensing interference signal and the initial phase of the reference signal satisfies the pre-derived initial phase condition for strong suppression of photoelectric common-mode noise. In other words, the initial phases of the two interferometers only need to differ by a certain amount. Strong suppression of photoelectric common-mode noise can be achieved by using integer multiples of the signal; and the suppression effect is stable, avoiding the accidental mismatch problem that may occur in traditional adaptive filtering methods. It is particularly suitable for long-term autonomous working environments, and effectively suppresses 1 / f noise from phase noise sources such as lasers. The system structure is simple, requiring only a 3×3 reference interferometer to achieve noise suppression for multiple sensor interferometers, without the need for a complex phase feedback control system, which conforms to the design concept of passive hydrophones at the sensing end.

[0062] 2. The system and method employ an intensity compensation method to divide the intensity of the interference pulse by the intensity of the accompanying amplitude modulation pulse to eliminate the influence of the accompanying amplitude modulation. This improves the accuracy and stability of the ellipse fitting parameter calibration, enhances the precision of the ellipse fitting calibration, avoids inaccurate extraction of DC bias voltage and AC intensity, improves the phase-locked loop capability of the reference signal, and ultimately improves the common-mode noise suppression effect. Attached Figure Description

[0063] Figure 1 The graph shows the noise variation with the initial phase of the two interferometers after directly subtracting the demodulated signal from the sensor interferometer and the demodulated signal from the reference interferometer in one embodiment.

[0064] Figure 2 This is a graph showing the variation of the suppressed average phase noise with the algorithm center C value in one embodiment;

[0065] Figure 3 This is a schematic diagram of the common-mode noise suppression system of the PGC fiber optic hydrophone system in one embodiment;

[0066] Figure 4 This is a schematic diagram of the PGC pulse generation device in one embodiment;

[0067] Figure 5 This is a schematic diagram of the structure of a sensing interferometer in one embodiment;

[0068] Figure 6 This is a schematic diagram of the structure of a 3×3 reference interferometer in one embodiment;

[0069] Figure 7 This is a schematic diagram of the detection system in one embodiment;

[0070] Figure 8 This is a schematic diagram of five pulses received by the detection system within a single repetition cycle in one embodiment;

[0071] Figure 9 This is a flowchart illustrating a common-mode noise suppression method for a PGC fiber optic hydrophone system in one embodiment.

[0072] Figure 10 Here is a measured Lissajous figure showing the presence or absence of accompanying amplitude modulation effects in one embodiment; where, Figure 10 (a) Lissajous figures without associated amplitude modulation compensation; Figure 10 (b) Lissajous figures after accompanying amplitude modulation compensation;

[0073] Figure 11 This is a schematic diagram illustrating the output phase noise suppression effect in one embodiment;

[0074] Figure 12 A partial structural diagram of the experimental setup with eight sensor interferometers;

[0075] Figure 13 This is a schematic diagram of the internal structure of an 8-time-division multiplexing module;

[0076] Figure 14 This is a schematic diagram illustrating the noise suppression effect of the sensor channel; where, Figure 14 (a) shows the noise suppression effect of the first and second sensing channels. Figure 14 (b) shows the noise suppression effect of the 7th and 8th sensor channels. Detailed Implementation

[0077] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0078] Before describing the specific implementation of this application, we first derive the theoretical formula for the PSD value from the PGC noise model, and then use the PSD minimum value as a constraint to obtain the initial phase condition that achieves the optimal overall suppression effect of optoelectronic common-mode noise. This initial phase condition is then used as the initial phase condition for strong suppression of optoelectronic common-mode noise. The derivation process is as follows:

[0079] Assuming a sensing interferometer The initial phase of the obtained sensing interference signal is Reference interferometer The initial phase of the obtained reference interferometric signal is The phase noise source and multiplicative noise source picked up by the two interferometers are the same, that is , However, additive noise sources are different, namely This is because the interference signals obtained by the two interferometers need to be detected and acquired at different times by the same photodetector and analog-to-digital converter in the detection system, but the PSD (noise power spectral density) values ​​of the two interferometers are consistent, that is... Considering only noise, the time-domain output expression of the phase signal of the interference signals from the two interferometers after PGC detection is:

[0080] ;

[0081] in, The output phase noise of the sensing interferometer As a reference, the output phase noise of the interferometer For the time domain output of the sensor, For reference time domain output, As a phase noise source for the sensing interferometer, As a reference interferometer, the phase noise source As a source of phase noise, As a multiplicative noise source for the sensing interferometer, As a reference interferometer, the multiplicative noise source As a multiplicative noise source, As an additive noise source for the sensing interferometer, As a reference interferometer, the additive noise source The output phase noise PSD value of the additive noise source of the sensing interferometer. The output phase noise PSD value of the additive noise source of the reference interferometer.

[0082] After PGC signal detection and The time-domain signal obtained by subtraction for:

[0083] ;

[0084] in, and The phase noise source superposition coefficients are respectively in and The value at that location, and The superposition coefficients of the multiplicative noise sources are respectively in and The value at that location, and The superposition coefficients of additive noise sources are respectively in and The value at that location, Represents convolution operation. Let be the unit impulse response function of the low-pass filter. and These are first-order and second-order Bessel functions, respectively. For order, For PGC carrier frequency, For time, The amplitude of the DC voltage of the interference signal. The visibility of the interference signal fringes.

[0085] right Its spectrum is obtained by high-pass filtering and Fourier transform. for:

[0086] ;

[0087] in, Let be the transfer function of the low-pass filter. Angular frequency, The spectral amplitude of the phase noise source. The spectral amplitude of the multiplicative noise source. The spectral amplitude of the additive noise source in the sensing interferometer. The spectral amplitude of the additive noise source of the reference interferometer.

[0088] Then, based on the Wiener-Khinchin theorem and the white noise approximation condition, the time-domain signal obtained by subtraction is obtained. The PSD file is:

[0089] ;

[0090] in, The power spectral density of the phase noise source. The power spectral density of the multiplicative noise source. The power spectral density of the additive noise source in the sensing interferometer. The power spectral density of the additive noise source of the reference interferometer.

[0091] To reduce direct time domain signal The output phase noise, expressed in PSD value Using the minimum value as a constraint, the initial phase condition that achieves the optimal overall suppression effect of optoelectronic common-mode noise is obtained as follows: ,in, If the value is an integer, then the effects of phase noise sources and multiplicative noise sources will be completely eliminated, i.e.:

[0092] .

[0093] Furthermore, to verify the initial phase condition for strong suppression of optoelectronic common-mode noise mentioned above, the following is based on the PSD value. The phase noise suppression effect is simulated.

[0094] Set the simulation parameters as follows: , , , , , With the PGC detection algorithm's center C value (i.e., modulation depth) set to 2.46, the output phase noise value after direct subtraction can be obtained as a function of the initial phase of the sensing interference signal. Initial phase with reference interferometric signal The changing two-dimensional intensity map, the result is as follows Figure 1 As shown in the diagram, the distribution characteristics of the phase noise minimum presented in this two-dimensional intensity map clearly indicate that the initial phase condition for strong suppression of photoelectric common-mode noise is... ( (where the initial phase difference is an integer), meaning the initial phase difference between the two interferometers only needs to be an integer. A strong suppression effect can be achieved by using integer multiples of the value. Without loss of generality, for the convenience of research, we can use... As an initial phase condition for strong suppression effect, it is required that the initial phases of the interference signals of the two interferometers be locked.

[0095] As can be seen from the above equation, under the initial phase condition of strong suppression effect Under the condition that the power spectral density of the additive noise source, the DC voltage amplitude, and the fringe visibility are constant, the suppressed output phase noise PSD is compared with the center C value of the PGC detection algorithm and the initial phase of the interference signal. Closely related. That is, the average output phase noise after suppression can be optimized by setting the center C value of the PGC detection algorithm. To obtain the optimal center C value of the PGC detection algorithm that minimizes the average output phase noise after suppression, the above equation is simulated. The simulation parameters are set as follows: , , , The algorithm center C value is scanned from 1 to 5, and the results are calculated for different algorithm center C values. Follow The average value of the changes is used to obtain the curve of the suppressed average phase noise as a function of the algorithm center C value. Simulation results are derived from... Figure 2 As can be seen, the algorithm center C value that minimizes the average phase noise after suppression is 2.4530.

[0096] In one embodiment, such as Figure 3 As shown, a common-mode noise suppression system for a PGC fiber optic hydrophone system is provided, including: a PGC pulse generator, an arbitrary waveform generator (also known as a signal generator), a 1×2 coupler, two delay fibers, a sensing interferometer, a 3×3 reference interferometer, three attenuators, a detection system, and a demodulation system.

[0097] The PGC pulse generator receives signals from an arbitrary waveform generator, modulates and generates carrier pulses, and sends them to the first port of a 1×2 coupler. The carrier pulses are transmitted via the second port of the 1×2 coupler to a sensing interferometer to generate sensing interference pulses, and then via the third port of the 1×2 coupler to a 3×3 reference interferometer to generate two reference interference pulses. The sensing interference pulses output by the sensing interferometer are transmitted sequentially through a first attenuator (attenuator 1) and a first delay fiber (delay fiber 1) to the detection system. The first reference interference pulse output by the 3×3 reference interferometer is transmitted sequentially through a second attenuator (attenuator 2) and a second delay fiber (delay fiber 2) to the detection system, and the second reference interference pulse output by the 3×3 reference interferometer is transmitted sequentially through a third attenuator (attenuator 3) to the detection system. The detection system is used to sequentially analyze each received interference pulse. The system performs electrical signal conversion and digital-to-analog conversion, outputting the sensing interference signal, the first reference interference signal, and the second reference interference signal to the demodulation system. The detection system also receives two accompanying amplitude-modulated pulses generated during carrier pulse transmission and transmits them to the demodulation system. It uses an intensity compensation method to divide the intensity of the interference pulse by the intensity of the accompanying amplitude-modulated pulse to eliminate the influence of the accompanying amplitude modulation. After demodulating each interference signal using PGC, the demodulation system first calibrates the first and second reference interference signals using an elliptic fitting method after eliminating the influence of the accompanying amplitude modulation. Then, it linearly combines the two calibrated reference interference signals into a reference signal, ensuring that the relationship between the initial phase of the sensing interference signal and the initial phase of the reference signal satisfies the pre-derived initial phase condition for strong suppression of photoelectric common-mode noise, i.e., the initial phase difference between the sensing interference signal and the initial phase of the reference signal is satisfied. The integer multiples of the signal; then perform PGC detection on the sensing interference signal and the reference signal respectively, subtract the obtained time-domain outputs to obtain the time-domain output after photoelectric common-mode noise suppression; among them, the initial phase condition for strong suppression of photoelectric common-mode noise is derived from the PGC noise model, the theoretical formula of PSD value is derived, and the PSD minimum value is used as the constraint condition to solve the initial phase condition that achieves the best comprehensive suppression effect of photoelectric common-mode noise.

[0098] The aforementioned PGC fiber optic hydrophone system's common-mode noise suppression system uses a 3×3 reference interferometer to linearly combine two reference interference signals with a fixed phase difference into a reference signal. This ensures that the relationship between the initial phase of the sensing interference signal and the initial phase of the reference signal satisfies the pre-derived initial phase condition for strong photoelectric common-mode noise suppression. In other words, the initial phases of the two interferometers only need to differ by a certain amount. Strong suppression of photoelectric common-mode noise can be achieved by using integer multiples of the signal strength; the suppression effect is stable, avoiding the accidental mismatch problem that may occur in traditional adaptive filtering methods, making it particularly suitable for long-term autonomous working environments. At the same time, it effectively suppresses 1 / f noise from phase noise sources such as lasers; the system structure is simple, requiring only a 3×3 reference interferometer to achieve noise suppression for multiple sensor interferometers, without the need for a complex phase feedback control system, which conforms to the design concept of passive hydrophones at the sensing end; and the system adopts the light intensity compensation method, dividing the intensity of the interference pulse by the intensity of the accompanying amplitude modulation pulse to eliminate the influence of the accompanying amplitude modulation, thereby improving the accuracy and stability of ellipse fitting parameter calibration, improving the accuracy of ellipse fitting calibration, avoiding inaccurate extraction of DC bias voltage and AC intensity, improving the phase-locking capability of the reference signal, and ultimately improving the common-mode noise suppression effect.

[0099] In one embodiment, such as Figure 4 As shown, the PGC pulse generation device includes a laser, an optical isolator, and an acousto-optic modulator connected in sequence. The modulation interfaces of both the laser and the acousto-optic modulator are connected to the output of an arbitrary waveform generator. The laser is used to perform optical frequency modulation based on the sinusoidal signal input from the arbitrary waveform generator and outputs a continuous PGC optical signal to the optical isolator. The optical isolator ensures unidirectional transmission of the continuous PGC optical signal from the laser to the acousto-optic modulator. The acousto-optic modulator modulates the intensity of the received continuous PGC optical signal based on the pulse signal input from the arbitrary waveform generator, ultimately generating a carrier pulse.

[0100] In one embodiment, such as Figure 5 As shown, the sensing interferometer includes a 2×2 coupler, a first sensing fiber (sensing fiber 1), a second sensing fiber (sensing fiber 2), a first Faraday rotator (FRM 1), and a second Faraday rotator (FRM 2). The first port of the 2×2 coupler is used to receive carrier pulses, the second port of the 2×2 coupler is used to output the sensing interference pulses generated by the sensing interferometer, the third port of the 2×2 coupler is connected to the first Faraday rotator via the first sensing fiber, and the fourth port of the 2×2 coupler is connected to the second Faraday rotator via the second sensing fiber.

[0101] In one embodiment, such as Figure 6As shown, the 3×3 reference interferometer includes a 3×3 coupler, a first reference fiber (reference fiber 1), a second reference fiber (reference fiber 2), a third delay fiber (delay fiber 3), a third Faraday rotator (FRM 3), a fourth Faraday rotator (FRM 4), and a fifth Faraday rotator (FRM 5). The first port of the 3×3 coupler is used to receive carrier pulses; the second port of the 3×3 coupler is used to output the second reference interference pulse generated by the 3×3 reference interferometer; the third port of the 3×3 coupler is used to output the first reference interference pulse generated by the 3×3 reference interferometer; the fourth port of the 3×3 coupler is connected to the third Faraday rotator via the first reference fiber; the fifth port of the 3×3 coupler is connected to the fourth Faraday rotator via the third delay fiber; and the sixth port of the 3×3 coupler is connected to the fifth Faraday rotator via the second reference fiber.

[0102] In the 3×3 reference interferometer, the delay fiber 3 and FRM 4 serve two purposes: firstly, to implement the pulse delay method to suppress the influence of the cantilever arm echo; secondly, their reflected pulses, as the sampling pulses output by the laser, can be used as light intensity reference compensation pulses to suppress the accompanying amplitude modulation influence.

[0103] In one embodiment, such as Figure 7 As shown, the detection system includes a 1×3 coupler, a photodetector (referred to as the detector), and a digital-to-analog converter (DAC) connected in sequence. The 1×3 coupler receives the sensing interference pulse, the first reference interference pulse, the second reference interference pulse, and two accompanying amplitude-modulated pulses generated during carrier pulse transmission. The first accompanying amplitude-modulated pulse is generated by reflecting the carrier pulse from the PGC pulse generator after being reflected by the fourth Faraday rotator, then passing through the third delay fiber and the third attenuator. The second accompanying amplitude-modulated pulse is generated by reflecting the carrier pulse from the PGC pulse generator after being reflected by the fourth Faraday rotator, then passing through the third delay fiber, the second attenuator, and the second delay fiber. The photodetector converts the received interference pulses into electrical signals. The input of the DAC is connected to the output of an arbitrary waveform generator, and it performs digital-to-analog conversion on the converted electrical signals of each interference pulse based on the synchronization signal and acquisition trigger signal provided by the arbitrary waveform generator, outputting the sensing interference signal. First reference interferometry signal Second reference interference signal .

[0104] In one embodiment, the time division of each pulse received within the detection system is controlled by the length of each delay fiber. The five pulses received by the detection system within a single repetition cycle have a certain time delay but do not affect each other. Figure 8 As shown, the five pulses are the first reference interference pulses. Second reference interference pulse Sensing interference pulse First accompanying amplitude modulation pulse Second accompanying amplitude modulation pulse The arrival time interval between the first and second reference interference pulses is controlled by a second delay fiber; the arrival time interval between the second and sensing interference pulses is controlled by a first delay fiber; the arrival time interval between the sensing interference pulse and the first accompanying amplitude-modulated pulse is controlled by a third delay fiber within the 3×3 reference interferometer; and the arrival time interval between the first and second accompanying amplitude-modulated pulses is controlled by a second delay fiber. Specifically, in this embodiment, the arm difference between the 3×3 reference interferometer and the sensing interferometer is the same, with the lengths of the two sensing arms being 1.18 m and 1.7 m, respectively. The length of reference fiber 1 in the 3×3 reference interferometer is 1 m, and the length of reference fiber 2 is 1.52 m. Time division is achieved by adjusting the lengths of each delay fiber; specifically, the length of the first delay fiber is 126 m, the length of the second delay fiber is 65 m, and the length of the third delay fiber is 96 m.

[0105] It should be understood that during PGC pulse generation, the laser's optical frequency modulation is accompanied by co-frequency modulation of the output light intensity, i.e., accompanying amplitude modulation. This phenomenon reduces the accuracy of elliptic fitting calibration, leading to inaccurate extraction of DC bias voltage and AC intensity, reduced phase-locked loop capability of the reference signal, and ultimately affecting the common-mode noise suppression effect. The purpose of the accompanying amplitude-modulated pulse is to serve as a light intensity reference compensation pulse to suppress the influence of accompanying amplitude modulation, thereby improving the accuracy and stability of subsequent elliptic fitting parameter calibration.

[0106] In one embodiment, three attenuators are used to adjust the peak values ​​of each interference pulse input to the photodetector in the detection system, ensuring that the peak values ​​of the sensing interference pulse, the first reference interference pulse, and the second reference interference pulse are basically balanced and at their highest values ​​when the photodetector is not saturated, thereby reducing the influence of non-common-mode additive noise sources.

[0107] In one embodiment, such as Figure 9 As shown, a common-mode noise suppression method for a PGC fiber optic hydrophone system is provided. This method is based on the aforementioned common-mode noise suppression system for a PGC fiber optic hydrophone system and includes the following steps:

[0108] Step 1: Acquire the sensing interference signal output by the sensing interferometer. The first reference interference signal output by the 3×3 reference interferometer Second reference interference signal .

[0109] Step 2: The two reference interferometric signals are calibrated using an elliptic fitting method after eliminating the influence of accompanying amplitude modulation. This yields the DC bias voltage and AC amplitude coefficients of the two reference interferometric signals. The DC bias voltage of each reference interferometric signal is then removed. and They are represented as follows:

[0110] ;

[0111] in, and They are respectively and DC bias voltage. and They are respectively and AC amplitude coefficient; The phase term is generated by integrating the signal frequency. and They are respectively and The initial phase parameters.

[0112] Step 3, respectively, the sensing interference signals PGC signal detection is performed on the two reference interference signals after removing the DC bias voltage to obtain the sensing time-domain output, the first reference time-domain output, and the second time-domain output. The average of these outputs is then calculated to obtain the initial phase parameters of the sensing interference signal, the first reference interference signal, and the second reference interference signal, which are expressed as follows: , and .

[0113] Step 4, using , , , and Perform calculations (CAL) to obtain two superposition coefficients. and , respectively represented as:

[0114] .

[0115] Step 5, according to and right and A linear combination is performed to obtain the reference signal. This causes the sensing interference signal initial phase With reference signal initial phase The relationship between them satisfies the pre-derived initial phase condition for strong suppression of photoelectric common-mode noise, that is, the initial phase difference between the initial phase of the sensing interference signal and the initial phase of the reference signal is satisfied. Integer multiples of.

[0116] Step 6, for the reference signal Perform PGC signal detection to obtain the reference time domain output.

[0117] Step 7: Subtract the sensor time-domain output from the reference time-domain output to obtain the time-domain output after photoelectric common-mode noise suppression.

[0118] In one embodiment, an elliptic fitting method, after eliminating the influence of accompanying amplitude modulation, is used to calibrate the two reference interferometric signals to obtain the DC bias voltage and AC amplitude coefficients of the two reference interferometric signals, including:

[0119] After using the intensity compensation method to divide the intensity of the interference pulse by the intensity of the accompanying amplitude-modulated pulse to eliminate the influence of the accompanying amplitude modulation, the DC bias voltage and AC amplitude coefficients of the two reference interference signals are obtained using the elliptic fitting method; the elliptic fitting method includes:

[0120] Acquire reference interferometric signal pair over a period of time And draw it as a Lissajous figure;

[0121] The ellipse that best approximates the Lissajous figure is fitted using the least squares method. The equation of the ellipse is:

[0122] ;

[0123] in, These are the coefficients obtained after fitting;

[0124] Based on the fitting coefficients, the DC bias voltage is calculated as follows:

[0125] ; ;

[0126] Based on the fitting coefficients and the calculated DC bias voltage, the AC amplitude coefficients are calculated as follows:

[0127] ;

[0128] .

[0129] It should be understood that laser frequency modulation is accompanied by simultaneous amplitude modulation of the output light intensity, i.e., amplitude modulation. When using a laser with accompanying amplitude modulation for parameter calibration, the Lissajous figure will be severely distorted, and elliptic fitting will not yield accurate asymmetric parameters. Before parameter calibration, an intensity compensation method can be used, which involves dividing the intensity of the interference pulse by the intensity of the accompanying amplitude-modulated pulse, to eliminate the influence of the accompanying amplitude modulation. The effect is shown in [see figure]. Figure 10 .

[0130] Figure 11 This figure shows the noise suppression effect based on the method proposed in this application. 100 sets of data were continuously collected and averaged. The blue curve represents the phase noise spectrum of the sensor interferometer without noise suppression; the red curve represents the phase noise spectrum obtained from the reference interferometric signal synthesized with initial phase locking; the orange curve represents the phase noise spectrum after noise suppression using this method; and the purple curve shows the phase noise spectrum obtained using the traditional cross-multiplication-subtraction method. Figure 11 The results show that the phase noise obtained by the initial phase locking noise suppression method is generally lower than that obtained by the traditional cross-multiplication-subtraction noise suppression method, and has a good noise suppression effect.

[0131] In one embodiment, an application of the common-mode noise suppression method for a PGC fiber optic hydrophone system in an eight-sensor interferometer scenario is also provided. The purpose of the application is to use a single 3×3 reference interferometer to simultaneously suppress the initial phase-locked noise of eight sensor interferometers, so as to study the noise suppression performance of the common-mode noise suppression method for the PGC fiber optic hydrophone system in a deep-sea fiber optic vector hydrophone vertical array system.

[0132] A partial structural diagram of the experimental setup with eight sensor interferometers is shown below. Figure 12 As shown, the PGC pulse generation device, detection system, and demodulation system remain unchanged. In order to ensure light intensity balance, the coupler is changed from the original coupler with equal split ratio to a coupler with non-equal ratio.

[0133] Unlike the experimental setup for suppressing phase noise from a single-sensor interferometer, this eight-sensor interferometer setup uses an 8-time-division multiplexing module for beam splitting and delay. This 8-time-division multiplexing module is a commonly used 8-time-division multiplexing module in existing fiber optic vector hydrophone vertical array systems, and its internal structure is as follows: Figure 13 As shown, this 8-time-division module consists of a lumped input port IN for optical pulses, a lumped output port OUT for optical pulse sequences, and 8 pairs of sensor interferometer inputs. Internally, a series of couplers with different splitting ratios and fiber delay lines ensure that after connecting 8 identical sensor interferometers, a single pulse input and 8 pulses with equal peak values ​​and equal intervals are achieved.

[0134] Because of the multi-path splitting, the optical loss for each sensing interferometer is approximately 12 dB, also known as array loss. To compensate for the array loss and suppress the influence of additive noise sources as much as possible, an erbium-doped fiber amplifier (EDFA) is added to the optical transmitter. Simultaneously, a variable optical attenuator (VOA) is added to the input or output of the 8-sensor interferometer to adjust the peak power of the sensing interference pulses. Ultimately, the peak power of the 12 interference pulses within one pulse sampling period (sequentially the first reference interference pulse, the second reference interference pulse, the first to eighth sensing pulses, the first accompanying amplitude modulation pulse, and the second accompanying amplitude modulation pulse) is made to be essentially consistent and as close as possible to the saturation power of the photodetector.

[0135] In the experiment, tests were conducted every minute for a total of 500 tests, lasting approximately 8.5 hours. Figure 14 As can be seen, similar to the case of a single-sensor interferometer, this method can also effectively suppress phase noise simultaneously for eight short-arm long-sensor interferometers. This indicates that this method can achieve good suppression of background phase noise in practical array systems. In particular, the suppression effect of this method on low-frequency noise is particularly significant. The noise power spectral density values ​​after suppression for all eight sensor channels tend to flatten above 40 Hz, with an average of -105.5 dB at 50 Hz, -107.6 dB at 100 Hz, -108.4 dB at 250 Hz, and -108.9 dB at 1 kHz. The noise suppression effect averages 9.6 dB at 50 Hz, 9.2 dB at 100 Hz, 7.7 dB at 250 Hz, and 6.1 dB at 1 kHz. Meanwhile, from... Figure 14 As can be seen from the results, the phase noise suppression effect of this method is better than that of the traditional cross-multiplication and subtraction method within the test bandwidth. Figure 14The spectrum shows line spectra at 210.5 Hz and its second and third harmonics. These line spectra remain even after phase noise suppression. The residual line spectra have lower power spectral density values ​​without EDFA gain (in the case of a single-sensor interferometer), while they are higher with a larger EDFA gain (in the case of an eight-sensor interferometer). Investigation revealed that the signal source (AFG 31000, Tektronix) generating the laser's optical frequency modulation signal and the acousto-optic modulator's amplitude modulation signal consistently produces modulation sideband interference at 211 Hz and its higher harmonics on both sides of the main modulation signal frequency. This modulation sideband may introduce common-mode phase modulation, intensity modulation, and non-common-mode polarization modulation in the phase carrier, AOM (acousto-optic modulator) frequency shift, and AOM amplitude. While common-mode phase and intensity modulation can be effectively suppressed, polarization modulation, introduced by the non-ideal nature of the Faraday rotator, lacks common-mode characteristics and therefore cannot be effectively suppressed. The increase in EDFA gain exacerbates the impact of this non-common-mode polarization modulation noise, making the residual line spectra more pronounced. Despite the presence of the aforementioned residual line spectra, this method still possesses the overall capability to simultaneously suppress phase noise from eight sensor interferometers.

[0136] 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.

[0137] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application.

Claims

1. A common-mode noise suppression system for a PGC fiber optic hydrophone system, characterized in that, It includes a PGC pulse generator, an arbitrary waveform generator, a 1×2 coupler, two delay fibers, a sensing interferometer, a 3×3 reference interferometer, three attenuators, a detection system, and a demodulation system; The PGC pulse generator is used to receive signals from an arbitrary waveform generator, modulate and generate carrier pulses, and send them into a 1×2 coupler. The carrier pulses are input to the sensing interferometer and the 3×3 reference interferometer via the 1×2 coupler to generate sensing interferometer pulses and two reference interferometer pulses. Each interferometer pulse is input to the detection system after passing through a corresponding attenuator and a delay fiber. The detection system is used to convert each interference pulse into an electrical signal and then into a digital-to-analog signal, outputting the sensing interference signal. and two reference interference signals and The signal is sent to the demodulation system, where two accompanying amplitude modulation pulses generated by the carrier pulse transmission are simultaneously received and input into the demodulation system. The intensity of the interference pulse is divided by the intensity of the accompanying amplitude modulation pulse using the light intensity compensation method to eliminate the influence of the accompanying amplitude modulation. After demodulating each interfering signal using PGC, the demodulation system first uses an ellipse fitting method to eliminate the influence of accompanying amplitude modulation. and Perform calibration and combine into a reference signal , making Initial phase and The initial phase satisfies the pre-derived initial phase condition for strong suppression of optoelectronic common-mode noise, that is, the two initial phases differ by a certain amount. Integer multiples; then for and Subtract the time-domain outputs obtained from PGC detection to obtain the time-domain output after strong suppression of photoelectric common-mode noise; The 3×3 reference interferometer includes a 3×3 coupler, a first reference fiber, a second reference fiber, a third delay fiber, a third Faraday rotator, a fourth Faraday rotator, and a fifth Faraday rotator. The first port of the 3×3 coupler is used to receive a carrier pulse; the second port is used to output a second reference interference pulse generated by the 3×3 reference interferometer; the third port is used to output a first reference interference pulse generated by the 3×3 reference interferometer; the fourth port of the 3×3 coupler is connected to the third Faraday rotator via the first reference fiber; the fifth port of the 3×3 coupler is connected to the fourth Faraday rotator via the third delay fiber; and the sixth port of the 3×3 coupler is connected to the fifth Faraday rotator via the second reference fiber.

2. The common-mode noise suppression system for a PGC fiber optic hydrophone system according to claim 1, characterized in that, The PGC pulse generation device includes a laser, an optical isolator, and an acousto-optic modulator connected in sequence; wherein the modulation interfaces of the laser and the acousto-optic modulator are both connected to the output terminal of an arbitrary waveform generator. The laser is used to perform optical frequency modulation based on the sinusoidal signal input from the arbitrary waveform generator and output a PGC continuous optical signal to the optical isolator; Optical isolators are used to ensure unidirectional transmission of PGC continuous optical signals from the laser to the acousto-optic modulator. An acousto-optic modulator is used to intensity modulate a received PGC continuous optical signal based on a pulse signal input from an arbitrary waveform generator, ultimately generating a carrier pulse.

3. The common-mode noise suppression system for a PGC fiber optic hydrophone system according to claim 2, characterized in that, The sensing interferometer includes a 2×2 coupler, a first sensing fiber, a second sensing fiber, a first Faraday rotator, and a second Faraday rotator. The first port of the 2×2 coupler is used to receive carrier pulses, the second port of the 2×2 coupler is used to output sensing interference pulses generated by the sensing interferometer, the third port of the 2×2 coupler is connected to the first Faraday rotator via the first sensing fiber, and the fourth port of the 2×2 coupler is connected to the second Faraday rotator via the second sensing fiber.

4. The common-mode noise suppression system for a PGC fiber optic hydrophone system according to claim 1, characterized in that, The detection system includes a 1×3 coupler, a photodetector, and a digital-to-analog converter connected in sequence; The 1×3 coupler is used to receive the sensing interference pulse, the first reference interference pulse, the second reference interference pulse, and two accompanying amplitude modulation pulses generated during the carrier pulse transmission. The sensing interference pulse is input to the detection system via a first attenuator and a first delay fiber; the first reference interference pulse is input to the detection system via a second attenuator and a second delay fiber; and the second reference interference pulse is input to the detection system via a third attenuator. The first accompanying amplitude modulation pulse is generated by reflecting the carrier pulse emitted by the PGC pulse generator after being reflected by a fourth Faraday rotator, and then passing through a third delay fiber and a third attenuator. The second accompanying amplitude modulation pulse is generated by reflecting the carrier pulse emitted by the PGC pulse generator after being reflected by a fourth Faraday rotator, and then passing through a third delay fiber, a second attenuator, and a second delay fiber. The photodetector is used to convert the received interference pulses into electrical signals; The input of the digital-to-analog converter is connected to the output of the arbitrary waveform generator. Based on the synchronization signal and acquisition trigger signal provided by the arbitrary waveform generator, it performs digital-to-analog conversion on the electrical signals converted from each interference pulse, outputting the sensing interference signal. First reference interferometry signal Second reference interference signal .

5. The common-mode noise suppression system for a PGC fiber optic hydrophone system according to claim 4, characterized in that, The time division of each pulse received by the detection system is controlled by the length of each delay fiber. The five pulses received by the detection system in a single repetition cycle have a certain time delay but do not affect each other. The five pulses are the first reference interference pulse, the second reference interference pulse, the sensing interference pulse, the first accompanying amplitude modulation pulse, and the second accompanying amplitude modulation pulse. The arrival time interval between the first reference interference pulse and the second reference interference pulse is controlled by the second delay fiber, the arrival time interval between the second reference interference pulse and the sensing interference pulse is controlled by the first delay fiber, the arrival time interval between the sensing interference pulse and the first accompanying amplitude modulation pulse is controlled by the third delay fiber in the 3×3 reference interferometer, and the arrival time interval between the first accompanying amplitude modulation pulse and the second accompanying amplitude modulation pulse is controlled by the second delay fiber.

6. The common-mode noise suppression system for a PGC fiber optic hydrophone system according to claim 1, characterized in that, Three attenuators are used to adjust the peak values ​​of each interference pulse input to the photodetector in the detection system, ensuring that the peak values ​​of the sensing interference pulse, the first reference interference pulse, and the second reference interference pulse are basically balanced and at their highest values ​​when the photodetector is not saturated, thereby reducing the influence of non-common-mode additive noise sources.

7. The common-mode noise suppression system for a PGC fiber optic hydrophone system according to claim 1, characterized in that, The initial phase condition for strong suppression of optoelectronic common-mode noise is derived from the PGC noise model, using the theoretical formula for the PSD value and the minimum PSD value as a constraint. The derivation process includes: Assuming a sensing interferometer The initial phase of the obtained sensing interference signal is Reference interferometer The initial phase of the obtained reference interferometric signal is The phase noise source and multiplicative noise source picked up by the two interferometers are the same, that is , However, additive noise sources are different, namely This is because the interference signals obtained by the two interferometers need to be detected and acquired at different times by the same photodetector and digital-to-analog converter in the detection system, but the PSD values ​​of the two interferometers are consistent, that is... Considering only noise, the time-domain output expression of the phase signal of the interference signals from the two interferometers after PGC detection is: ； in, The output phase noise of the sensing interferometer As a reference, the output phase noise of the interferometer For the time domain output of the sensor, For reference time domain output, As a phase noise source for the sensing interferometer, As a reference interferometer's phase noise source, As a source of phase noise, As a multiplicative noise source for the sensing interferometer, As a reference interferometer, the multiplicative noise source As a multiplicative noise source, As an additive noise source for the sensing interferometer, As a reference interferometer, the additive noise source The output phase noise PSD value of the additive noise source of the sensing interferometer. The output phase noise PSD value of the additive noise source of the reference interferometer; After PGC signal detection and The time-domain signal obtained by subtraction for: ； in, and The phase noise source superposition coefficients are respectively in and The value at that location, and The superposition coefficients of the multiplicative noise sources are respectively in and The value at that location, and The additive noise source superposition coefficients are respectively in and The value at that location, Represents convolution operation. Let be the unit impulse response function of the low-pass filter. and These are first-order and second-order Bessel functions, respectively. For order, For PGC carrier frequency, For time, The DC voltage amplitude of the interference signal. The visibility of the interference signal fringes; right Its spectrum is obtained by high-pass filtering and Fourier transform. for: ； in, Let be the transfer function of the low-pass filter. Angular frequency, The spectral amplitude of the phase noise source. The spectral amplitude of the multiplicative noise source. The spectral amplitude of the additive noise source in the sensing interferometer. The spectral amplitude of the additive noise source of the reference interferometer; Then, based on the Wiener-Khinchin theorem and the white noise approximation condition, the time-domain signal obtained by subtraction is obtained. The PSD file is: ； in, The power spectral density of the phase noise source. The power spectral density of the multiplicative noise source. The power spectral density of the additive noise source in the sensing interferometer. The power spectral density of the additive noise source of the reference interferometer; To reduce direct time domain signal The output phase noise, expressed in PSD value Using the minimum value as a constraint, the optimal initial phase condition for achieving strong overall suppression of optoelectronic common-mode noise is obtained as follows: ,in, If the value is an integer, then the effects of phase noise sources and multiplicative noise sources will be completely eliminated, i.e.: 。 8. A common-mode noise suppression method for a PGC fiber optic hydrophone system, characterized in that, The method is implemented based on the common-mode noise suppression system of the PGC fiber optic hydrophone system according to any one of claims 1-7, and the method includes: Step 1: Acquire the sensing interference signal output by the sensing interferometer. The first reference interference signal output by the 3×3 reference interferometer Second reference interference signal ; Step 2: The two reference interferometric signals are calibrated using the ellipse fitting method after eliminating the influence of accompanying amplitude modulation, obtaining the DC bias voltage and AC amplitude coefficient of the two reference interferometric signals, and then the DC bias voltage of the two reference interferometric signals is removed respectively; wherein, and They are represented as follows: ； in, and They are respectively and DC bias voltage. and They are respectively and AC amplitude coefficient; The phase term is generated by integrating the signal frequency. and They are respectively and The initial phase parameters; Step 3, respectively, the sensing interference signals PGC signal detection is performed on the two reference interference signals after removing the DC bias voltage to obtain the sensing time-domain output, the first reference time-domain output, and the second time-domain output. The average of these outputs is then calculated to obtain the initial phase parameters of the sensing interference signal, the first reference interference signal, and the second reference interference signal, which are expressed as follows: , and ; Step 4, using , , , and Calculations were performed to obtain two superposition coefficients. and , respectively represented as: ； Step 5, according to and right and A linear combination is performed to obtain the reference signal. This causes the sensing interference signal Initial phase and reference signal The relationship between the initial phases satisfies the pre-derived initial phase condition for strong suppression of photoelectric common-mode noise, that is, the initial phase difference between the initial phase of the sensing interference signal and the initial phase of the reference signal is satisfied. Integer multiples of; Step 6, for the reference signal Perform PGC signal detection to obtain the reference time domain output; Step 7: Subtract the sensor time-domain output from the reference time-domain output to obtain the time-domain output after strong suppression of photoelectric common-mode noise.

9. A common-mode noise suppression method for a PGC fiber optic hydrophone system according to claim 8, characterized in that, The two reference interferometric signals were calibrated using an elliptic fitting method after eliminating the influence of accompanying amplitude modulation, obtaining the DC bias voltage and AC amplitude coefficients of the two reference interferometric signals, including: After using the intensity compensation method to divide the intensity of the interference pulse by the intensity of the accompanying amplitude-modulated pulse to eliminate the influence of the accompanying amplitude modulation, the DC bias voltage and AC amplitude coefficients of the two reference interference signals are obtained using the elliptic fitting method; the elliptic fitting method includes: Acquire reference interferometric signal pair over a period of time And draw it as a Lissajous figure; The ellipse that best approximates the Lissajous figure is fitted using the least squares method. The equation of the ellipse is: ； in, These are the coefficients obtained after fitting; Based on the fitting coefficients, the DC bias voltage is calculated as follows: ； ； Based on the fitting coefficients and the calculated DC bias voltage, the AC amplitude coefficients are calculated as follows: ； 。

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