A phase-shift PGC demodulation method and demodulation system for interferometric fiber optic hydrophone

Abstract

The present invention discloses an interferometric fiber optic hydrophone phase-shift PGC demodulation method and demodulation system. First, a laser is used to generate an optical signal, which is then sinusoidally frequency modulated to output a sinusoidally frequency-modulated light wave. The sinusoidally frequency-modulated light wave is input into an optical pulse modulator for processing to output periodic light pulses. The light pulses are subjected to fiber splitting, fiber delay, and fiber beam combining to obtain a light pulse sequence. The light pulse sequence is phase-modulated by a phase modulator and then input into an optical fiber interferometer for interference processing, outputting an interference light pulse sequence. The interference light pulse sequence is input into an optoelectronic converter for optoelectronic conversion and digital sampling. The sampled signal is input into a signal processing system for PGC demodulation processing and high-pass filtering. The demodulated phase signals after high-pass filtering are summed and averaged to obtain the final demodulated phase signal. This method can obtain a stable, low-noise demodulated phase signal without adding additional optoelectronic detection and signal acquisition hardware.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing, and in particular relates to an interference type optical fiber hydrophone phase shift PGC demodulation method and a demodulation system. Background Art

[0002] Interferometric fiber optic hydrophone is currently the most widely used fiber optic hydrophone. Its sensing core is the fiber optic interferometer. The measured acoustic signal is loaded into the interference signal of the fiber optic interferometer in the form of phase. Therefore, achieving stable detection of the interferometer phase is the key to fiber optic hydrophone technology.

[0003] Phase self-noise and noise stability are important performance indicators of fiber-optic hydrophone systems. Commonly used phase detection algorithms for interferometric fiber-optic hydrophones include phase carrier modulation (PGC) demodulation, 3×3 coupler phase-shift detection, and heterodyne methods. While the PGC demodulation method offers excellent low-frequency noise performance, its phase self-noise varies with the interferometer's initial phase difference. When external environmental disturbances cause the interferometer's initial phase difference to drift, this results in significant phase noise fluctuations. The 3×3 coupler phase-shift detection method is susceptible to external low-frequency noise and interference, and its phase noise is also related to the interferometer's initial phase difference. The heterodyne method requires a matched optical structure, in which both the matched interferometer and the transmission fiber between the matched interferometer and the fiber-optic hydrophone interferometer participate in the interference process. This makes it susceptible to external environmental interference, which degrades the system's low-frequency noise performance.

[0004] The present invention proposes a phase-shifted PGC demodulation method and demodulation system for an interferometric fiber optic hydrophone. The method adopts ramp wave phase modulation and combines it with an unbalanced fiber optic interferometer structure to obtain three PGC modulated interference signals with different initial phases. The phase-shifted PGC demodulation algorithm is used to complete the phase solution. Without adding additional photoelectric detection and signal acquisition hardware, a stable low-noise demodulated phase output can be obtained, effectively improving the phase self-noise and noise stability performance of the system. At the same time, the method has good algorithm redundancy performance and can be conveniently combined with time division multiplexing technology for application in large-scale interferometric fiber optic hydrophone array systems. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies in the prior art, provide a phase-shift PGC demodulation method and demodulation system for interferometric fiber optic hydrophones with high noise stability, and provide an effective low-noise signal detection solution for interferometric fiber optic hydrophone applications.

[0006] A phase-shift PGC demodulation method for an interferometric optical fiber hydrophone comprises the following steps:

[0007] S1. Use a laser to generate an optical signal, perform sinusoidal frequency modulation on the optical signal, output a sinusoidal frequency modulated light wave, input the sinusoidal frequency modulated light wave into an optical pulse modulator, and after processing, output a periodic optical pulse;

[0008] S2. Performing optical fiber splitting on the optical pulse using a first coupler to obtain three optical pulses, performing optical fiber time delay and optical fiber combining on the three optical pulses, and outputting an optical pulse sequence consisting of three optical pulses;

[0009] S3, phase-modulating the optical pulse sequence by a phase modulator to obtain a phase-modulated optical pulse sequence, inputting the phase-modulated optical pulse sequence into a fiber interferometer, and outputting an interference optical pulse sequence after interference processing;

[0010] S4, inputting the interference light pulse sequence into a photoelectric converter for photoelectric conversion and digital sampling to obtain a sampling signal, inputting the sampling signal into a signal processing system for time division decomposition processing to obtain three-way time division decomposition sampling signals;

[0011] S5. Perform PGC demodulation processing and high-pass filtering on the three sampling signals after time division processing to obtain three demodulated phase signals after high-pass filtering. Sum and average the three demodulated phase signals after high-pass filtering to obtain the final demodulated phase signal.

[0012] Preferably, in S2, the light pulse is subjected to optical fiber splitting using a first coupler to obtain three light pulses, specifically comprising: inputting the light pulse into the input end of the first optical fiber coupler, performing beam splitting processing through the first optical fiber coupler, outputting the first light pulse through the first output port of the first optical fiber coupler, outputting the second light pulse through the second output port of the first optical fiber coupler, and outputting the third light pulse through the third output port of the first optical fiber coupler.

[0013] Preferably, in S2, the three light pulses are subjected to fiber delay and fiber combining processing to output a light pulse sequence consisting of three light pulses, specifically comprising: directly inputting the first light pulse into the first input port of the second fiber coupler, inputting the second light pulse into the first fiber delay line, and inputting it into the second input port of the second fiber coupler after delay processing, inputting the third light pulse into the second fiber delay line, and inputting it into the third input port of the second fiber coupler after delay processing, and the second fiber coupler performs fiber combining processing on the input first light pulse and the second and third light pulses after delay processing to output a light pulse sequence.

[0014] Preferably, the length of the first optical fiber delay line is L, and the length of the second optical fiber delay line is 2L, where L is specifically set to:

[0015]

[0016] Where L is the length of the first optical fiber delay line, n is the refractive index of the optical fiber core, c is the speed of light in vacuum, and T s is the repetition time period of the light pulse.

[0017] Preferably, the sampling signal in S4 includes optical relative intensity noise or circuit noise. In S4, the sampling signal is input into the signal processing system for time-division decomposition to obtain three-way time-division decomposition sampling signals. When the sampling signal includes optical relative intensity noise, the time-division decomposition sampling signal can be expressed as follows:

[0018]

[0019] When the sampling signal includes circuit noise, the sampling signal after time division processing can be expressed as follows:

[0020]

[0021] Where V i (t) is the sampling signal after time division processing of the i-th solution at time t, A is the DC amplitude of the sampling signal, B is the AC amplitude of the sampling signal, n Ii (t) is the optical relative intensity noise of the sampling signal after time division processing of the i-th channel at time t, n Ci (t) is the circuit noise of the sampled signal after time division processing of the i-th channel at time t, C is the modulation depth, ω m is the PGC modulation frequency, is the phase of the i-th sampling signal at time t.

[0022] Preferably, in S5, the three-way time-division processed sampling signals are subjected to PGC demodulation processing and high-pass filtering to obtain three-way high-pass filtered demodulated phase signals, which specifically includes:

[0023] S51, performing phase-locked detection and low-pass filtering on any one of the three sampling signals after time division processing to obtain two detection signals;

[0024] S52, using an inverse tangent algorithm to solve the two detection signals to obtain a demodulated phase signal;

[0025] S53, performing high-pass filtering on the demodulated phase signal to obtain a demodulated phase signal after high-pass filtering;

[0026] S54 , selecting another channel from the three channels of sampled signals after time division processing, until all three channels of sampled signals after time division processing are selected, and processing through steps S51 to S53 to obtain three channels of demodulated phase signals after high-pass filtering.

[0027] Preferably, in S51, one of the three sampling signals after time division processing is randomly selected for phase-locked detection and low-pass filtering to obtain two detection signals. When the sampling signal includes optical relative intensity noise, the specific formula of the two detection signals is:

[0028]

[0029] When the sampling signal includes circuit noise, the specific formula for the two-way detection signal is:

[0030]

[0031] Where, are the first and second detection signals of the sampling signal after time division processing of the i-th channel introduced by the optical relative intensity noise at time t, B is the AC amplitude of the sampling signal, are the first and second additive noises introduced by the optical relative intensity noise into the sampling signal after the time division processing of the i-th channel, They are the first and second detection signals of the sampling signal after the i-th channel time division processing introduced by the circuit noise at time t, are the first and second additive noises introduced by the circuit noise into the sampling signal after the time division processing of the i-th path, is the phase of the sampled signal after time division processing of the i-th channel at time t, J k (C) is the kth order Bessel function (k=1, 2, ...).

[0032] Preferably, in S52, an inverse tangent algorithm is used to solve the two detection signals to obtain a demodulated phase signal. When the sampling signal contains optical relative intensity noise, the formula for the demodulated phase signal is specifically:

[0033]

[0034] When the sampling signal contains circuit noise, the formula for demodulating the phase signal is:

[0035]

[0036] Where, is the demodulated phase signal of the i-th channel at time t, B is the AC amplitude of the sampling signal, J k (C) is the kth order Bessel function (k=1,2,...), are the first and second additive noises introduced by the optical relative intensity noise in the sampling signal after time division processing of the i-th channel at time t, are the first and second additive noises introduced by circuit noise into the sampled signal after time division processing of the i-th channel at time t, is the phase of the sampled signal after time division processing of the i-th channel at time t.

[0037] Preferably, in S5, the three demodulated phase signals are summed and averaged to obtain a final demodulated phase signal. The final demodulated phase signal is specifically:

[0038]

[0039] Where, is the final demodulated phase signal at time t, is the first demodulated phase signal at time t, is the second demodulated phase signal at time t, is the third demodulated phase signal at time t.

[0040] An interferometric fiber optic hydrophone phase-shift PGC demodulation system adopts an interferometric fiber optic hydrophone phase-shift PGC demodulation method for demodulation. The system includes a laser, an optical pulse modulator, a first optical fiber coupler, a first optical fiber delay line, a second optical fiber delay line, a second optical fiber coupler, a phase modulator, an optical fiber interferometer, an optoelectronic converter, and a signal processing system. The laser is connected to the optical pulse modulator, the optical pulse modulator is connected to the input end of the first optical fiber coupler, the first output end of the first optical fiber coupler is directly connected to the first input end of the second optical fiber coupler, the second output end of the first optical fiber coupler is connected to the second input end of the second optical fiber coupler through the first optical fiber delay line, the third output end of the first optical fiber coupler is connected to the third input end of the second optical fiber coupler through the second optical fiber delay line, one end of the phase modulator is connected to the output end of the second optical fiber coupler, and the other end is connected to the optical fiber interferometer. One end of the optoelectronic converter is connected to the optical fiber interferometer, and the other end is connected to the signal processing system. The signal processing system is also connected to the laser, the optical pulse modulator, and the phase modulator.

[0041] The laser is used to generate an optical signal, which is then input into the optical pulse modulator after sinusoidal frequency modulation;

[0042] The optical pulse modulator is used to generate periodic optical pulses;

[0043] The first optical fiber coupler is used for optical fiber beam splitting. Periodic optical pulses are input from the input end of the first optical fiber coupler and are processed to obtain three optical pulses accordingly.

[0044] The first optical fiber delay line and the second optical fiber delay line are used to delay the optical pulse;

[0045] The second optical fiber coupler is used to combine the three input optical pulses to generate an optical pulse sequence;

[0046] The phase modulator is used to perform phase modulation on the optical pulse sequence to obtain a phase-modulated optical pulse sequence;

[0047] The fiber optic interferometer is used to sense external acoustic signals, interfere with the phase-modulated optical pulse sequence, and output an interference optical pulse sequence;

[0048] The photoelectric converter is used to perform photoelectric conversion and digital sampling on the interference light pulse sequence, generate a digital sampling signal, and output it to the signal processing system through a cable;

[0049] The signal processing system is used to demodulate the received digital sampling signal, output a sinusoidal wave signal to the laser to perform sinusoidal frequency modulation on the optical signal, output a pulse modulation signal to the optical pulse modulator to generate optical pulses, and output a phase modulation signal of a specific waveform to the phase modulator for phase modulation.

[0050] The above-mentioned interferometric fiber optic hydrophone phase-shift PGC demodulation method and demodulation system adopts ramp wave phase modulation technology and combines it with an unbalanced interferometer structure to obtain three interference outputs with different initial phases. It can flexibly select PGC demodulation, 3X3 coupler phase-shift demodulation and phase-shift PGC demodulation algorithm demodulation, and has good algorithm redundancy capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a flow chart of a phase-shift PGC demodulation method for an interferometric fiber optic hydrophone according to an embodiment of the present invention;

[0052] Figure 2 This is a diagram of an optical pulse sequence and its phase modulation waveform generated in a phase-shift PGC demodulation system according to an embodiment of the present invention;

[0053] Figure 3 This is a diagram showing the output interference light pulse and its phase waveform of the fiber interferometer in the phase-shift PGC demodulation system in one embodiment of the present invention;

[0054] Figure 4 1 is a schematic structural diagram of an interferometric fiber optic hydrophone phase-shift PGC demodulation system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings.

[0056] A phase-shift PGC demodulation method for an interferometric optical fiber hydrophone, comprising:

[0057] S1. Use a laser to generate an optical signal, perform sinusoidal frequency modulation on the optical signal, output a sinusoidal frequency modulated light wave, input the sinusoidal frequency modulated light wave into an optical pulse modulator, and after processing, output a periodic optical pulse;

[0058] S2. Performing optical fiber splitting on the optical pulse using a first coupler to obtain three optical pulses, performing optical fiber time delay and optical fiber combining on the three optical pulses, and outputting an optical pulse sequence consisting of three optical pulses;

[0059] S3, phase-modulating the optical pulse sequence by a phase modulator to obtain a phase-modulated optical pulse sequence, inputting the phase-modulated optical pulse sequence into a fiber interferometer, and outputting an interference optical pulse sequence after interference processing;

[0060] S4, inputting the interference light pulse sequence into a photoelectric converter for photoelectric conversion and digital sampling to obtain a sampling signal, inputting the sampling signal into a signal processing system for time division decomposition processing to obtain three-way time division decomposition sampling signals;

[0061] S5. Perform PGC demodulation processing and high-pass filtering on the three sampling signals after time division processing to obtain three demodulated phase signals after high-pass filtering. Sum and average the three demodulated phase signals after high-pass filtering to obtain the final demodulated phase signal.

[0062] Specifically, see Figure 1 、 Figure 2 and Figure 3 , Figure 1 FIG1 is a flow chart of a phase-shift PGC demodulation method for an interferometric fiber optic hydrophone according to an embodiment of the present invention. Figure 2 FIG1 is a diagram of an optical pulse sequence and its phase modulation waveform generated in a phase-shift PGC demodulation system according to an embodiment of the present invention. Figure 3 FIG1 is a diagram showing the interference light pulse output and its phase waveform by the fiber interferometer in the phase-shift PGC demodulation system in one embodiment of the present invention.

[0063] First, a laser is used to generate an optical signal, which is then sinusoidally modulated and fed into an optical pulse modulator through an optical fiber to output periodic optical pulses (see Figure 2 (a)), the optical pulse width is T p , the optical pulse repetition frequency is f s , the light pulse repetition time period is T s Then, the optical pulse is input to the first optical fiber coupler through the optical fiber, and the optical pulse is split by the first optical fiber coupler to obtain three optical pulses. The three optical pulses are subjected to optical fiber delay and optical fiber beam combining to generate an optical pulse sequence consisting of three optical pulses. The optical pulse sequence is then sequentially input to the phase modulator and a specific phase modulation waveform is applied (see Figure 2 (c) is phase modulated to obtain a phase-modulated optical pulse sequence, which is input into a fiber interferometer to generate interference, and a set of interference optical pulse sequences is output (through phase modulation, the interference signals of adjacent interference optical pulses have a phase difference of 2π / 3, see Figure 3Then, the interference light pulse sequence is input into the photoelectric converter for photoelectric conversion and digital sampling to obtain corresponding sampling signals. The sampling signals are output to the signal processing system through a cable for time division processing to obtain three-way time-division processed sampling signals. The three-way time-division processed sampling signals are demodulated by a phase-shift PGC demodulation algorithm and high-pass filtered. The average of the three-way high-pass filtered demodulated signals is used as the final demodulated phase signal.

[0064] In one embodiment, in S2, the optical pulse is subjected to optical fiber splitting using a first coupler to obtain three optical pulses, specifically including: inputting the optical pulse into the input end of the first optical fiber coupler, performing beam splitting processing through the first optical fiber coupler, outputting the first optical pulse through the first output port of the first optical fiber coupler, outputting the second optical pulse through the second output port of the first optical fiber coupler, and outputting the third optical pulse through the third output port of the first optical fiber coupler.

[0065] In one embodiment, in S2, three optical pulses are subjected to optical fiber delay and optical fiber combining processing to output an optical pulse sequence consisting of three optical pulses, specifically including: directly inputting the first optical pulse into the first input port of the second optical fiber coupler, inputting the second optical pulse into the first optical fiber delay line, and inputting the second input port of the second optical fiber coupler after delay processing, inputting the third optical pulse into the second optical fiber delay line, and inputting the third input port of the second optical fiber coupler after delay processing, and the second optical fiber coupler performs optical fiber combining processing on the input first optical pulse and the second and third optical pulses after delay processing to output an optical pulse sequence.

[0066] Specifically, a light pulse is input into a first fiber coupler via an optical fiber, where it is split into three beams. The first light pulse is output via the first output port of the first fiber coupler and directly input into the first input port of the second fiber coupler. The second light pulse is output from the second output port of the first fiber coupler to the first fiber delay line and, after a certain fiber delay, is input into the second input port of the second fiber coupler. The third light pulse is output from the third output port of the first fiber coupler to the second fiber delay line and, after a certain fiber delay, is input into the third input port of the second fiber coupler. The second fiber coupler combines the three light pulses, directly input and delayed, to generate a light pulse train consisting of three light pulses. The first and second fiber couplers form a 3×3 fiber coupler.

[0067] In one embodiment, the length of the first optical fiber delay line is L, and the length of the second optical fiber delay line is 2L. L is specifically set to:

[0068]

[0069] Where L is the length of the first optical fiber delay line, n is the refractive index of the optical fiber core, c is the speed of light in vacuum, and T s is the repetition time period of the light pulse.

[0070] Specifically, the optical pulse is divided into three beams by the first optical fiber coupler, and then directly input, delayed input through the first optical fiber delay line, and delayed input through the second optical fiber delay line to the second optical fiber coupler. A set of optical pulse sequences containing three optical pulses is generated at the output port of the second coupler, and the time interval between each optical pulse is T s / 3, the time interval between adjacent light pulse sequences is T s , T s is the optical pulse repetition time period, and the optical path loss is controlled to keep the peak powers of the three optical pulses consistent. The generated optical pulse sequence is as follows: Figure 3 shown.

[0071] In one embodiment, the fiber interferometer in S3 includes a signal arm and a reference arm, and there is a length difference between the fiber length of the signal arm and the fiber length of the reference arm.

[0072] Specifically, see Figure 3 , Figure 3 This is a diagram showing the output interference light pulse and its phase waveform of the fiber interferometer in the phase-shift PGC demodulation system in one embodiment of the present invention. Figure 3 (a) is the light pulse returned by the interferometer signal arm, Figure 3 (b) is the light pulse returned from the reference arm of the interferometer, Figure 3 (c) is the interference light pulse at the output end of the interferometer.

[0073] The fiber optic hydrophone uses an unbalanced Michelson interferometer structure. The interferometer consists of a signal arm and a reference arm. There is a length difference l between the optical fiber lengths of the two arms. Due to the existence of the length difference l, there will be a time difference between the two beams of light returning from the signal arm and the reference arm. When the optical pulse width T p When the time difference is greater than τ, the two optical pulses will overlap and interfere at the output of the interferometer, such as Figure 3 As shown, the light pulses returning from the signal arm and the reference arm interfere with each other in the overlapping shaded area. For a set of input light pulse sequences, three interference light pulses are generated: the first interference light pulse, the second interference light pulse, and the third interference light pulse.

[0074] In one embodiment, the sampling signal in S4 includes optical relative intensity noise or circuit noise. In S4, the sampling signal is input into a signal processing system for time-division decomposition to obtain three time-division decomposition sampling signals. When the sampling signal includes optical relative intensity noise, the time-division decomposition sampling signals can be expressed as follows:

[0075]

[0076] When the sampling signal includes circuit noise, the sampling signal after time division processing can be expressed as follows:

[0077]

[0078] Where V i (t) is the sampling signal after time division processing of the i-th solution at time t, A is the DC amplitude of the sampling signal, B is the AC amplitude of the sampling signal, n Ii (t) is the optical relative intensity noise of the sampling signal after time division processing of the i-th channel at time t, n Ci (t) is the circuit noise of the sampled signal after time division processing of the i-th channel at time t, C is the modulation depth, ω m is the PGC modulation frequency, is the phase of the i-th sampling signal at time t.

[0079] Specifically, when there is no noise in the system, the interference light pulse sequence is input into the photoelectric converter, which samples the light at a sampling frequency of 3f. s Sampling is performed at each interfering light pulse to obtain a sampling signal, which is then input into the signal processing system for time-division demultiplexing and decimation by 1 out of 3. The three-way time-division demultiplexed sampling signals corresponding to the three interfering light pulses are obtained, which can be expressed as follows:

[0080]

[0081] Where V1(t), V2(t), and V3(t) are the sampling signals of the first, second, and third channels after time division processing, respectively. They are the phases of the first, second, and third interference light pulses, respectively. The phases of each interference light pulse contain the measured phase signal and the interferometer initial phase The phase difference between each interference light pulse is 2π / 3, A is the DC amplitude of the sampling signal, B is the AC amplitude of the sampling signal, C is the modulation depth, ω m is the PGC modulation frequency.

[0082] When there is noise in the system, according to the noise transfer characteristics of the PGC demodulation algorithm, these noises will be converted into phase noise of the final demodulated phase signal. This application mainly considers the following two types of noise in the PGC demodulation process. The transmission of the demodulated phase signal to the output is: optical relative intensity noise n I (t) and circuit noise n COptical relative intensity noise (t) includes the static optical relative intensity noise of the laser and the additional optical relative intensity noise generated by the modulated laser. Circuit noise primarily comprises the total additive circuit noise, such as that from photoelectric conversion and ADC quantization. Generally, these noise types are considered uncorrelated. The noise transmission behavior of each type can be considered separately. When all noise types are present simultaneously in the system, their transmission behavior can be combined.

[0083] When there is optical relative intensity noise n in the system I (t), the formula of the sampled signal after time division processing can be expressed as:

[0084]

[0085] in,

[0086] Where V i (t) is the sampling signal after time division processing of the i-th channel at time t, n Ii (t) is the optical relative intensity noise of the sampling signal after the time division processing of the i-th channel at time t. For the convenience of analysis, the optical relative intensity noise of the sampling signal after the time division processing of the i-th channel at time t is n Ii (t) is decomposed into a superposition of second-order wide stationary band-limited noise, are all second-order wide stationary band-limited noises independent of the optical relative intensity noise in the i-th sampling signal, and the noise bandwidth is [-ω c / 2,ω c / 2], subscript i represents the i-th sampling signal.

[0087] When there is circuit noise in the system C (t), the formula for solving the sampling signal after time division processing can be obtained by referring to the above method, and the details will not be repeated here.

[0088] In one embodiment, in S5, the three-way time-division processed sampling signals are subjected to PGC demodulation processing and high-pass filtering, and three-way high-pass filtered demodulated phase signals are obtained accordingly, specifically including:

[0089] S51, performing phase-locked detection and low-pass filtering on any one of the three sampling signals after time division processing to obtain two detection signals;

[0090] S52, using an inverse tangent algorithm to solve the two detection signals to obtain a demodulated phase signal;

[0091] S53, performing high-pass filtering on the demodulated phase signal to obtain a demodulated phase signal after high-pass filtering;

[0092] S54 , selecting another channel from the three channels of sampled signals after time division processing, until all three channels of sampled signals after time division processing are selected, and processing through steps S51 to S53 to obtain three channels of demodulated phase signals after high-pass filtering.

[0093] In one embodiment, in S51, phase-locked detection is performed on any one of the three sampling signals after time division processing, and low-pass filtering is performed to obtain two detection signals. When the sampling signal includes optical relative intensity noise, the specific formulas of the two detection signals are:

[0094]

[0095]

[0096] When the sampling signal includes circuit noise, the specific formula for the two-way detection signal is:

[0097]

[0098] Where, are the first and second detection signals of the sampling signal after time division processing of the i-th channel introduced by the optical relative intensity noise at time t, B is the AC amplitude of the sampling signal, are the first and second additive noises introduced by the optical relative intensity noise into the sampling signal after the time division processing of the i-th channel, They are the first and second detection signals of the sampling signal after the i-th channel time division processing introduced by the circuit noise at time t, are the first and second additive noises introduced by the circuit noise into the sampling signal after the time division processing of the i-th path, is the phase of the sampled signal after time division processing of the i-th channel at time t, J k (C) is the kth order Bessel function (k=1, 2, ...).

[0099] In one embodiment, in S52, the arctangent algorithm is used to solve the two detection signals to obtain a demodulated phase signal. When the sampling signal contains optical relative intensity noise, the formula for the demodulated phase signal is specifically:

[0100]

[0101] When the sampling signal contains circuit noise, the formula for demodulating the phase signal is:

[0102]

[0103] Where, is the demodulated phase signal of the i-th channel at time t, B is the AC amplitude of the sampling signal, Jk (C) is the kth order Bessel function (k=1,2,...), are the first and second additive noises introduced by the optical relative intensity noise in the sampled signal after time division processing of the i-th channel at time t, are the first and second additive noises introduced by circuit noise into the sampled signal after time division processing of the i-th channel at time t, is the phase of the sampled signal after time division processing of the i-th channel at time t.

[0104] In one embodiment, in S5, the three demodulated phase signals are summed and averaged to obtain a final demodulated phase signal. The final demodulated phase signal is specifically:

[0105]

[0106] Where, is the final demodulated phase signal at time t, is the first demodulated phase signal at time t, is the second demodulated phase signal at time t, is the third demodulated phase signal at time t.

[0107] Specifically, when there is optical relative intensity noise n in the system I At (t), according to the principle of PGC demodulation algorithm, the three-way time-division processed sampling signal V i (t) is synchronously multiplied with the 1-fold and 2-fold frequency signals of the carrier signal, and after low-pass filtering, two detection signals are obtained:

[0108]

[0109] in, are the first and second detection signals of the sampling signal after the i-th channel is de-time-division processed by the optical relative intensity noise at time t, respectively. i (t) is the sampled signal after time division processing of the i-th solution at time t, * is the convolution operator, cosω m t is a frequency-doubled signal, cos2ω m t is the double frequency signal, h LPF (t) is the impulse response function of the low-pass filter, are the first and second additive noises introduced by the optical relative intensity noise into the sampling signal after the time division processing of the i-th solution at time t, J k (C) is the k-th order Bessel function (k = 1, 2, ...), and B is the AC amplitude of the sampled signal. The first additive noise and the second additive noise can be derived as follows:

[0110]

[0111] Where, J k (C) is the kth order Bessel function, a ek ,a ok ,b ek ,b ok are error term coefficients. In order to simplify the expressions of formulas (8) and (9), define a ek ,a ok ,b ek ,b ok The four error term coefficients are as follows:

[0112]

[0113]

[0114] The two detection signals are processed by the inverse tangent algorithm to obtain the demodulated phase signal. The specific formula is:

[0115]

[0116] Among them, J k (C) is the kth order Bessel function, is the first additive noise introduced by the optical relative intensity noise into the sampling signal after the i-th channel time division processing at time t, is the second additive noise introduced by the optical relative intensity noise into the sampling signal after the i-th path time division processing at time t, where i = 1, 2, 3.

[0117] When there is circuit noise in the system C (t), the formulas of the detection signal and the demodulated phase signal can be obtained by referring to the above method, and the details will not be repeated here.

[0118] The three demodulated phase signals are summed and averaged to obtain the final demodulated phase signal. The specific formula is:

[0119]

[0120] Where, is the final demodulated phase signal at time t, is the first demodulated phase signal at time t, is the second demodulated phase signal at time t, is the third demodulated phase signal at time t.

[0121] When there is optical relative intensity noise n in the system I At (t), the first additive noise and the second additive noise are converted into the noise in the i-th demodulated phase signal after arc tangent solution. Then the i-th demodulated phase signal can also be expressed as:

[0122]

[0123] Where, is the demodulated phase signal of the i-th channel, is the noise introduced into the i-th demodulated phase signal by the optical relative intensity noise.

[0124] Substituting formulas (8) to (13) into formula (14) for simplified calculation and comparing with formula (16), we can obtain that the noise in the demodulated phase signal output by the system caused by the optical relative intensity noise can be expressed as:

[0125]

[0126] It can be seen that the full frequency band of the optical relative intensity noise will be transferred to the demodulated phase signal, and the noise of the demodulated phase signal generated Interferometer Phase It is related to system parameters such as modulation depth C. The measured phase is included and the interferometer initial phase The initial phase of the interferometer Usually it is disturbed by the external environment and produces random slow drift. Therefore, for a single-channel sampling signal, the noise of the demodulated phase signal output is The noise power spectrum of the output demodulated phase signal fluctuates as the initial phase of the interferometer changes. Through simulation analysis, it can be seen that the maximum fluctuation of the noise power spectrum of the output demodulated phase signal can reach 15dB. When C≈2.55, the noise of the output demodulated phase signal fluctuates as the initial phase of the interferometer changes. The fluctuation is the smallest, with a fluctuation range of about 3dB.

[0127] When the input optical relative intensity noise is Gaussian white noise, we have:

[0128]

[0129] in, for The single sideband power spectral density, for The single sideband power spectral density, S ω {n Ii} is n Ii The single sideband power spectral density, It is a second-order broad stationary band-limited noise independent of the optical relative intensity noise.

[0130] Taking the power spectrum of formula (17) and using formula (18), we can obtain the noise power spectrum of the demodulated phase signal output by the system caused by the optical relative intensity noise:

[0131]

[0132] When there is circuit noise in the system C (t) can also be calculated by taking the circuit noise n of the i-th sampling signal as Ci (t) is decomposed into the superposition of band-limited noise, and the specific formula is:

[0133]

[0134] in, They are all second-order wide stationary band-limited noises independent of circuit noise, and the noise bandwidth is [-ω c / 2,ω c / 2].

[0135] Using the same analysis process as for optical relative intensity noise transfer, the noise of the demodulated phase signal output by the system due to circuit noise can be expressed as:

[0136]

[0137] When the input circuit noise is Gaussian white noise, the noise power spectrum of the demodulated phase signal output by the system caused by the circuit noise is:

[0138]

[0139] Among them, S ω {n Ci} is n Ci The single sideband power spectral density.

[0140] From formula (21), we can see that the circuit noise only has (ω m / 2,5ω m / 2) The noise within the frequency band will be transmitted to the final demodulated phase signal. The noise of the demodulated phase signal converted from it is still related to the initial phase of the interferometer and will fluctuate with the drift of the initial phase of the interferometer, causing the noise level of the final demodulated phase signal of the system to fluctuate significantly.

[0141] By observing formulas (19) and (22), it can be seen that the noise of the demodulated phase signal after demodulation and conversion by the PGC inverse tangent algorithm is related to the initial phase of the interferometer, regardless of the relative intensity noise or circuit noise. If the interferometer output under different initial phase conditions can be obtained, and the law that the noise of the demodulated phase signal changes with the initial phase of the interferometer is used, by averaging the demodulated phase signals with different initial phases, stable noise can be obtained, eliminating the influence of the initial phase change of the interferometer on the noise of the demodulated phase signal.

[0142] When optical relative intensity noise exists in the system, considering that the sampling time of the three-way interference light pulses cannot be absolutely simultaneous, and the optical relative intensity noise is usually broadband white noise with a short coherence time, the optical relative intensity noise in the three-way interference light signal is set as three independent noises with the same power spectrum characteristics. Ii (i=1,2,3). Based on this assumption, the phase noises caused by the optical relative intensity noise in the three demodulated phase signals can be obtained according to formula (17):

[0143]

[0144] According to formulas (23), (24) and (25), the noise of the demodulated phase signal output by the system caused by the optical relative intensity noise can be calculated:

[0145]

[0146] When the input optical relative intensity noise is Gaussian white noise, for the three sampling signals, since the optical intensity noise comes from the same source, they have the same noise spectrum level, that is, S ω {n I1}=S ω {n I2}=S ω {n I3}, uniformly denoted as S ω {n I}, the power spectrum of the noise of the demodulated phase signal of formula (26) is made, and according to formula (18), the power spectrum of the output demodulated phase signal noise caused by the optical relative intensity noise can be simplified as:

[0147]

[0148] According to the trigonometric function relationship, because:

[0149]

[0150] So we have:

[0151]

[0152] Substituting equations (28), (29) and (30) into equation (27), we can obtain the noise power spectrum of the final output demodulated phase signal caused by the optical relative intensity noise:

[0153]

[0154] When there is circuit noise in the system C (t), according to formula (21), since the three interference light pulses are photoelectrically converted and sampled at different times, the circuit noises of each path are uncorrelated. Therefore, the circuit noise is set as three independent noises with the same power spectrum characteristics. and The noise in the three demodulated phase signals caused by circuit noise is:

[0155]

[0156] According to formulas (32), (33) and (34), the noise of the system output demodulation phase signal caused by circuit noise can be calculated. For the three sampling signals, since they have the same signal sampling circuit, the circuit noise has the same noise spectrum level, that is, S ω {n C1}=S ω {n C2}=S ω {n C3}, uniformly denoted as S ω {n C Referring to the above reasoning, we can further deduce that the noise power spectrum of the final output demodulated phase signal caused by circuit noise is:

[0157]

[0158] Comparing the conventional PGC demodulation algorithm with the phase-shifted PGC demodulation algorithm proposed in the present invention, the noise power spectra of the final output demodulated phase signal caused by the optical relative intensity noise and circuit noise can be expressed as follows:

[0159] (1) Conventional PGC algorithm

[0160]

[0161] (2) Phase-shift PGC algorithm

[0162]

[0163]

[0164] It can be seen that compared with the conventional PGC demodulation algorithm, the phase-shifted PGC demodulation algorithm proposed in the present invention has a noise spectrum that is no longer consistent with the noise spectrum of the interferometer phase signal, whether it is for the light relative intensity noise or the circuit noise. Therefore, the system will not be affected by the initial phase drift of the interferometer caused by the external environment, and will obtain a stable noise output.

[0165] An interferometric fiber optic hydrophone phase-shift PGC demodulation system adopts an interferometric fiber optic hydrophone phase-shift PGC demodulation method for demodulation. The system includes a laser, an optical pulse modulator, a first optical fiber coupler, a first optical fiber delay line, a second optical fiber delay line, a second optical fiber coupler, a phase modulator, an optical fiber interferometer, an optoelectronic converter, and a signal processing system. The laser is connected to the optical pulse modulator, the optical pulse modulator is connected to the input end of the first optical fiber coupler, the first output end of the first optical fiber coupler is directly connected to the first input end of the second optical fiber coupler, the second output end of the first optical fiber coupler is connected to the second input end of the second optical fiber coupler through the first optical fiber delay line, the third output end of the first optical fiber coupler is connected to the third input end of the second optical fiber coupler through the second optical fiber delay line, one end of the phase modulator is connected to the output end of the second optical fiber coupler, and the other end is connected to the optical fiber interferometer. One end of the optoelectronic converter is connected to the optical fiber interferometer, and the other end is connected to the signal processing system. The signal processing system is also connected to the laser, the optical pulse modulator, and the phase modulator.

[0166] The laser is used to generate an optical signal, which is then input into the optical pulse modulator after sinusoidal frequency modulation;

[0167] The optical pulse modulator is used to generate periodic optical pulses;

[0168] The first optical fiber coupler is used for optical fiber beam splitting. Periodic optical pulses are input from the input end of the first optical fiber coupler and are processed to obtain three optical pulses accordingly.

[0169] The first optical fiber delay line and the second optical fiber delay line are used to delay the optical pulse;

[0170] The second optical fiber coupler is used to combine the three input optical pulses to generate an optical pulse sequence;

[0171] The phase modulator is used to perform phase modulation on the optical pulse sequence to obtain a phase-modulated optical pulse sequence;

[0172] The fiber optic interferometer is used to sense external acoustic signals, interfere with the phase-modulated optical pulse sequence, and output an interference optical pulse sequence;

[0173] The photoelectric converter is used to perform photoelectric conversion and digital sampling on the interference light pulse sequence, generate a digital sampling signal, and output it to the signal processing system through a cable;

[0174] The signal processing system is used to demodulate the received digital sampling signal, output a sinusoidal wave signal to the laser to perform sinusoidal frequency modulation on the optical signal, output a pulse modulation signal to the optical pulse modulator to generate optical pulses, and output a phase modulation signal of a specific waveform to the phase modulator for phase modulation.

[0175] Specifically, see Figure 4 , Figure 4 FIG. 1 is a schematic structural diagram of an interferometric fiber optic hydrophone phase-shift PGC demodulation system according to an embodiment of the present invention.

[0176] An interferometric fiber optic hydrophone phase-shift PGC demodulation system includes a laser 1, an optical pulse modulator 2, a first optical fiber coupler 3, a first optical fiber delay line 4, a second optical fiber delay line 5, a second optical fiber coupler 6, a phase modulator 7, an optical fiber interferometer 8, an optoelectronic converter 9, and a signal processing system 10. The light emitted by the laser 1 is sinusoidally frequency modulated and then input to the input port of the optical pulse modulator 2 via an optical fiber. After passing through the optical pulse modulator 2, a corresponding optical pulse output is generated; the optical pulse enters the input port of the first optical fiber coupler 3 through the optical fiber and is divided into three beams of light in the first optical fiber coupler 3. The first beam of light is output from the first output port of the first optical fiber coupler 3 and directly input to the first input port of the second optical fiber coupler 6; the second beam of light is output from the second output port of the first optical fiber coupler 3 to the optical fiber delay line 4, and after a certain length of optical fiber delay, is input to the second input port of the second optical fiber coupler 6; the third beam of light is output from the third output port of the first optical fiber coupler 3 to the second optical fiber delay line 5, and after a certain length of optical fiber delay, is input to the second optical fiber coupler 6. The third input port of the combiner 6; then the second fiber coupler 6 combines the three beams of light to generate a light pulse sequence consisting of three light pulses, which is output to the input port of the fiber interferometer 8 through the output port of the second fiber coupler 6, and interferes after passing through the fiber interferometer 8, outputting a group of interference light pulse sequences; the interference light pulse sequence is input to the input port of the photoelectric converter 9 from the output port of the fiber interferometer 8, and after photoelectric conversion and digital sampling are completed in the photoelectric converter 9, a sampled digital signal is generated; the sampled digital signal is output from the output port of the photoelectric converter 9 to the input port of the signal processing system 10 through a cable, and is processed by the phase shift PGC demodulation algorithm in the signal processing system 10 to obtain the measured phase information output.

[0177] In a further embodiment, the laser is a tunable narrow-linewidth laser, such as a fiber laser, a semiconductor laser, or a solid-state laser.

[0178] In a further embodiment, the optical pulse modulator is an optical device that generates optical pulses, such as an acousto-optic modulator (AOM) or a semiconductor optical pulse amplifier (SOA).

[0179] In a further solution, the fiber optic interferometer is the sensing optical component of the fiber optic hydrophone, which adopts an unbalanced reflective Michelson fiber optic interferometer structure. The interferometer includes a signal arm and a sensing arm, and the arm difference between the two arms is l. A Faraday rotating mirror is used as the reflection end to eliminate the influence of polarization fading.

[0180] In a further solution, the photoelectric converter is a photoelectric signal conversion device, including a photodetector, a preamplifier and an analog-to-digital converter, which converts the interference light pulse signal output by the fiber optic interferometer into an electrical signal, and digitally samples the electrical signal to obtain a corresponding sampling signal.

[0181] In a further embodiment, the signal processing system is a digital signal processing device, such as an FPGA, a DSP, or a computer.

[0182] The above-mentioned interferometric fiber optic hydrophone phase-shift PGC demodulation method and demodulation system adopts ramp phase modulation technology and combines it with an unbalanced interferometer structure to obtain three interference outputs with different initial phases. It can flexibly select PGC demodulation, 3x3 coupler phase-shift demodulation, and phase-shift PGC demodulation algorithm demodulation, and has good algorithm redundancy capability, which is specifically manifested as follows:

[0183] (1) When the system phase self-noise and noise stability requirements are high, the phase-shift PGC demodulation scheme is selected to obtain good noise performance;

[0184] (2) When the requirements for noise stability are not high but the requirements for system power consumption are high, the PGC demodulation scheme is selected to turn off the modulation signal of the phase modulator to reduce system power consumption. At this time, the sampling rate of the PGC demodulation algorithm can be 3 times that of the phase-shift PGC demodulation algorithm, which is also conducive to improving the dynamic range.

[0185] (3) When the laser frequency modulation failure causes the PGC modulation to fail to meet the requirements or the system dynamic range requirements are high, the laser frequency modulation can be turned off and the 3X3 coupler phase shift demodulation algorithm can be selected. Under the condition of the same sampling rate, the dynamic range can be improved by about 20dB.

[0186] The above describes in detail the interferometric fiber-optic hydrophone phase-shift PGC demodulation method and system provided by the present invention. Specific examples are used herein to illustrate the principles and implementations of the present invention. The above examples are intended only to facilitate understanding of the core concepts of the present invention. It should be noted that those skilled in the art will be able to make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications fall within the scope of protection of the claims.

Claims

1. A phase-shift PGC demodulation method for an interferometric fiber optic hydrophone, characterized in that: The method comprises: S1. Using a laser to generate an optical signal, performing sinusoidal frequency modulation on the optical signal to output a sinusoidal frequency modulated light wave, inputting the sinusoidal frequency modulated light wave into an optical pulse modulator, and outputting a periodic optical pulse after processing; S2. Performing optical fiber splitting on the optical pulse using a first coupler to obtain three optical pulses, performing optical fiber time delay and optical fiber combining on the three optical pulses, and outputting an optical pulse sequence consisting of the three optical pulses; S3, phase-modulating the optical pulse sequence by a phase modulator to obtain a phase-modulated optical pulse sequence, inputting the phase-modulated optical pulse sequence into a fiber interferometer, and outputting an interference optical pulse sequence after interference processing; S4, inputting the interference light pulse sequence into a photoelectric converter for photoelectric conversion and digital sampling to obtain a sampling signal, inputting the sampling signal into a signal processing system for time division decomposition processing to obtain three-way time division decomposition sampling signals; S5. Perform PGC demodulation and high-pass filtering on the three sampling signals after time division processing to obtain three demodulated phase signals after high-pass filtering, sum and average the three demodulated phase signals after high-pass filtering to obtain a final demodulated phase signal.

2. The interferometric fiber optic hydrophone phase shift PGC demodulation method according to claim 1, wherein: In S2, the optical pulse is subjected to optical fiber splitting using a first coupler to obtain three optical pulses, specifically comprising: inputting the optical pulse into the input end of the first optical fiber coupler, performing beam splitting processing through the first optical fiber coupler, outputting the first optical pulse through the first output port of the first optical fiber coupler, outputting the second optical pulse through the second output port of the first optical fiber coupler, and outputting the third optical pulse through the third output port of the first optical fiber coupler.

3. The interferometric fiber optic hydrophone phase shift PGC demodulation method according to claim 2, wherein: In S2, the three optical pulses are subjected to optical fiber delay and optical fiber combining processing to output an optical pulse sequence consisting of the three optical pulses, specifically comprising: directly inputting the first optical pulse into the first input port of the second optical fiber coupler, inputting the second optical pulse into the first optical fiber delay line, and inputting the second optical pulse into the second input port of the second optical fiber coupler after delay processing, inputting the third optical pulse into the second optical fiber delay line, and inputting the third optical pulse into the third input port of the second optical fiber coupler after delay processing, and the second optical fiber coupler performs optical fiber combining processing on the input first optical pulse and the second and third optical pulses after delay processing to output an optical pulse sequence.

4. The interferometric fiber optic hydrophone phase shift PGC demodulation method according to claim 3, wherein: The length of the first optical fiber delay line is L, and the length of the second optical fiber delay line is 2L. The specific setting of L is: Where L is the length of the first optical fiber delay line, n is the refractive index of the optical fiber core, c is the speed of light in vacuum, and T s is the repetition time period of the light pulse.

5. The interferometric fiber optic hydrophone phase shift PGC demodulation method according to claim 4, wherein: The sampling signal in S4 contains optical relative intensity noise or circuit noise. In S4, the sampling signal is input into the signal processing system for time-division decomposition to obtain three-way time-division decomposition sampling signals. When the sampling signal includes optical relative intensity noise, the time-division decomposition sampling signals can be expressed as follows: When the sampling signal includes circuit noise, the sampling signal after the time division processing can be expressed as follows: Where V i (t) is the sampling signal after time division processing of the i-th solution at time t, A is the DC amplitude of the sampling signal, B is the AC amplitude of the sampling signal, n Ii (t) is the optical relative intensity noise of the sampling signal after time division processing of the i-th channel at time t, n Ci (t) is the circuit noise of the sampled signal after time division processing of the i-th channel at time t, C is the modulation depth, ω m is the PGC modulation frequency, is the phase of the i-th sampling signal at time t.

6. The interferometric fiber optic hydrophone phase shift PGC demodulation method according to claim 5, characterized in that: In S5, the three sampling signals after the time division processing are subjected to PGC demodulation processing and high-pass filtering, and three demodulated phase signals after high-pass filtering are obtained accordingly, specifically including: S51, performing phase-locked detection and low-pass filtering on any one of the three sampling signals after the time division processing to obtain two detection signals; S52, using an inverse tangent algorithm to solve the two detection signals to obtain a demodulated phase signal; S53, performing high-pass filtering on the demodulated phase signal to obtain a demodulated phase signal after high-pass filtering; S54 , selecting another channel from the three channels of sampled signals after time division processing, until all three channels of sampled signals after time division processing are selected, and processing through steps S51 to S53 to obtain three channels of high-pass filtered demodulated phase signals.

7. The interferometric fiber optic hydrophone phase shift PGC demodulation method according to claim 6, wherein: In S51, one of the three sampling signals after the de-time division processing is randomly selected for phase-locked detection and low-pass filtering to obtain two detection signals. When the sampling signal includes optical relative intensity noise, the specific formulas of the two detection signals are: When the sampling signal includes circuit noise, the specific formulas of the two detection signals are: Where, are the first and second detection signals of the sampling signal after time division processing of the i-th channel introduced by the optical relative intensity noise at time t, B is the AC amplitude of the sampling signal, are the first and second additive noises introduced by the optical relative intensity noise into the sampling signal after the time division processing of the i-th channel, They are the first and second detection signals of the sampling signal after the i-th channel time division processing introduced by the circuit noise at time t, are the first and second additive noises introduced by the circuit noise into the sampling signal after the time division processing of the i-th path, is the phase of the sampled signal after time division processing of the i-th channel at time t, J k (C) is the kth order Bessel function, k = 1, 2, ... .

8. The interferometric fiber optic hydrophone phase shift PGC demodulation method according to claim 7, wherein: In S52, the arctangent algorithm is used to solve the two detection signals to obtain a demodulated phase signal. When the sampling signal contains optical relative intensity noise, the formula of the demodulated phase signal is specifically: When the sampling signal contains circuit noise, the formula for the demodulated phase signal is specifically: Where, is the demodulated phase signal of the i-th channel at time t, B is the AC amplitude of the sampling signal, J k (C) is the kth order Bessel function, are the first and second additive noises introduced by the optical relative intensity noise in the sampling signal after time division processing of the i-th channel at time t, are the first and second additive noises introduced by circuit noise into the sampled signal after time division processing of the i-th channel at time t, is the phase of the sampled signal after time division processing of the i-th channel at time t.

9. The interferometric fiber optic hydrophone phase shift PGC demodulation method according to claim 8, wherein: In S5, the three demodulated phase signals are summed and averaged to obtain a final demodulated phase signal. The final demodulated phase signal is specifically: Where, is the final demodulated phase signal at time t, is the first demodulated phase signal at time t, is the second demodulated phase signal at time t, is the third demodulated phase signal at time t.

10. An interferometric fiber optic hydrophone phase-shift PGC demodulation system, employing the interferometric fiber optic hydrophone phase-shift PGC demodulation method according to any one of claims 1 to 9 for demodulation, the system comprising a laser, an optical pulse modulator, a first optical fiber coupler, a first optical fiber delay line, a second optical fiber delay line, a second optical fiber coupler, a phase modulator, an optical fiber interferometer, an optoelectronic converter, and a signal processing system, wherein the laser is connected to the optical pulse modulator, the optical pulse modulator is connected to the input end of the first optical fiber coupler, and the first output end of the first optical fiber coupler is directly connected to the second optical fiber coupler. The first input end of the optical fiber coupler is connected to the second input end of the second optical fiber coupler through a first optical fiber delay line, the second output end of the first optical fiber coupler is connected to the third input end of the second optical fiber coupler through a second optical fiber delay line, one end of the phase modulator is connected to the output end of the second optical fiber coupler, and the other end is connected to the optical fiber interferometer, one end of the photoelectric converter is connected to the optical fiber interferometer, and the other end is connected to the signal processing system, and the signal processing system is also connected to the laser, the optical pulse modulator, and the phase modulator, wherein: The laser is used to generate an optical signal, which is then input into an optical pulse modulator after being sinusoidally frequency modulated; The optical pulse modulator is used to generate periodic optical pulses; The first optical fiber coupler is used for optical fiber splitting, and the periodic optical pulse is input from the input end of the first optical fiber coupler and processed to obtain three optical pulses accordingly; The first optical fiber delay line and the second optical fiber delay line are used to delay the optical pulse; The second optical fiber coupler is used to combine the three input optical pulses to generate an optical pulse sequence; The phase modulator is used to perform phase modulation on the optical pulse sequence to obtain a phase-modulated optical pulse sequence; The optical fiber interferometer is used to sense external acoustic signals, generate interference with the phase-modulated optical pulse sequence, and output an interference optical pulse sequence; The photoelectric converter is used to perform photoelectric conversion and digital sampling on the interference light pulse sequence to generate a digital sampling signal, and output the digital sampling signal to the signal processing system via a cable; The signal processing system is used to demodulate the received digital sampling signal, output a sinusoidal wave signal to the laser to perform sinusoidal frequency modulation on the optical signal, output a pulse modulation signal to the optical pulse modulator to generate an optical pulse, and output a phase modulation signal of a specific waveform to the phase modulator for phase modulation.

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