CN116429237A - Demodulation method and demodulation system for phase shift PGC of interference type optical fiber hydrophone - Google Patents
Demodulation method and demodulation system for phase shift PGC of interference type optical fiber hydrophone Download PDFInfo
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Abstract
The invention discloses a demodulation method and a demodulation system for phase shift PGC of an interference type optical fiber hydrophone. Firstly, a laser is adopted to generate an optical signal, sinusoidal frequency modulation is carried out, sinusoidal frequency modulation light waves are output, sinusoidal frequency modulation light waves are input into an optical pulse modulator to be processed and output periodic optical pulses, the optical pulses are subjected to optical fiber beam splitting, optical fiber delay and optical fiber beam combination processing to obtain an optical pulse sequence, the optical pulse sequence is input into an optical fiber interferometer to be subjected to interference processing after being subjected to phase modulation through a phase modulator, an interference optical pulse sequence is output, the interference optical pulse sequence is input into a photoelectric converter to be subjected to photoelectric conversion and digital sampling, a sampling signal is input into a signal processing system to be subjected to PGC demodulation processing and high-pass filtering, and demodulation phase signals after high-pass filtering are summed and averaged to obtain a final demodulation phase signal. Under the condition of not additionally adding photoelectric detection and signal acquisition hardware, the method can obtain stable low-noise demodulation phase signals.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a demodulation method and a demodulation system for phase shift PGC of an interference type optical fiber hydrophone.
Background
The interference type optical fiber hydrophone is the most widely used optical fiber hydrophone at present, the sensing core is an optical fiber interferometer, and the detected acoustic signals are loaded in the interference signals of the optical fiber interferometer in a phase form, so that the stable detection of the phase of the interferometer is the key of the optical fiber hydrophone technology.
Phase self-noise and noise stability are important performance indicators for fiber optic hydrophone systems. The phase detection algorithm of the conventional interference type optical fiber hydrophone mainly comprises phase carrier modulation (PGC) demodulation, a 3×3 coupler phase shift detection method, a heterodyne method and the like, wherein the PGC demodulation method has good low-frequency noise performance, but the phase self-noise of the PGC demodulation method changes along with the change of the initial phase difference of an interferometer, and when the initial phase difference drift of the interferometer is caused by external environment disturbance, the phase noise greatly fluctuates; the 3 x 3 coupler phase shift detection method is susceptible to external low-frequency noise and low-frequency interference, and the phase noise is also related to the initial phase difference of the interferometer; the heterodyne method adopts a matched optical structure, wherein a matched interferometer and transmission optical fibers between the matched interferometer and the optical fiber hydrophone interferometer participate in the interference process, are easily affected by external environment interference, and reduce the low-frequency noise performance of the system.
The invention provides an interference type optical fiber hydrophone phase shift PGC demodulation method and a demodulation system, which adopt oblique wave phase modulation and combine an unbalanced optical fiber interferometer structure to obtain three paths of PGC modulation interference signals with different initial phases, and adopt a phase shift PGC demodulation algorithm to complete phase resolution, so that stable low-noise demodulation phase output can be obtained under the condition of not additionally adding photoelectric detection and signal acquisition hardware, the phase self-noise and noise stability performance of the system can be effectively improved, and meanwhile, the system has better algorithm redundancy performance, and can be conveniently combined with a time division multiplexing technology to be applied to a large-scale interference type optical fiber hydrophone array system.
Disclosure of Invention
The invention aims to overcome the defects and shortcomings in the prior art, provides a high-noise-stability phase shift PGC demodulation method and demodulation system for an interference type optical fiber hydrophone, and provides an effective low-noise signal detection scheme for application of the interference type optical fiber hydrophone.
A phase shift PGC demodulation method of an interference type optical fiber hydrophone comprises the following steps:
s1, generating an optical signal by using a laser, performing sinusoidal frequency modulation on the optical signal, outputting sinusoidal frequency modulated light waves, inputting the sinusoidal frequency modulated light waves to an optical pulse modulator, and outputting periodic optical pulses after processing;
S2, carrying out optical fiber beam splitting on the light pulses by adopting a first coupler to obtain three light pulses, carrying out optical fiber delay and optical fiber beam combination treatment on the three light pulses, and outputting an optical pulse sequence consisting of the three light pulses;
s3, performing phase modulation on the optical pulse sequence through a phase modulator to obtain a phase modulated optical pulse sequence, inputting the phase modulated optical pulse sequence into an optical fiber interferometer, performing interference treatment, and outputting an interference optical pulse sequence;
s4, inputting the interference light pulse sequence into a photoelectric converter for photoelectric conversion and digital sampling to obtain a sampling signal, and inputting the sampling signal into a signal processing system for time division decomposition processing to obtain three paths of sampling signals after time division decomposition processing;
and S5, performing PGC demodulation processing and high-pass filtering on the three paths of time division-resolved sampling signals to obtain three paths of high-pass filtered demodulation phase signals, summing the three paths of high-pass filtered demodulation phase signals, and taking an average value to obtain a final demodulation phase signal.
Preferably, in S2, the optical pulse is split by using a first coupler to obtain three optical pulses, which specifically includes: the optical pulse is input to the input end of the first optical fiber coupler, the beam splitting treatment is carried out through the first optical fiber coupler, the first optical pulse is output through the first output port of the first optical fiber coupler, the second optical pulse is output through the second output port of the first optical fiber coupler, and the third optical pulse is output through the third output port of the first optical fiber coupler.
Preferably, in S2, the optical fiber delay and the optical fiber beam combination processing are performed on the three light pulses, and an optical pulse sequence composed of the three light pulses is output, which specifically includes: the first optical pulse is directly input to a first input port of a second optical fiber coupler, the second optical pulse is input to a first optical fiber delay line, the second optical pulse is input to a second input port of the second optical fiber coupler after delay processing, the third optical pulse is input to a second optical fiber delay line, the third optical pulse is input to a third input port of the second optical fiber coupler after delay processing, and the second optical fiber coupler performs optical fiber beam combination processing on the input first optical pulse and the second and third optical pulses after delay processing and outputs an optical pulse sequence.
Preferably, the length of the first optical fiber delay line is L, the length of the second optical fiber delay line is 2L, and the specific arrangement of L is as follows:
wherein 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, T s The time period is repeated for the light pulse.
Preferably, the sampled signal in S4 contains optical relative intensity noise or circuit noise, and in S4, the sampled signal is input to a signal processing system to perform time division demodulation processing, so as to obtain three paths of sampled signals after time division demodulation processing, and when the sampled signals include the optical relative intensity noise, the sampled signals after time division demodulation processing can be expressed as follows by a formula:
When the sampling signal includes circuit noise, the time-division-resolved sampling signal can be expressed as:
wherein V is i (t) is the sampling signal after the ith time solution time division processing at the moment t, A is the direct current amplitude value of the sampling signal, B is the alternating current amplitude value of the sampling signal, n Ii (t) is the optical relative intensity noise of the sampling signal after the ith time-division solution processing at the moment t, n Ci (t) is the circuit noise of the sampling signal after the ith time-division solution processing at the moment t, C is the modulation depth omega m For the modulation frequency of the PGC,
the phase of the i-th sampling signal at the time t.
Preferably, in S5, PGC demodulation processing and high-pass filtering are performed on the three paths of sampling signals after the time division demodulation processing, so as to obtain three paths of demodulation phase signals after the high-pass filtering, which specifically includes:
s51, taking one path from any one path of sampling signals after three paths of time division and solution processing to carry out phase-locked detection and low-pass filtering to obtain two paths of detection signals;
s52, resolving the two paths of detection signals by adopting an arctangent algorithm to obtain a demodulation phase signal;
s53, performing high-pass filtering on the demodulation phase signals to obtain demodulation phase signals after high-pass filtering;
s54, another path is taken from the three paths of time division-resolved sampling signals until all the paths of time division-resolved sampling signals are selected, and the three paths of high-pass filtered demodulation phase signals are obtained through processing in steps S51 to S53.
Preferably, in S51, any one of the three paths of sampling signals after the time division and solution processing is taken to perform phase-locked detection and low-pass filtering to obtain two paths of detection signals, and when the sampling signals include optical relative intensity noise, the specific formulas of the two paths of detection signals are as follows:
when the sampling signal includes circuit noise, the specific formula of the two paths of detection signals is as follows:
in the method, in the process of the invention,
the first and second detection signals of the sampling signal after the ith time-division solution processing are respectively introduced by the optical relative intensity noise at the t moment, B is the alternating current amplitude of the sampling signal, and +.>
Introducing first and second additive noise of the sampling signal after ith path of solution time division processing for t moment by optical relative intensity noise,/for the sampling signal>
The first and second path detection signals of the sampling signal after the ith path of time division processing are respectively introduced by circuit noise at the moment t,
first and second additive noise of the sampling signal after ith time division processing is introduced by circuit noise at t moment>
For the phase of the sampling signal after the time division processing of the ith solution at the moment of t, J k (C) Is a k-th order bessel function (k=1, 2.).
Preferably, in S52, the arctangent algorithm is adopted to calculate the two paths of detection signals to obtain a demodulation phase signal, and when the sampling signal contains optical relative intensity noise, the formula of the demodulation phase signal is specifically as follows:
When the sampling signal contains circuit noise, the formula for demodulating the phase signal is specifically:
in the method, in the process of the invention,
demodulating phase signal for ith path at t moment, B is alternating current amplitude of sampling signal, J k (C) For the kth order bessel function (k=1, 2,.),/i>
First and second additive noise introduced by optical relative intensity noise in sampling signal after time division processing of ith solution at t moment +.>
First and second additive noise introduced by circuit noise in sampling signal after ith time division processing at t moment>
And solving the phase of the sampling signal after time division processing for the ith path at the t moment.
Preferably, in S5, the three demodulation phase signals are summed and averaged to obtain a final demodulation phase signal, where the final demodulation phase signal is specifically:
in the method, in the process of the invention,
for final demodulation of the phase signal at time t +.>
Demodulating the phase signal for the first path at time t, < >>
Demodulating the phase signal for the second path at time t, < >>
And demodulating the phase signal for the third path at the time t.
The system comprises a laser, an optical pulse modulator, a first optical fiber coupler, a first optical fiber delay line, a second optical fiber coupler, a phase modulator, an optical fiber interferometer, an optical-to-electrical converter and a signal processing system, wherein the laser is connected with the optical pulse modulator, the optical pulse modulator is connected with the input end of the first optical fiber coupler, the first output end of the first optical fiber coupler is directly connected with the first input end of the second optical fiber coupler, the second output end of the first optical fiber coupler is connected with 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 with 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 with the output end of the second optical fiber coupler, the other end of the phase modulator is connected with the optical fiber interferometer, one end of the optical-to-electrical converter is connected with the optical fiber interferometer, the other end of the phase modulator is connected with the signal processing system, and the signal processing system is also connected with the laser pulse modulator, the optical pulse modulator and the phase modulator, wherein the phase modulator is connected with the interference modulator:
The laser is used for generating an optical signal, and the optical signal is input to the optical pulse modulator after being modulated by sinusoidal frequency;
the optical pulse modulator is used for generating periodic optical pulses;
the first optical fiber coupler is used for splitting optical fibers, periodic light pulses are input from the input end of the first optical fiber coupler, and three light pulses are correspondingly obtained after processing;
the first optical fiber delay line and the second optical fiber delay line are used for delaying the optical pulse;
the second optical fiber coupler is used for synthesizing the three input optical pulses to generate an optical pulse sequence;
the phase modulator is used for carrying out phase modulation on the optical pulse sequence to obtain an optical pulse sequence after phase modulation;
the optical fiber interferometer is used for sensing external acoustic signals, generating interference on the optical pulse sequence after phase modulation and outputting the interference optical pulse sequence;
the photoelectric converter is used for performing photoelectric conversion and digital sampling on the interference light pulse sequence, generating a digital sampling signal and outputting the digital sampling signal to the signal processing system through a cable;
the signal processing system is used for demodulating the received digital sampling signal, outputting a sine wave signal to the laser for carrying out sine frequency modulation on the optical signal, outputting a pulse modulation signal to the optical pulse modulator for generating optical pulses, and outputting a phase modulation signal with a specific waveform to the phase modulator for carrying out phase modulation.
According to the demodulation method and the demodulation system for the phase shift PGC of the interference type optical fiber hydrophone, the oblique wave phase modulation technology is adopted, and the unbalanced interferometer structure is combined, so that three paths of interference outputs with different initial phases are obtained, PGC demodulation, 3X3 coupler phase shift demodulation and phase shift PGC demodulation algorithm demodulation can be flexibly selected, and the demodulation method and the demodulation system have good algorithm redundancy capability.
Drawings
FIG. 1 is a flow chart of a method for demodulating an interferometric fiber optic hydrophone phase shifted PGC in accordance with one embodiment of the present invention;
FIG. 2 is a diagram of an optical pulse train and its phase modulation waveform generated in a phase-shifted PGC demodulation system according to one embodiment of the present invention;
FIG. 3 is a diagram showing the waveform of the interference light pulses and their phase output from the fiber optic interferometer in a phase shift PGC demodulation system according to one embodiment of the present invention;
fig. 4 is a schematic diagram of a phase-shifting PGC demodulation system with an interferometric fiber optic hydrophone according to an embodiment of the invention.
Detailed Description
In order to make the technical scheme of the present invention better understood by those skilled in the art, the present invention will be further described in detail with reference to the accompanying drawings.
The phase shift PGC demodulation method of the interference type optical fiber hydrophone specifically comprises the following steps:
s1, generating an optical signal by using a laser, performing sinusoidal frequency modulation on the optical signal, outputting sinusoidal frequency modulated light waves, inputting the sinusoidal frequency modulated light waves to an optical pulse modulator, and outputting periodic optical pulses after processing;
S2, carrying out optical fiber beam splitting on the light pulses by adopting a first coupler to obtain three light pulses, carrying out optical fiber delay and optical fiber beam combination treatment on the three light pulses, and outputting an optical pulse sequence consisting of the three light pulses;
s3, performing phase modulation on the optical pulse sequence through a phase modulator to obtain a phase modulated optical pulse sequence, inputting the phase modulated optical pulse sequence into an optical fiber interferometer, performing interference treatment, and outputting an interference optical pulse sequence;
s4, inputting the interference light pulse sequence into a photoelectric converter for photoelectric conversion and digital sampling to obtain a sampling signal, and inputting the sampling signal into a signal processing system for time division decomposition processing to obtain three paths of sampling signals after time division decomposition processing;
and S5, performing PGC demodulation processing and high-pass filtering on the three paths of time division-resolved sampling signals to obtain three paths of high-pass filtered demodulation phase signals, summing the three paths of high-pass filtered demodulation phase signals, and taking an average value to obtain a final demodulation phase signal.
Specifically, referring to fig. 1, fig. 2 and fig. 3, fig. 1 is a flowchart of a phase shift PGC demodulation method of an interferometric fiber optic hydrophone according to an embodiment of the invention, fig. 2 is a light pulse sequence and a phase modulation waveform diagram generated in a phase shift PGC demodulation system according to an embodiment of the invention, and fig. 3 is a light pulse and a phase waveform diagram output by an optical fiber interferometer in a phase shift PGC demodulation system according to an embodiment of the invention.
Firstly, a laser is adopted to generate an optical signal, after sinusoidal frequency modulation, the optical signal is input into an optical pulse modulator through an optical fiber to output periodic optical pulses (see fig. 2 (a)), and the optical pulse width is T p The repetition frequency of the light pulse is f s The repetition time period of the light pulse is T s The method comprises the steps of carrying out a first treatment on the surface of the Then inputting the light pulse to a first optical fiber coupler through an optical fiber, splitting the light pulse by the first optical fiber coupler to obtain three light pulses, and carrying out optical fiber delay and optical fiber beam combination treatment on the three light pulses to generate an optical pulse sequence consisting of the three light pulses; sequentially inputting the optical pulse sequences into a phase modulator, applying a specific phase modulation waveform (shown in fig. 2 (c)) to perform phase modulation to obtain a phase modulated optical pulse sequence, inputting the phase modulated optical pulse sequence into an optical fiber interferometer to generate interference, and outputting a group of interference optical pulse sequences (the interference signals of adjacent interference optical pulses have a phase difference of 2 pi/3 through phase modulation, shown in fig. 3 (d) and (e)); then, the interference light pulse sequence is input into a photoelectric converter to carry out photoelectric conversion and digital sampling, a sampling signal is correspondingly obtained, the sampling signal is output to a signal processing system through a cable to carry out time division decomposition processing, a sampling signal after three time division decomposition processing is obtained, and the three time division decomposition processing is carried out The processed sampling signals are demodulated through a phase shift PGC demodulation algorithm and subjected to high-pass filtering, and the average value of the demodulated signals after three paths of high-pass filtering is used as a final demodulation phase signal.
In one embodiment, in S2, the optical pulse is split by using a first coupler to obtain three optical pulses, which specifically includes: the optical pulse is input to the input end of the first optical fiber coupler, the beam splitting treatment is carried out through the first optical fiber coupler, the first optical pulse is output through the first output port of the first optical fiber coupler, the second optical pulse is output through the second output port of the first optical fiber coupler, and the third optical pulse is output through the third output port of the first optical fiber coupler.
In one embodiment, the optical fiber delay and optical fiber beam combination processing are performed on the three light pulses in S2, and an optical pulse sequence composed of the three light pulses is output, which specifically includes: the first optical pulse is directly input to a first input port of a second optical fiber coupler, the second optical pulse is input to a first optical fiber delay line, the second optical pulse is input to a second input port of the second optical fiber coupler after delay processing, the third optical pulse is input to a second optical fiber delay line, the third optical pulse is input to a third input port of the second optical fiber coupler after delay processing, and the second optical fiber coupler performs optical fiber beam combination processing on the input first optical pulse and the second and third optical pulses after delay processing and outputs an optical pulse sequence.
Specifically, an optical pulse is input into a first optical fiber coupler through an optical fiber, is split into three beams in the first optical fiber coupler, is output through a first output port of the first optical fiber coupler, and is directly input into a first input port of a second optical fiber coupler; the second optical pulse is output to the first optical fiber delay line from the second output port of the first optical fiber coupler, and is input to the second input port of the second optical fiber coupler after being delayed by a certain length of optical fiber; the third light pulse is output to the second optical fiber delay line from the third output port of the first optical fiber coupler, is input to the third input port of the second optical fiber coupler after being delayed by a certain length of optical fiber, and the second optical fiber coupler synthesizes three light pulses which are directly input and are input in a delayed manner to generate an optical pulse sequence consisting of three light pulses. The first fiber coupler and the second fiber coupler are 3 x 3 fiber couplers.
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, where the specific setting of L is:
wherein 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, T s The time period is repeated for the light pulse.
Specifically, after dividing the light pulse into three beams by the first optical fiber coupler, respectively inputting the three beams directly, inputting the three beams by the first optical fiber delay line delay, inputting the three beams by the second optical fiber delay line delay to the second optical fiber coupler, generating a group of light pulse sequences containing three beams of light pulses at the output port of the second optical fiber coupler, wherein the time interval between the light pulses is T s 3, the time interval between adjacent light pulse sequences is T s ，T s For the repetition time period of the light pulse, the light path loss is controlled to ensure that the peak power of the three light pulses is consistent, and the generated light pulse sequence is shown in figure 3.
In one embodiment, the fiber optic 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.
Specifically, referring to fig. 3, fig. 3 is a waveform diagram of an interference light pulse output by a fiber interferometer in a phase shift PGC demodulation system according to an embodiment of the invention. Wherein, fig. 3 (a) is the light pulse returned by the interferometer signal arm, fig. 3 (b) is the light pulse returned by the interferometer reference arm, and fig. 3 (c) is the interference light pulse at the interferometer output.
The fiber optic hydrophone adopts an unbalanced Michelson interferometer structure, the interferometer comprises a signal arm and a reference arm, and a length difference l exists between the fiber lengths of the two arms. Due to the difference in length l, there will be time between the two light waves returned via the signal arm and the reference arm Difference of each other
When the light pulse width T p Above the time difference τ, the two light pulses overlap and interfere at the interferometer output, as shown in FIG. 3, where the light pulses returned by the signal arm and the reference arm interfere in the overlapping shadows. For a set of input light pulse sequences, three interference light pulses will be generated, a first interference light pulse, a second interference light pulse and a third interference light pulse, respectively.
In one embodiment, the sampled signal in S4 contains optical relative intensity noise or circuit noise, and in S4, the sampled signal is input to the signal processing system to perform time division demodulation processing, so as to obtain a three-way time division-resolved sampled signal, and when the sampled signal includes the optical relative intensity noise, the time division-resolved sampled signal can be expressed as follows by a formula:
when the sampling signal includes circuit noise, the time-division-resolved sampling signal can be expressed as:
wherein V is i (t) is the sampling signal after the ith time solution time division processing at the moment t, A is the direct current amplitude value of the sampling signal, B is the alternating current amplitude value of the sampling signal, n Ii (t) is the optical relative intensity noise of the sampling signal after the ith time-division solution processing at the moment t, n Ci (t) is the circuit noise of the sampling signal after the ith time-division solution processing at the moment t, C is the modulation depth omega m For the modulation frequency of the PGC,
the phase of the i-th sampling signal at the time t.
In particular, when no noise is present in the systemInputting the interference light pulse sequence into a photoelectric converter, wherein the sampling frequency of the photoelectric converter is 3f s Sampling is carried out at each interference light pulse to obtain sampling signals, the sampling signals are input into a signal processing system for time division decomposition, extraction of 3 times 1 is carried out, three paths of sampling signals after time division decomposition corresponding to three interference light pulses are obtained, and the sampling signals are expressed as follows by a formula:
wherein V is 1 (t)、V 2 (t)、V 3 (t) the sampling signals after the first path, the second path and the third path of time division and time division are respectively processed,
the phases of the first interference light pulse, the second interference light pulse and the third interference light pulse respectively comprise detected phase signals +.>
And interferometer initial phase +.>
The phase difference between the phases of each interference light pulse is 2 pi/3, A is the DC amplitude of the sampling signal, B is the AC amplitude of the sampling signal, C is the modulation depth, omega m The frequency is modulated for PGCs.
When noise is present in the system, it will be converted into phase noise of the final demodulated phase signal according to the noise transfer characteristics of the PGC demodulation algorithm. The following two types of noise are mainly considered in this application Transfer of the demodulated phase signal to the output during PGC demodulation: optical relative intensity noise n I (t) and Circuit noise n C And (t) the optical relative intensity noise comprises the optical relative intensity noise of static operation of the laser, the additional optical relative intensity noise generated by modulating the laser and the like, and the circuit noise is mainly the total noise of the additive circuits such as photoelectric conversion, ADC quantization and the like. In general, the noise transmission conditions when various noises exist independently can be considered, and the transmission conditions can be overlapped when various noises exist simultaneously.
When there is optical relative intensity noise n in the system I At (t), the formula for time-division-processed sample signals at this time can be expressed as:
wherein, the liquid crystal display device comprises a liquid crystal display device,
wherein V is i (t) is the sampling signal after the ith time division processing at the moment t, n Ii (t) the optical relative intensity noise of the sampled signal after the ith time-division processing of the t time instant solution, and for the convenience of analysis, the optical relative intensity noise n of the sampled signal after the ith time-division processing of the t time instant solution Ii (t) decomposing into a superposition of second order wide stationary band-limited noise,
two-order wide and stable band-limited noise with independent optical relative intensity noise in the ith sampling signal and noise band width of [ -omega c /2,ω c /2]The index i indicates the i-th sampling signal.
When there is circuit noise n in the system C In the step (t), a formula of the sampling signal after the time division solution processing can be obtained by referring to the above method, and details are not repeated.
In one embodiment, in S5, PGC demodulation processing and high-pass filtering are performed on the three paths of sampling signals after the time division demodulation processing, so as to obtain three paths of demodulation phase signals after the high-pass filtering, which specifically includes:
s51, taking one path from any one path of sampling signals after three paths of time division and solution processing to carry out phase-locked detection and low-pass filtering to obtain two paths of detection signals;
s52, resolving the two paths of detection signals by adopting an arctangent algorithm to obtain a demodulation phase signal;
s53, performing high-pass filtering on the demodulation phase signals to obtain demodulation phase signals after high-pass filtering;
s54, another path is taken from the three paths of time division-resolved sampling signals until all the paths of time division-resolved sampling signals are selected, and the three paths of high-pass filtered demodulation phase signals are obtained through processing in steps S51 to S53.
In one embodiment, in S51, one of the three paths of sampling signals after the time division and solution processing is taken to perform phase-locked detection and low-pass filtering to obtain two paths of detection signals, and when the sampling signals include optical relative intensity noise, the specific formulas of the two paths of detection signals are as follows:
When the sampling signal includes circuit noise, the specific formula of the two paths of detection signals is as follows:
in the method, in the process of the invention,
the first and second detection signals of the sampling signal after the ith time-division solution processing are respectively introduced by the optical relative intensity noise at the t moment, B is the alternating current amplitude of the sampling signal, and +.>
Introducing first and second additive noise of the sampling signal after ith path of solution time division processing for t moment by optical relative intensity noise,/for the sampling signal>
The first and second path detection signals of the sampling signal after the ith path of time division processing are respectively introduced by circuit noise at the moment t,
first and second additive noise of the sampling signal after ith time division processing is introduced by circuit noise at t moment>
For the phase of the sampling signal after the time division processing of the ith solution at the moment of t, J k (C) Is a k-th order bessel function (k=1, 2.).
In one embodiment, in S52, the arctangent algorithm is used to calculate the two paths of detection signals to obtain a demodulation phase signal, where when the sampling signal includes optical relative intensity noise, the formula of the demodulation phase signal is specifically:
when the sampling signal contains circuit noise, the formula for demodulating the phase signal is specifically:
in the method, in the process of the invention,
demodulating phase signal for ith path at t moment, B is alternating current amplitude of sampling signal, J k (C) For the kth order bessel function (k=1, 2,.),/i>
First and second additive noise introduced by optical relative intensity noise in sampling signal after time division processing of ith solution at t moment +.>
First and second additive noise introduced by circuit noise in sampling signal after ith time division processing at t moment>
And solving the phase of the sampling signal after time division processing for the ith path at the t moment.
In one embodiment, in S5, the three demodulation phase signals are summed and averaged to obtain a final demodulation phase signal, where the final demodulation phase signal is specifically:
in the method, in the process of the invention,
for final demodulation of the phase signal at time t +.>
Demodulating the phase signal for the first path at time t, < >>
Demodulating the phase signal for the second path at time t, < >>
And demodulating the phase signal for the third path at the time t.
In particular, when there is optical relative intensity noise n in the system I At the time of (t), according to the principle of PGC demodulation algorithm, the three paths of time-division-processed sampling signals V are subjected to time division i (t) synchronously multiplying the carrier signal 1 frequency multiplication signal and the carrier signal 2 frequency multiplication signal respectively, and obtaining two paths of detection signals after low-pass filtering:
wherein, the liquid crystal display device comprises a liquid crystal display device,
first and second detection signals of the sampling signal after the ith time-division processing by introducing optical relative intensity noise at the time t are respectively V i (t) is the sampled signal after the ith time division processing at the time t, which is the convolution operator, cos omega m t is a frequency multiplication signal, cos2 omega m t is a frequency doubling signal, h LPF (t) is the impulse response function of the low-pass filter,>
first and second additive noise of the sampling signal after the ith-path solution time division processing are respectively introduced by optical relative intensity noise at the moment t, J k (C) As a k-th order bessel function (k=1, 2.), B is the ac amplitude of the sampled signal. Wherein the first additive noise and the second additive noise may be derived by:
wherein J is k (C) As a k-th order Bessel function, a ek ,a ok ,b ek ,b ok Are error term coefficients. To simplify the expression of formulas (8) and (9), define a ek ,a ok ,b ek ,b ok The 4 error term coefficients are specifically as follows:
the two paths of detection signals are calculated and processed by adopting an arctangent algorithm to obtain a demodulation phase signal, and the specific formula is as follows:
wherein J is k (C) As a bessel function of the kth order,
introducing first additive noise of sampling signal after ith path of solution time division processing by optical relative intensity noise at t moment +.>
From optical phase at time tAnd introducing second additive noise of the sampling signal after the ith time division solution processing to the intensity noise, wherein i=1, 2 and 3.
When there is circuit noise n in the system C In the step (t), the formulas of the detection signal and the demodulation phase signal can be obtained by referring to the above method, and detailed description is omitted.
Summing the three demodulation phase signals and taking an average value to obtain a final demodulation phase signal, wherein the specific formula is as follows:
in the method, in the process of the invention,
for final demodulation of the phase signal at time t +.>
Demodulating the phase signal for the first path at time t, < >>
Demodulating the phase signal for the second path at time t, < >>
And demodulating the phase signal for the third path at the time t.
When there is optical relative intensity noise n in the system I At the time of (t), the first additive noise and the second additive noise are converted into noise in the ith demodulation phase signal after being subjected to inverse tangent solution
The i-th demodulation phase signal can also be expressed as:
in the method, in the process of the invention,
demodulating the phase signal for the i-th path,/>
Noise in the phase signal is demodulated for the ith path introduced by the optical relative intensity noise.
Substituting equations (8) through (13) into equation (14) for simplified calculation and comparing with equation (16) for analysis, the noise in the demodulated phase signal output by the system due to the optical relative intensity noise can be expressed as:
it can be seen that the full band of the optical relative intensity noise is transferred to the demodulation phase signal and the noise of the demodulation phase signal is generated 
Phase +.>
And the modulation depth C. Due to interferometer phase
Includes the measured phase->
And interferometer initial phase +.>
While the interferometer initial phase +.>
Usually, random drift is generated due to disturbance of external environment, so that noise of demodulation phase signals output by a single-path sampling signal is +.>
Fluctuations will occur as the initial phase of the interferometer changes. As shown by simulation analysis, the highest fluctuation of the noise power spectrum of the output demodulation phase signal can reach 15dB, and when C is approximately equal to 2.55, the noise of the output demodulation phase signal follows +.>
The fluctuation of (2) is minimum and the fluctuation range is about 3dB.
When the input optical relative intensity noise is white gaussian noise, there are:
wherein, the liquid crystal display device comprises a liquid crystal display device,
is>
Is->
Single sideband power spectral density, S ω {n Ii Is n } is Ii Is>
Is second-order wide-stationary band-limited noise independent of optical relative intensity noise.
Taking the power spectrum of the formula (17), and obtaining the noise power spectrum of the demodulation phase signal output by the system due to the optical relative intensity noise by using the formula (18) as follows:
when there is circuit noise n in the system C (t) at the same time, the ith sampling signal can be usedNumber circuit noise n Ci (t) decomposing into a superposition of band-limited noise, the specific formula is:
wherein, the liquid crystal display device comprises a liquid crystal display device,
two-order wide-stable band-limited noise with independent circuit noise and noise band width of [ -omega c /2,ω c /2]。
Using the same analysis as the optical relative intensity noise transfer, the noise that can give rise to the demodulated phase signal output by the system due to circuit noise can be expressed as:
when the input circuit noise is Gaussian white noise, the noise power spectrum of the demodulation phase signal output by the system due to the circuit noise is obtained as follows:
wherein S is ω {n Ci Is n } is Ci Single sideband power spectral density of (a).
As can be seen from equation (21), only (ω) of the circuit noise m /2,5ω m And/2) the noise in the frequency band is transferred to the final demodulation phase signal, the noise of the demodulation phase signal converted by the noise transfer circuit is still related to the initial phase of the interferometer, and the noise is fluctuated along with the drift of the initial phase of the interferometer, so that the noise level of the final demodulation phase signal of the system is fluctuated with larger amplitude.
As can be seen from the observations of equations (19) and (22), both for the optical relative intensity noise and for the circuit noise, the noise of the demodulated phase signal after demodulation by PGC arctangent algorithm is related to the interferometer initial phase. If the interferometer output of the interferometer under different initial phase conditions can be obtained, stable noise can be obtained by carrying out average processing on the demodulation phase signals of different initial phases by utilizing the law that the noise of the demodulation phase signals changes along with the initial phase of the interferometer, and the influence of the initial phase change of the interferometer on the noise of the demodulation phase signals is eliminated.
When optical relative intensity noise exists in the system, the optical relative intensity noise in the three-path interference optical signal is set as three independent noise n with the same power spectrum characteristic in consideration that the sampling time of the three-path interference optical pulse cannot be absolutely synchronous, and the optical relative intensity noise is usually broadband white noise and has short coherence time Ii (i=1, 2, 3), based on this assumption, the phase noise caused by the optical relative intensity noise in the three-way demodulated phase signal can be obtained according to the formula (17) as:
noise of the demodulated phase signal of the system output caused by the optical relative intensity noise can be calculated according to formulas (23), (24) and (25):
when the input optical relative intensity noise is Gaussian white noise, the three sampling signals have the same noise spectrum level due to the same optical intensity noise source, namely S ω {n I1 }＝S ω {n I2 }＝S ω {n I3 Collectively denoted as S ω {n I Power spectrum the noise of the demodulated phase signal of equation (26) and according to equation (18), the output demodulated phase signal noise power spectrum due to the optical relative intensity noise can be reduced to:
according to the trigonometric function relation, because:
so there are:
substituting equations (28), (29) and (30) into equation (27) yields the noise power spectrum of the final output demodulated phase signal due to the optical relative intensity noise as:
When there is circuit noise n in the system C At (t), according to equation (21), due to photoelectric conversion and sampling of three interference light pulses at different times, the circuit noises are uncorrelated, thereby setting the circuit noises as three independent noises having the same power spectrum characteristics
And->
The noise in the three paths of demodulation phase signals caused by the circuit noise is respectively:
the noise of the system output demodulation phase signal caused by the circuit noise can be calculated from the formulas (32), (33) and (34). For three-way sampling signals, the circuit noise has the same noise spectrum level, i.e. S, due to the same signal sampling circuit ω {n C1 }＝S ω {n C2 }＝S ω {n C3 Collectively denoted as S ω {n C }. With reference to the above reasoning, the noise power spectrum of the final output demodulation phase signal caused by circuit noise is further derived as follows:
comparing the conventional PGC demodulation algorithm with the phase shift PGC demodulation algorithm proposed in the present invention, the noise power spectrum of the final output demodulation phase signal caused by the optical relative intensity noise and the circuit noise can be expressed as:
(1) Conventional PGC algorithm
(2) Phase shift PGC algorithm
It can be seen that compared with the conventional PGC demodulation algorithm, the phase shift PGC demodulation algorithm provided by the invention has the advantages that the noise spectrum of the final output demodulation phase signal caused by the phase shift PGC demodulation algorithm, whether the phase shift PGC demodulation algorithm is used for light relative intensity noise or circuit noise, is no longer in phase with the interferometer 
In this regard, the system will be able to obtain a stable noise output, independent of the initial phase drift of the interferometer caused by the external environment.
The system comprises a laser, an optical pulse modulator, a first optical fiber coupler, a first optical fiber delay line, a second optical fiber coupler, a phase modulator, an optical fiber interferometer, an optical-to-electrical converter and a signal processing system, wherein the laser is connected with the optical pulse modulator, the optical pulse modulator is connected with the input end of the first optical fiber coupler, the first output end of the first optical fiber coupler is directly connected with the first input end of the second optical fiber coupler, the second output end of the first optical fiber coupler is connected with 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 with 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 with the output end of the second optical fiber coupler, the other end of the phase modulator is connected with the optical fiber interferometer, one end of the optical-to-electrical converter is connected with the optical fiber interferometer, the other end of the phase modulator is connected with the signal processing system, and the signal processing system is also connected with the laser pulse modulator, the optical pulse modulator and the phase modulator, wherein the phase modulator is connected with the interference modulator:
The laser is used for generating an optical signal, and the optical signal is input to the optical pulse modulator after being modulated by sinusoidal frequency;
the optical pulse modulator is used for generating periodic optical pulses;
the first optical fiber coupler is used for splitting optical fibers, periodic light pulses are input from the input end of the first optical fiber coupler, and three light pulses are correspondingly obtained after processing;
the first optical fiber delay line and the second optical fiber delay line are used for delaying the optical pulse;
the second optical fiber coupler is used for synthesizing the three input optical pulses to generate an optical pulse sequence;
the phase modulator is used for carrying out phase modulation on the optical pulse sequence to obtain an optical pulse sequence after phase modulation;
the optical fiber interferometer is used for sensing external acoustic signals, generating interference on the optical pulse sequence after phase modulation and outputting the interference optical pulse sequence;
the photoelectric converter is used for performing photoelectric conversion and digital sampling on the interference light pulse sequence, generating a digital sampling signal and outputting the digital sampling signal to the signal processing system through a cable;
the signal processing system is used for demodulating the received digital sampling signal, outputting a sine wave signal to the laser for carrying out sine frequency modulation on the optical signal, outputting a pulse modulation signal to the optical pulse modulator for generating optical pulses, and outputting a phase modulation signal with a specific waveform to the phase modulator for carrying out phase modulation.
Specifically, referring to fig. 4, fig. 4 is a schematic structural diagram of an interference type optical fiber hydrophone phase-shifting PGC demodulation system according to an embodiment of the invention.
An interference type optical fiber hydrophone phase shift PGC demodulation device comprises 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, a photoelectric detector 9 and a signal processing system 10. After being modulated by sine frequency, the light emitted by the laser 1 is input into an input port of the optical pulse modulator 2 through an optical fiber, and then is output by corresponding optical pulse after passing through the optical pulse modulator 2; 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, and the first beam of light is output by the first output port of the first optical fiber coupler 3 and is directly input into the first input port of the second optical fiber coupler 6; the second beam of light is output to the optical fiber delay line 4 through the second output port of the first optical fiber coupler 3, and is input to the second input port of the second optical fiber coupler 6 after being delayed by a certain length of optical fiber; the third beam of light is output to the second optical fiber delay line 5 from the third output port of the first optical fiber coupler 3, and is input to the third input port of the second optical fiber coupler 6 after being subjected to optical fiber delay with a certain length; then the second optical fiber coupler 6 synthesizes the three light beams to generate an optical pulse sequence composed of three light pulses, the optical pulse sequence is output to an input port of the optical fiber interferometer 8 through an output port of the second optical fiber coupler 6, interference is generated after passing through the optical fiber interferometer 8, and a group of interference optical pulse sequences are output; the interference light pulse sequence is input into an input port of a photoelectric converter 9 through an output port of an optical fiber interferometer 8, photoelectric conversion is carried out in the photoelectric converter 9, and digital sampling is completed, so that a sampling 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 the measured phase information output is obtained after the sampled digital signal is processed by a phase shift PGC demodulation algorithm in the signal processing system 10.
In a further aspect, the laser is a tunable narrow linewidth laser, such as a fiber laser, a semiconductor laser, a solid state laser, or the like.
In a further aspect, 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), or the like.
In a further scheme, the optical fiber interferometer is a sensing optical component of an optical fiber hydrophone, an unbalanced reflection type Michelson optical fiber interferometer structure is adopted, the interferometer comprises a signal arm and a sensing arm, the arm difference of the two arms is l, and a Faraday rotation reflecting mirror is adopted as a reflecting end to eliminate the influence of polarization fading.
In a further scheme, the photoelectric converter is a photoelectric signal conversion device, and comprises a photoelectric detector, a preamplifier and an analog-to-digital converter, wherein the photoelectric signal conversion device is used for converting an interference light pulse signal output by the optical fiber interferometer into an electric signal and digitally sampling the electric signal to obtain a corresponding sampling signal.
In a further aspect, the signal processing system is a digital signal processing device, such as an FPGA, DSP or computer.
According to the demodulation method and the demodulation system for the phase shift PGC of the interference type optical fiber hydrophone, the oblique wave phase modulation technology is adopted, and the unbalanced interferometer structure is combined, so that three interference outputs with different initial phases are obtained, PGC demodulation, 3X3 coupler phase shift demodulation and phase shift PGC demodulation algorithm demodulation can be flexibly selected, and the demodulation method and the demodulation system have good algorithm redundancy capability, and are specifically characterized in that:
(1) When the requirements on the self-noise and the noise stability of the system phase are higher, a phase shift PGC demodulation scheme is selected, so that good noise performance can be obtained;
(2) When the noise stability requirement is not high and the system power consumption requirement is high, a PGC demodulation scheme is selected, the modulation signal of the phase modulator is closed to reduce the system power consumption, and the sampling rate of the PGC demodulation algorithm can be 3 times that of the phase shift PGC demodulation algorithm, so that the dynamic range is improved;
(3) When the PGC modulation cannot meet the requirement or the requirement on the dynamic range of the system is higher due to the failure of the laser frequency modulation, the laser frequency modulation can be turned off, a 3X3 coupler phase shift demodulation algorithm is selected, and the dynamic range can be improved by about 20dB under the condition of the same sampling rate.
The method and the system for demodulating the phase shift PGC of the interference type optical fiber hydrophone provided by the invention are described in detail. The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to facilitate an understanding of the core concepts of the invention. It should be noted that it will be apparent to those skilled in the art that various modifications and adaptations of the invention can be made without departing from the principles of the invention and these modifications and adaptations are intended to be within the scope of the invention as defined in the following claims.
Claims (10)
1. A method for demodulating an interferometric fiber optic hydrophone phase shifted PGC, the method comprising:
s1, generating an optical signal by using a laser, performing sinusoidal frequency modulation on the optical signal, outputting sinusoidal frequency modulated light waves, inputting the sinusoidal frequency modulated light waves into an optical pulse modulator, and outputting periodic optical pulses after processing;
s2, carrying out optical fiber beam splitting on the optical pulses by adopting a first coupler to obtain three optical pulses, carrying out optical fiber delay and optical fiber beam combination treatment on the three optical pulses, and outputting an optical pulse sequence consisting of the three optical pulses;
s3, carrying out phase modulation on the optical pulse sequence through a phase modulator to obtain a phase modulated optical pulse sequence, inputting the phase modulated optical pulse sequence into an optical fiber interferometer, and outputting an interference optical pulse sequence through interference treatment;
s4, inputting the interference light pulse sequence into a photoelectric converter for photoelectric conversion and digital sampling to obtain a sampling signal, and inputting the sampling signal into a signal processing system for time division decomposition processing to obtain three paths of sampling signals after time division decomposition processing;
and S5, performing PGC demodulation processing and high-pass filtering on the three paths of the sampling signals subjected to the time division demodulation processing to obtain three paths of demodulation phase signals subjected to the high-pass filtering, summing the three paths of demodulation phase signals subjected to the high-pass filtering, and taking an average value to obtain a final demodulation phase signal.
2. The method for demodulating the phase-shifted PGC of the interference type optical fiber hydrophone according to claim 1, wherein in S2, the optical pulse is split by the optical fiber using the first coupler to obtain three optical pulses, specifically comprising: the optical pulse is input to the input end of the first optical fiber coupler, the beam splitting treatment is carried out through the first optical fiber coupler, the first optical pulse is output through the first output port of the first optical fiber coupler, the second optical pulse is output through the second output port of the first optical fiber coupler, and the third optical pulse is output through the third output port of the first optical fiber coupler.
3. The method for demodulating the phase shift PGC of the interference type optical fiber hydrophone according to claim 2, wherein the step S2 of performing optical fiber delay and optical fiber beam combination processing on the three optical pulses outputs an optical pulse sequence consisting of the three optical pulses, specifically includes: the first optical pulse is directly input to a first input port of a second optical fiber coupler, the second optical pulse is input to a first optical fiber delay line, the second optical pulse is input to a second input port of the second optical fiber coupler after delay processing, the third optical pulse is input to a second optical fiber delay line, the third optical pulse is input to a third input port of the second optical fiber coupler after delay processing, and the second optical fiber coupler performs optical fiber beam combination processing on the input first optical pulse and the second and third optical pulses after delay processing and outputs an optical pulse sequence.
4. The method for demodulating the phase shift PGC of the interference type optical fiber hydrophone according to claim 3, wherein the length of the first optical fiber delay line is L, the length of the second optical fiber delay line is 2L, and the specific arrangement of L is as follows:
wherein 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, T s The time period is repeated for the light pulse.
5. The method for demodulating the phase-shifted PGC of the interferometric fiber optic hydrophone of claim 4, wherein the sampled signal in S4 contains optical relative intensity noise or circuit noise, and the sampled signal is input to a signal processing system for time-division-resolving processing in S4 to obtain a three-way time-division-resolved sampled signal, and when the sampled signal includes the optical relative intensity noise, the time-division-resolved sampled signal can be expressed as:
when the sampling signal includes circuit noise, the time-division-resolved sampling signal may be expressed as:
wherein V is i (t) is the sampling signal after the ith time solution time division processing at the moment t, A is the direct current amplitude value of the sampling signal, B is the alternating current amplitude value of the sampling signal, n Ii (t) is the optical relative intensity noise of the sampling signal after the ith time-division solution processing at the moment t, n Ci (t) is the circuit noise of the sampling signal after the ith time-division solution processing at the moment t, C is the modulation depth omega m For the modulation frequency of the PGC,
the phase of the i-th sampling signal at the time t.
6. The method for demodulating the phase shift PGC of the interference type optical fiber hydrophone according to claim 5, wherein in S5, PGC demodulation processing and high-pass filtering are performed on three paths of the sample signals after the time division demodulation processing, so as to obtain three paths of demodulated phase signals after the high-pass filtering, respectively, specifically including:
s51, any one of the three paths of sampling signals after the time division and demodulation processing is taken to carry out phase-locked detection and low-pass filtering, so that two paths of detection signals are obtained;
s52, resolving the two paths of detection signals by adopting an arctangent algorithm to obtain demodulation phase signals;
s53, carrying out high-pass filtering on the demodulation phase signal to obtain a demodulation phase signal after high-pass filtering;
s54, another path is taken from the three paths of sampling signals after the time division and solution processing until all the three paths of sampling signals after the time division and solution processing are selected, and the three paths of demodulation phase signals after the high-pass filtering are obtained through the processing of steps S51 to S53.
7. The method for demodulating the phase-shifted PGC of the interferometric fiber optic hydrophone according to claim 6, wherein in S51, one of the three sampled signals after the time division demodulation is phase-locked detected and low-pass filtered to obtain two detected signals, and when the sampled signals include optical relative intensity noise, the specific formulas of the two detected signals are as follows:
When the sampling signal comprises circuit noise, the specific formulas of the two paths of detection signals are as follows:
in the method, in the process of the invention,
respectively introducing optical relative intensity noise into sampling signals after ith path of solution time division processing at t momentB is the alternating current amplitude of the sampling signal, +.>
Introducing first and second additive noise of the sampling signal after ith path of solution time division processing for t moment by optical relative intensity noise,/for the sampling signal>
The first and second path detection signals of the sampling signal after the ith path of time division processing are respectively introduced by circuit noise at the moment t,
first and second additive noise of the sampling signal after ith time division processing is introduced by circuit noise at t moment>
For the phase of the sampling signal after the time division processing of the ith solution at the moment of t, J k (C) Is a k-th order bessel function (k=1, 2.).
8. The method for demodulating the phase shift PGC of the interferometric fiber optic hydrophone according to claim 7, wherein in S52, the two paths of the detected signals are resolved by using an arctangent algorithm to obtain a demodulated phase signal, and when the sampled signal contains optical relative intensity noise, the formula of the demodulated phase signal is specifically as follows:
when the sampling signal contains circuit noise, the formula of the demodulation phase signal is specifically:
In the method, in the process of the invention,
demodulating phase signal for ith path at t moment, B is alternating current amplitude of sampling signal, J k (C) For the kth order bessel function (k=1, 2,.),/i>
First and second additive noise introduced by optical relative intensity noise in sampling signal after time division processing of ith solution at t moment +.>
First and second additive noise introduced by circuit noise in sampling signal after ith time division processing at t moment>
And solving the phase of the sampling signal after time division processing for the ith path at the t moment.
9. The method for demodulating the phase-shifted PGC of the interferometric fiber optic hydrophone of claim 8, wherein in S5, summing and averaging three demodulation phase signals to obtain a final demodulation phase signal, the final demodulation phase signal is specifically:
in the method, in the process of the invention,
for final demodulation of the phase signal at time t +.>
Demodulating the phase signal for the first path at time t, < >>
Demodulating the phase signal for the second path at time t, < >>
And demodulating the phase signal for the third path at the time t.
10. An interferometric fiber optic hydrophone phase shift PGC demodulation system for demodulation using the method of demodulating an interferometric fiber optic hydrophone phase shift PGC according to any one of claims 1-9, the system comprising a laser, an optical pulse modulator, a first fiber coupler, a first fiber delay line, a second fiber coupler, a phase modulator, a fiber interferometer, an optical-to-electrical converter, and a signal processing system, the laser being connected to the optical pulse modulator, the optical pulse modulator being connected to an input of the first fiber coupler, a first output of the first fiber coupler being directly connected to a first input of the second fiber coupler, a second output of the first fiber coupler being connected to a second input of the second fiber coupler via the first fiber delay line, a third output of the first fiber coupler being connected to a third input of the second fiber coupler via the second fiber delay line, one end of the phase modulator being connected to an output of the second coupler, the other end being connected to the interferometer, and the optical-to the signal processing system, wherein the optical pulse modulator is connected to the other end of the optical pulse modulator, the optical-to the signal processing system:
The laser is used for generating an optical signal, and the optical signal is input to the optical pulse modulator after being modulated by sinusoidal frequency;
the optical pulse modulator is used for generating periodic optical pulses;
the first optical fiber coupler is used for splitting optical fibers, the periodic light pulses are input from the input end of the first optical fiber coupler, and three light pulses are correspondingly obtained after processing;
the first optical fiber delay line and the second optical fiber delay line are used for delaying the optical pulse;
the second optical fiber coupler is used for synthesizing the three input optical pulses to generate an optical pulse sequence;
the phase modulator is used for carrying out phase modulation on the optical pulse sequence to obtain an optical pulse sequence after phase modulation;
the optical fiber interferometer is used for sensing external acoustic signals, generating interference on the optical pulse sequence after the phase modulation and outputting an interference optical pulse sequence;
the photoelectric converter is used for carrying out photoelectric conversion and digital sampling on the interference light pulse sequence, generating a digital sampling signal and outputting the digital sampling signal to the signal processing system through a cable;
the signal processing system is used for demodulating the received digital sampling signal, outputting a sine wave signal to the laser for carrying out sine frequency modulation on the optical signal, outputting a pulse modulation signal to the optical pulse modulator for generating optical pulses, and outputting a phase modulation signal with a specific waveform to the phase modulator for carrying out phase modulation.
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