CN-121740212-B - PGC optical fiber hydrophone system common mode noise suppression method and system

CN121740212BCN 121740212 BCN121740212 BCN 121740212BCN-121740212-B

Abstract

The application relates to a method and a system for suppressing common mode noise of a PGC optical fiber hydrophone system, and belongs to the technical field of optical fiber sensing. The application introduces a 3X 3 reference interferometer into the PGC-based optical fiber hydrophone system, and combines two paths of reference interference signals with fixed phase difference into a reference signal by using the 3X 3 reference interferometer, so that the relation between the initial phase of the sensing interference signal and the initial phase of the reference signal meets the pre-deduced initial phase condition of strong suppression effect of photoelectric common mode noise, namely, the initial phases of the two interferometers only need to be different In the noise suppression process, a light intensity compensation method is adopted, the intensity of interference pulses is divided by the intensity of accompanying amplitude modulation pulses so as to eliminate the influence of accompanying amplitude modulation, the phase locking capacity of reference signals is improved, and finally the common mode noise suppression effect can be improved.

Inventors

WANG JIANFEI
LI YATAO
ZHAO JIAZE
MENG ZHOU
CHEN MO
HU XIAOYANG
LU YANG
BIAN QIANG
CHEN YU

Assignees

中国人民解放军国防科技大学

Dates

Publication Date: 20260512
Application Date: 20260228

Claims (9)

1. The common mode noise suppression system of the PGC optical fiber hydrophone system is characterized by comprising a PGC pulse generating device, an arbitrary waveform generator, a1 multiplied by 2 coupler, two delay optical fibers, a sensing interferometer, a 3 multiplied by 3 reference interferometer, three attenuators, a detection system and a demodulation system; The PGC pulse generating device is used for receiving signals of any waveform generator, modulating and generating carrier pulses and sending the carrier pulses to the 1X 2 coupler, wherein the carrier pulses are input into the sensing interferometer and the 3X 3 reference interferometer through the 1X 2 coupler to generate sensing interference pulses and two reference interference pulses, and each interference pulse is input into the detection system after passing through the corresponding attenuator and the delay optical fiber respectively; The detection system is used for performing electric signal conversion and digital-to-analog conversion on each interference pulse and outputting a sensing interference signal And two reference interference signals And (3) with Receiving two associated amplitude modulation pulses generated by carrier pulse transmission at the same time, inputting the two associated amplitude modulation pulses into a demodulation system, and dividing the interference pulse intensity by the associated amplitude modulation pulse intensity by utilizing a light intensity compensation method to eliminate the influence of the associated amplitude modulation; after the demodulation system adopts PGC to demodulate each interference signal, firstly, an elliptic fitting method pair after eliminating the influence of associated amplitude modulation is utilized And (3) with Calibrating and combining into a reference signal So that Initial phase and phase The primary phase meets the pre-deduced primary phase condition of strong suppression of photoelectric common mode noise, namely, the difference of two primary phases Integer times of (2), and then to And Respectively carrying out the subtraction of the time domain outputs obtained by PGC detection to obtain the time domain output after the strong suppression of the photoelectric common mode noise; The 3X 3 reference interferometer comprises a 3X 3 coupler, a first reference optical fiber, a second reference optical fiber, a third delay optical fiber, a third Faraday rotator, a fourth Faraday rotator and a fifth Faraday rotator, wherein a first port of the 3X 3 coupler is used for receiving carrier pulses, a second port of the 3X 3 coupler is used for outputting second reference interference pulses generated by the 3X 3 reference interferometer, a third port of the 3X 3 coupler is used for outputting first reference interference pulses generated by the 3X 3 reference interferometer, a fourth port of the 3X 3 coupler is connected to the third Faraday rotator through the first reference optical fiber, a fifth port of the 3X 3 coupler is connected to the fourth Faraday rotator through the third delay optical fiber, and a sixth port of the 3X 3 coupler is connected to the fifth Faraday rotator through the second reference optical fiber.
2. The PGC fiber hydrophone system common mode noise suppression system according to claim 1, wherein the PGC pulse generator comprises a laser, an optical isolator and an acousto-optic modulator which are connected in sequence, wherein the modulation interfaces of the laser and the acousto-optic modulator are connected with the output end of an arbitrary waveform generator; the laser is used for carrying out optical frequency modulation according to the sine signal input by the arbitrary waveform generator and outputting a PGC continuous optical signal to the optical isolator; the optical isolator is used for ensuring the unidirectional transmission of PGC continuous optical signals from the laser to the direction of the acousto-optic modulator; The acousto-optic modulator is used for modulating the intensity of the received PGC continuous optical signal according to the pulse signal input by the arbitrary waveform generator, and finally generating carrier pulses.
3. The system of claim 2, wherein the sensing interferometer comprises a2 x2 coupler, a first sensing fiber, a second sensing fiber, a first faraday rotator, and a second faraday rotator, wherein a first port of the 2 x2 coupler is configured to receive the carrier pulse, a second port of the 2 x2 coupler is configured to output a sensing interference pulse generated by the sensing interferometer, a third port of the 2 x2 coupler is coupled to the first faraday rotator via the first sensing fiber, and a fourth port of the 2 x2 coupler is coupled to the second faraday rotator via the second sensing fiber.
4. The system of claim 1, wherein the detection system comprises a1 x 3 coupler, a photodetector, and a digital-to-analog converter connected in sequence; The 1X 3 coupler is used for receiving a sensing interference pulse, a first reference interference pulse, a second reference interference pulse and two associated amplitude modulation pulses generated in the carrier pulse transmission process, wherein the sensing interference pulse is input into the detection system through a first attenuator and a first delay optical fiber, the first reference interference pulse is input into the detection system through a second attenuator and a second delay optical fiber, the second reference interference pulse is input into the detection system through a third attenuator, the first associated amplitude modulation pulse is generated through a third delay optical fiber and a third attenuator after the carrier pulse sent by the PGC pulse generating device is reflected by a fourth Faraday optical mirror, and the second associated amplitude modulation pulse is generated through the third delay optical fiber, the second attenuator and the second delay optical fiber after the carrier pulse sent by the PGC pulse generating device is reflected by the fourth Faraday optical mirror; The photoelectric detector is used for carrying out electric signal conversion on each received interference pulse; The input end of the digital-to-analog converter is connected with the output end of the arbitrary waveform generator and is used for carrying out digital-to-analog conversion on the electric signals converted by each interference pulse according to the synchronous signals and the acquisition trigger signals provided by the arbitrary waveform generator and outputting sensing interference signals First reference interference signal And a second reference interference signal 。
5. The system of claim 4, wherein the time division of each pulse received in the detection system is controlled by the length of each delay fiber, and the 5 pulses received in the detection system in a single repetition period have a certain time delay, and do not affect each other, wherein the 5 pulses are respectively a first reference interference pulse, a second reference interference pulse, a sensing interference pulse, a first accompanying amplitude modulation pulse and a second accompanying amplitude modulation pulse; The time interval between the arrival of the first reference interference pulse and the arrival of the second reference interference pulse are regulated and controlled through a second delay optical fiber, the time interval between the arrival of the second reference interference pulse and the arrival of the sensing interference pulse are regulated and controlled through a first delay optical fiber, the time interval between the arrival of the sensing interference pulse and the arrival of the first accompanying amplitude modulation pulse are regulated and controlled through a third delay optical fiber in the 3 x 3 reference interferometer, and the time interval between the arrival of the first accompanying amplitude modulation pulse and the arrival of the second accompanying amplitude modulation pulse are regulated and controlled through a second delay optical fiber.
6. A PGC fiber optic hydrophone system common mode noise suppression system as claimed in claim 1, wherein three attenuators are used to adjust the peak values of each interference pulse input to the photodetectors in the detection system, ensuring that the peak values of the sensing interference pulse, the first reference interference pulse and the second reference interference pulse are substantially balanced and at a maximum value in the state where the photodetectors are not saturated, thereby reducing the effects of additive noise sources other than common mode.
7. The PGC fiber optic hydrophone system common mode noise suppression system according to claim 1, wherein the initial phase condition of the strong suppression of the photoelectric common mode noise is an initial phase condition of the best effect of the strong suppression of the photoelectric common mode noise obtained by deriving a theoretical formula of PSD value from a PGC noise model and using a minimum value of PSD as a constraint condition, the derivation process includes: Supposing sensing interferometer The primary phase of the obtained sensing interference signal is Reference interferometer The primary phase of the obtained reference interference signal is The phase noise source and the multiplicative noise source picked up by the two interferometers are the same, namely , While additive noise sources are different, i.e This is because the interference signals obtained by the two interferometers need to be detected and acquired at different times by the same photodetector and D/A converter in the detection system, but the PSD values of the two interferometers are identical, i.e When only noise is considered, the time domain output expression of the phase signals output by the interference signals of the two interferometers after the interference signals are detected by the PGC is as follows: ; Wherein, the To sense the output phase noise of the interferometer, For the output phase noise of the reference interferometer, In order to sense the time-domain output, For the reference time-domain output to be referred to, For sensing the phase noise source of the interferometer, As a source of phase noise for the reference interferometer, As a source of the phase noise, As a source of multiplicative noise for the sensing interferometer, As a multiplicative noise source of the reference interferometer, As a source of multiplicative noise, As an additive noise source for the sensing interferometer, As an additive noise source of the reference interferometer, The output phase noise PSD value of the additive noise source of the sensing interferometer, An output phase noise PSD value that is an additive noise source of the reference interferometer; after the detection of the PGC signal, And (3) with Subtracting the resulting time domain signals The method comprises the following steps: ; Wherein, the And Respectively, the phase noise source superposition coefficients are in And The value of the position is taken out, And Respectively, the multiplicative noise source superposition coefficients are in And The value of the position is taken out, And Respectively, additive noise source superposition coefficients are in And The value of the position is taken out, Representing a convolution operation and, Is the unit impulse response function of the low pass filter, And A first order bezier function and a second order bezier function, For the order of the number of steps, For the carrier frequency of the PGC, In order to be able to take time, For the amplitude of the direct voltage of the interference signal, Visibility of interference signal fringes; For a pair of High-pass filtering and Fourier transforming to obtain its frequency spectrum The method comprises the following steps: ; Wherein, the Is the transfer function of the low-pass filter, In order to be of an angular frequency, Is the spectral amplitude of the phase noise source, For the spectral amplitude of the multiplicative noise source, For sensing the spectral amplitude of the additive noise source of the interferometer, Spectral amplitude of an additive noise source that is a reference interferometer; Then, the time domain signal obtained by subtraction is obtained according to the wiener-Xin Qin theorem and the white noise approximate condition The PSD of (2) is: ; Wherein, the Is the power spectral density of the phase noise source, For the power spectral density of the multiplicative noise source, The power spectral density of the additive noise source of the sensing interferometer, A power spectral density of an additive noise source that is a reference interferometer; to reduce direct time domain signals With PSD value The minimum value is taken as a constraint condition, and the initial phase condition for realizing the optimal comprehensive strong suppression effect of the photoelectric common mode noise is obtained by solution , wherein, Being an integer, the phase noise source effects and multiplicative noise source effects will be completely cancelled at this time, i.e.: 。
8. A method of PGC fiber optic hydrophone system common mode noise suppression, the method being implemented based on a PGC fiber optic hydrophone system common mode noise suppression system as claimed in any of claims 1-7, the method comprising: Step 1, obtaining a sensing interference signal output by a sensing interferometer And a first reference interference signal output by a 3 x 3 reference interferometer And a second reference interference signal ; Step 2, calibrating the two reference interference signals by adopting an elliptic fitting method after eliminating the influence of associated amplitude modulation to obtain direct current bias voltages and alternating current amplitude coefficients of the two reference interference signals, and respectively removing the direct current bias voltages of the two reference interference signals, And Expressed as: ; Wherein, the And Respectively is And Is used for the direct current bias voltage of the (c), And Respectively is And Is a coefficient of ac amplitude; Is a phase term resulting from the integration of the signal frequency; And Respectively is And Is a primary phase parameter of (a); Step 3, respectively sensing interference signals PGC signal detection is carried out on the two reference interference signals after the DC offset voltage is removed, sensing time domain output, first reference time domain output and second time domain output are obtained, average is carried out, initial phase parameters of the sensing interference signals, the first reference interference signals and the second reference interference signals are respectively obtained, and the initial phase parameters are respectively expressed as 、 And ; Step 4, utilizing 、、、 And Calculating to obtain two superposition coefficients And Expressed as: ; step 5, according to And For a pair of And Performing linear combination to obtain reference signals So that the interference signal is sensed Initial phase and reference signal The relation between the initial phases meets the pre-deduced initial phase condition of the strong suppression of the photoelectric common mode noise, namely the initial phase difference between the initial phase of the sensing interference signal and the initial phase of the reference signal Integer multiples of (2); Step 6, for the reference signal Performing PGC signal detection to obtain reference time domain output; and 7, subtracting the sensing time domain output from the reference time domain output to obtain the time domain output after the strong suppression of the photoelectric common mode noise.
9. The method for suppressing common-mode noise of a PGC fiber optic hydrophone system according to claim 8, wherein calibrating the two reference interference signals by an elliptic fitting method after eliminating the associated amplitude modulation effects to obtain dc offset voltages and ac amplitude coefficients of the two reference interference signals comprises: After the intensity of the interference pulse is divided by the intensity of the associated amplitude modulation pulse by adopting a light intensity compensation method to eliminate the influence of the associated amplitude modulation, the DC bias voltage and the AC amplitude coefficient of two reference interference signals are obtained by adopting an elliptic fitting method, wherein the elliptic fitting method comprises the following steps: Acquiring reference interference signal pairs for a period of time And drawing to form a Lissajous figure; Fitting an ellipse closest to the lissajous diagram by using a least square method, wherein the equation of the ellipse is as follows: ; Wherein, the Is the coefficient obtained after fitting; according to the fitting coefficient, the DC offset voltage is calculated as follows: ; ; According to the fitting coefficient and the calculated DC offset voltage, an AC amplitude coefficient is calculated as follows: ; 。

Description

PGC optical fiber hydrophone system common mode noise suppression method and system Technical Field The application relates to the technical field of optical fiber sensing, in particular to a PGC optical fiber hydrophone system common mode noise suppression method and system. Background In a deep sea fiber optic hydrophone system, photoelectric noise is a key factor affecting the detection performance of the system. Such noise sources include light source noise, optical amplifier noise, acousto-optic modulator noise, photodetector noise, analog to digital converter noise, cable transmission noise, additional noise introduced by signal detection methods, and the like. As the application of the optical fiber hydrophone system gradually goes to deep sea, the photoelectric noise of the system gradually exceeds the environmental noise, so that comprehensive suppression of phase noise converted by various photoelectric noise sources is needed to meet the application requirements of the deep sea. In the prior art, an acoustic insensitive interferometer is generally introduced into a system as a reference interferometer, phase noise generated by the noise source is picked up by the reference interferometer, and can be regarded as common mode noise of the reference interferometer and the sensing interferometer, and then the common mode noise can be suppressed by using a direct subtraction, cross multiplication subtraction or self-adaptive filtering method. However, it has been found in practice that in a phase-generated carrier (PGC) signal detection system, the noise suppression effect of the above-described direct subtraction, cross-multiply subtraction, or adaptive filtering common-mode noise suppression method is not stable. The method can not inhibit high-frequency phase noise sources and intensity noise sources by direct subtraction, can inhibit phase common-mode noise sources by cross multiplication subtraction, but can not inhibit phase noise converted by the intensity noise sources through a signal detection method because a PGC method is still needed to detect phase signals finally, and can not avoid accidental mismatch situations by completing an initial phase matching process by an adaptive filtering method, which is unacceptable for a deep sea optical fiber vector hydrophone vertical array system which works completely autonomously. Disclosure of Invention Based on the above, it is necessary to provide a method and a system for suppressing common mode noise of a PGC optical fiber hydrophone system, which can comprehensively suppress the noise of a photoelectric device, the noise of optical cable transmission, and the additional noise introduced by photoelectric signal detection as common mode noise, so as to effectively suppress the photoelectric common mode noise of a deep sea optical fiber hydrophone system. A PGC optical fiber hydrophone system common mode noise suppression system comprises a PGC pulse generating device, an arbitrary waveform generator, a1 multiplied by 2 coupler, two delay optical fibers, a sensing interferometer, a 3 multiplied by 3 reference interferometer, three attenuators, a detection system and a demodulation system; The PGC pulse generating device is used for receiving signals of an arbitrary waveform generator, modulating and generating carrier pulses and transmitting the carrier pulses to the 1X 2 coupler, wherein the carrier pulses are input into the sensing interferometer and the 3X 3 reference interferometer through the 1X 2 coupler to generate sensing interference pulses and two reference interference pulses; The detection system is used for performing electric signal conversion and digital-to-analog conversion on each interference pulse and outputting a sensing interference signal And two reference interference signalsAnd (3) withReceiving two associated amplitude modulation pulses generated by carrier pulse transmission at the same time, inputting the two associated amplitude modulation pulses into a demodulation system, and dividing the interference pulse intensity by the associated amplitude modulation pulse intensity by utilizing a light intensity compensation method to eliminate the influence of the associated amplitude modulation; after the demodulation system adopts PGC to demodulate each interference signal, firstly, an elliptic fitting method pair after eliminating the influence of associated amplitude modulation is utilized And (3) withCalibrating and combining into a reference signalSo thatInitial phase and phaseThe primary phase meets the pre-deduced primary phase condition of strong suppression of photoelectric common mode noise, namely, the difference of two primary phasesInteger multiples of (2); Re-pairing AndAnd respectively subtracting the time domain outputs obtained by PGC detection to obtain the time domain output after the photoelectric common mode noise suppression. In one embodiment, the PGC pulse generating device comprises a laser, an optical