CN-122001480-A - Phase noise compensation method and distributed optical fiber acoustic wave sensing system

CN122001480ACN 122001480 ACN122001480 ACN 122001480ACN-122001480-A

Abstract

The invention relates to a phase noise compensation method and a distributed optical fiber acoustic wave sensing system, which comprises the steps of S1, receiving a light source phase noise signal and a coherent receiving signal of a scattering signal for sensing through a group of coherent receivers, S2, respectively carrying out low-pass and high-pass filtering on the coherent receiving signal to extract a light source phase noise reference signal and a sensing signal, S3, respectively carrying out phase noise extraction and reconstruction on a transmitted detection light signal and a local oscillation light signal in the coherent receiving process based on the phase noise reference signal, S4, compensating phase noise introduced by the local oscillation light according to the reconstructed phase noise signal, carrying out time domain and frequency domain reconstruction on the detection light signal to obtain a matched filtering kernel function after phase noise compensation, and S5, carrying out signal demodulation based on the coherent receiving signal after phase noise compensation and the reconstructed matched filtering kernel function. Compared with the prior art, the invention can realize high-precision phase noise compensation under the condition of low complexity.

Inventors

CHEN JIAGENG
XIAO ZHENGYUAN
HE ZUYUAN
LI HANZHAO
YU XUHUI

Assignees

上海交通大学
宁波联河光子技术有限公司

Dates

Publication Date: 20260508
Application Date: 20241101

Claims (10)

1. A phase noise compensation method for a distributed optical fiber acoustic wave sensing system, the distributed optical fiber acoustic wave sensing system adopting a coherent receiving architecture, the method comprising: s1, simultaneously receiving phase noise signals comprising a light source and coherent receiving signals of scattered signals used for sensing in a distributed optical fiber acoustic wave sensing system through a group of coherent receivers; s2, respectively carrying out low-pass filtering and high-pass filtering on the coherent receiving signals, and extracting phase noise reference signals and sensing signals of the light source; S3, based on the phase noise reference signal, extracting and reconstructing phase noise signals of a detection optical signal emitted by the distributed optical fiber acoustic wave sensing system and a local oscillation optical signal in a coherent receiving process respectively; S4, compensating phase noise introduced by local oscillation light in the sensor signal obtained by filtering according to the reconstructed phase noise signal, and obtaining a matched filtering kernel function after phase noise compensation by reconstructing time domain and frequency domain of the detection light signal in the sensor system according to the reconstructed phase noise signal; s5, performing signal demodulation based on the coherent received signal after phase noise compensation and the reconstructed matched filtering kernel function.
2. The method for compensating phase noise of a distributed optical fiber acoustic wave sensing system according to claim 1, wherein the method for simultaneously receiving the phase noise signal including the light source and the coherent receiving signal including the scattered signal for sensing in the distributed optical fiber acoustic wave sensing system by a group of coherent receivers comprises: The laser output by the coherent light source (1) is divided into two beams by the first coupler (2), the first beam enters the optical modulator (3) to be modulated into detection light, and the other beam enters the second coupler (6); the detection light output by the light modulator (3) enters an optical fiber (5) to be detected through the optical circulator (4), and the generated scattered light enters a third coupler (7) through the optical circulator (4); The second coupler (6) divides the laser output by the light source into two beams, wherein one beam enters the third coupler (7) together with scattered light generated by detection and enters the signal end of the coherent receiver (9), and the other beam enters the delay light path (8) and enters the local end of the coherent receiver (9) through delay; The optical signals input by the signal end and the local end in the coherent receiver (9) are subjected to photoelectric conversion after being subjected to beat frequency, and phase noise signals containing a light source and coherent receiving signals of scattering signals used for sensing in the distributed optical fiber acoustic wave sensing system are received at the same time, wherein the coherent receiver (9) is provided with two input optical interfaces for double-beam interference so as to extract phase difference information, and then the phase difference information is converted into observable electric signals through a photoelectric conversion device and output.
3. The method for compensating phase noise of distributed optical fiber acoustic wave sensing system according to claim 2, wherein the phase noise signal of the light source and the scattered signal for sensing in the distributed optical fiber acoustic wave sensing system are simultaneously received by a group of coherent receivers, the phase noise signal of the light source is from homodyne detection, the frequency band is near the baseband, the scattered signal for sensing is from heterodyne detection, and the frequency band is at the intermediate frequency.
4. A phase noise compensation method for a distributed optical fiber acoustic wave sensing system according to claim 3, wherein the phase noise signal of the optical source and the coherent receiving signal of the scattered signal for sensing are simultaneously received by a group of coherent receivers, and the complex time series expression is: E LO (t)＝ρ 1 E cw (t-τ d ) represents a signal received by a local end of the coherent receiver (9), ρ 1 represents insertion loss introduced by an optical path in the system, E cw (t) represents an electric field vector of output light of the coherent light source (1), τ d is a delay amount introduced by a delay optical path (8), E Sig (t)＝ρ 2 E cw (t)+ρ 3 E R (t) represents a signal received by the local end of the coherent receiver (9), ρ 2 、ρ 3 is insertion loss introduced by a corresponding optical path, and E R (t) represents a scattered light signal returned by the optical circulator (4); The complex-valued time sequence of the coherent received signal is spread as: Wherein E 0 is the output light intensity of a coherent light source (1), omega 0 represents the light source angular frequency, phi N (t) represents the light source phase noise, R (tau) represents the response of the optical fiber to be tested, and k (t) represents the complex function used for modulating the detection signal emitted by the generation sensing system, which is an autocorrelation function with a thumbtack envelope.
5. The method for compensating phase noise of distributed optical fiber acoustic wave sensing system according to claim 4, wherein the low-pass filtering and the high-pass filtering are performed on the coherent received signals respectively, and the phase noise reference signal and the sensing signal of the light source are extracted, specifically: the coherent receiving signal S co (t) is subjected to low-pass filtering to obtain a phase noise reference signal of the light source High-pass filtering the coherent received signal S co (t) to obtain a sensing signal
6. The method for compensating phase noise of distributed optical fiber acoustic wave sensing system according to claim 5, wherein the extracting and reconstructing of phase noise signals are performed on the probe optical signals transmitted in the distributed optical fiber acoustic wave sensing system and the local oscillation optical signals in the coherent receiving process based on the phase noise reference signals, respectively, specifically: 1) Taking a principal value delta phi A (t) of an irradiance angle for a light source phase noise reference signal S p (t): 2) Integrating and scaling the principal value delta phi A (t) of the radial angle to obtain the phase noise reference phi A (t) of the reconstructed light source, and carrying out different time delays on phi A (t) according to the optical path length of the actual light path to obtain the phase noise reference of the detected light signal Phase noise reference for local oscillator optical signals Where τ k 、τ s is the corresponding delay.
7. The method of claim 6, wherein the phase noise reference is obtained by performing a value of the sensing signal S R (t) based on the reconstructed phase noise signal And compensating phase noise introduced by local oscillation light in the filtered sensing signal.
8. The method for compensating phase noise of a distributed optical fiber acoustic wave sensing system according to claim 6, wherein the reconstructing the phase noise signal according to the reconstructing obtains a matched filtering kernel function after compensating the phase noise by reconstructing a time domain and a frequency domain of a detection optical signal in the sensing system, specifically comprising: 1) The detection pulse is actually transmitted by the sensing system in the digital domain, and the detection pulse comprises phase disturbance and intensity disturbance to which the detection pulse is subjected: Wherein w (t) represents the intensity disturbance of the detection pulse by the optical modulator (3); to simulate the phase noise from the light source that the probe pulse contains, A phase noise reference for the probe optical signal; 2) Constructing a matched filtering kernel function k B (t) subjected to phase noise compensation on a frequency domain, so that a cross-correlation result of the matched filtering kernel function k B (t) and a standard kernel function k (t) is in a form of being free from disturbance of phase noise: Wherein, the Representing the pair of fourier transforms, Representing the autocorrelation result of the standard kernel function k (t) and its fourier transform, Representing the fourier transform of k (t), the set of branches defined on the real set is:
9. The method for compensating phase noise of distributed optical fiber acoustic wave sensing system according to claim 1, wherein the demodulation signal after phase noise compensation is obtained by performing signal demodulation based on the coherent received signal after phase noise compensation and the reconstructed matched filter kernel function, specifically by performing cross-correlation operation on the coherent received signal after phase noise compensation and the reconstructed matched filter kernel function.
10. A distributed fiber optic acoustic wave sensing system, the system comprising: the coherent light source (1) is used for outputting continuous laser disturbed by phase noise and generating detection pulse light and local oscillation light; A first coupler (2) for splitting the continuous laser light output from the coherent light source (1); the optical modulation unit (3) is used for modulating the laser after the light is split by the first coupler (2) to generate detection pulse light; the optical circulator (4) is used for injecting the detection pulse light output by the optical modulator (3) into the optical fiber (5) to be detected and receiving back scattered light returned by the optical fiber (5) to be detected; A second coupler (6) for further splitting the continuous laser light outputted from the first coupler (2); a third coupler (7) for combining the continuous laser light from the second coupler (6) with the back-scattered light from the optical circulator (4); A delay light path (8) for delaying the continuous laser from the second coupler (6) to generate a fixed phase difference with the other output laser of the second coupler (6); The coherent receiver (9) is used for generating beat frequency signals of the back scattered light and the light source continuous laser after the back scattered light and the light source continuous laser are combined and converting the beat frequency signals into electric signals; the digital signal processing module (10) is configured to receive an electrical signal generated by the coherent receiver (9), perform demodulation processing of phase noise compensation by using the method according to any one of claims 1 to 9, and finally obtain a response of the optical fiber (5) to be measured after the phase noise compensation.

Description

Phase noise compensation method and distributed optical fiber acoustic wave sensing system Technical Field The invention relates to the field of distributed optical fiber sensing, in particular to a phase noise compensation method and a distributed optical fiber acoustic wave sensing system. Background The distributed optical fiber acoustic wave sensing technology utilizes Rayleigh scattering in the optical fiber to extract and convert the disturbance of the outside to the sensing optical fiber from the change of the characteristic parameters of the optical signal into a processable electric signal, thereby realizing the distributed acoustic measurement with high precision and high space-time resolution. In the field of distributed optical fiber acoustic wave sensors, a coherent receiving technology and an optical pulse compression technology are common means for further improving the system performance. The coherent receiving finger firstly interferes the echo signal with a local reference signal to generate a beat signal, then detects the beat signal, and improves the signal-to-noise ratio of the coherent receiving signal through the high power of the local oscillator. The optical pulse compression means selecting a long-duration signal having good correlation characteristics as a detection pulse instead of a short-duration narrow pulse signal, and at the same time, after the completion of the reception of the backscattered signal, performing a pulse compression operation such as a matched filtering operation based on a kernel function constructed in the digital domain containing time-frequency information of the detection pulse to accurately recover the information in the optical fiber to be measured. The technology breaks the trade-off relation between the detection precision and the spatial resolution, and can further improve the average power of the detection light signals injected into the sensing optical fiber by the system on the premise of limited peak power of the detection signals. Although the two techniques can significantly improve the performance of the distributed optical fiber acoustic wave sensor, the phase noise level in the system is also more strictly required. The coherent receiving is based on double-beam interference, so that the disturbance of the phase noise carried by the local oscillation light is completely introduced into the coherent receiving signal through beat frequency, and the disturbance of the phase noise to the kernel function affects the signal quality of the matched filtering result, including the reduction of phase distortion and peak-side lobe suppression ratio by relying on the good autocorrelation characteristic of the kernel function. Therefore, in the distributed optical fiber acoustic wave sensing system applying the two technologies, phase noise has become an important problem to be solved urgently, on one hand, the selection range of a system light source is limited, and on the other hand, further improvement of system performance is affected. At present, a plurality of schemes aiming at compensating and suppressing phase noise of a distributed optical fiber acoustic wave sensing system exist, wherein a part of schemes are based on the auxiliary interferometer to capture phase noise information of a light source, and accurate compensation is realized by taking the information as a reference. Such phase noise compensation schemes often require an additional coherent receiving module for specifically extracting the light source phase noise, which can introduce additional equipment overhead and complexity to the system. In terms of cost, a series of optical passive devices such as couplers, optical mixers and the like are added in the system, and matched active optical devices such as balanced photoelectric detectors and analog acquisition cards for acquiring data are also needed, and in terms of complexity, the additional optical and electrical devices increase the difficulty of system modularization and make synchronization and triggering between different devices more complicated. Therefore, there is a need to design a simplified phase noise compensation scheme for a coherent reception and optical pulse compression distributed optical fiber acoustic wave sensor, which can achieve a good phase noise compensation effect without introducing any additional devices. Disclosure of Invention The invention aims to overcome the defects of the prior art and provide a phase noise compensation method and a distributed optical fiber acoustic wave sensing system, by multiplexing the original coherent receiver in the system, meanwhile, the phase noise signal of the light source and the sensing signal generated by detection are received, and the distributed optical fiber acoustic wave sensor can be simplified on the premise of reducing the cost and complexity of the system. The aim of the invention can be achieved by the following technical scheme: according to a first asp