CN-121978023-A - Distributed single detection method and device for optical fiber group birefringence and phase birefringence

CN121978023ACN 121978023 ACN121978023 ACN 121978023ACN-121978023-A

Abstract

The invention belongs to the technical field of optical fiber sensing, and discloses a distributed single detection method and device for optical fiber group birefringence and phase birefringence, which are based on definite distinction and complete modeling of phase birefringence and group birefringence physical mechanism, the method optimizes signal interpretation from a theoretical level, effectively suppresses noise and various interferences, and remarkably improves the accuracy and reliability of parameter measurement. By performing efficient cross-correlation operation on the optical frequency domain and the distance domain, two types of birefringence distribution information are synchronously acquired in single measurement, so that the data processing and feature extraction efficiency is greatly improved, and the method is particularly suitable for high-resolution long-distance distributed sensing analysis. The theoretical model and the solving method have universal applicability, so that the robustness and the stability of the system under different application environments are improved.

Inventors

WANG CHENHUAN
LIU JI
ZHENG SUOZHEN
WU JINHUI

Assignees

中北大学

Dates

Publication Date: 20260505
Application Date: 20260206

Claims (9)

1. The distributed single detection method for the optical fiber phase birefringence is applied to a polarized light frequency domain reflection type distributed optical fiber sensing system, and is characterized by comprising the following steps of: in the same optical frequency scanning process, interference signals corresponding to two mutually orthogonal polarization states in the polarization maintaining optical fiber to be measured are obtained; performing Fourier transform on the two polarization interference signals respectively to obtain corresponding distance domain complex signals; Performing distance domain alignment processing on the two distance domain signals to enable the two polarization states to correspond to the same distance sampling points at the same physical position; Windowing and converting the two polarization state signals into an optical frequency domain in a distance domain respectively; Performing cross-correlation operation on the two polarized light frequency domain signals at the same distance position to obtain the light frequency domain movement amount between the two polarized light states at the position; And calculating to obtain a phase birefringence result distributed along the length direction of the optical fiber according to the deterministic mapping relation between the optical frequency domain movement amount and the relative phase change rate.
2. The method according to claim 1, characterized in that: The distance domain alignment processing is completed in an interpolation compensation mode, so that the distance domain sampling points of the two polarization states are in one-to-one correspondence at the same physical position.
3. The method according to claim 1, characterized in that: the mapping relation between the optical frequency domain movement amount and the relative phase change rate is a linear proportional relation, and the proportional relation is determined by the optical frequency scanning range.
4. The distributed single detection method for the birefringence of the optical fiber group is applied to a polarized light frequency domain reflection type distributed optical fiber sensing system and is characterized by comprising the following steps of: in the same optical frequency scanning process, interference signals corresponding to two mutually orthogonal polarization states in the polarization maintaining optical fiber to be measured are obtained; performing Fourier transform on the two polarization interference signals respectively to obtain a distance domain signal; Windowing is carried out on the two polarized signals in the distance domain respectively; Performing cross-correlation operation on the two polarized distance domain signals at the same distance position to obtain the distance domain position offset of the two polarized states at the position; and carrying out derivative operation on the distance domain position offset along the length direction of the optical fiber to obtain a group birefringence result distributed along the optical fiber.
5. The method according to claim 4, wherein: The distance domain position offset is determined by the correlation peak position difference of the two polarization state distance domain signals.
6. The method according to claim 4, wherein: The group birefringence result is obtained by differential derivation of the offset of adjacent discrete distance sampling points.
7. The utility model provides a device for realizing optical fiber crowd birefringence and phase birefringence distributed single detection, includes light source module, supplementary interference module, main interference module, polarization resolution detection module, collection module and processing module, its characterized in that: the light source module is used for outputting an optical signal of optical frequency linear scanning; The auxiliary interference module forms an unequal arm interference structure and is used for generating beat frequency signals corresponding to the optical frequency scanning one by one; the acquisition module takes the beat frequency signal as an external clock trigger signal to realize equal optical frequency interval sampling; The main interference module is a polarization maintaining structure and is used for acquiring two mutually orthogonal polarization state backscattering interference signals in the polarization maintaining optical fiber to be measured; the polarization resolution detection module is used for separating and synchronously detecting interference signals of two polarization states; the processing module is used for respectively carrying out joint distance domain analysis and cross-correlation processing on the two polarization state signals in the same optical frequency scanning data, so as to synchronously obtain a distributed detection result of group birefringence and phase birefringence.
8. The apparatus of claim 7, wherein the polarization-resolved detection module comprises a polarization beam splitting structure and a dual-path balanced detection structure for acquiring interference signals of a fast-axis polarization state and a slow-axis polarization state, respectively.
9. The apparatus of claim 7, wherein the processing module is configured to synchronize the output of the group birefringence distribution result and the phase birefringence distribution result of the optical fiber without performing multiple optical frequency scans and without switching the polarization state.

Description

Distributed single detection method and device for optical fiber group birefringence and phase birefringence Technical Field The invention belongs to the technical field of optical fiber sensing, and particularly relates to a distributed single detection method and device for optical fiber group birefringence and phase birefringence. Background The Polarization Maintaining Fiber (PMF) is used as one of special optical fibers, and a special fiber core shape or a stress rod is added during manufacturing to form high birefringence, so that the polarization state of a transmitted light wave can be stably maintained, and the PMF becomes a key base material of a series of high-precision optical systems and is widely applied to the fields of optical fiber sensing, optical fiber communication and the like. As an important parameter for ensuring the polarization state of the transmission fiber, the value of the birefringence needs to be kept stable. However, birefringence is not uniform due to defects in the fabrication process and impurities in the fabrication material and varies with the position of the polarization maintaining fiber. Therefore, the method for measuring the distributed birefringence of the optical fiber has practical significance for reducing the birefringence non-uniformity and reducing the optical fiber sensing noise in the optical fiber design. In the method of measuring fiber birefringence, external influences (torsion, lateral pressure) can be applied to the measured fiber, the optical phase or wavelength of the light source can be modulated, and low coherence interferometry techniques are used, however, they do not allow distributed birefringence detection. In the research process of a polarization-maintaining frequency domain reflection system (P-OFDR), the problem of distributed birefringence detection is solved, and parameter sensing is carried out according to the problem. In view of the chromatic dispersion problem of the optical fiber, the birefringence is divided into phase birefringence and group birefringence, which differ by λ (dB/dλ), (λ being wavelength, and B being phase birefringence). In addition, the difference between the two is greatly influenced by the type of the optical fiber. The difference of the stress-induced birefringence fiber is 10-30%, and the shape-induced birefringence elliptic core fiber has larger difference and can even reach 100-150% (under the wavelength 1550 nm). Therefore, it is important to distinguish and exploit phase and group birefringence in detection and demodulation. Although measurement and sensing of fiber distributed birefringence are well realized by the P-OFDR system in the prior art, there is no theoretical analysis that can distinguish the group birefringence from the phase birefringence of the fiber and systematically analyze it. In fact, there are studies that explicitly propose and realize distributed group birefringence detection using the P-OFDR system, however, eight measurements are required and the measurement distance is short, and measurement of phase birefringence is lacking. Disclosure of Invention Aiming at the problems existing in the prior art, the invention provides a distributed single detection method and device for optical fiber group birefringence and phase birefringence. The invention is realized in such a way that a distributed single detection method for optical fiber group birefringence and phase birefringence comprises the following steps: s1, in the distributed strain sensing device, two mutually perpendicular polarization state signals are obtained and then subjected to Fourier transformation, and distance domains of the two signals are aligned through an interpolation compensation method; S2, in the distributed strain sensing device, two mutually perpendicular polarization state signals are obtained and then subjected to Fourier transformation, windows are respectively taken from the two signals in a distance domain, the position offset results of all positions are obtained after cross correlation, the offset results are derived for the distance, and the distributed group birefringence results are obtained after conversion after the derivation. Further, the S1 specifically includes: Coefficient of dispersion With effective refractive indexIt can be written as: (1) Wherein the method comprises the steps of In order for the group to have a refractive index,Is the wavelength of light in free space, and thus, the propagation constantAccording to equation (1) can be written as: (2) In the P-OFDR system, local oscillation light Can be written as: (3) Wherein, the Is the initial optical frequency of the tunable optical source,Is the sweep rate of the frequency,Is phase noise, measuring lightWritten as (4) Wherein, the Representing the backscattering coefficient, z represents any point on the fiber,Representing the light field phase, can be expressed in time and space, and expressed by the formulas (2) and (2)Carry-in,