Phase Jump Correction in Optical Fiber Demodulation
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Solution Overview
Problem
Polarization-induced fading in optical fiber phase demodulation systems leads to phase jumps, causing incorrect phase compensation and affecting the accuracy of vibration monitoring, particularly in long-range distributed optical fiber sensing applications.
Innovation Solution
A method involving the establishment of a prediction model using historical demodulated phase data to identify and correct phase jumps by building an autoregressive moving average model and initializing a Kalman prediction model, which compares predicted and actual phase values to determine and correct jump points, thereby stabilizing the demodulation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If arctangent demodulation method based on 3×3 fiber coupler is used, then phase information can be demodulated, but phase jumps occur due to polarization-induced fading
Solution Approach 1:
The patent introduces an intermediary variable λ (lambda) that represents the polarization state dependence. By modeling the demodulated phase as φ_demodulated = φ_actual + λ, where λ varies with polarization state, the method separates the actual phase information from polarization-induced errors. This intermediary parameter allows the system to identify and correct phase jumps by detecting abnormal variations in λ, thereby resolving the contradiction between achieving phase demodulation and maintaining demodulation stability.
Solution Approach 2:
The patent applies preliminary action by performing phase unwrapping and jump detection before final phase calculation. The method first demodulates the phase using arctangent operation, then performs preliminary processing including detecting phase jumps through comparison with adjacent sampling points, and only then applies the correction algorithm. This preliminary detection and correction approach prevents polarization-induced phase jumps from affecting subsequent vibration signal processing.
2Loss of information
If phase deconvolution algorithm is applied to restore real phase change, then vibration information can be recovered, but wrong phase compensation occurs when polarization-induced fading happens
Solution Approach 1:
The patent implements feedback by continuously monitoring the demodulated phase values and comparing adjacent sampling points to detect phase jumps. The correction algorithm uses feedback from the detected jump points to adjust the phase compensation process. Specifically, when a phase jump is detected, the algorithm applies corrective phase unwrapping based on the jump magnitude and direction, ensuring that the restored phase information accurately reflects the actual vibration-induced phase changes rather than polarization artifacts.
3Area of stationary object
If distributed optical fiber vibration sensing covers long range, then monitoring coverage is improved, but polarization state changes cause signal fading
Solution Approach 1:
The patent applies parameter changes by transforming the phase demodulation from direct arctangent calculation to a corrected phase unwrapping approach that accounts for polarization state variations. The method changes the parameter representation from raw demodulated phase to corrected phase by adding compensation terms based on detected jump points. This parameter transformation allows the system to maintain reliable signal interpretation over long distances where polarization state changes are more frequent and significant.
Data Source
AI summary
A method for correcting a phase jump caused by polarization-induced fading in optical fiber phase demodulation, including the steps of: 1, selecting a demodulated phase in the case of non-depolarization as historical sample data; 2, determining an autoregressive coefficient and a moving average coefficient of the autoregressive moving average model for the demodulated phase; 3, establishing a Kalman prediction model for the demodulated phase, and deriving recursive equations of the Kalman prediction model for the demodulated phase; and 4, judging whether a jump point exists in the actual demodulated phase, determining polarization states of lights if the jump point exists, and correcting the jump point when the polarization states of the lights are in polarization orthogonality by replacing the actual demodulated phase with a predicted phase value. The disclosure ensures the correctness of subsequent vibration-based signal processing.