Optical Fiber DAS I/Q Correction for Phase Noise Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optical fiber Distributed Acoustic Sensing (DAS) technology faces challenges in achieving high-accuracy phase demodulation due to inherent errors such as DC bias, amplitude imbalance, and phase imbalance, leading to phase noise that is difficult to remove in signal processing, affecting the quality of seismic data acquisition.
Innovation Solution
A method and system for correcting imbalance in In-phase/Quadrature (I/Q) demodulation of optical fiber DAS data, involving DC bias correction, amplitude imbalance correction using Hilbert transform, and phase imbalance correction, to obtain accurate and efficient noise suppression and improved data acquisition quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If In-phase/Quadrature (I/Q) phase demodulation is used to obtain RBS phase information, then the DAS technology can sense acoustic vibration information, but DC bias, amplitude imbalance and phase imbalance cause the output I/Q values to vary elliptically, resulting in non-linear relationship between demodulation phase and physical quantity, which seriously affects phase demodulation accuracy and generates phase noise that is difficult to remove
Solution Approach 1:
The patent applies preliminary action by performing DC bias correction, amplitude imbalance correction, and phase imbalance correction on the I/Q signals before phase demodulation. These preprocessing steps eliminate the elliptical variation of I/Q values caused by inherent errors, ensuring that the subsequent phase demodulation operates on corrected signals with linear relationship to physical quantities, thereby preventing phase noise generation at its source rather than attempting to remove it afterward
Solution Approach 2:
The patent employs parameter changes by systematically adjusting and correcting the parameters of the I/Q signals through three sequential correction stages: DC bias correction modifies the offset parameters, amplitude imbalance correction adjusts the magnitude parameters using Hilbert transform, and phase imbalance correction fixes the phase relationship parameters. These parameter transformations convert the elliptical I/Q trajectory into a circular one, restoring the linear relationship between demodulation phase and physical quantity
2Device complexity
If inherent errors of optical fiber sensing device are present, then the device can operate with simple structure, but DC bias, amplitude imbalance and phase imbalance cause I/Q values to vary elliptically, making demodulation phase non-linear with physical quantity and seriously affecting phase demodulation accuracy
Solution Approach 1:
The patent introduces an intermediary correction system that processes the I/Q signals between the optical fiber sensing device and the phase demodulation stage. This intermediary comprises three correction modules: DC bias correction module, amplitude imbalance correction module using Hilbert transform, and phase imbalance correction module. These intermediaries process the signals to eliminate elliptical variation and restore linearity, achieving high measurement precision without modifying the simple structure of the optical fiber sensing device itself
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively corrects I/Q signals, suppresses optical fiber demodulation noise, and enhances the quality of optical fiber DAS data acquisition by accurately addressing the imbalances, resulting in improved signal-to-noise ratio and reduced phase noise.
Implementation Method 1
performing amplitude imbalance correction on the I/Q signals I1 and Q1 after DC bias correction by using Hilbert transform to obtain I/Q signals I2 and Q2 after amplitude imbalance correction; and performing phase imbalance correction on the I/Q signals I2 and Q2 after amplitude imbalance correction by using Hilbert transform
Implementation Method 2
The DAS technology mainly utilizes Rayleigh backscattering (RBS) of laser when laser propagates through the optical fiber. RBS changes accordingly when a medium surrounding the optical fiber vibrates.
Data Source
AI summary
A method for correcting imbalance in IQ demodulation of optical fiber DAS data is disclosed. The method includes obtaining I/Q signals I0 and Q0 of each sampling on an optical fiber from a DAS acquisition instrument; performing DC bias correction on the I/Q signals I0 and Q0 to obtain I/Q signals I1 and Q1 after DC bias correction; performing amplitude imbalance correction on the I/Q signals I1 and Q1 after DC bias correction by using Hilbert transform to obtain I/Q signals I2 and Q2 after amplitude imbalance correction; and performing phase imbalance correction on the I/Q signals I2 and Q2 after amplitude imbalance correction by using Hilbert transform to obtain I/Q signals I3 and Q3 after phase imbalance correction. It is possible to perform accurate correction on I/Q signals, accurately and efficiently suppress optical fiber demodulation noise, and improve optical fiber DAS data acquisition quality.