Dispersive White Light Interferometer Demodulation via Spectral Correlation
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Solution Overview
Problem
Existing methods for demodulating optical path differences in dispersive white light interferometric sensors, such as EFPI sensors, face challenges in resolving interference patterns due to reduced visibility and noise, especially in long fiber applications like wellbore monitoring, necessitating a high accuracy and precision demodulation technique.
Innovation Solution
A method involving the generation of test interferometry spectra for various optical path differences, correlation with measured spectra to determine the optical path difference corresponding to the highest correlation function value, and using computer-generated test spectra to accurately determine the air gap length in sensors like extrinsic fiber Fabry-Perot interferometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct analysis of interference pattern is used, then measurement precision is improved, but device complexity increases due to reduced visibility and noise in long fiber applications
Solution Approach 1:
The patent creates a digital copy of the interference pattern through computer-generated test spectra. Instead of directly analyzing the noisy physical interference pattern from long fibers, the system generates virtual test spectra representing expected interference patterns under various optical path differences, then correlates these digital copies with the measured spectrum. This copying approach simplifies processing by working with idealized digital models rather than directly processing degraded physical signals.
Solution Approach 2:
The patent introduces a correlation function as an intermediary between the measured interference pattern and the optical path difference determination. The correlation function acts as a mediator that compares test spectra with measured spectra, transforming the complex direct analysis problem into a simpler pattern matching problem. This intermediary function systematically processes the relationship between spectral data and physical parameters, reducing the complexity of direct signal analysis.
2Adaptability or versatility
If long lead in fiber is used, then adaptability to wellbore monitoring is improved, but measurement precision deteriorates due to reduced interference visibility
Solution Approach 1:
The patent changes the parameter domain from direct spatial interference analysis to spectral correlation analysis. By transforming the problem into a spectral domain comparison using correlation functions, the system can maintain measurement precision even with long fibers where interference visibility is reduced. The parameter transformation allows the system to work effectively with degraded signals from long fiber deployments in wellbore environments.
3Ease of operation
If traditional demodulation methods are used, then ease of operation is maintained, but measurement precision deteriorates in noisy environments
Solution Approach 1:
The patent implements a feedback mechanism through iterative correlation analysis. The system generates test spectra based on assumed optical path differences, correlates these with measured spectra, and uses the correlation results to refine the optical path difference determination. This feedback loop continuously improves measurement precision by comparing predicted interference patterns with actual measurements, allowing the system to operate simply while achieving high precision in noisy environments.
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
This approach provides robust, reliable, and accurate determination of optical path length in dispersive white light interferometric sensors, enhancing resolution and precision, particularly in challenging environments like wellbore monitoring.
Implementation Method 1
Combination of both reflected light portions in the lead in fiber creates an interference pattern that is related to the size of the air gap
Implementation Method 2
A broadband light source is applied to the lead in fiber, some of which is reflected by the fiber end and other portions of which are reflected by the end of the reflected fiber
Implementation Method 3
dispersive white light interferometric sensor
Data Source
AI summary
A method for demodulating signals from a dispersive, white light interferometer includes generating test interferometry spectra from an interferometer forming part of a sensor for various values of interferometer sensor optical path length. The various test spectra are correlated to a measured spectrum from the sensor to generate a correlation function. The sensor optical path length resulting in the correlation function value reaching a maximum is selected as the optical path length.