Fiber Event Detection Using Spectral Diversity Against Coherent Fading
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Solution Overview
Problem
Existing optical sensing systems face challenges with coherent fading, or speckle noise, which leads to false positive and false negative detections of fiber events due to destructive interference in optical backscattering, making it difficult to extract reliable optical sensing information along optical fibers.
Innovation Solution
The system employs optical frequency division multiplexing (OFDM) to evaluate reliability metrics using the magnitude of the Jones matrix for different subcarriers, generating final Jones matrices and selecting reliable fiber locations for detection, and characterizing the reliability of fiber-event detections based on sub-carrier reliability metrics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical backscattering is used for sensing, then sensing capability is provided, but coherent fading causes false positive and false negative detections
Solution Approach 1:
The patent segments the optical signal into multiple independent wavelength channels (e.g., 5 different wavelengths). By dividing the sensing function across multiple wavelengths, the system avoids the coherent fading problem that affects single-wavelength systems, as different wavelengths experience independent fading patterns. This segmentation allows the system to maintain reliable detection by combining information from multiple channels.
Solution Approach 2:
The patent changes the wavelength parameter of the optical signal to create a multi-wavelength sensing system. By measuring at multiple wavelengths (e.g., 1550nm, 1555nm, 1560nm, 1565nm, 1570nm), the system transforms a single-parameter measurement into a multi-parameter measurement, enabling discrimination between true fiber events and coherent fading artifacts through spectral analysis.
2Measurement precision
If single-wavelength sensing is used, then system simplicity is maintained, but detection accuracy is reduced due to speckle noise
Solution Approach 1:
The patent segments the optical signal into multiple independent wavelength channels (e.g., 5 different wavelengths). By dividing the sensing function across multiple wavelengths, the system avoids the coherent fading problem that affects single-wavelength systems, as different wavelengths experience independent fading patterns. This segmentation allows the system to maintain reliable detection by combining information from multiple channels.
Solution Approach 2:
The patent changes the wavelength parameter of the optical signal to create a multi-wavelength sensing system. By measuring at multiple wavelengths (e.g., 1550nm, 1555nm, 1560nm, 1565nm, 1570nm), the system transforms a single-parameter measurement into a multi-parameter measurement, enabling discrimination between true fiber events and coherent fading artifacts through spectral analysis.
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 enhances the detection of fiber events by reducing false negatives and improving the reliability of event detection along optical fibers, extending the effective length of optical probing techniques.
Implementation Method 1
Distributed acoustic/vibration sensing (DAS/DVS) allows for detection of mechanical and/or chemical perturbation at various locations along an optical fiber using Rayleigh backscattering
Implementation Method 2
perform phase-sensitive measurements on a part of the transmitted light received from the same end of the optical fiber line
Data Source
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AI summary
In certain embodiments, an optical transceiver transmits multi-carrier light into an end of an optical fiber line and performs phase-sensitive (preferably OTDR) measurements of a part of the transmitted light received at the same end of the optical fiber line. A digital processor determines sub-carrier dual-polarization channel matrices for sets of frequency (e.g., sub-carrier center frequency), time, and location values based on the measurements, each sub-carrier channel matrix describing the part of the light received in response to being passively redirected back at the time and location values of a corresponding one of the sets. The digital processor generates final channel matrices based on (linear or non-linear) functions of corresponding sub-carrier channel matrices and sub-carrier reliability metrics derived from the sub-carrier channel matrices. The final channel matrices (and, in some embodiments, corresponding final reliability metrics) are used to detect fiber events along the optical fiber line.