Coherent Modem Disturbance Localization in Optical Fiber Links
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Solution Overview
Problem
Existing optical fiber networks lack real-time, high-sensitivity, and long-range capabilities for detecting and localizing environmental disturbances such as seismic events, with conventional methods limited by low signal-to-noise ratio, compatibility issues, and the need for bidirectional signal processing.
Innovation Solution
A coherent modem-based system that leverages clock and carrier phase information, combined with chromatic dispersion measurements, to detect and approximate the location of disturbances using forward transmitted signals, enabling real-time localization over long distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional distributed sensing methods (DAS, OTDR) are used, then localization capability is provided, but sensing range is limited to around 100-150 kilometers due to low signal-to-noise ratio
Solution Approach 1:
The patent changes the measurement parameter from intensity-based detection (conventional DAS/OTDR) to phase-based detection using coherent optical signals. By measuring optical phase variations instead of light intensity, the system achieves high signal-to-noise ratio that enables sensing ranges exceeding 1000 kilometers, resolving the contradiction between measurement precision and sensing range.
2Measurement precision
If bidirectional correlation methods are used for disturbance localization, then localization capability is achieved, but real-time monitoring capabilities are limited
Solution Approach 1:
The patent extracts and utilizes only the forward-transmitted signal phase information for disturbance localization, eliminating the need for bidirectional signal correlation. By processing single-direction coherent optical signals, the system achieves both high localization accuracy and real-time monitoring capability, resolving the contradiction between measurement precision and productivity.
3Measurement precision
If laser interferometry with fiber Bragg grating is used, then disturbance detection is achieved, but the system requires specially installed reflecting fiber Bragg grating at each fiber span
Solution Approach 1:
The patent makes the coherent optical communication system itself serve multiple functions: both data transmission and disturbance sensing/localization. By using the existing coherent modem infrastructure without requiring additional fiber Bragg gratings or specialized components, the system achieves high detection accuracy while eliminating complex system configuration, resolving the contradiction between measurement precision and device complexity.
4Length of stationary object
If coherent optical communication signals are used for sensing, then long-range sensing is enabled, but the system must differentiate between phase variations due to chromatic dispersion and those due to environmental disturbances
Solution Approach 1:
The patent employs feedback mechanisms where the coherent modem continuously monitors and tracks chromatic dispersion effects, using this information to differentiate between dispersion-induced phase variations and disturbance-induced phase variations. This feedback approach enables long-range sensing while managing the complexity of phase variation 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
Enables high signal-to-noise ratio, real-time localization of disturbances over 10,000 km or more, reducing DSP complexity and eliminating the need for cross-correlation processing, while providing accurate disturbance detection and localization.
Implementation Method 1
Environmental disturbances can induce vibration, pressure, or temperature changes to an optical fiber, which can alter the optical path length of the fiber link. This distortion results in an optical phase variation
Implementation Method 2
The frequency variation results in a group delay variation in the presence of chromatic dispersion
Data Source
AI summary
Aspects of the subject disclosure may include, for example, obtaining an estimate of a phase of a reference associated with a signal received over an optical channel, obtaining an estimate of a frequency of a carrier associated with the signal, and based on the estimate of the phase of the reference and the estimate of the frequency of the carrier, estimating a location dependent property associated with a disturbance to the optical channel to determine a location estimate for the disturbance. Other embodiments are disclosed.