Undersea Fiber Polarization Sensing for Span-Level Disturbance Location
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Solution Overview
Problem
Existing undersea fiber optic communication systems face challenges in accurately determining the location, magnitude, and characteristics of environmental disturbances such as earthquakes due to limitations in sensing technology, including low signal-to-noise ratio and inability to pinpoint disturbance locations along the cable length.
Innovation Solution
The method employs a supervisory system of undersea fiber optic cables to monitor the polarization transfer matrix by isolating disturbance locations through eigenvalues of the polarization transfer matrix, utilizing existing infrastructure to return optical signals periodically, and employing cheaper lasers with larger phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase monitoring is used to detect environmental disturbances, then disturbance detection capability is provided, but precise determination of location and characteristics is difficult
Solution Approach 1:
The patent uses polarization state changes (analogous to color changes) to encode disturbance location information. By monitoring how the polarization state of light changes as it travels through different segments of the fiber optic cable, the system can precisely determine where disturbances occur along the cable length, converting unlocatable phase changes into locatable polarization modifications.
Solution Approach 2:
The patent divides the optical fiber cable into multiple segments or spans and uses polarization multiplexing to independently monitor each segment. This segmentation allows the system to identify which specific segment experienced a disturbance, thereby providing precise location information that was previously unavailable with conventional phase monitoring.
2Reliability
If existing supervisory infrastructure is utilized for sensing, then deployment cost is reduced, but signal-to-noise ratio is low
Solution Approach 1:
The patent makes the existing supervisory infrastructure multi-functional by enabling it to perform both its original cable monitoring function and new seismic disturbance detection function simultaneously. The same fiber optic cables and supervisory systems that monitor cable health are now also used to detect earthquakes and environmental disturbances, eliminating the need for separate sensing infrastructure and improving signal-to-noise ratio through dedicated sensing capabilities.
Solution Approach 2:
The patent changes the monitoring parameter from conventional cable performance metrics to polarization state parameters. By measuring polarization changes in the light signals already present in the supervisory system, the patent extracts seismic disturbance information without adding complex new hardware, thereby improving signal-to-noise ratio while minimizing infrastructure complexity.
3Measurement precision
If polarization transfer matrix monitoring is implemented, then disturbance location isolation is achieved, but system complexity increases
Solution Approach 1:
The patent uses polarization states as an intermediary to carry disturbance location information. Instead of directly measuring physical disturbances or using complex location identification systems, the polarization state of light acts as a mediator that encodes spatial information about where disturbances occur along the fiber, simplifying the overall system architecture while maintaining high measurement precision.
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 precise location information about disturbances with a high signal-to-noise ratio, overcoming limitations of previous methods by using existing infrastructure without additional cost, and enabling accurate detection of disturbances like earthquakes.
Implementation Method 1
optical signals are transmitted over optical fibers
Implementation Method 2
disturbances on an optical fiber causes a change in the phase and polarization of light traversing the fiber
Implementation Method 3
monitoring the polarization of interrogation light instead of its phase
Data Source
AI summary
An advance in the art is made according to aspects of the present disclosure directed to methods for earthquake sensing that employ a supervisory system of undersea fiber optic cables. Earthquakes and other environmental disturbances are detected by monitoring the polarization of interrogation light instead of its phase. More specifically, our methods monitor the transfer matrix rather than just polarization and isolate disturbance location by monitoring eigenvalues of the polarization transfer matrix. From results obtained we have demonstrated experimentally that we can monitor disturbances that affect signal polarization on a span-by-span basis using High Loss Loop Back (HLLB) paths. It is shown that by measuring the polarization rotation matrix and determining the polarization rotation angle we can identify the span where the disturbance occurred with 35 dB extinction with no limitation on the magnitude of the disturbance and the number of affected spans.