COTDR Fault Location in Undersea Optical Amplifiers
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Solution Overview
Problem
In multi-span optical transmission systems, coherent optical time domain reflectometry (COTDR) struggles to accurately locate faults in optical amplifiers due to the presence of optical isolators that prevent backscattered signals from returning along the same fiber, making it difficult to monitor amplifier performance without additional telemetry channels.
Innovation Solution
A method is developed to generate and compare COTDR traces to create a difference trace, which is then analyzed using linear combinations of difference trace vectors to identify and locate faults in optical amplifiers, allowing for the elimination of telemetry channels by interpreting changes in backscattered signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If optical isolators are used in repeaters to limit signal propagation to a single direction, then signal directionality is improved, but backscattered signal return is blocked making amplifier fault location difficult
Solution Approach 1:
The patent introduces bidirectional couplers as intermediary devices at each repeater location to mediate between the optical isolators and the COTDR system. These couplers provide a controlled path for backscattered signals to return to the COTDR unit while maintaining the isolators' function of preventing unwanted signal propagation, thus resolving the contradiction between signal directionality and fault detectability
Solution Approach 2:
The patent segments the optical transmission system into multiple spans with discrete repeaters, each equipped with bidirectional couplers. This segmentation allows the COTDR system to receive backscattered signals from specific amplifier locations by analyzing reflections at each coupler interface, enabling localized fault detection despite the presence of isolators in each segment
2Measurement precision
If bidirectional couplers are added to enable backscattered signal return, then amplifier monitoring capability is improved, but device complexity increases
Solution Approach 1:
The bidirectional couplers are designed to serve multiple functions: enabling COTDR signal return, maintaining amplifier operation, and providing fault location capability. By making these components multi-functional, the patent reduces the need for additional dedicated monitoring equipment, thereby limiting the increase in overall device complexity while achieving precise amplifier monitoring
Solution Approach 2:
The patent merges the monitoring function with the existing repeater structure by integrating bidirectional couplers into the repeater components. This consolidation allows the same hardware infrastructure to serve both signal amplification and fault monitoring purposes, reducing the need for separate monitoring channels and minimizing additional complexity
3Measurement precision
If COTDR traces are compared to reference traces to identify faults, then fault detection accuracy is improved, but signal processing complexity increases
Solution Approach 1:
The patent establishes reference COTDR traces during normal operating conditions before faults occur. These pre-established references serve as baseline patterns for comparison, allowing the system to quickly identify deviations indicating faults without requiring complex real-time analysis algorithms, thus improving detection accuracy while limiting processing complexity
Solution Approach 2:
The patent creates simplified representations of normal system behavior through reference traces that can be stored and compared against current measurements. By using these copied baseline patterns rather than complex theoretical models, the system achieves high fault detection accuracy through straightforward pattern matching and comparison operations
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 enables the accurate identification and location of optical amplifier faults within the transmission path, enhancing in-service monitoring capabilities and reducing the need for additional telemetry channels, thereby improving the overall health monitoring of optical transmission systems.
Implementation Method 1
In COTDR, an optical pulse is launched into an optical fiber and backscattered signals returning to the launch end are monitored
Implementation Method 2
Backscattering and reflection also occur from discrete elements such as couplers, which create a unique signature
Data Source
AI summary
A method is provided for locating a fault in one or more optical amplifiers operating in saturation and located along an optical transmission path. The method begins by generating a coherent optical time domain reflectometry (COTDR) trace representing a backscattered and/or reflected optical power level along the transmission path and comparing the trace to a reference trace to generate a difference trace that represents a change in gain. The change in gain is assigned to at least one of the optical amplifiers based on the difference trace. The method comprises assigning the difference trace to faults in the optical amplifiers, equating the difference trace with a linear combination of difference trace vectors each arising from a fault in a different one of the optical amplifiers, and iterating to determine a coefficient value associated with each difference trace vector. Each nonzero coefficient value denotes a fault in an optical amplifier.