Digital Coherent Receiver Phase Control Stabilization
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Solution Overview
Problem
Digital coherent receivers face challenges in maintaining stable phase control due to polarization mode dispersion and fluctuations, leading to errors in phase compensation and dephasing, especially when sudden changes in polarization occur.
Innovation Solution
The implementation of a digital coherent receiver with plural equalization filters having different characteristics before phase detectors and sensitivity monitoring phase shifters, using a square sum of sensitivity monitoring signals to correct phase detection values, stabilizes phase control even under polarization mode dispersion or fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If selection-diversity combining is employed using only phase detection values with high sensitivities, then the SN ratio is improved, but errors in phase control occur when sudden polarization changes cause detected values to increase from low levels below the threshold
Solution Approach 1:
The patent applies preliminary action by calculating a moving average of sensitivity monitoring values before they are used for phase detection. This preprocessing step ensures that when sudden polarization changes occur, the threshold-based selection uses smoothed, predictive values rather than raw instantaneous values, preventing errors caused by abrupt transitions from low to high sensitivity states
Solution Approach 2:
The patent implements feedback by continuously monitoring sensitivity values and using them to dynamically adjust which phase detection results are selected and combined. The moving average of sensitivity monitoring values feeds back into the selection process, creating a closed-loop system that adapts to polarization changes while maintaining stable phase control
2Reliability
If multiple equalization filters with different characteristics are used before phase detectors, then phase following capability is maintained under polarization mode dispersion, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the phase detection function into multiple parallel processing paths, each with a different equalization filter. This allows the system to handle different polarization mode dispersion conditions simultaneously through segmented processing channels, improving reliability without requiring complex sequential processing
Solution Approach 2:
The patent implements universality by designing multiple equalization filters with different characteristics that can handle various polarization conditions. Each filter serves as a specialized processor for specific dispersion scenarios, and the system universally handles all polarization states by selecting from these pre-configured filters based on sensitivity monitoring
Data Source
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AI summary
A digital coherent receiver includes a sampling phase detector to detect a phase of a sampled digital signal, and a phase adjustor to adjust the sampling phase of the digital signal based upon the detected phase. The phase detector includes filters to equalize the digital signal with different equalization characteristics; sensitivity monitoring phase detectors, each connected to one of the filters and outputting a phase detection signal representing the phase of the output signal from the associated filter together with a sensitivity monitoring signal representing the sensitivity of the phase detection; sensitivity correction coefficient generators, each generating a sensitivity correction coefficient for correcting the associated phase detection signal using a square sum of the sensitivity monitoring signals; and an adder to add the phase detection signals that have been corrected by the sensitivity correction coefficients, and output a phase signal.