Phase Slip Reduction in Coherent Optical Receivers
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Solution Overview
Problem
Optical communication systems face significant phase slips due to phase estimation errors, which are persistent and undesirable, especially in systems with high data rates and strict reliability requirements, where existing methods either require expensive lasers or increased power and bandwidth to reduce phase noise.
Innovation Solution
A method is introduced that reduces phase slips by constructing a trellis diagram with nodes labeled by phase estimates modulo 2π/N, assigning weights and branch lengths based on phase differences, and determining a shortest path to interpolate demodulation angles, effectively addressing the modulo 2π/N uncertainty and reducing phase slip occurrences without high reference symbol density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If phase estimation techniques are used in optical communication receivers, then demodulation can be performed, but phase slips occur causing large and persistent phase estimation errors
Solution Approach 1:
The phase estimation problem is segmented into discrete phase states represented by nodes in a trellis diagram. Each node corresponds to a specific phase estimate modulo 2π/N, breaking the continuous phase estimation into discrete, manageable states that can be tracked and corrected systematically
Solution Approach 2:
The trellis structure is constructed in advance with all possible phase state transitions defined before processing the actual signal. Node weights and branch lengths are pre-calculated based on phase differences, allowing the receiver to efficiently trace the most likely phase trajectory without real-time complex calculations
2Reliability
If expensive lasers or increased power and bandwidth are used, then phase noise can be reduced, but system cost and complexity increase
Solution Approach 1:
The patent replaces physical hardware solutions (expensive lasers, increased power amplification) with a signal processing approach using trellis-based phase estimation. This substitutes complex mechanical/optical systems with algorithmic processing, achieving phase noise reduction through computational methods rather than hardware upgrades
Solution Approach 2:
The invention changes the parameter space by working with phase estimates modulo 2π/N rather than absolute phase values. This parameter transformation allows the system to track phase changes relative to a reference without requiring absolute phase accuracy, reducing the demand on laser quality and power
3Measurement precision
If high reference symbol density is used, then phase estimation accuracy improves, but bandwidth consumption increases
Solution Approach 1:
The trellis-based phase estimation uses feedback from previously estimated phase states to inform current phase estimates. By tracking the most likely phase trajectory through the trellis and using this historical information, the system achieves accurate phase estimation with fewer reference symbols, reducing the feedback overhead compared to methods requiring dense reference symbol insertion
Data Source
AI summary
Disclosed herein are methods and techniques for reducing phase slips in optical communications systems and in particular methods and techniques that operate in receivers for a coherent communication system transmitting modulated data symbols exhibiting N-ary symmetrical constellation and predetermined reference symbols.