Multi-channel Optical Transmitter Mitigating Polarization-Dependent Loss
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Solution Overview
Problem
Multiple-channel optical fiber communication systems face significant performance degradation due to polarization-dependent loss (PDL), which existing solutions attempt to address with high complexity schemes that are not efficient for high-speed communications.
Innovation Solution
A method where a combination of symbols is transmitted over each channel instead of a single symbol, using a multi-channel optical transmitter and receiver that store sequences of mappings, allowing for inverse mapping operations to average mutual information and mitigate loss by varying channel usage over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional signaling techniques (QPSK or 16QAM) are used, then the system is simple to implement, but the achievable information rate becomes dependent on the rotation angle between PDL axes with different attenuations, causing significant performance degradation in worst case scenarios
Solution Approach 1:
The patent applies dynamics by making the mapping between symbol vectors and transmission channels time-varying. Instead of a fixed mapping, the system uses different mappings at different time instances, allowing the system to adapt to changing PDL conditions and avoid worst-case scenarios where fixed mappings would fail.
Solution Approach 2:
The patent changes the mapping parameter dynamically over time. By varying the mapping between symbol vectors and transmission channels according to a predetermined sequence, the system transforms the static mapping problem into a dynamic one, ensuring that no single mapping is always subjected to the worst PDL conditions.
2Reliability
If multi-dimensional constellation points schemes are used to overcome PDL, then PDL tolerance is improved, but the complexity becomes prohibitively high compared to potential gains in high-speed communications
Solution Approach 1:
The patent segments the data stream into multiple sub-streams, with each sub-stream mapped to a different transmission channel. This segmentation allows the system to distribute the impact of PDL across multiple channels rather than concentrating it on a single channel, achieving PDL tolerance without requiring complex multi-dimensional constellation points.
Solution Approach 2:
The patent employs periodic action by using a predetermined periodic sequence of mappings. The mapping pattern repeats over time, ensuring that each sub-stream experiences different channel conditions periodically. This periodic variation in mapping achieves PDL mitigation while maintaining relatively simple coding complexity compared to multi-dimensional schemes.
3Device complexity
If a single symbol is transmitted over each transmission channel, then the transmission is simple, but the probability of symbol reception deteriorates when transmission channels experience high loss
Solution Approach 1:
The patent merges multiple symbols into a symbol vector that is transmitted across multiple channels simultaneously. Instead of transmitting single symbols on single channels, the system combines multiple symbol transmissions into a unified structure where the failure of one channel does not result in complete information loss, thereby improving symbol reception probability.
Solution Approach 2:
The patent applies dynamics by varying the mapping between symbol vectors and transmission channels over time. This dynamic remapping ensures that the system can adapt to changing channel conditions, improving the probability that at least some symbols in each vector will be successfully received even when individual channels experience high loss.
Data Source
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AI summary
An optical communications system (100) including a multi-channel optical transmitter (1) comprising a plurality of symbol generators (12), each symbol generator (12) being configured for generating a symbol stream (121), a digital mapping module (13) for performing a mapping on each symbol vector, an emission unit (10) configured for emitting a multi-channel signal (8) carrying the symbol vectors, and a multi-channel optical receiver (3) comprising a reception unit (20) configured for extracting symbol vectors, a digital inverse mapping module (23) for performing the inverse mapping on the received symbol vector, and for reconstructing the data streams from the restored symbol vectors.