Nonlinear Compensation for Optical Coherent Communication
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Solution Overview
Problem
Current digital signal processing techniques fail to effectively mitigate both intra- and inter-channel fiber nonlinear distortions in high-speed coherent optical systems, particularly in WDM transmission systems, due to computational complexity and limited electrical bandwidth, leading to additive sensitivity penalties in long-haul transmission.
Innovation Solution
A nonlinear compensating scheme that includes an optical link interface, symbol processing unit, filtering unit, perturbation calculating unit, and compensating unit, which processes and filters complex symbols to generate and remove inter- and intra-channel nonlinear perturbation terms, allowing for efficient compensation of nonlinear distortions across different wavelengths and polarizations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital back-propagation (DBP) is used for multi-channel nonlinear compensation, then compensation effectiveness is improved, but computational complexity becomes too high for practical DSP implementation
Solution Approach 1:
The patent transforms the nonlinear compensation problem into a linear filtering problem by changing the mathematical parameters and approach. Instead of using computationally intensive DBP algorithms, the invention employs linear filter coefficients that can be calculated and applied efficiently in DSP circuits, maintaining compensation effectiveness while dramatically reducing computational complexity
Solution Approach 2:
The patent replaces the complex computational mechanism of DBP with a simpler linear filtering mechanism. By substituting the mechanical/computational process of back-propagation with an equivalent linear filtering operation, the system achieves the same compensation goal with much lower computational requirements suitable for practical DSP implementation
2Device complexity
If intra-channel mitigation schemes are implemented, then computational complexity is reduced, but effectiveness is drastically reduced in fully-loaded WDM transmission systems
Solution Approach 1:
The patent creates a universal linear filtering scheme that serves multiple functions simultaneously. The same linear filter coefficients can be applied to compensate for both intra-channel and inter-channel nonlinearities in fully-loaded WDM systems, making the solution broadly applicable across different transmission scenarios without requiring separate complex processing for each channel
Solution Approach 2:
The patent processes different wavelength channels separately through the linear filtering operation. By applying the filtering scheme to each channel's complex symbols independently while accounting for inter-channel interference, the system achieves effective mitigation in fully-loaded WDM systems without excessive computational complexity
3Reliability
If linear impairments are compensated in the digital domain, then compensation effectiveness is improved, but fiber nonlinear impairments remain unaddressed and are treated as additive Gaussian noise
Solution Approach 1:
The patent introduces linear filter coefficients as an intermediary element that bridges the gap between linear and nonlinear impairment compensation. These filter coefficients act as a mediator that, when applied to the received complex symbols, simultaneously address both linear distortions and nonlinear phase noise that was previously treated as additive Gaussian noise
Solution Approach 2:
The patent merges the compensation of linear and nonlinear impairments into a single unified linear filtering operation. By combining these previously separate compensation tasks into one integrated process using linear filter coefficients, the system achieves effective mitigation of both impairment types without requiring separate complex processing stages
Data Source
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AI summary
This application relates to a compensating apparatus for compensating nonlinear distortions induced on an optical signal during transmission through an optical link. The apparatus comprises an optical link interface configured to receive a sequence of first complex symbols (ax, ay) at a first wavelength (λa) of the optical signal and to receive a sequence of second complex symbols (bx, by) at a second wavelength (λb) of the optical signal. The apparatus also includes a symbol processing unit and a filtering unit. The symbol processing unit may be configured to process the second complex symbols (bx, by) using a nonlinear operation, thereby obtaining processed second complex symbols (db, qb). The filtering unit may be configured to linearly filter the processed second complex symbols (db, qb) to produce a second sequence of filter coefficients (f(ab), g(ab)) associated with inter-channel nonlinearity. The apparatus further comprises a perturbation calculating unit configured to generate a sequence of inter-nonlinear perturbation terms (Δaxinter, Δayinter) associated with the received first complex symbols (ax, ay) based on the received first complex symbols (ax, ay) and the second sequence of filter coefficients (f(ab), g(ab)). The apparatus also comprises a compensating unit configured to remove the inter-nonlinear perturbation terms (Δaxinter, Δayinter) from the corresponding first complex symbols (ax, ay) to compensate the nonlinear distortions induced on the first complex symbols (ax, ay) by the second complex symbols (bx, by).