Digital Filter for Optical Nonlinearity Compensation Memory Reduction
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Solution Overview
Problem
Optical communications systems face challenges in reducing memory requirements for electrical domain compensation of intra-channel nonlinearity, particularly at high levels of chromatic dispersion over long fiber lengths, where existing methods are either impractically complex or costly.
Innovation Solution
A digital filter processing system that uses a reduced data set stored in RAM to generate a predistorted electrical signal, mitigating intra-channel nonlinearity by applying a compensation function, which is then converted into a predistorted optical signal for transmission, thereby extending compensation capabilities over longer distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical domain compensation is applied to mitigate intra-channel nonlinearity over long fiber spans, then signal quality is improved, but memory requirements for storing compensation data increase exponentially
Solution Approach 1:
The patent divides the fiber link into multiple spans and applies compensation iteratively across each span rather than attempting to compensate for the entire link at once. This segmentation allows the system to manage memory requirements by processing smaller segments sequentially, where each span's compensation data can be stored and applied independently before moving to the next span.
Solution Approach 2:
The patent pre-calculates and stores compensation data for individual fiber spans before actual signal transmission. By performing the complex compensation calculations in advance for each span and storing only the essential compensation parameters rather than full compensation datasets, the system reduces memory requirements while maintaining the ability to apply effective compensation during signal transmission.
2Measurement precision
If higher resolution compensation data is used to accurately mitigate dispersion effects, then compensation precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies different compensation strategies to different spans based on their specific characteristics. Rather than using uniform high-resolution compensation across all spans, the system tailors the compensation approach to each individual span's dispersion properties, using higher precision only where necessary and simpler methods where adequate performance is achieved with less complexity.
Solution Approach 2:
The patent applies compensation iteratively across multiple passes rather than attempting single-pass perfect compensation. In each iteration, compensation is applied to reduce dispersion effects, and subsequent passes refine the compensation. This partial action approach achieves high overall precision without requiring exponentially complex single-pass processing.
Data Source
AI summary
A digital filter processes an input signal to be conveyed through an optical communications system. The processing generates a predistorted signal using a compensation function that mitigates impairments of the optical communications system. The input signal has a sample period of T, while the predistorted signal has a sample period of T/2. The digital filter has a first branch including a respective first T-spaced filter for processing the input signal using the compensation function to generate a corresponding first output signal comprising nT/2 samples with n odd. A second branch includes a respective second T-spaced filter for processing the input signal with a delay of T relative to the first branch using the compensation function to generate a corresponding second output signal comprising nT/2 samples with n even. A combiner operates to combine the first and second output signals to generate the predistorted signal having a sample period of T/2.