Chromatic Dispersion Estimation Using Signal Peak Cost Function
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Solution Overview
Problem
Long-haul optical communication systems face performance limitations due to inter-symbol interference (ISI) caused by fiber-optic impairments such as chromatic dispersion (CD), polarization mode dispersion (PMD), and phase noise, which existing methods struggle to accurately compensate for without increasing non-linearity or computational complexity.
Innovation Solution
A digital coherent optical receiver employs a signal-peak-based cost function to efficiently estimate chromatic dispersion (CD) by sweeping a range of frequency domain equalizer (FDEQ) configurations and computing a goodness measure based on signal peaks, allowing for optimal CD compensation without complex operations like multiplications and divisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chromatic dispersion compensation is performed using fiber of opposite-sign dispersion, then CD compensation is achieved, but non-linearity effects increase
Solution Approach 1:
The patent replaces the physical fiber-based CD compensation method with a digital signal processing approach. Instead of using optical fibers with opposite dispersion to compensate chromatic dispersion, the invention uses digital filters and signal processing algorithms to estimate and compensate CD effects in the electrical domain after photodetection, thereby avoiding the non-linearity problems associated with optical fiber-based compensation.
2Measurement precision
If digital signal processing is used to compensate fiber-optic impairments, then CD compensation accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent extracts and utilizes specific characteristic features from the received signal - namely signal peaks and their timing information - to estimate chromatic dispersion. By focusing on these extracted features rather than processing the entire signal with complex algorithms, the method achieves accurate CD estimation while reducing computational complexity compared to full-signal digital processing approaches.
Solution Approach 2:
The patent employs blind estimation techniques where the system uses the signal's own characteristics (peaks, timing, power waveform) to estimate and compensate chromatic dispersion without requiring external training sequences or reference signals. This self-service approach reduces the complexity of the processing system while maintaining estimation accuracy.
3Measurement precision
If complex cost functions with multiplications and divisions are used for CD estimation, then estimation accuracy is improved, but processing efficiency decreases
Solution Approach 1:
The patent changes the parameter basis for CD estimation from complex cost functions involving multiplications and divisions to a simplified metric based on signal peak timing and power waveform characteristics. By transforming the estimation problem into one that uses peak detection and timing measurement, the system achieves accurate CD estimation while dramatically improving processing efficiency and reducing computational operations.
Data Source
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AI summary
An apparatus comprises a front end configured to receive an optical signal, and convert the optical signal into a plurality of digital signals, and a processing unit coupled to the front end and configured to determine a best-match chromatic dispersion (CD) estimate in the optical signal by optimizing a cost function based on signal peaks of the plurality of digital signals.