Digital Filter Amplitude Correction in Coherent Optical Receivers
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Solution Overview
Problem
In digital filters used for coherent optical communication, coefficient control that minimizes mean square error can lead to deviations in the amplitude of transmission signal components, affecting subsequent signal processing units and reducing signal processing accuracy.
Innovation Solution
A gain adjustment method that involves converting optical signals to electrical signals, performing first signal processing, adaptive equalization using a digital filter, correcting the amplitude of the filter output based on amplitude and phase information, and subsequent second signal processing to improve signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coefficient control that minimizes mean square error is performed in the digital filter, then crosstalk and linear distortion between polarization multiplexed signals are equalized, but the amplitude of the transmission signal component in the digital filter output deviates from the expected value
Solution Approach 1:
The patent uses feedback by calculating the amplitude deviation between the actual digital filter output and the expected transmission signal amplitude, then using this deviation information to control the digital filter coefficient and correct the amplitude. This closed-loop feedback mechanism resolves the contradiction by continuously adjusting the filter to maintain both equalization performance and amplitude accuracy.
Solution Approach 2:
The patent changes the digital filter coefficient parameter based on the calculated amplitude deviation. By dynamically adjusting the filter coefficient in response to amplitude errors, the system maintains accurate amplitude representation while preserving the equalization benefits of the digital filter.
2Measurement precision
If the amplitude of the transmission signal component deviates from the expected value, then subsequent signal processing units are affected, but adding amplitude correction increases device complexity
Solution Approach 1:
The patent merges the amplitude correction function with the existing digital filter by using the same filter structure to perform both equalization and amplitude control. The amplitude correction is integrated into the filter coefficient control mechanism, avoiding the need for separate correction hardware or processing stages.
Solution Approach 2:
The digital filter performs self-correction by using its own output amplitude deviation information to adjust its coefficient. The system uses internal feedback where the filter monitors its own performance and automatically corrects amplitude errors without requiring external intervention or additional complex processing units.
Data Source
AI summary
A gain adjustment method in an optical transmission system that performs communication by a digital coherent system including an optical transmission device and an optical reception device includes converting an optical signal transmitted from the optical transmission device into an electrical signal, converting the electrical signal from an analog signal to a digital signal, performing first signal processing on the digital signal, performing adaptive equalization processing on the digital signal subjected to the first signal processing using a digital filter, correcting an amplitude of an output signal of the digital filter based on information of the amplitude and a phase of the output signal of the digital filter and the amplitude of a known transmission signal, and performing second signal processing on the output signal of the digital filter whose amplitude has been corrected.