Optical Receiver Tap Number Control for Polarization Variation
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Solution Overview
Problem
Existing digital coherent receivers struggle to maintain transmission quality when faced with rapid polarization variations occurring in several tens of microseconds, as adaptive control of the step size parameter is insufficient in such scenarios.
Innovation Solution
An optical receiver is designed with an adaptive equalizer using two finite impulse response filters to compensate for waveform distortions in polarization multiplexed light, accompanied by a tap number controller that adjusts the number of taps based on calculated margins to improve bit error ratio performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive control on step size parameter is performed, then transmission quality is improved for gradual polarization variation, but transmission quality degrades for rapid polarization variation occurring in several tens of microseconds
Solution Approach 1:
The patent applies dynamics by making the number of taps in the finite impulse response filter adjustable and adaptive. The tap number controller dynamically changes the filter length based on the polarization variation characteristics, allowing the system to adapt to different polarization variation speeds. For rapid variations, a larger number of taps is used to capture more historical signal information, while for gradual variations, a smaller number of taps suffices, thus resolving the contradiction between reliability and adaptability.
Solution Approach 2:
The patent changes the parameter of the filter (number of taps) based on the polarization variation conditions. The tap number controller adjusts this parameter according to the calculated margin, which reflects the severity of polarization variation. This parameter change enables the system to maintain high transmission quality across different polarization variation scenarios, addressing the limitation of fixed step size control.
2Measurement precision
If the number of taps of finite impulse response filter is increased, then waveform distortion compensation is improved, but device complexity and processing load increase
Solution Approach 1:
The patent makes the filter configuration dynamic by allowing the tap number to be adjusted based on actual transmission conditions. Rather than using a fixed large number of taps that would always increase complexity, the system dynamically sets the appropriate tap number according to polarization variation characteristics, achieving high compensation accuracy only when needed while reducing complexity in normal conditions.
Solution Approach 2:
The patent changes the filter parameter (number of taps) adaptively based on the polarization variation margin. The tap number controller monitors transmission quality and adjusts the tap number accordingly, increasing it only when polarization variation requires more aggressive compensation. This parameter change strategy balances compensation accuracy with device complexity.
Data Source
AI summary
A coherent receiver performing coherent detection on polarization multiplex light into which first polarization light and second polarization light are multiplexed, and splitting the polarization multiplex light into the first polarization light and the second polarization light, an adaptive equalizer compensating the waveform distortion of a signal superimposed onto the first polarization light by using a first FIR filter, compensating the waveform distortion of a signal superimposed onto the second polarization light by using a second FIR filter, and by decoding each of the signals whose waveform distortion has been compensated, generating their respective decoded data, an error ratio calculator calculating the bit error ratio of each decoded data generated by the adaptive equalizer, a margin calculator calculating a margin from the bit error ratio of an error correction limit in each bit error ratio calculated by the error ratio calculator, and a tap number controller setting up the numbers of taps of the first and second FIR filters by referring to the respective margins calculated by the margin calculator are included.