Coherent Receiver Imperfection Compensation via Dual Equalizer Adaptation
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Solution Overview
Problem
Current coherent optical receiver compensation techniques are limited by the need for factory calibration, inability to adapt during operation, and inability to cope with nonlinear impairments, especially high-order PMD, PDL, and CD, requiring special training sequences and increasing complexity.
Innovation Solution
A device that uses an agnostic adaptation algorithm to equalize the receive signal with two separate equalizers, estimating the link response during operation and calculating the target output for the receiver equalizer based on the link transfer function, allowing for compensation of nonlinear impairments without special training sequences and reducing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If factory calibration is used for compensation, then initial setup is simplified, but the system cannot adapt to component changes over time and requires time-consuming external equipment
Solution Approach 1:
The patent implements dynamic adaptation by continuously tracking component characteristics changes over time through real-time monitoring and adjustment of compensation parameters, allowing the system to adapt to aging and temperature effects without factory recalibration
Solution Approach 2:
The system uses feedback from the coherent receiver to automatically adjust compensation parameters based on measured imperfections, eliminating the need for external calibration equipment and enabling continuous optimization of compensation accuracy
2Productivity
If high-order constellations are used at high line rates, then spectral efficiency is improved, but sensitivity to transponder imperfections increases
Solution Approach 1:
The system performs preliminary compensation of identified imperfections before signal transmission through the coherent receiver, preventing distortion accumulation and maintaining signal integrity for high-order constellations at high line rates
Solution Approach 2:
The system applies preliminary anti-action by pre-compensating for expected imperfections such as IQ skew and nonlinearities before they degrade the signal, thereby protecting the high-order constellation integrity
3Use of energy by moving object
If electrical driver and modulator operate at high-power levels, then signal power utilization is improved, but nonlinear distortion increases
Solution Approach 1:
The system converts the harmful nonlinear distortion generated by high-power operation into a measurable imperfection that can be characterized and compensated, transforming a disadvantage into an opportunity for adaptive correction
Solution Approach 2:
The system dynamically adjusts compensation parameters based on the actual operating conditions and measured nonlinear distortion characteristics, optimizing the balance between power utilization and distortion suppression
Data Source
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AI summary
The present invention relates to optical communications, in particular between an optical transmitter and a coherent optical receiver over an optical link. The invention provides a device for compensating imperfections at the coherent optical receiver. The device is configured to: obtain a receive signal from the receiver; adapt a first equalizer based on a target output for the first equalizer; compensate the receive signal with the first equalizer in order to compensate imperfections caused by the receiver; and compensate the receive signal further with a second equalizer, in order to compensate imperfections caused by a link between a transmitter and the receiver. The device is further configured to: estimate a channel response based on a configuration of the second equalizer; extract a transfer function of the link from the channel response; and calculate the target output for the first equalizer based on the transfer function and based on bit decisions obtained from the receive signal.