OPC and CVDNN Nonlinear Compensation for Coherent QAM Systems
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Solution Overview
Problem
Digital nonlinear compensation methods in optical communication systems are unable to effectively improve channel capacity, as they are computationally complex, limited in signal quality improvement, and cannot increase input signal power beyond a certain threshold, thereby restricting bit error rate performance and channel capacity.
Innovation Solution
The method involves deploying optical phase conjugation (OPC) and a trained complex-valued deep neural network (CVDNN) for nonlinear compensation in coherent high-capacity high-order QAM systems, where OPC generates an idler to simulate nonlinear effects, and the CVDNN performs phase recovery and compensation on the constellation diagram to enhance signal quality and channel capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital backpropagation is used to equalize nonlinear effects, then deterministic nonlinear effects can be effectively compensated, but computational complexity increases with transmission distance and dispersion accumulation
Solution Approach 1:
The patent introduces an optical phase conjugation module as an intermediary device in the optical transmission system. This module performs optical phase conjugation on the transmitted signal to generate an idler signal that carries phase information inverted relative to the original signal. By placing this intermediary device in the optical domain rather than processing everything digitally, the system achieves nonlinear compensation without proportionally increasing computational complexity with transmission distance.
Solution Approach 2:
The patent replaces part of the digital signal processing mechanism with an optical mechanism. Instead of using purely digital backpropagation to compensate for nonlinear effects accumulated over long distances, the system uses optical phase conjugation to pre-compensate or counteract nonlinear distortions in the optical domain. This substitution reduces the burden on digital processors and maintains real-time processing capability.
2Device complexity
If Volterra series nonlinear equalizer is used, then computational complexity is reduced compared to digital backpropagation, but it only equalizes nonlinear effects within a single channel
Solution Approach 1:
The optical phase conjugation module serves multiple functions simultaneously: it compensates for nonlinear effects in the signal channel, generates an idler that can be used for phase recovery, and provides benefits across multiple wavelength channels in WDM systems. This multi-functional approach allows a single device to address both computational complexity reduction and enhanced channel coverage capability.
Solution Approach 2:
The generated idler signal acts as an intermediary that carries phase information useful for phase recovery processes. This intermediary signal enables the system to handle phase ambiguities that would otherwise require complex digital processing, thereby extending the equalizer's effectiveness across multiple channels without proportionally increasing complexity.
3Measurement precision
If machine learning-based soft decision is used, then decision margin of constellation diagram is optimized, but nonlinear equalization performance is limited for signals with severe degradation
Solution Approach 1:
The optical phase conjugation performs preliminary compensation of nonlinear effects before the signal undergoes severe degradation. By pre-inverting the phase distortions in the optical domain, the signal arrives at the receiver with reduced nonlinear impairment, making subsequent machine learning-based soft decision more effective and improving performance under severe degradation conditions.
Solution Approach 2:
The patent replaces part of the digital signal processing function with an optical mechanism. The optical phase conjugation module handles the heavy lifting of nonlinear compensation in the optical domain, allowing the machine learning-based soft decision to focus on finer optimizations like decision margin improvement rather than struggling with severely degraded signals.
4Reliability
If digital nonlinear compensation methods are used, then bit error rate performance is improved to a certain extent, but input signal power cannot be increased beyond a certain threshold
Solution Approach 1:
The optical phase conjugation module acts as an intermediary that enables the system to operate at higher input signal powers without suffering from excessive nonlinear distortions. By pre-compensating for nonlinear effects, the module allows the transmitter to use higher power levels to improve signal-to-noise ratio and channel capacity, while the nonlinear compensation prevents performance degradation that would otherwise limit the usable power range.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly improves signal power and quality, thereby enhancing channel capacity in WDM coherent optical communication systems, allowing for better bit error rate performance and increased channel capacity.
Implementation Method 1
coupling the signal light and the pump light to enter a highly nonlinear optical fiber (HNLF), and performing four-wave mixing to generate phase-conjugated idler
Implementation Method 2
deploying an optical phase conjugation (OPC) on an intermediate link of communication between a transmitter and receiver, receiving an idler generated by performing phase conjugation on a transmitted signal based on the OPC
Data Source
AI summary
The invention provides a method for nonlinear compensation of coherent high-capacity high-order QAM system, including: deploying an OPC on an intermediate link of communication between a transmitter and receiver, and performing phase conjugation on a transmitted signal based on the OPC to generate idler; performing phase recovery on a compensated signal at the receiver to obtain a constellation diagram, simulating a nonlinear function relationship between a transmitted signal and a received signal by using a trained and learned CVDNN, and performing nonlinear compensation on the constellation diagram to obtain the compensated constellation diagram; and calculating a Q-factor based on the compensated constellation diagram, and evaluating communication performance by the Q-factor. Nonlinear compensation is performed on a transmitted signal by using an OPC+CVDNN method to equalize nonlinear degradation of an optical fiber in a WDM coherent optical communication system.