Optical Non-linearity Compensation via Phase Modulation
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Solution Overview
Problem
Existing methods for compensating optical non-linearities in long-haul optical transmission systems are impractical, computationally complex, and inefficient, often requiring expensive or exotic components, and fail to significantly improve received signal quality due to challenges in modeling and implementing effective inverse systems.
Innovation Solution
A method involving the generation of an information-bearing signal with closely-spaced sub-carriers and application of time-varying phase modulation, either in the electrical or optical domain, to mitigate non-linear effects in optical channels, using techniques like OFDM and phase modulation to simplify system modeling and reduce computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high launch power is used in optical fibres, then the optical signal-to-noise ratio is improved, but optical non-linearities increase causing signal distortion
Solution Approach 1:
The patent applies preliminary action by pre-compensating for optical non-linearities at the transmitter before signal transmission. The system calculates expected non-linear distortion based on transmission parameters and applies inverse compensation to the signal, so that when the signal propagates through the optical fibre, the pre-applied compensation counteracts the non-linear effects, maintaining signal quality without requiring high launch power that would exacerbate non-linearities
2Measurement precision
If conventional non-linearity compensation methods are used, then some signal quality improvement is achieved, but the system complexity and computational requirements become impractically high
Solution Approach 1:
The patent applies parameter changes by transforming the complex non-linearity compensation problem into a simpler parameter-based calculation. Instead of implementing full physical models of non-linear propagation, the system uses simplified parameters (launch power, fibre length, non-linearity coefficient) to compute compensation factors that are applied to the signal. This reduces computational complexity from solving partial differential equations to simple algebraic calculations while maintaining effective compensation
Solution Approach 2:
The patent substitutes complex physical compensation mechanisms with electronic/digital signal processing. Rather than using physical components with negative non-linear coefficients or complex optical phase conjugation setups, the invention uses digital computation to calculate and apply compensation phases to the electrical signals before optical modulation, replacing mechanical/optical complexity with computational simplicity
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 enables substantial simplification of system propagation models, reduces computational costs, and improves received signal quality by effectively compensating for non-linearities, allowing for increased transmission distances and reduced amplifier spacing without the need for complex components.
Implementation Method 1
an optical source for generating an optical carrier wave
Implementation Method 2
application of time-varying phase modulation, either in the electrical or optical domain
Data Source
AI summary
A method of transmitting information over a non-linear optical channel includes the step (152) of generating an information-bearing signal, preferably an OFDM signal, which includes a plurality of closely-spaced sub-carriers in the frequency domain. A time-varying phase modulation is determined (154), which is a first function, and preferably a linear function, of the transmitted optical power corresponding with the information-bearing signal. The information-bearing signal and the time-varying phase modulation are applied (156) to an optical source in order to generate a corresponding transmitted optical signal having substantially the stated transmitted optical power characteristic. The first function of transmitted optical power is selected so as to mitigate the effect of the non-linearity of the optical channel upon the transmitted optical signal. In alternative arrangements, a time-varying phase modulation, being a second function of optical power, is computed (162) and applied (164) to a signal received following transmission through a non-linear optical channel. The two alternative arrangements provide, respectively, for pre-compensation and post-compensation of non-linear propagation effects that may be carried out entirely within the electrical domain, for example using digital signal processing techniques.