Nonlinear Optical Impairment Calculation via Covariance Matrix
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Solution Overview
Problem
Traditional methods for calculating nonlinear optical transmission impairments in optical transmission systems are time-consuming, requiring hundreds of calculation steps and repeated use of FFTs, making it impractical for rapid validation of optical channel trails in optical networks.
Innovation Solution
A method that calculates per-span nonlinear field variance and covariance between spans, represented as a covariance matrix, allowing for the rapid estimation of total nonlinear field variance without sequential FFT calculations, using power scaling rules and empirical functions based on fiber attributes and modulation formats.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional SSF propagation simulations with repeated FFT calculations are used, then calculation accuracy of nonlinear optical impairments is maintained, but validation time becomes unacceptably long
Solution Approach 1:
The patent segments the optical fiber link into multiple spans and calculates nonlinear field variance for each span independently. This allows parallel processing of different spans and eliminates the need for sequential FFT calculations across the entire link, significantly reducing validation time while maintaining accuracy through proper accounting of inter-span correlations via covariance matrices.
Solution Approach 2:
The patent changes the calculation parameters from time-domain waveforms requiring repeated FFTs to frequency-domain power spectral density representations. By working directly with power spectra and using analytical expressions for nonlinear field variance and covariance, the method avoids iterative time-domain simulations while preserving calculation accuracy.
2Measurement precision
If hundreds of calculation steps with repeated FFTs are performed for each fiber span, then accuracy of nonlinear phase and chromatic dispersion calculation is ensured, but computational complexity increases significantly
Solution Approach 1:
The patent extracts and pre-calculates the nonlinear field variance and covariance parameters for each span pair, separating these computations from the main validation process. By computing these parameters once and reusing them across multiple validation scenarios, the method reduces computational complexity while maintaining accuracy for subsequent link budget calculations.
Solution Approach 2:
The patent performs preliminary calculations of nonlinear field variance and covariance matrices before the actual validation process. These pre-computed parameters are stored and reused during validation, eliminating the need for repeated complex FFT calculations and reducing overall computational complexity while ensuring accurate nonlinear impairment estimation.
3Reliability
If tens of thousands of optical channel trails are validated using conventional SSF methods, then comprehensive network validation is achieved, but processing time extends to many hours
Solution Approach 1:
The patent segments the validation process into independent span-level calculations with covariance-based correlation accounting. This enables parallel processing of multiple optical channel trails and fiber spans simultaneously, increasing validation throughput by orders of magnitude while maintaining comprehensive network validation through proper correlation modeling.
Solution Approach 2:
The patent uses pre-computed nonlinear field variance and covariance parameters as templates that can be copied and applied to multiple optical channel trails with similar characteristics. This approach allows rapid validation of tens of thousands of trails by reusing calculated parameters rather than performing full SSF simulations for each trail, dramatically improving productivity while maintaining reliability.
Data Source
AI summary
A method of estimating nonlinear transmission impairments of an Optical Channel (OCh) trail in an optical communications network. A per-span nonlinear field variance is calculated for each span of the trail. The per-span nonlinear field variance represents nonlinearly induced noise due to the transmission impairments of that span. The nonlinearly induced noise being imparted to a signal transmitted through the trail and detected by the receiver. A respective covariance between the nonlinear fields contributed by each span pair of the OCh trail is computed. The covariance represents the correlation of the nonlinearly induced noise imparted to the signal within the first span of a span pair with the nonlinearly induced noise imparted to the signal within the second span of the pair. A covariance matrix is populated using the computed per-span variance values and covariance values. A total nonlinear field variance is computed by summing over the covariance matrix elements.