Optical Fiber Link Nonlinear Impairment Evaluation via Sub-span Segmentation

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Solution Overview

Problem

Current methods for evaluating nonlinear impairment in optical fiber links are computationally intensive and time-consuming, particularly for dispersion uncompensated links with non-uniform fiber span lengths and mixed fiber types, limiting their efficiency in modeling and simulation.

Innovation Solution

A method that partitions the optical fiber link into sub-spans based on chromatic dispersion equivalence, allowing for the acquisition of sub-span function parameters including noise variance and correlations, which are used to determine nonlinear impairment independently of fiber type, length, and stimulated Raman scattering, enabling faster evaluation and modeling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the enhanced Gaussian noise (eGN) model is used to evaluate nonlinear impairment, then accuracy is improved by including modulation format impact, but computation time increases significantly due to multiple integrations and massive computation

Engineering Contradiction:

Improvenonlinear impairment evaluation accuracyVSAvoidcomputation time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The optical fiber link is segmented into multiple sub-spans based on chromatic dispersion equivalence. Each sub-span is characterized by acquiring function parameters including noise variance and correlations. This segmentation transforms the complex full-link evaluation into manageable sub-problems that can be processed independently and then combined, dramatically reducing computation time while maintaining accuracy for arbitrary links with non-uniform fiber span lengths and mixed fiber types

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the evaluation parameters from requiring multiple integrations to using pre-acquired sub-span function parameters. By transforming the problem from direct numerical integration to parameter-based evaluation, the computation is accelerated from seconds to milliseconds while preserving the accuracy benefits of the eGN model including modulation format effects

Inventive Principle:

Principle #35Parameter changes

2Reliability

If dispersion compensation fiber/module is used, then linear impairments are compensated, but nonlinear impairment increases due to coherent NLI generation and additional losses

Engineering Contradiction:

Improvelinear impairment compensationVSAvoidnonlinear impairment

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The invention replaces the physical dispersion compensation mechanism (dispersion compensation fiber or modules) with a digital signal processing approach. The receiver DSP performs chromatic dispersion compensation through digital filtering and signal processing, eliminating the need for additional optical components that would introduce losses and coherent nonlinear effects. This substitution maintains linear impairment compensation while avoiding the harmful side effects of optical dispersion compensation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If the Gaussian noise (GN) model is used, then computation efficiency is improved, but accuracy deteriorates with 5-15% reach loss due to neglecting modulation format effects

Engineering Contradiction:

Improvecomputation efficiencyVSAvoidnonlinear impairment evaluation accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The link is divided into sub-spans where the modulation format impact is captured in the sub-span function parameters. This segmentation allows the efficient computation structure to be maintained while incorporating the previously neglected modulation format effects, achieving both speed and accuracy

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention modifies the GN model parameters to include modulation format-dependent characteristics in the sub-span function parameters. By changing the parameter set to include these effects, the model achieves eGN-level accuracy while maintaining the computational efficiency of the original GN model through the simplified evaluation approach

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11190272B1Method and apparatus for evaluating nonlinear impairment of an optical fiber link

Publication Date: 2021.11.30 HUAWEI TECH CO LTD

AI summary

There is provided a method and apparatus for evaluating nonlinear impairment of an optical fiber link. The method includes partitioning a natural span of the optical fiber link into multiple sub-spans, each of the multiple sub-spans determined based on chromatic dispersion (CD) equivalence; The method further includes for each of the multiple sub-spans, acquiring sub-span function parameters and a sub-span input power indicative of input power at a particular sub-span, the sub-span function parameters including noise variance and correlations between the particular sub-span and others of the multiple sub-spans. The method additionally includes determining the nonlinear impairment of the optical fiber link based on the sub-span input power and the sub-span function parameters acquired for each of the multiple sub-spans.