Nonlinear Impairment Compensation in Dispersion-Managed Optical Links

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Solution Overview

Problem

Existing methods for compensating nonlinear impairments in dispersion-managed optical fiber links, such as Mid-Span Optical Phase Conjugation and Digital Backward Propagation, face limitations due to asymmetry in transmission links and complex setups, and require symmetric power evolution, which is not achievable with conventional EDFA amplification.

Innovation Solution

A method involving phase conjugation with an equivalent optical link configuration, where the equivalent link is designed based on the characteristics of the transmission link to compensate for nonlinear effects, using a novel configuration of EDFAs and optical fibers, allowing for effective nonlinearity compensation even in asymmetric links.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If Mid-Span Optical Phase Conjugation is used to compensate nonlinear distortion, then nonlinear impairment compensation is achieved, but the transmission link requires symmetric properties which are not typical and implementation requires cumbersome optical set-up with nonlinear optics

Engineering Contradiction:

Improvenonlinear distortion compensationVSAvoidoptical set-up complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the optical-domain phase conjugation mechanism with an electrical-domain digital signal processing approach. Instead of using nonlinear optical devices to generate phase conjugated waves, the system uses digital back-propagation algorithms that compute the inverse of the nonlinear distortion based on measured or estimated channel characteristics, thereby eliminating the need for complex optical set-up while achieving the same compensation effect

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent creates a digital copy or model of the transmission channel's nonlinear characteristics and uses this model to simulate and reverse the distortion effects. By constructing an equivalent digital representation of the optical channel and applying inverse operations in the electrical domain, the system achieves compensation without requiring physical optical phase conjugation hardware

Inventive Principle:

Principle #26Copying

2Reliability

If Digital Backward Propagation is used to compensate fiber impairments, then nonlinear distortion compensation is achieved, but the technique requires solving complex BP-equations using split step method with multiple parameters

Engineering Contradiction:

Improvenonlinear distortion compensationVSAvoidcomputational complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies a simplified version of digital back-propagation that focuses on compensating the dominant nonlinear effects rather than solving the complete nonlinear Schrödinger equation with all parameters. By targeting the most significant impairment mechanisms and using approximate models, the system achieves practical compensation with reduced computational burden while maintaining effective performance

Inventive Principle:

Principle #16Partial or excessive action

3Productivity

If optical power per channel is increased to achieve high OSNR for higher modulation order, then transmission capacity is improved, but intra-channel nonlinear distortion increases

Engineering Contradiction:

Improvetransmission capacityVSAvoidintra-channel nonlinear distortion

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent transforms the harmful nonlinear distortion effects into beneficial compensation opportunities by measuring the actual distortion introduced by the high power transmission and then applying precise inverse operations. The system uses the distorted signal itself as input to the compensation algorithm, which calculates and applies the exact reverse transformation, thereby converting the harmful nonlinear effect into a correctable artifact that can be eliminated

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 efficient compensation of nonlinear impairments, allowing for increased transmission capacity or distance by minimizing accumulated nonlinear phase shift, and can be optimized through simulation to maximize transmission performance.

Implementation Method 1

applying a phase conjugation to the transmission link, the phase conjugation responsive to an input wave over the transmission link and providing a conjugated version of the input wave

Methodology Applied

Scientific EffectPhase conjugation:

Data Source

PatentUS9071356B2Method for the compensation of nonlinear impairments in dispersion-managed optical fiber links using phase conjugation and equivalent optical link

Publication Date: 2015.06.30 NEC CORP

AI summary

A method for nonlinearity compensation for an optical transmission link includes determining a dispersion effect of a transmission link; applying a phase conjugation to the transmission link, the phase conjugation responsive to an input wave over the transmission link and providing a conjugated version of the input wave; and configuring an optimum equivalent link responsive to the phase conjugation after the transmission link to compensate for a non-linear dispersion effect from said transmission link.