WDM Receiver DSP for Nonlinear Distortion Compensation

Solution Overview

Problem

Conventional WDM systems face significant bit-error rate (BER) penalties due to nonlinear distortions such as the Kerr effect, self-phase modulation, cross-phase modulation, and four-wave mixing, which limit their data-transport capacity and reliability.

Innovation Solution

A WDM receiver is configured with a digital signal processor that performs dispersion-compensation, equalization, and backward-propagation processing to generate a dispersion-compensated signal, which is then subjected to additional dispersion-application and equalization steps to mitigate intra-channel and inter-channel nonlinear distortions, thereby reducing BER and enhancing data-transport capacity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional WDM systems transmit optical signals through optical fiber, then data transport capacity is achieved, but nonlinear distortions (Kerr effect, SPM, XPM, FWM) cause increased bit-error rate

Engineering Contradiction:

Improvedata transport capacityVSAvoidbit-error rate

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies preliminary dispersion compensation and equalization processing to the received optical signal before detection. By pre-compensating for chromatic dispersion and applying equalization filters, the system reduces the impact of nonlinear distortions before they can significantly degrade the signal, thereby maintaining lower bit-error rates while preserving data transport capacity

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback mechanisms where the received signal characteristics are analyzed and used to adjust equalization parameters and dispersion compensation settings. This adaptive feedback loop allows the system to optimize performance in real-time, compensating for varying nonlinear distortion levels and maintaining reliable transmission at high data rates

Inventive Principle:

Principle #23Feedback

2Productivity

If optical signals are transmitted over long distances through optical fiber, then data transport capacity increases, but linear impairments (chromatic dispersion, polarization mode dispersion) and nonlinear impairments accumulate

Engineering Contradiction:

Improvedata transport capacityVSAvoidlinear and nonlinear impairments

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary dispersion compensation and equalization processing to the received optical signal before detection. By pre-compensating for chromatic dispersion and applying equalization filters, the system reduces the impact of nonlinear distortions before they can significantly degrade the signal, thereby maintaining lower bit-error rates while preserving data transport capacity

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback mechanisms where the received signal characteristics are analyzed and used to adjust equalization parameters and dispersion compensation settings. This adaptive feedback loop allows the system to optimize performance in real-time, compensating for varying nonlinear distortion levels and maintaining reliable transmission at high data rates

Inventive Principle:

Principle #23Feedback

3Reliability

If intra-channel and inter-channel nonlinear distortions are present in WDM systems, then signal quality deteriorates, but advanced signal processing increases device complexity

Engineering Contradiction:

Improvesignal qualityVSAvoidsignal processing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the signal processing into distinct functional blocks: dispersion compensation module, equalization processing stage, and nonlinear distortion compensation stage. Each module handles specific aspects of signal degradation, allowing for optimized processing of intra-channel and inter-channel distortions separately, which improves signal quality while managing computational complexity through modular architecture

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent dynamically adjusts equalization parameters and filter coefficients based on the detected signal characteristics and distortion levels. By adapting parameters such as equalization tap weights, dispersion compensation values, and filter bandwidths in real-time, the system effectively compensates for varying nonlinear distortions without requiring excessively complex fixed-structure processors

Inventive Principle:

Principle #35Parameter changes

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

The described signal processing chain effectively reduces nonlinear distortions, leading to a lower bit-error rate and higher data-transport capacity compared to conventional WDM receivers, by partially compensating for inter-channel interference and other nonlinear effects.

Implementation Method 1

After propagating through a length of optical fiber, the received optical signal may be distorted

Methodology Applied

Scientific EffectOptical fiber propagation: Optical Fibre

Implementation Method 2

the received optical signal may be distorted due to linear impairments, such as chromatic dispersion (CD)

Methodology Applied

Scientific EffectChromatic dispersion: Dispersion (of waves)

Implementation Method 3

nonlinear impairments, such as the Kerr effect, including one or more of self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM)

Methodology Applied

Scientific EffectKerr effect: Kerr Effect

Implementation Method 4

the Kerr effect, including one or more of self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM)

Methodology Applied

Scientific EffectSelf-phase modulation: Kerr Effect

Implementation Method 5

the Kerr effect, including one or more of self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM)

Methodology Applied

Scientific EffectCross-phase modulation: Kerr Effect

Implementation Method 6

the Kerr effect, including one or more of self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM)

Methodology Applied

Scientific EffectFour-wave mixing: Kerr Effect

Data Source

PatentUS10305603B2Optical communication with some compensation of nonlinear distortions

Publication Date: 2019.05.28 NOKIA OF AMERICA CORP

AI summary

A WDM receiver configured to apply electronic equalization processing to both dispersion-compensated and dispersion-distorted versions of the received communication signal. In an example embodiment, the receiver's DSP first generates an equalized dispersion-compensated signal corresponding to the communication signal. The DSP then performs electronic dispersion-application processing on the equalized dispersion-compensated signal to generate a dispersion-distorted version thereof. The DSP then applies decision-aided electronic equalization processing to the dispersion-distorted version of the signal, subjects the resulting equalized signal to another round of dispersion-compensation processing, and recovers the data encoded in the communication signal using the resulting dispersion-compensated signal. This chain of signal processing tends to be effective in reducing nonlinear distortions of the intra-channel type and also some effects of nonlinear inter-channel interference, which advantageously enables the WDM receiver to support a lower BER and/or a higher data-transport capacity than those achievable with conventional WDM receivers.