OPDBP Pilot Tone Compensation for XPolM and XPM in Coherent Channels

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Solution Overview

Problem

Current fiber optic communication systems face significant signal distortion due to nonlinear cross polarization (XPolM) and cross phase modulation (XPM) noise from neighboring channels, particularly in high data rate PM channels coexisting with legacy OOK channels, which limits the unregenerated reach and quality factor of high data rate signals.

Innovation Solution

The OPDBP technique employs a pilot tone-based orthogonal polarization detection scheme with broadband filtering, allowing for the simultaneous compensation of XPolM and XPM noise by using spectrally separable pilot tones on orthogonal polarizations, which are filtered within a sub-GHz to several GHz range to capture nonlinear cross phase modulation induced polarization and phase variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If conventional coherent PDM systems use high speed ADC/DSP for polarization and phase tracking, then the system can track polarization variations, but the tracking speed is limited to less than 1 MHz which is insufficient for compensating XPolM occurring at 1 GHz

Engineering Contradiction:

Improvetracking speedVSAvoidcompensation effectiveness

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent replaces the conventional high-speed ADC/DSP electronic tracking system with an optical-domain pilot tone based compensation system. Pilot tones are modulated onto the signal and processed through optical filtering and detection, substituting electronic signal processing with optical processing to achieve higher effective tracking speeds for polarization and phase variations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces pilot tones as intermediary signals that carry polarization and phase information. These pilot tones are modulated onto the main signal, transmitted through the fiber, and then extracted to provide continuous tracking information about polarization variations and phase shifts caused by XPolM and XPM, enabling compensation without direct high-speed electronic measurement.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If pilot based approaches use low pass filters with bandwidth less than 100 MHz to minimize ASE noise, then noise is reduced, but the nonlinear noise in the 1 GHz to 3 GHz spectral range cannot be captured

Engineering Contradiction:

ImproveASE noise impactVSAvoidnonlinear noise capture capability

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent changes the bandwidth parameter of the low pass filter from the conventional less than 100 MHz to a broader range of 100 MHz to 1 GHz. This parameter adjustment allows the system to capture the nonlinear noise components in the 1 GHz to 3 GHz spectral range while still maintaining acceptable ASE noise levels, thereby improving the accuracy of nonlinear compensation.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If existing pilot aided approaches are used for XPM compensation, then partial XPM compensation is achieved, but XPolM compensation is not possible

Engineering Contradiction:

ImproveXPM compensation capabilityVSAvoidXPolM compensation capability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent creates a universal compensation system that can handle both XPM and XPolM effects simultaneously. The pilot tone based orthogonal polarization detection scheme is designed to track and compensate for both cross-phase modulation and cross-polarization modulation effects, making the system versatile for compensating multiple types of nonlinear distortions in polarization multiplexed channels.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Productivity

If high data rate PM channels coexist with legacy OOK neighboring channels, then spectral efficiency is improved, but nonlinear cross talk penalty from XPolM and XPM reduces unregenerated reach by several dBs

Engineering Contradiction:

Improvespectral efficiencyVSAvoidunregenerated reach

Core Design Contradiction:

ProductivityVSLength of stationary object

Solution Approach 1:

The patent converts the harmful nonlinear cross-talk effects (XPolM and XPM) from legacy OOK channels into trackable signals by using pilot tones. The pilot tones experience the same nonlinear effects as the data signal, allowing the receiver to measure and compensate for these effects, thereby transforming the harmful interference into a useful source of compensation information.

Inventive Principle:

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

Data Source

PatentUS9419725B2Systems and methods for the compensation of nonlinear cross polarization and cross phase modulation in dual polarization coherent channels

Publication Date: 2016.08.16 CIENA CORP

AI summary

The present disclosure provides systems and methods for the compensation of signal distortion in fiber optic communication systems and the like. More specifically, the present disclosure provides an orthogonal polarization detection and broadband pilot (OPDBP) technique for the compensation of nonlinear cross polarization (i.e. nonlinear cross polarization modulation) (XPolM) induced noise and nonlinear nonlinear cross phase modulation (XPM) induced noise in a high data rate polarization multiplexed (PM) multilevel-quadrature amplitude modulated (M-QAM) channel due to neighboring channels. This approach allows for the compensation of both XPolM and XPM simultaneously, providing several dBs of optical reach extension. The approach uses a pilot tone based orthogonal polarization detection scheme with broadband (i.e. a few GHz wide) filtering of the pilot tones.