Few-Mode Fiber Link Mode Delay Compensation

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Solution Overview

Problem

Current optical fiber designs face challenges in achieving low differential mode group delay and slope between LP01 and LP11 modes, which hinders demultiplexing of optical signals in the time domain using MIMO techniques, especially in long-haul transmission systems.

Innovation Solution

The design of an optical fiber link comprising two few-mode fibers with carefully selected lengths and refractive index profiles to achieve either positive or negative differential mode group delay and slope, ensuring an absolute value of differential mode group delay between LP01 and LP11 modes is less than 0.1 ns/km across a wide wavelength range, thereby compensating for these delays and slopes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If large effective-area single-mode fibers are designed to reduce nonlinearity penalties, then nonlinearity is reduced, but spectral efficiency increases slowly

Engineering Contradiction:

Improvenonlinearity penaltyVSAvoidspectral efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent changes the fundamental parameter of fiber mode structure by transitioning from single-mode to few-mode fibers with specific core sizes (10-20 μm) and refractive index profiles. This enables simultaneous achievement of low nonlinearity (through large effective area) and high spectral efficiency (through multiple propagating modes that can be multiplexed), resolving the contradiction between these two performance aspects.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If few-mode fibers are used to increase spectral efficiency, then spectral efficiency increases, but differential mode group delay between LP01 and LP11 modes becomes large

Engineering Contradiction:

Improvespectral efficiencyVSAvoiddifferential mode group delay

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent applies preliminary anti-action by designing fibers with pre-calculated refractive index profiles (including depressed-index regions) that deliberately create negative differential mode group delay to counterbalance the positive delay inherent in few-mode fiber structures. This preliminary design ensures that the net differential mode group delay remains below 0.1 ns/km, enabling successful time-domain demultiplexing while maintaining high spectral efficiency.

Inventive Principle:

Principle #9Preliminary anti-action

3Length of moving object

If fiber length is increased for long-haul transmission, then transmission distance increases, but differential mode group delay accumulates

Engineering Contradiction:

Improvetransmission distanceVSAvoiddifferential mode group delay

Core Design Contradiction:

Length of moving objectVSLoss of time

Solution Approach 1:

The patent changes the refractive index profile parameter by introducing depressed-index regions at specific radial positions in the core. This modifies the mode propagation characteristics to achieve negative differential mode group delay, which compensates for the accumulated positive delay over long distances, enabling the system to maintain low net delay even over 1000 km transmission spans.

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

This approach enables the construction of optical fiber links with minimal differential mode group delay and slope, facilitating efficient signal demultiplexing and enhancing spectral efficiency, even over distances greater than 1000 km.

Implementation Method 1

a first optical fiber having a core which supports the propagation and transmission of an optical signal with X linearly polarized (LP) modes

Methodology Applied

Scientific EffectOptical mode propagation: Waveguide (optics)

Implementation Method 2

said optical fiber having a positive differential mode group delay between the LP01 and LP11 modes at a wavelength between 1530-1570

Methodology Applied

Scientific EffectDifferential mode group delay: Dispersion (of waves)

Data Source

PatentUS8995803B2Mode delay managed few moded optical fiber link

Publication Date: 2015.03.31 CORNING INC

AI summary

An optical fiber link suitable for use in a mode division multiplexing (MDM) optical transmission system is disclosed. The link has a first optical fiber having a core which supports the propagation and transmission of an optical signal with X LP modes at a wavelength of 1550 nm, wherein X is an integer greater than 1 and less than or equal to 20, the first fiber having a positive differential mode group delay between the LP01 and LP11 modes at a wavelength between 1530-1570. The link also has a second optical fiber having a core which supports the propagation and transmission of an optical signal with Y LP modes at a wavelength of 1550 nm, wherein Y is an integer greater than 1 and less than or equal to 20, said optical fiber having a negative differential mode group delay between the LP01 and LP11 modes at a wavelength between 1530-1570.