Multimode Optical Fiber Core Radius Tuning for Bandwidth

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Solution Overview

Problem

Multimode optical fibers face limitations in bandwidth due to perturbations in the refractive index profile, which can result in delay errors of the outermost guided mode groups, even with optimized offset designs, affecting their performance in data center applications with tight bends.

Innovation Solution

A method of manufacturing multimode optical fibers involves determining a refractive index profile and selecting core and cladding parameters to minimize relative time delays, including specific core shape parameters and draw tensions, to achieve a target optical fiber core shape and refractive index profile, ensuring minimal delay of the outermost guided mode group and optimizing bandwidth.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an offset moat design is used to minimize relative delays of outermost mode groups, then bandwidth is improved, but perturbations of the refractive index profile still result in delay errors

Engineering Contradiction:

ImprovebandwidthVSAvoidrefractive index profile accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies parameter changes by systematically varying the core shape parameter alpha (α) and the offset distance of the moat region to optimize bandwidth performance. By adjusting these parameters and calculating their impact on mode group delays, the invention finds optimal values that minimize delay errors even in the presence of manufacturing perturbations, thus resolving the contradiction between improving bandwidth and dealing with manufacturing precision limitations.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the core shape parameter alpha is precisely matched between core and moat regions, then optical fiber performance is improved, but any error at the core-moat interface has a negative impact on bandwidth

Engineering Contradiction:

Improveoptical fiber performanceVSAvoidcore-moat interface accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by pre-calculating the optimal core shape parameter alpha and moat offset distance before manufacturing, taking into account potential interface errors. The invention determines these parameters in advance such that even with manufacturing variations at the core-moat interface, the bandwidth performance is maintained at an optimized level, thus resolving the contradiction between improving performance and dealing with manufacturing precision limitations.

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If multiple cladding layers are deposited to control refractive index profile, then manufacturing precision is improved, but process complexity increases

Engineering Contradiction:

Improverefractive index profile controlVSAvoidcladding deposition process

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent applies local quality by implementing a multi-layer cladding structure where each layer has a specific refractive index tailored to its position and function. The first cladding layer (with higher refractive index) and second cladding layer (with lower refractive index containing fluorine) are designed with distinct local properties to achieve precise overall refractive index profile control, resolving the contradiction between improving manufacturing precision and managing process complexity.

Inventive Principle:

Principle #3Local quality

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 minimizes the relative time delay of the outermost guided mode group, thereby enhancing the bandwidth of the multimode optical fibers, ensuring reliable performance in data center applications with tight bends and reducing the impact of manufacturing variations.

Implementation Method 1

depositing the cladding material on the optical fiber core preform to form an optical fiber preform

Methodology Applied

Scientific EffectPhysical Vapour Deposition: Physical Vapour Deposition

Implementation Method 2

drawing the multimode optical fiber from the optical fiber preform at tension T

Methodology Applied

Scientific EffectThermal Expansion: Thermal Expansion

Implementation Method 3

selecting a draw tension T that obtains (produces) a predetermined (target) optical fiber core shape parameter

Methodology Applied

Scientific EffectStress Relaxation: Stress Relaxation

Data Source

PatentUS9481599B2Method of making a multimode optical fiber

Publication Date: 2016.11.01 CORNING INC

AI summary

A method of making a multimode optical fiber is disclosed. In one embodiment the method includes calculating a core radius that maximizes the bandwidth of the multimode optical fiber wherein the effect of draw tension is accounted for. The embodiments herein illustrate how core radius can be tuned so the time delay of the outermost guided mode group is reduced. The resultant core radius may be targeted for a value off-nominal from what would be expected for a particular commercial optical fiber type.