Few-mode optical fiber with high-refractive-index mode filter layers

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Solution Overview

Problem

Conventional single-mode optical fibers face challenges in maintaining low bending loss when operated at small bending radii, leading to significant losses that impact communication systems, and existing few-mode optical fibers require connection to single-mode fibers at both ends, limiting their practical use.

Innovation Solution

A few-mode optical fiber design featuring a core surrounded by multiple high-refractive-index mode filter layers and claddings, which filters out high-order modes by strongly coupling them to cladding defect modes, ensuring low bending loss and single-mode transmission even at small bending radii.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a conventional single-mode optical fiber is operated at a small bending radius to facilitate laying and reduce occupied space, then the ease of operation is improved, but the bending loss increases significantly

Engineering Contradiction:

Improveease of layingVSAvoidbending loss

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The patent changes the structural parameters of the optical fiber by introducing a high-refractive-index layer between the core and cladding, and adjusting the refractive index distribution profile. This parameter modification enables the fiber to maintain low bending loss while allowing small bending radius operation, resolving the contradiction between ease of laying and bending loss.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite refractive index structure combining core, high-refractive-index layer, and cladding with different refractive indices. This composite structure creates an optimized light confinement profile that reduces bending loss while maintaining flexibility for easy installation.

Inventive Principle:

Principle #40Composite materials

2Loss of energy

If a few-mode optical fiber is used to achieve low bending loss, then the bending loss is reduced, but the device complexity increases due to multiple cladding layers

Engineering Contradiction:

Improvebending lossVSAvoidcladding structure complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent applies local quality by introducing a high-refractive-index layer only in the specific region between core and cladding where it is most needed for bending loss reduction, rather than uniformly complicating the entire fiber structure. This localized modification achieves low bending loss with minimal added complexity.

Inventive Principle:

Principle #3Local quality

3Loss of energy

If a few-mode optical fiber is used to reduce bending loss, then the bending loss is improved, but the manufacturing precision requirements increase

Engineering Contradiction:

Improvebending lossVSAvoidrefractive index distribution precision

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The patent optimizes the refractive index parameters of the high-refractive-index layer to achieve a balance between bending loss performance and manufacturability. By carefully selecting the refractive index value and layer thickness, the patent reduces sensitivity to manufacturing tolerances while maintaining low bending loss.

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 optical fiber achieves low bending loss (<1×10−3 dB/turn) at a bending radius greater than 7.5 mm, enabling stable single-mode transmission and simplifying manufacturing while allowing connection to single-mode fibers, enhancing communication system performance.

Implementation Method 1

filters out high-order modes by strongly coupling them to cladding defect modes

Methodology Applied

Scientific EffectMode coupling:

Implementation Method 2

The cladding includes: a first inner cladding surrounding the core; a first high-refractive-index mode filter layer surrounding the first inner cladding

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 3

capable of a single-mode operation and characterized by a low bending loss in the fundamental mode of the optical fiber

Methodology Applied

Scientific EffectLight transmission: Light

Implementation Method 4

A few-mode optical fiber includes: a core and a cladding surrounding the core

Methodology Applied

Scientific EffectWaveguide effect: Waveguide (optics)

Data Source

PatentUS10451797B2Few-mode optical fiber

Publication Date: 2019.10.22 INFORMATION & COMMNUNICATION BRANCH STATE GRID JIANGXI ELECTRIC POWER CO

AI summary

Provided is a few-mode optical fiber. The optical fiber includes: a core and a cladding enclosing the core. The cladding includes: a first inner cladding surrounding the core; a first high-refractive-index mode filter layer surrounding the first inner cladding; a second inner cladding surrounding the first high-refractive-index mode filter layer; a second high-refractive-index mode filter layer surrounding the second inner cladding; and an outer cladding surrounding the second high-refractive-index mode filter layer.