Optical Fiber Resin Interface for Light Leakage Suppression

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Solution Overview

Problem

Conventional optical fibers experience light leakage in coated sections closer to the light-exit end than coating-removed sections, leading to heat generation and reduced reliability due to light absorption by the secondary coating.

Innovation Solution

The optical fiber is designed with an intermediate-refractive-index resin part in the coating-removed section, which has a refractive index lower than the core but higher than the primary coating, reducing light leakage by confining light within the core and minimizing heat generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the coating-removed section is left without any covering medium, then the manufacturing process is simplified, but light leakage occurs and heat is generated due to light absorption by the secondary coating

Engineering Contradiction:
Improvemanufacturing process simplicityVSAvoidfiber reliability
Core Design Contradiction:
Ease of manufactureVSReliability

Solution Approach 1:

A resin part with intermediate refractive index is introduced as a mediator between the core and the external environment in the coating-removed section. This resin part has a refractive index lower than the core but higher than air, serving as an intermediate layer that gradually transitions the refractive index. This intermediary structure prevents sudden light refraction and leakage while avoiding the need for complex multi-layer coatings, thus maintaining manufacturing simplicity while improving reliability.

Inventive Principle:
Principle #24Intermediary (Mediator)

Solution Approach 2:

The refractive index parameter is strategically changed by filling the coating-removed section with a resin part whose refractive index is specifically controlled to be between that of the core and air. This parameter change creates a gradual refractive index transition zone that reduces light leakage angle and prevents light from reaching the secondary coating, thereby eliminating heat generation without complicating the manufacturing process.

Inventive Principle:
Principle #35Parameter changes

2Object-affected harmful factors

If a low-refractive-index medium is used to cover the coating-removed section, then light leakage is reduced, but the NA of the optical waveguide in the coated section becomes smaller than in the coating-removed section, causing light to enter from the coated section

Engineering Contradiction:
Improvelight leakage reductionVSAvoidlight energy loss
Core Design Contradiction:
Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The refractive index of the covering medium is precisely controlled to fall within a specific range: lower than the core but higher than air. This parameter optimization achieves a balance - it reduces light leakage by creating a refractive index barrier, yet maintains sufficient NA in the coated sections to prevent light from entering the coating-removed section from the coated sections.

Inventive Principle:
Principle #35Parameter changes

3Strength

If the secondary coating is made of material with low transparency, then mechanical strength is improved, but heat generation increases due to light absorption

Engineering Contradiction:
Improvemechanical strengthVSAvoidheat generation
Core Design Contradiction:
StrengthVSTemperature

Solution Approach 1:

The resin part with intermediate refractive index serves as a protective intermediary layer that blocks light from reaching the secondary coating in the coating-removed section. This intermediary structure allows the secondary coating to maintain its low-transparency material composition for mechanical strength while preventing light absorption and heat generation by stopping light before it reaches the secondary coating.

Inventive Principle:
Principle #24Intermediary (Mediator)

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 configuration effectively prevents or reduces light leakage into the second coated section, thereby reducing heat generation and enhancing the reliability of the optical fiber by minimizing absorption and degradation.

Implementation Method 1

an intermediate-refractive-index resin part in the coating-removed section, which has a refractive index lower than the core but higher than the primary coating, reducing light leakage by confining light within the core

Methodology Applied
Scientific EffectRefraction: Refraction

Data Source

PatentEP3525018B1Optical fiber and fiber laser
Publication Date: 2025.06.04 FUJIKURA LTD
  • EP3525018B1 patent drawingFigure 1~2
  • EP3525018B1 patent drawingFigure 3~4
  • EP3525018B1 patent drawingFigure 5~6

AI summary

The present invention comprises a core (11) and a primary coating (12) that is lower in refractive index than the core (11) and that covers the side surface of the core (11) except in a coating-removed section (10). The side surface of the core (11), in at least part of the coating-removed section (10), is covered with an intermediate-refractive-index resin part (14) that is lower in refractive index than the core (11) and that is higher in refractive index than the primary coating (12).