Dual Diameter Ferrule with Smooth Contours for Thermal Stress Reduction

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Solution Overview

Problem

Fiber breakage occurs at the interface between the end of the glass fiber and the ferrule in fiber optic cables due to thermal expansion differences, leading to increased failure rates under temperature fluctuations.

Innovation Solution

A fiber optic ferrule with a smooth and continuous axial passage featuring dual diameters, one for the inner fiber and another for the outer coating, along with a tapered section to reduce epoxy volume and minimize thermal stress, is used to securely mount the fiber optic cable, allowing the coating to extend beyond the buffer layer and be received in a conically shaped pocket to reduce epoxy contact with the fiber.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If epoxy is used to hold the fiber to the ferrule, then the fiber is securely mounted, but thermal expansion differences cause fiber breakage at the interface area

Engineering Contradiction:

Improvefiber mounting securityVSAvoidfiber breakage resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The ferrule passage is segmented into multiple diameter portions: a first portion with diameter matching the fiber (125 microns), a second portion with larger diameter for the coating (250 microns), and a third portion with intermediate diameter forming a transition zone. This segmentation allows different materials (fiber, coating, epoxy) to occupy different spatial zones, reducing thermal stress concentration at any single interface.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the ferrule passage have different diameters and functions: the first portion provides precise fiber positioning, the second portion accommodates the coating with clearance, and the third portion creates a gradual transition zone. This local variation in geometry optimizes the mechanical and thermal environment for each material layer, minimizing differential expansion effects.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If a single diameter passage is used in the ferrule, then manufacturing is simpler, but the fiber interface area experiences higher thermal stress

Engineering Contradiction:

Improveferrule passage fabricationVSAvoidthermal stress on fiber

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The passage diameter varies along the axial dimension of the ferrule, creating a three-dimensional gradient structure rather than a uniform two-dimensional cross-section. This dimensional variation allows the passage to accommodate multiple material layers (fiber, coating, epoxy) with different thermal properties, reducing stress while maintaining manufacturability through techniques like precision molding or drilling with progressive reaming.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Strength

If the coating extends beyond the buffer layer, then the fiber is better protected, but the epoxy contact area with the fiber increases

Engineering Contradiction:

Improvefiber protectionVSAvoidepoxy-induced thermal stress

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The ferrule passage is divided into distinct zones: the second diameter portion (250 microns) accommodates the coating extending beyond the buffer layer, while the third diameter portion provides a transition zone that limits epoxy contact with the fiber. This segmentation allows the coating to extend for protection while the epoxy is confined to areas where it cannot directly contact the fiber, eliminating the harmful effect.

Inventive Principle:

Principle #1Segmentation

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 solution effectively reduces thermal-induced stress on the fiber, minimizing breakage by reducing the volume of epoxy in contact with the fiber and accommodating differences in thermal expansion, thereby enhancing the reliability of fiber optic connections.

Implementation Method 1

Differences in thermal expansion are believed to cause the breakage

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

adhesively holding the fiber to the ferrule

Methodology Applied

Scientific EffectAdhesion: Adhesive

Data Source

PatentUS12013577B2Cable and dual inner diameter ferrule device with smooth internal contours and method

Publication Date: 2024.06.18 COMMSCOPE TECHNOLOGIES LLC

AI summary

A fiber optic ferrule includes a body extending from a first end to a second opposite end, with the body including an axial passage extending between the first and the second ends. The axial passage includes a first diameter portion having a diameter of at least 125 microns, a second diameter portion having a diameter of at least 250 microns and less than a diameter of a buffer, and a smooth and continuous transition between the first and the second diameter portions. The second diameter portion is positioned between the first diameter portion and the second end. The axial passage further defines a tapered shape at the second end extending inward from the second end toward the second diameter portion. In certain embodiments, another smooth and continuous transition can be provided between the taper shape and the second diameter portion. In certain embodiments, the axial passage is smooth and continuous between the first and the second ends of the body. A hub holds the ferrule. A method of assembling a terminated fiber optic cable is also provided.