Double Clad Fiber Tapered Cladding Heat Redistribution

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Solution Overview

Problem

Double-clad fiber lasers face limitations in power scaling due to uneven waste heat distribution, with high heat generation at the launch end leading to thermal damage and reduced pump energy input, as conventional cladding shapes do not effectively redistribute thermal energy along the fiber length.

Innovation Solution

A geometrically modified fiber with a tapered cladding shape is introduced, modulating the cladding mode scattering coefficient to redirect pump energy absorption further down the fiber, reducing thermal stress at the launch end by allowing helical cladding modes to propagate and intersect the core further along the fiber, thereby redistributing heat flux.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If conventional cladding shapes are used, then pump energy is absorbed at the launch end, but thermal stress concentrates at the launch end causing damage

Engineering Contradiction:

Improvepump energy absorptionVSAvoidthermal stress at launch end

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The cladding shape is modified locally at the launch end to have a different geometry (e.g., flattened or oval cross-section) compared to the rest of the fiber. This local geometric change alters the mode distribution and pump absorption characteristics specifically at the launch end, redistributing heat generation away from this critical region while maintaining effective pump energy absorption throughout the fiber.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Instead of absorbing pump energy uniformly or preferentially at the launch end as in conventional designs, the invention inverts the approach by designing the cladding shape to reduce pump absorption at the launch end and enhance it further down the fiber. This inversion of the absorption profile directly inverts the heat generation distribution, protecting the launch end from thermal damage.

Inventive Principle:

Principle #13The other way round (Inversion)

2Power

If pump power is increased to enhance power output, then power scaling is improved, but thermal damage risk increases

Engineering Contradiction:

Improvepower outputVSAvoidthermal damage resistance

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The invention changes the geometric parameters of the cladding (cross-sectional shape, aspect ratio) to modify the optical mode distribution and pump absorption characteristics. This parameter change enables the fiber to handle higher pump powers by redistributing thermal load, thereby improving power scaling capability while maintaining reliability through reduced peak thermal stress.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If cladding shape is modified to redistribute heat, then thermal stress is reduced, but device complexity increases

Engineering Contradiction:

Improvethermal stress distributionVSAvoidcladding geometry

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The fiber is segmented into two distinct sections: a launch end section with modified cladding geometry designed for heat redistribution, and a remainder section with conventional circular cladding. This segmentation allows the complex geometric modification to be applied only where needed (at the launch end) rather than throughout the entire fiber, reducing overall manufacturing complexity while achieving the thermal management objective.

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

This approach increases the amount of pump radiation that can be launched, enhancing power output and reducing thermal damage, allowing for more efficient energy conversion and increased power scaling capabilities.

Implementation Method 1

modulating the cladding mode scattering coefficient to redirect pump energy absorption further down the fiber

Methodology Applied

Scientific EffectCladding mode scattering: Scattering

Implementation Method 2

allowing helical cladding modes to propagate and intersect the core further along the fiber, thereby redistributing heat flux

Methodology Applied

Scientific EffectHelical mode propagation:

Implementation Method 3

the core absorbs a portion of the intersecting pump radiation that is in the cladding

Methodology Applied

Scientific EffectAbsorption: Absorption (EM radiation)

Implementation Method 4

The ability of the double-clad fiber to convert low-quality, low brightness pump radiation into high brightness, signal radiation

Methodology Applied

Scientific EffectBrightness conversion:

Data Source

PatentUS10156675B1Method and apparatus for the modulation of pump absorption in a clad optical fiber that is used in lasers and amplifiers

Publication Date: 2018.12.18 BAE SYSTEMS INFORMATION ANDELECTRONIC SYSTEMS INTEGRATION INC

AI summary

A fiber optic modulator of pump energy comprising a piece of double clad fiber where the inner cladding layer has a changing cross sectional shape and may have a changing cross sectional area along the length of the fiber. The modulator fiber regulates how pump energy in the inner cladding layer is absorbed into the core of the fiber along the length of the fiber. This regulates how heat is generated in the fiber due to absorption into core.