Optical Fiber Refractive Index Profile for Thermal Lensing

Solution Overview

Problem

High-power fiber-based applications experience significant thermal lensing issues due to light absorption and amplification, which traditional compensation methods from solid-state lasers are not applicable to, leading to efficiency and beam quality reductions.

Innovation Solution

An optical fiber with a designed-in effective refractive index profile that changes as a function of position, either through doping or stress profiles, to offset thermal lensing effects, and a system with a similar refractive index profile in optical elements to compensate for thermal lensing in optical fibers and other media.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If light absorption and amplification occur in high-power fiber-based applications, then power output increases, but thermal lensing causes beam quality and efficiency to deteriorate

Engineering Contradiction:

Improvepower outputVSAvoidbeam quality

Core Design Contradiction:

PowerVSEase of operation

Solution Approach 1:

The patent applies local quality by creating a spatially varying refractive index profile within the optical fiber core through controlled doping concentration gradients. This non-uniform refractive index distribution compensates for the thermally induced lensing effects that occur locally in the core, allowing high power output to be maintained while preserving beam quality through localized optical property modification.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent implements parameter changes by modifying the refractive index profile parameter through controlled doping variations. The dopant concentration is specifically engineered to create a refractive index distribution that counteracts thermal lensing, transforming the optical parameters of the fiber core to compensate for thermally induced distortions during high-power operation.

Inventive Principle:

Principle #35Parameter changes

2Power

If light absorption and amplification occur in high-power fiber-based applications, then power output increases, but thermal lensing causes efficiency to deteriorate

Engineering Contradiction:

Improvepower outputVSAvoidefficiency

Core Design Contradiction:

PowerVSLoss of energy

Solution Approach 1:

The patent applies local quality by creating a spatially varying refractive index profile within the optical fiber core through controlled doping concentration gradients. This non-uniform refractive index distribution compensates for the thermally induced lensing effects that occur locally in the core, allowing high power output to be maintained while preserving beam quality through localized optical property modification.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent implements parameter changes by modifying the refractive index profile parameter through controlled doping variations. The dopant concentration is specifically engineered to create a refractive index distribution that counteracts thermal lensing, transforming the optical parameters of the fiber core to compensate for thermally induced distortions during high-power operation.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If a designed-in refractive index profile is introduced to compensate thermal lensing, then beam quality is maintained, but manufacturing complexity increases

Engineering Contradiction:

Improvebeam qualityVSAvoidmanufacturing complexity

Core Design Contradiction:

Ease of operationVSEase of manufacture

Solution Approach 1:

The patent applies preliminary action by pre-engineering the refractive index profile through controlled doping during the fiber manufacturing process. The dopant concentration gradient is established in advance during fabrication, creating a built-in compensation mechanism that automatically counteracts thermal lensing during operation, eliminating the need for post-manufacturing adjustments or additional compensating components.

Inventive Principle:

Principle #10Preliminary action

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 mitigates thermal lensing by introducing a refractive index profile that counteracts thermal distortions, maintaining beam quality and efficiency in high-power fiber-based applications.

Implementation Method 1

the amplification and/or absorption of the guided light causing thermal lensing in the fiber core that is induced by a change in a refractive index as a function of position

Methodology Applied

Scientific EffectThermal lensing:

Implementation Method 2

designed-in effective refractive index profile being selected to at least partially offset thermal lensing in the fiber core

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentEP2447748B1Compensation of thermally induced refractive index distortions in an optical gain medium or other optical element

Publication Date: 2017.10.18 RAYTHEON CO

AI summary

In various embodiments, an optical element, e.g., an optical fiber, may be configured to compensate for thermal lensing. For example, thermal lensing may be caused by light power dissipation within an optical fiber, which may include a fiber core that guides amplified light along the longitudinal dimension of the fiber core. Thermal lensing from a thermally induced change in material refractive index as a function of position along dimensions perpendicular to the fiber's longitudinal dimension may be at least partially compensated or offset when light is guided by the fiber core by a designed-in effective refractive index profile selected such that the designed-in material refractive index of the fiber core changes as a function of transverse position within the fiber core, or by selection of a favorable cross-sectional core shape in a plane perpendicular to the longitudinal dimension of the fiber core.