Cladding Light Stripper for High Power Fiber Lasers
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Solution Overview
Problem
High power fiber lasers face issues with parasitic pump signals being supported by the cladding, which deteriorate the quality of the main signal and are difficult to remove efficiently, leading to increased power loss and beam divergence, especially as the length of the active fiber increases.
Innovation Solution
A light stripper with a coating having a refractive index greater than the cladding is applied to the fiber, effectively decoupling undesirable light from the cladding before the signal is output, utilizing materials that can withstand high temperatures and optimizing the geometry and length of the stripper for efficient removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the length of the active fiber is increased to improve pump light absorption, then the conversion efficiency of pump light is improved, but parasitic pump light in the cladding increases and deteriorates beam quality
Solution Approach 1:
The patent extracts and removes parasitic pump light from the cladding using a dedicated light stripper component. The light stripper is positioned along the active fiber to continuously remove cladding-mode pump light that would otherwise propagate parasitically and degrade beam quality, while allowing the active fiber length to be optimized for pump absorption.
Solution Approach 2:
The light stripper acts as an intermediary component between the active fiber and the environment. It selectively interacts with cladding-mode light through its specific refractive index properties, removing parasitic pump light while leaving core-mode signal light unaffected, thus mediating the conflict between pump absorption efficiency and beam quality.
2Object-generated harmful factors
If a light stripper with refractive index matching is used to remove cladding light, then parasitic pump light is removed, but complex cooling systems are required to manage heat
Solution Approach 1:
The patent changes the refractive index parameter of the light stripper coating to be higher than that of the cladding, creating a favorable index contrast for light extraction. This parameter optimization enables efficient parasitic light removal while minimizing heat generation, eliminating the need for complex cooling systems.
Solution Approach 2:
The light stripper uses a simple coating structure with materials that can withstand operating temperatures without requiring active cooling. The design accepts that the coating will experience thermal stress but selects materials and geometries that passively manage heat, avoiding expensive and complex cooling infrastructure.
3Object-generated harmful factors
If the refractive index of the coating is increased to improve light coupling out, then parasitic light removal is improved, but temperature management becomes more challenging
Solution Approach 1:
The patent optimizes the coating refractive index to a specific value higher than the cladding index, balancing light extraction efficiency with thermal management. This parameter optimization ensures sufficient parasitic light coupling out while keeping temperature rise within acceptable limits for the coating materials.
Solution Approach 2:
The light stripper employs composite material structures with specific refractive index properties and thermal characteristics. The coating materials are selected to provide both optical functionality (high enough index for light extraction) and thermal resilience (withstanding operating temperatures without degradation), creating a multi-functional composite solution.
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 allows for the substantial removal of parasitic pump light and stray signal light from the cladding, improving beam quality and reducing power loss, without the need for complex cooling systems, thus enhancing the performance and cost-effectiveness of high power fiber laser systems.
Implementation Method 1
A light stripper with a coating having a refractive index greater than the cladding is applied to the fiber, effectively decoupling undesirable light from the cladding
Data Source
AI summary
A powerful fiber laser system is configured with at least one gain block. The gain block includes an input fiber guiding a pump light, a multiclad active fiber receiving the pump light so that a major portion is absorbed in the core of the active fiber while a minor portion of the pump light propagates in the inner cladding of the active fiber, and a multiclad output fiber. The multiclad output fiber is configured with a core, guiding a signal lased by the core of the active fiber upon absorption of the major portion of the pump light, an inner cladding receiving the minor portion of the pump light and an outer cladding. The inner and outer claddings of the multiclad output fiber have respective refractive indexes which are selected so that the refractive index of the outer cladding is higher than that one of the inner cladding. The configuration of the output fiber allows for the removal of substantially the entire light from the inner cladding of the output fiber before the signal is emitted through the downstream end of the output fiber.