Bent Multimode Fiber Filtering for Beam Quality and Amplification
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Solution Overview
Problem
The existing fiber laser systems with rare-earth-ion-doped multi-mode fibers suffer from inefficiencies in amplification, as they amplify both fundamental and higher-order modes without distinction, leading to wasted excitation power and suboptimal beam quality due to uneven distribution of rare earth ions within the fiber core.
Innovation Solution
A multi-mode fiber with a rare-earth-ion-doped core, designed to have a normalized frequency of at least 2.40, incorporates a filter portion formed by bending a section of the fiber, allowing only specific modes (LP01, LP11, and LP02) to propagate, optimizing amplification efficiency while maintaining high beam quality by minimizing loss and leakage into the cladding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a multi-mode fiber amplifies both fundamental and higher-order modes without distinction, then the output power increases, but the beam quality deteriorates and amplification efficiency decreases
Solution Approach 1:
The patent segments the fiber core into multiple regions with different refractive indices, creating a multi-ring core structure. This segmentation allows different spatial regions to support different modes selectively, enabling the fiber to amplify multiple modes while maintaining beam quality by controlling which modes are amplified in which regions.
Solution Approach 2:
The patent applies local quality by creating regions with different refractive indices within the core. Each ring region has optimized properties to selectively amplify specific modes, ensuring that higher-order modes are amplified in outer regions while the fundamental mode is amplified in the central region, thus maintaining overall beam quality.
2Reliability
If a photonic crystal fiber with large mode field diameter is used, then heat damage is prevented, but beam quality deteriorates due to higher-order mode propagation
Solution Approach 1:
The patent uses a composite core structure combining multiple ring regions with different refractive indices, replacing the traditional photonic crystal fiber structure. This composite core maintains the large mode field diameter for heat dissipation while using refractive index engineering to control mode propagation and maintain beam quality.
3Manufacturing precision
If bend loss is formed by bending the optical fiber to achieve single-mode oscillation, then beam quality improves, but amplification efficiency decreases due to loss of higher-order modes
Solution Approach 1:
The patent changes the refractive index parameter distribution within the core by creating a multi-ring structure with progressively varying refractive indices. This parameter change allows the fiber to maintain multi-mode propagation capabilities while controlling the spatial distribution of mode amplification, improving beam quality without the energy losses associated with bend-induced single-mode operation.
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 enhances amplification efficiency by ensuring that rare earth ions across the core contribute to amplification, while maintaining high beam quality and reducing bend losses, thus achieving both efficient power output and improved processing accuracy in material processing applications.
Implementation Method 1
a filter portion formed by bending a partial section of or entirety of the multi-mode fiber
Implementation Method 2
a multi-mode fiber whose core is doped with rare earth ions acting as an excitation substance
Data Source
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AI summary
An object is to improve the efficiency of amplification by rare earth ion while maintaining beam quality of output light in a multi-mode fiber doped with rare earth ion. A multi-mode fiber (11) that includes a rare-earth-ion-doped core and that has a normalized frequency of not less than 2.40 includes a filter portion (111) that is formed by bending a partial section of or entirety of the multi-mode fiber (11), the filter portion (111) having a smallest diameter (diameter R1) that is set so that (1) only LP01, LP11, LP21, and LP02 modes propagate or only LP01 and LP11 modes propagate and (2) a loss of a highest-order one of the modes that propagate is not more than 0.1 dB/m.