Amplification Optical Fiber Structure for Beam Quality and Raman Suppression
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Solution Overview
Problem
Existing amplification optical fibers face challenges in maintaining beam quality while preventing reductions in light amplification efficiency, particularly due to stimulated Raman scattering and multimode propagation caused by increased power density.
Innovation Solution
The amplification optical fiber is designed with a core doped entirely with a rare earth element, featuring a relative effective refractive index difference of 0.05% or more for LP01 mode and less than 0.05% for LP21 mode, along with a specific effective area and refractive index profile to suppress higher order mode amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the diameter of the core is increased to increase the effective area, then the energy density of light inside the core is reduced and stimulated Raman scattering is prevented, but the light trapping force increases and multimode propagation occurs causing beam quality deterioration
Solution Approach 1:
The patent applies local quality by creating a refractive index distribution where the core has a higher refractive index than the cladding, with specific control over the relative refractive index difference (0.003 ≤ Δn/n_clad < 0.008). This localized refractive index variation enables selective mode guidance - the core structure is optimized to guide fundamental modes while allowing higher-order modes to radiate into the cladding, thus maintaining beam quality without requiring a larger core diameter that would trigger Raman scattering
2Object-affected harmful factors
If the relative refractive index difference is reduced to increase the effective area, then stimulated Raman scattering is prevented, but the light trapping force decreases and beam quality deteriorates
Solution Approach 1:
The patent employs parameter changes by precisely controlling the relative refractive index difference within a specific range (0.003 ≤ Δn/n_clad < 0.008) and the core diameter (20 μm ≤ d_core < 30 μm). These parameter optimizations create a balance where the refractive index difference is sufficient to guide fundamental modes effectively while being small enough to reduce the light trapping force that would otherwise cause higher-order mode propagation and beam quality degradation
3Shape
If the gain medium is doped to a part of the core to suppress higher order mode amplification, then beam quality is maintained, but the amplification efficiency is reduced
Solution Approach 1:
The patent extracts the mode selection function from the gain medium doping pattern and transfers it to the refractive index profile design. Instead of using selective doping to suppress higher-order modes, the invention uses the cladding structure with specific refractive index difference to cause higher-order modes to radiate away. This allows the gain medium to be uniformly doped throughout the core, maximizing amplification efficiency while the refractive index profile maintains beam quality by preventing higher-order mode propagation
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 ensures efficient light amplification with maintained beam quality, preventing deterioration and stimulated Raman scattering, while allowing high-power light emission.
Implementation Method 1
a rare earth element suitable for being pumped by pumping light to cause stimulated emission is provided, which propagates through the core
Implementation Method 2
a cladding having a refractive index lower than a refractive index of the core... in light propagating through the core
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
An amplification optical fiber 10 includes: a core 11; an inner cladding 12 having a refractive index lower than a refractive index of the core 11, wherein an active element pumped by pumping light is entirely doped to the core 11, and a relative effective refractive index difference of light in an LP01 mode is 0.05% or more and a relative effective refractive index difference of light in an LP21 mode is less than 0.05% in light propagating through the core 11.