Active-Doped Optical Fiber Core Structure for Raman Suppression
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Solution Overview
Problem
Fiber laser devices face issues with beam quality deterioration due to stimulated Raman scattering, particularly when the power density of light in optical fibers increases, leading to unstable amplification and unintended wavelength emission.
Innovation Solution
An active element-added optical fiber with a core structure that includes a first region doped with an active element and a second region without the active element, where the refractive index is maximized in specific radial ranges to suppress higher mode amplification and increase the effective cross-sectional area, thereby reducing stimulated Raman scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the power density of light in optical fiber is increased, then the light condensing property and beam quality are improved, but stimulated Raman scattering occurs causing unstable amplification and unintended wavelength emission
Solution Approach 1:
The patent applies local quality by creating a core with non-uniform active element concentration distribution. The active element concentration is highest at the center (0≤r≤0.1d) and decreases toward the outer region (0.1d<r≤0.8d), with the region near the cladding (0.9d≤r≤d) having minimal active element concentration. This localized concentration gradient optimizes light condensing property at the center while suppressing stimulated Raman scattering at the periphery, thereby maintaining both high power density and amplification stability.
2Area of stationary object
If the core diameter is increased to suppress stimulated Raman scattering, then the effective cross-sectional area increases, but beam quality deteriorates due to excitation of higher modes
Solution Approach 1:
The patent employs local quality by implementing a radially varying active element concentration profile within the core. The concentration is maximized at the center (0≤r≤0.1d) where fundamental mode propagation occurs, and gradually decreases toward the outer regions (0.1d<r≤0.8d), with minimal concentration near the cladding interface (0.9d≤r≤d). This localized distribution suppresses higher mode excitation while maintaining a large effective cross-sectional area, thereby preventing beam quality deterioration even with increased core size.
Solution Approach 2:
The patent applies parameter changes by optimizing the active element concentration distribution as a continuous function of radial position. The concentration parameter is varied from high at the center (0≤r≤0.1d) to low at the periphery (0.9d≤r≤d), creating a gradient that suppresses stimulated Raman scattering and higher mode excitation. This parameter optimization allows the core to maintain a large effective cross-sectional area while preserving beam quality.
3Productivity
If the active element concentration is increased throughout the core, then the amplification efficiency is improved, but stimulated Raman scattering increases causing beam quality deterioration
Solution Approach 1:
The patent implements local quality by creating a non-uniform active element concentration distribution where the concentration is highest at the center (0≤r≤0.1d) and decreases toward the outer regions (0.1d<r≤0.8d), with minimal concentration near the cladding (0.9d≤r≤d). This localized high concentration at the center maximizes amplification efficiency for fundamental mode light, while the reduced concentration at the periphery suppresses stimulated Raman scattering, thereby resolving the contradiction between productivity and harmful factors.
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 suppresses beam quality deterioration and enhances the amplification efficiency of the basic mode while minimizing the amplification of higher modes, leading to stable and high-quality light emission.
Implementation Method 1
the core includes a first region and a second region, the first region ranges from a central axis to a predetermined radius (i.e., ra), and is doped with and an active element pumped (or excited) by pumping light (or excitation light)
Implementation Method 2
the average value of the refractive index in the region of 0.1 d≤r≤0.8 ra may be higher than the average value of the refractive index in the region of 1.1 ra≤r≤0.9 d
Data Source
AI summary
An active element-doped optical fiber includes: a core that includes first and second regions. The first region ranges from a central axis to a predetermined radius, and is doped with an active element excited by excitation light. The second region surrounds the first region with no gap, extends to an outer peripheral surface of the core, and is not doped with the active element. The core satisfies 0.1 d<ra<d, where ra is a radius of the first region and d is a radius of the core. The core has, in a region of 0.2 d<r≤0.9 d, a maximum value position at which a refractive index becomes maximum, where r is a distance from a central axis of the core in a radial direction.