Optical Fiber Design for Stable Beam Quality
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Solution Overview
Problem
Fiber laser devices face instability in beam quality due to stimulated Raman scattering, which occurs when power density increases in optical fibers, leading to unintended wavelength emission and amplitude fluctuations, despite attempts to suppress this through core diameter and refractive index adjustments.
Innovation Solution
An optical fiber design that allows light with wavelengths between 1000 nm and 1100 nm to propagate in both LP01 and LP11 modes, with a propagation constant difference between 1735 rad/m and 4000 rad/m, increasing the effective sectional area and suppressing stimulated Raman scattering, while maintaining stable beam quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the diameter of the core is increased to suppress stimulated Raman scattering, then the effective sectional area increases, but the light confining power increases causing the optical fiber to convert into a multimode
Solution Approach 1:
The patent changes the refractive index parameter by reducing the relative refractive index difference between core and clad to suppress stimulated Raman scattering while maintaining single-mode operation through controlled parameter optimization
2Area of stationary object
If the relative refractive index difference of the core with respect to a clad is reduced to suppress stimulated Raman scattering, then the effective sectional area increases, but the light propagating in the core is easily affected by macro bend and micro bend
Solution Approach 1:
The patent optimizes the relative refractive index difference parameter to balance two opposing requirements: reducing it enough to increase effective sectional area and suppress SRS, but maintaining it sufficient to provide adequate bend resistance for reliable light propagation
3Area of stationary object
If the effective sectional area of the light in the LP01 mode is increased by using an optical fiber including a core capable of propagating light in a few modes, then stimulated Raman scattering is suppressed, but beam quality deteriorates due to excitation of modes other than basic mode
Solution Approach 1:
The patent carefully controls the propagation constant difference parameter to ensure it falls within the specific range of 1735-4000 rad/m, which simultaneously achieves increased effective sectional area for SRS suppression while maintaining beam quality by preventing excessive mode excitation
Solution Approach 2:
The patent utilizes controlled multi-mode propagation dynamics where both LP01 and LP11 modes are allowed to propagate with specific propagation constant differences, creating a dynamic balance that suppresses SRS while maintaining acceptable beam quality through mode interference effects
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 design effectively suppresses beam quality deterioration and stimulated Raman scattering, allowing for stable light propagation and emission with reduced wavelength shifts, even when bent at specific radii, by optimizing the propagation constant difference and core refractive index differences.
Implementation Method 1
when power density of light in an optical fiber increases, wavelength conversion of the light due to the stimulated Raman scattering easily occurs
Data Source
AI summary
An optical fiber includes a core that propagates a light that includes a wavelength equal to or larger than 1000 nm and equal to or smaller than 1100 nm. The light propagates in the core at least in an LP01 mode and an LP11 mode. A difference between a propagation constant of the light in the LP01 mode and a propagation constant of the light in the LP11 mode is 1735 rad/m or larger and 4000 rad/m or smaller.