Optical Fiber Young's Modulus Profile for Beam Quality
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Solution Overview
Problem
Fiber laser devices face challenges in emitting light beams of excellent beam quality, particularly when the core diameter is large, as higher modes such as the LP02 mode are excited alongside the fundamental LP01 mode, leading to reduced beam quality and inefficient wavelength conversion due to increased power in higher modes.
Innovation Solution
An optical fiber design with varying Young's modulus and refractive index profiles across different regions, specifically attenuating the LP02 mode through stimulated Brillouin scattering by concentrating acoustic waves in regions where the LP02 mode intensity exceeds the LP01 mode intensity, while maintaining low loss in the LP01 mode, and using active elements and dopants to enhance amplification and beam quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a multimode fiber with large core diameter is used to propagate high power light beam, then the power transmission capability is improved, but the beam quality deteriorates due to excitation of higher modes
Solution Approach 1:
The patent applies local quality by creating a specific Young's modulus distribution within the fiber core. A first region with lower Young's modulus is formed in the central area where the LP01 mode intensity is highest, while a second region with higher Young's modulus is formed at the periphery. This localized modification of mechanical properties selectively suppresses the LP02 mode without significantly affecting the LP01 mode, enabling high power transmission while maintaining excellent beam quality.
2Reliability
If only a light beam in the LP01 mode is entered to an optical fiber, then the beam quality is improved, but the power transmission capability is limited due to single mode operation
Solution Approach 1:
The patent changes the mechanical parameter (Young's modulus) distribution within the fiber core to resolve the contradiction between beam quality and power transmission. By creating a specific Young's modulus profile with a lower modulus region in the center and higher modulus region at the periphery, the fiber can support multiple modes while selectively suppressing the LP02 mode through modified stimulated Brillouin scattering characteristics, thereby achieving both high power transmission and excellent beam quality.
3Power
If a light beam in the LP02 mode is excited in the amplification optical fiber, then the power in higher modes is increased, but the wavelength conversion efficiency deteriorates
Solution Approach 1:
The patent converts the potentially harmful effect of LP02 mode excitation into a beneficial outcome by utilizing the Young's modulus distribution to control stimulated Brillouin scattering. The specific Young's modulus profile causes acoustic waves to be generated that selectively attenuate the LP02 mode through enhanced Brillouin scattering, while the LP01 mode remains unaffected. This transforms the problem of higher mode excitation into a mechanism for selective mode suppression, improving wavelength conversion efficiency.
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 optical fiber effectively attenuates the LP02 mode while maintaining high beam quality by selectively reducing Young's modulus and refractive index in specific regions, resulting in improved beam quality and efficient amplification of the LP01 mode, even with larger core diameters.
Implementation Method 1
attenuating the LP02 mode through stimulated Brillouin scattering by concentrating acoustic waves in regions where the LP02 mode intensity exceeds the LP01 mode intensity
Data Source
Figure 1
Figure 2A~2E
Figure 3~4
AI summary
An optical fiber 10 propagates a light beam at a predetermined wavelength at least in an LP01 mode and an LP02 mode. In regions 11a and 11c in which the intensity of a light beam in the LP02 mode is greater than the intensity of a light beam in the LP01 mode, at least a part of a Young's modulus in the region 11c on the circumferential side of the region 11b in the core in which the intensity of the light beam in the LP01 mode is greater than the intensity of the light beam in the LP02 mode is smaller than a Young's modulus in the region 11b in which the intensity of the light beam in the LP01 mode is greater than the intensity of the light beam in the LP02 mode.