Optical Fiber Young's Modulus Distribution for Beam Quality
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Solution Overview
Problem
Fiber laser apparatuses 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, leading to inefficient wavelength conversion and beam condensation due to the propagation of light beams with greater power in these modes.
Innovation Solution
An optical fiber is designed with a dopant that alters Young's modulus, ensuring that the waveguide region in the cladding has a smaller Young's modulus than the core region, causing acoustic waves to gather in the cladding and thereby attenuating the LP02 mode more than the LP01 mode, while maintaining low loss in the LP01 mode, thus improving 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 optical fiber structure. The dopant concentration is varied locally to achieve different Young's modulus values in different regions, particularly making the Young's modulus in the waveguide region smaller than in the core region. This local differentiation allows selective attenuation of higher modes while maintaining power transmission capability.
Solution Approach 2:
The patent changes the physical parameter of Young's modulus through dopant distribution to control mode propagation characteristics. By adjusting the Young's modulus in different regions of the fiber, the patent achieves selective attenuation of higher modes (such as LP02) while allowing fundamental mode (LP01) to propagate with minimal loss, thus improving beam quality without sacrificing power transmission.
2Power
If a light beam in higher mode is emitted, then the power output is improved, but the wavelength conversion efficiency deteriorates
Solution Approach 1:
The patent converts the harmful effect of higher mode excitation into a beneficial outcome by using the Young's modulus distribution to selectively attenuate higher modes. The natural tendency of higher modes to be excited in multimode fibers is transformed into an opportunity to control mode composition, ensuring that only fundamental mode reaches the wavelength conversion element, thereby improving conversion efficiency while maintaining high power output.
3Power
If a light beam in higher mode is emitted, then the power output is improved, but the beam condensation capability deteriorates
Solution Approach 1:
The patent uses local quality differentiation in Young's modulus distribution to control the spatial distribution of light modes. By creating regions with different mechanical properties through selective dopant placement, the fiber structure preferentially attenuates higher modes that have poor beam condensation characteristics, allowing only fundamental mode with excellent beam condensation capability to propagate, thus maintaining tight beam focus while preserving power output.
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 minimizing loss in the LP01 mode, resulting in a light beam of excellent beam quality even with a large core diameter, enhancing beam condensation and wavelength conversion efficiency.
Implementation Method 1
stimulated Brillouin scattering is caused by an interaction between a light beam and acoustic waves propagated through an optical fiber. Such a tendency is observed that the acoustic waves are gathered at a portion where a Young's modulus is small.
Data Source
Figure 1
Figure 2A~2E
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AI summary
An optical fiber propagates a light beam at a predetermined wavelength at least in an LP01 mode and an LP02 mode. A dopant that changes a Young's modulus is doped to at least a part of a waveguide region 12a of a cladding 12 through which a light beam at a predetermined wavelength is propagated and to a region 11b in a core 11 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. At least a part of the Young's modulus in the waveguide region 12a of the cladding 12 is smaller than a Young's modulus in the region 11b in the core 11 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.