Fiber Laser Multimode Grating Mode Selective Amplification
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Solution Overview
Problem
Fiber laser devices struggle to emit light of excellent beam quality due to inefficient wavelength conversion of light with multiple modes, particularly when using multimode fibers, which affects the processing capabilities and power propagation.
Innovation Solution
A fiber laser device design featuring a multimode amplification optical fiber with active element doping, paired with first and second fiber Bragg gratings (FBGs) where the fundamental-mode light beam wavelengths are matched and higher-mode light beam wavelengths are unmatched, allowing for differential propagation and amplification, resulting in improved beam quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a multimode fiber is used for amplification optical fiber to increase output power, then the power handling capability is improved, but the beam quality deteriorates due to multiple modes propagation
Solution Approach 1:
The patent applies local quality by creating an uneven active element concentration distribution within the core of the amplification optical fiber. Specifically, the active element concentration is set to be higher in regions where the LP01 mode intensity is high compared to regions where LP02 or LP03 mode intensities are high. This selective doping strategy amplifies the fundamental mode more strongly than higher-order modes, thereby maintaining beam quality while utilizing the high power capacity of multimode fiber.
2Power
If light with multiple modes is input to wavelength conversion element, then the power is improved, but the wavelength conversion efficiency deteriorates
Solution Approach 1:
The patent changes the parameter of active element concentration distribution to selectively amplify different modes. By configuring the concentration to be higher in LP01 mode intensity regions and lower in higher-order mode regions, the system transforms the mode composition of the output light, suppressing higher-order modes and enhancing fundamental mode content before the light reaches the wavelength conversion element, thereby improving 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 device achieves excellent beam quality by amplifying fundamental-mode light beams while reducing the amplification of higher-mode light beams, enhancing the light's condensing properties and processing efficiency.
Implementation Method 1
a core doped with an active element that emits light in a pumped state
Implementation Method 2
a first FBG formed on a core of a multimode optical fiber, the first FBG reflecting at least a part of light emitted from the active element; and a second FBG formed on a core of a multimode optical fiber, the second FBG reflecting the light reflected off the first FBG
Data Source
Figure 1~2
Figure 3~4B
Figure 5~6B
AI summary
A fiber laser device (1) includes an amplification optical fiber (10) having a core (11) doped with an active element, a first FBG (35) reflecting at least a part of light emitted from the active element, and a second FBG (45) reflecting the light reflected off the first FBG (35) at a reflectance lower than the reflectance of the first FBG (35). The wavelength of a fundamental-mode light beam reflected off the first FBG (35) and the wavelength of a fundamental-mode light beam reflected off the second FBG (45) are matched with each other. The wavelengths of higher-mode light beams reflected off the first FBG (35) and the wavelengths of higher-mode light beams reflected off the second FBG are unmatched with each other.