Amplifying Optical Fiber Radial Doping for Beam Quality
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Solution Overview
Problem
Double-clad optical fibers used in fiber laser devices often suffer from reduced beam quality due to the excitation of higher-order modes like LP02 and LP03, which can outpace the amplification of the fundamental LP01 mode, leading to inefficient laser output.
Innovation Solution
The amplification optical fiber is designed with a core where the active element is concentrated at higher levels in regions where the LP01 mode intensity exceeds that of LP02 and LP03 modes, ensuring the LP01 mode is amplified at a higher factor than higher-order modes through specific intensity and concentration distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a double-clad fiber with multi-mode core propagation is used to achieve high power laser output, then the laser output power is improved, but the beam quality deteriorates due to excitation of higher-order modes
Solution Approach 1:
The patent applies local quality by creating a non-uniform active element concentration distribution within the core, with higher concentration at the center and lower concentration toward the periphery. This spatial variation in active element concentration selectively enhances amplification of the LP01 mode while suppressing higher-order modes, thereby maintaining beam quality while achieving high power output.
2Device complexity
If the active element is uniformly distributed in the core, then the amplification is simplified, but the beam quality deteriorates because higher-order modes are amplified at higher rates
Solution Approach 1:
The patent implements local quality through a radially varying active element concentration profile, where the concentration is highest at the core center and decreases toward the periphery. This creates different amplification characteristics in different radial zones, suppressing higher-order modes that have significant field intensity at the periphery while maintaining amplification of the fundamental mode.
3Power
If the active element concentration is increased at the core center, then the LP01 mode amplification is enhanced, but the higher-order modes may still be excited and reduce beam quality
Solution Approach 1:
The patent resolves this contradiction by implementing a continuous radial gradient in active element concentration, with maximum concentration at the center and progressively lower concentration toward the periphery. This gradient structure ensures that the LP01 mode, which has its maximum intensity at the center, receives the strongest amplification, while higher-order modes with significant peripheral intensity experience reduced amplification in those regions.
Solution Approach 2:
The patent applies parameter changes by systematically varying the active element concentration as a function of radial position. This continuous parameter variation creates a gain profile that matches the intensity distribution of the desired LP01 mode while suppressing gain for higher-order modes, thereby achieving selective mode amplification.
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 approach enhances the beam quality of the output light by prioritizing the amplification of the LP01 mode over higher-order modes, resulting in improved laser performance even when higher-order modes are excited.
Implementation Method 1
an active element which amplifies light with a predetermined wavelength is added to the core at a higher concentration than a central portion of the core
Data Source
Figure 1~2
Figure 3(A)~3(D)
Figure 4(A)~4(D)
AI summary
The invention provides an amplification optical fiber, which can output light with a good beam quality even when a higher-order mode is excited, and an optical fiber amplifier using the amplification optical fiber. An amplification optical fiber 50 has a core 51 and a clad 52 covering the core 51. The core 51 propagates light with a predetermined wavelength in at least an LP01 mode, and an LP02 mode, and an LP03 mode. When the LP01 mode, the LP02 mode, and the LP03 mode are standardized by power, in at least a part of a region where the intensity of the LP01 mode is larger than at least one of the intensities of the LP02 mode and the LP03 mode, the active element is added to the core 51 at a higher concentration than the central portion of the core.