Spiral-Wound Fiber Laser Amplifier Layout for TMI Suppression
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Solution Overview
Problem
High-power fiber laser apparatuses experience Transverse Mode Instability (TMI) due to thermal gratings and mode coupling, leading to reduced beam quality and conversion efficiency from pumping light to signal light.
Innovation Solution
An optical device with an amplifying fiber wound in a spiral manner on a single plane, featuring inner and outer sections with specific arc portions to filter higher-order modes and reduce thermal grating formation, ensuring the fiber does not intersect on the same plane, and incorporating mode filters near fusion spliced portions to remove higher-order modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the power of pumping light is increased to improve conversion efficiency, then more signal light is generated, but Transverse Mode Instability occurs causing beam quality deterioration
Solution Approach 1:
The amplifying fiber is wound in a spiral configuration on a planar surface, transitioning from a linear to a spatial arrangement. This dimensional change allows the fiber to be arranged in an outer section and an inner section with different curvature radii, enabling simultaneous achievement of high conversion efficiency and beam quality by controlling mode propagation in different spatial regions
Solution Approach 2:
The amplifying fiber is designed with different sections having distinct properties: the outer section has a larger curvature radius for high-power amplification with good heat dissipation, while the inner section has a smaller curvature radius to act as a mode filter. This local differentiation allows each section to optimize for its specific function, resolving the contradiction between power conversion and beam quality
2Productivity
If higher-order modes are propagated to increase amplification efficiency, then more rare earth ions are utilized, but thermal grating formation increases causing TMI phenomenon
Solution Approach 1:
The amplifying fiber is segmented into an outer section and an inner section with distinct functions. The outer section propagates higher-order modes for efficient amplification, while the inner section filters these modes to prevent thermal grating accumulation. This segmentation allows the system to benefit from higher-order mode amplification while eliminating their harmful thermal effects
Solution Approach 2:
The higher-order modes, which initially cause thermal grating and TMI, are converted into a beneficial resource. They are first used for amplification in the outer section, then deliberately filtered in the inner section. This approach transforms the harmful thermal effects into a controlled process that actually improves overall system performance by enabling efficient use of rare earth ions
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
Enhances conversion efficiency from pumping light to signal light by minimizing TMI, maintaining beam quality, and reducing temperature rise in the amplifying fiber, thereby increasing reliability and efficiency.
Implementation Method 1
the at least two first arc portions (AR1) function as a mode filter designed to remove higher-order modes higher than the LP11 mode
Implementation Method 2
a fiber laser apparatus in which a filter unit is provided in an amplifying fiber to which rare earth ions are added to a core
Data Source
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AI summary
This optical device includes: a resonator fiber including an HR-FBG, a resonator fiber including an OC-FBG, and an amplifying fiber having an end portion connected to the resonator fiber and an end portion connected to the resonator fiber, and having a normalized frequency equal to 5.13 or higher. The amplifying fiber is wound so as not to intersect on one plane and so as to have an end located on an inside thereof, and has an outer section in which the amplifying fiber is wound in a circular manner and an inner section in which the amplifying fiber is wound so as to have at least two arc portions having a radius of curvature set such that a higher-order mode higher than an LP11 mode has loss.