High Power Fiber Laser Beam Quality via Coreless Termination
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Solution Overview
Problem
Current high power fiber laser systems face challenges in maintaining high beam quality as power increases, with existing methods sacrificing beam quality when scaling output power, resulting in a high M2 factor and poor combiner output quality due to broad far-field divergence and large effective area.
Innovation Solution
A fiber laser system is configured with SM fiber lasers whose terminal ends are arranged around a central SM fiber, subjected to heat and tension to elongate and radially shrink, maintaining a Gaussian shape and minimizing core diameters to achieve a small far-field divergence and low M2 factor, with a termination block using a quartz core to manage power density and prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple SM fiber laser outputs are combined to increase power output, then power scaling is achieved, but beam quality deteriorates due to high M2 factor and broad far-field divergence
Solution Approach 1:
Multiple single-mode fiber laser outputs are combined into a single composite beam by arranging fiber terminal ends in a specific geometric pattern (e.g., hexagonal close-packing) and fusing them together. The individual Gaussian beams merge to form a super-Gaussian intensity profile, achieving power scaling while maintaining controlled beam quality through the merging process.
Solution Approach 2:
The effective area and far-field divergence characteristics of the combined beam are controlled by changing the geometric arrangement parameters of the fiber terminal ends. By optimizing the packing geometry and relative positions of individual fiber outputs, the system achieves desired beam divergence and M2 factor while maintaining high power output.
2Speed
If fiber core diameter is increased to reduce far-field divergence, then beam divergence decreases, but beam quality deteriorates due to loss of Gaussian shape
Solution Approach 1:
The patent creates a composite beam structure by combining multiple single-mode fiber outputs with optimized core diameters. The individual fibers maintain their Gaussian beam characteristics with appropriate core sizes, while their spatial arrangement and fusion create a composite intensity profile that achieves reduced divergence without sacrificing the Gaussian nature of individual modes.
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 system achieves a high power output with a minimally possible M2 factor, maintaining high beam quality and reducing the risk of damage from power density, while simplifying the application of anti-reflective coatings and preventing backreflected light issues.
Implementation Method 1
subjected to heat and tension to elongate and radially shrink
Implementation Method 2
subjected to heat and tension to elongate and radially shrink
Implementation Method 3
The combined single modes of respective fibers translate into a multimode (MM) combiner output
Implementation Method 4
The beam quality may be characterized by an M2 factor. The lower the M2 factor, the higher the beam quality. In a diffraction-limited Gaussian beam, the M2 factor is as low as one
Implementation Method 5
a termination block using a quartz core to manage power density and prevent damage
Implementation Method 6
the far-field divergence of the SM beam can be measured as θ—divergence half-angle
Implementation Method 7
The MFD of each propagating beam is relatively small, and therefore, a far field divergence thereof is broad
Data Source
AI summary
A high power fiber laser system has a combiner configured of a plurality of single mode (SM) fibers which are fused together so as to define an output end of the fiber combiner. The fused SM fibers radiate respective fiber outputs, which collectively define a multimode (MM) combiner output. The SM fibers each are configured with such an optimally small numerical apertures (NA) that the MM combiner output is characterized by a minimally possible beam quality factor (M2) for the plurality of SM fibers. To reduce the possibility of burning of the components of the fiber laser system with a multi-kilowatt combiner output, a coreless termination block is fused to the output end of the fiber combiner and configured so as to provide expansion of the combiner output without modifying the minimally possible M2 factor thereof.