Tree-Array QCL Branch Structure for CW Beam Combining
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Solution Overview
Problem
Traditional tree-array quantum cascade lasers (QCLs) face low yield due to fabrication challenges with narrow ridges, leading to impractical applications, and broad-area configurations were believed to have poor beam quality and not operate in continuous wave (CW) mode effectively.
Innovation Solution
A beam combining configuration using broad-area QCLs with a tree array structure, featuring branch active regions with ridge widths greater than 10 μm and a low number of stages, achieves high beam quality and CW power by optimizing the ridge width and using InP spacers for thermal management, enabling fundamental mode operation and high power concentration in the central far-field lobe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If narrow ridge widths are used in traditional tree-array QCLs, then mode overlap is reduced and beam quality is improved, but fabrication yield decreases due to manufacturing challenges
Solution Approach 1:
The patent changes the ridge width parameter from narrow (traditional) to broad (>10 μm), fundamentally altering the geometric parameter to resolve the contradiction. This parameter change enables easier fabrication while maintaining beam quality through other mechanisms (mode filtering, phase synchronization)
Solution Approach 2:
Instead of using narrow ridges to achieve single-mode operation, the patent inverts the approach by using broad-area ridges and relying on the tree-array structure and phase synchronization to achieve coherent beam combination and fundamental mode operation, thereby resolving the fabrication difficulty while maintaining beam quality
2Ease of manufacture
If broad-area QCL configurations are used, then ridge width is increased and fabrication is simplified, but beam quality was believed to deteriorate and CW operation was thought to be ineffective
Solution Approach 1:
The patent merges multiple broad-area QCL elements into a tree-array structure with coherent beam combination. By synchronizing the phase and amplitude of multiple broad-area emitters, the system achieves high beam quality and CW power output, overcoming the individual limitations of broad-area configurations
Solution Approach 2:
The patent transitions from single-element operation to multi-element array operation, adding the dimension of spatial arrangement and phase control. The tree-array geometry with specific branching ratios enables coherent combination of multiple broad-area beams, achieving high-quality output that neither single element could produce alone
3Power
If the number of stages is increased in QCL active regions, then laser gain is enhanced, but thermal management becomes more difficult and CW operation is compromised
Solution Approach 1:
The patent segments the total stage count across multiple separate active regions in the tree-array structure. Each active region contains a manageable number of stages (reducing local heat generation), while the coherent combination of multiple segments achieves the required total gain, effectively distributing thermal load
Solution Approach 2:
The patent implements a nested structure where multiple active regions with fewer stages each are embedded within the broader tree-array configuration. This nesting allows each segment to be thermally managed independently while collectively achieving high laser gain through coherent beam combination
4Power
If tree-array structure with many elements is used, then output power is increased, but device complexity and fabrication difficulty increase
Solution Approach 1:
The patent applies local quality by making each individual active region simple and identical in structure, while the overall tree-array configuration provides the complexity for high power output. Each local element is optimized for simplicity and uniformity, reducing fabrication difficulty while the global structure achieves the desired performance
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 configuration enables the production of multi-watt CW optical power with high beam quality, overcoming yield issues and achieving up to 50 W output power from a single 16-element array, while maintaining a high fill-factor and reducing mode overlap, making it suitable for practical applications.
Implementation Method 1
a semiconductor layer adjacent the substrate and defining a plurality of branch active regions, and a stem region coupled to output ends of the plurality of branch active regions
Data Source
AI summary
A QCL may include a substrate, and a semiconductor layer adjacent the substrate. The semiconductor layer may define branch active regions, and a stem region coupled to output ends of the branch active regions. Each branch active region may have a number of stages less than 30.