Inverted Refractive Index Mesa for VECSEL Thermal Stability
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Solution Overview
Problem
Current IV-VI semiconductor lasers face inefficiencies due to temperature-dependent refractive index, leading to increased lasing threshold and reduced output power, making them difficult to operate at high temperatures and increasing complexity and cost.
Innovation Solution
A vertical emitting laser device with a transversally confined active gain layer stack, featuring mesas with a higher refractive index at the center and lower refractive index at the edges, which inverts the refractive index gradient to guide the laser mode and reduce threshold power, enhancing power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If IV-VI semiconductor lasers are operated at high temperatures, then the laser can be used in more applications, but the temperature-dependent refractive index causes anti-guiding effect that increases lasing threshold and reduces output power
Solution Approach 1:
The patent inverts the natural refractive index gradient that causes anti-guiding at high temperatures. By creating a mesa structure where the center has higher refractive index than the edges (opposite to the temperature-induced gradient), the invention achieves light guiding effect that compensates for thermal effects, enabling stable operation at elevated temperatures
Solution Approach 2:
The patent applies local quality by creating a mesa structure with spatially varying refractive index - the center region (lasing spot) has different optical properties than the surrounding edges. This local differentiation creates the necessary light guiding effect in specific regions while maintaining overall device functionality at high temperatures
2Use of energy by moving object
If the refractive index gradient is inverted to improve light guiding, then wall-plug efficiency increases, but the device structure becomes more complex
Solution Approach 1:
The patent segments the active gain layer into a mesa structure with distinct center and edge regions. This segmentation creates the refractive index differential necessary for light guiding while maintaining a relatively simple overall device architecture that can be integrated into existing laser designs
3Power
If mesa structure is used to confine light transversally, then lasing threshold is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent utilizes parameter changes by varying the mesa diameter to optimize the balance between light confinement and manufacturing feasibility. By adjusting this geometric parameter, the invention achieves effective transverse mode confinement while accommodating practical manufacturing tolerances
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 design significantly improves the wall-plug efficiency, allowing operation at higher temperatures and enabling continuous wave emission, reducing device size, and increasing reliability, with the ability to switch between different lasing regimes and achieve precise emission spot definition.
Implementation Method 1
a first refractive index of at least a part of the lasing spot region is higher than a second refractive index of a neighboring region of the active gain layer stack... thus increasing a transversal confinement factor
Data Source
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Figure 5
AI summary
The present invention relates to an active gain layer stack (21) for a vertical emitting laser device, the active gain layer stack (21) comprising a semiconductor material, wherein the semiconductor material is structured such that it forms at least one mesa (24) extending in a vertical direction. A transversally neighbouring region (25) that at least partly surrounds said mesa (24) has a second refractive index (n 2). At least part of said mesa (24) has a first refractive index (n 1) and a part of the neighbouring region (25) transversally adjacent to said part of the mesa (24) has second refractive index (n 2). Said first refractive index (n 1) is higher than said second refractive index (n 2) and a diameter in transversal direction of said mesa (24) is chosen such that a transversal confinement factor in the active gain layer stack (21) is increased. The present invention also relates to a laser device including such a stack, further to a method of operation of such a stack, and also to a method of manufacturing of such a stack. The VECSEL comprises a IV-VI gain material grown on the lower mirror and an external cavity mirror. A plurality of mesa (22) may be grown on a single substrate (23). Anti-guiding is prevented by the lower refractive index of the surrounding material (25) improving the single transversal mode operation.