GaN Light Emitting Element with Concave Mirror for Diffraction Loss Control
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Solution Overview
Problem
In surface emitting laser elements with GaN-based compound semiconductors, increased resonator length leads to diffraction loss and thermal saturation, making it difficult to maintain laser oscillation and efficient light emission.
Innovation Solution
A light emitting element configuration with a first and second compound semiconductor layer, a first light reflecting layer on a concave mirror portion, and a second light reflecting layer with a flat shape, incorporating light convergence/divergence changing means to control the light state, ensuring reliable laser oscillation and reduced diffraction loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the resonator length LOR is increased to suppress thermal saturation, then thermal saturation is reduced, but diffraction loss increases making laser oscillation difficult
Solution Approach 1:
The patent applies curvature to the light reflecting layers by forming them on a concave mirror portion with a specific radius of curvature. This curved configuration modifies the resonator's optical path to reduce diffraction loss while maintaining the longer resonator length needed for thermal saturation suppression. The concave mirror geometry focuses and confines the laser beam more effectively, preventing excessive beam spread that would otherwise cause high diffraction loss in a long resonator.
Solution Approach 2:
The patent changes the geometric parameters of the resonator by specifying a resonator length LOR of 5 μm or more (significantly longer than conventional 1 μm) and a concave mirror radius of curvature within a specific range. These parameter changes enable the system to achieve both thermal saturation suppression through increased length and reduced diffraction loss through optimized curvature, resolving the contradiction between these two requirements.
2Ease of manufacture
If a flat light reflecting layer is used, then manufacturing is simpler, but diffraction loss increases in long resonators
Solution Approach 1:
The patent forms the light reflecting layer on a concave mirror portion rather than using a flat surface. This curvature is achieved through established semiconductor manufacturing techniques such as substrate bonding and selective etching, which, while adding some process steps, remain compatible with standard fabrication workflows. The curved geometry provides significant reduction in diffraction loss, justifying the additional manufacturing complexity.
Solution Approach 2:
The patent introduces a concave mirror portion as an intermediary structure between the substrate and the light reflecting layer. This intermediate element serves as a form tool that imparts the desired curvature to the reflecting layer during manufacturing, enabling the creation of the curved optical surface through conventional processing methods while achieving the optical performance benefits of a non-flat geometry.
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 configuration effectively manages diffraction loss and thermal saturation, enabling reliable laser oscillation and controlled light emission even with longer resonator lengths, improving manufacturing tolerance and yield.
Implementation Method 1
a first light reflecting layer disposed on a concave mirror portion
Implementation Method 2
diffraction loss increases
Implementation Method 3
light convergence/divergence changing means, in which the first light reflecting layer is formed on a concave mirror portion
Implementation Method 4
a material used for the light reflecting layer (for example, a material such as SiO2 or Ta2O5) has a lower value of thermal conductivity than the GaN-based compound semiconductor
Data Source
AI summary
A light emitting element includes: a laminated structure 20 obtained by laminating a first compound semiconductor layer 21, an active layer 23, and a second compound semiconductor layer 22; a first light reflecting layer 41 disposed on a first surface side of the first compound semiconductor layer 21; a second light reflecting layer 42 disposed on a second surface side of the second compound semiconductor layer 22; and light convergence/divergence changing means 50. The first light reflecting layer 41 is formed on a concave mirror portion 43. The second light reflecting layer 42 has a flat shape. When light generated in the active layer 23 is emitted to the outside, a light convergence/divergence state before the light is incident on the light convergence/divergence changing means 50 is different from a light convergence/divergence state after the light passes through the light convergence/divergence changing means 50.