Semiconductor Waveguide Oblique Coupling for Speckle Reduction
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Solution Overview
Problem
Laser sources with narrowband emission spectra, such as semiconductor lasers, often result in reduced imaging quality due to speckle, making it difficult to achieve high light intensity in large-area projection devices.
Innovation Solution
A radiation-emitting semiconductor component with a semiconductor body featuring a waveguide that extends between a mirror surface and a coupling-out surface, where the waveguide is perpendicular to the mirror surface and oblique to the coupling-out surface, preventing coherent radiation emission and increasing the spectral width of the emitted radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a semiconductor laser with ridge waveguide geometry is used, then the emission spectrum becomes very narrowband, but the imaging quality is reduced due to speckle
Solution Approach 1:
The waveguide is designed with asymmetric orientation relative to the coupling-out surface: it extends perpendicularly to the mirror surface but obliquely to the coupling-out surface. This asymmetric geometry prevents the coupling-out surface from forming a resonator surface, thereby avoiding coherent radiation and speckle while maintaining directional emission and high spectral width
Solution Approach 2:
Instead of making the coupling-out surface perpendicular to the waveguide (as in conventional lasers), the invention inverts this relationship by making the waveguide oblique to the coupling-out surface. This inversion prevents feedback of radiation into the waveguide, eliminating stimulated emission and coherent radiation that cause speckle
2Illumination intensity
If the coupling-out surface is made perpendicular to the waveguide to maximize light extraction, then radiation is coupled back into the waveguide causing stimulated emission, but this reduces spectral width and increases coherence
Solution Approach 1:
The waveguide is oriented asymmetrically with respect to the coupling-out surface, extending obliquely rather than perpendicularly. This asymmetric arrangement allows efficient light extraction while preventing radiation from coupling back into the waveguide, thus avoiding stimulated emission and maintaining broad spectral width
Solution Approach 2:
The invention changes the geometric parameter of the waveguide-coupling-out surface interface from perpendicular (0° angle) to oblique (non-zero angle). This parameter change prevents feedback while maintaining high extraction efficiency, resolving the contradiction between light extraction and spectral width
3Power
If a highly reflective mirror surface is used to increase output power, then more radiation is reflected back into the waveguide, but this increases coherent radiation and speckle
Solution Approach 1:
The asymmetric orientation of the waveguide relative to the mirror surface and coupling-out surface ensures that even with high reflectivity, reflected radiation does not couple back into the waveguide. The oblique angle at the coupling-out surface breaks the feedback path, allowing high output power without coherent radiation buildup
Solution Approach 2:
The invention converts the potentially harmful effect of high reflectivity (which would normally cause feedback and coherent radiation) into a benefit. By combining high mirror reflectivity with asymmetric waveguide geometry, the reflected radiation is directed away from the waveguide, increasing output power while preventing speckle formation
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 enhances imaging quality by reducing speckle patterns and achieving high optical output powers with a broader spectral width, making it suitable for use in projectors.
Implementation Method 1
The semiconductor component has a waveguide, which is provided for laterally guiding the radiation generated in the active region
Implementation Method 2
The mirror surface is provided with a highly reflective coating, that is to say a coating which reflects at least 80%, preferably at least 90%, of the radiation generated in the active region
Implementation Method 3
The waveguide meets the coupling-out surface obliquely with respect to a normal to the coupling-out surface
Data Source
AI summary
A radiation-emitting semiconductor component includes a semiconductor body. The semiconductor body has a semiconductor layer sequence having an active region provided for generating radiation. The semiconductor component has a waveguide, which is provided for laterally guiding the radiation generated in the active region and which extends between a mirror surface and a coupling-out surface. The waveguide meets the mirror surface perpendicularly and forms an acute angle with a normal to the coupling-out surface.