Semiconductor Laser Diode Filter Layer for Substrate Light
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Solution Overview
Problem
Edge-emitting laser diodes with transparent substrates suffer from substrate light emission, which degrades beam quality and causes imaging aberrations in projected images due to scattered and spontaneous light, especially in flying spot technology applications.
Innovation Solution
Incorporating a filter layer with a roughened substrate underside and/or an absorber layer to scatter and absorb substrate light, while maintaining the desired laser mode emission, thereby improving beam quality by reducing substrate light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a transparent substrate is used for blue or green emitting InGaN laser diodes, then the substrate allows light transmission, but scattered light and spontaneous emission propagate in the substrate and emerge from the coupling-out facet, degrading beam quality
Solution Approach 1:
The patent extracts and removes the harmful substrate light emission by introducing a filter layer that selectively absorbs scattered light and spontaneous emission from the substrate, while allowing the desired laser light to pass through unaffected
Solution Approach 2:
The filter layer acts as an intermediary element between the substrate and the coupling-out facet, mediating the transmission of light by allowing desired laser light to pass while blocking harmful scattered light and spontaneous emission
2Object-generated harmful factors
If the coupling-out facet is offset toward the rear with respect to the front edge of the heat sink, then part of the substrate light emission is masked out, but only a small part of substrate light emission is reduced and laser power is undesirably reduced
Solution Approach 1:
The filter layer is positioned locally at the coupling-out facet where substrate light emission occurs, providing targeted suppression of harmful light without affecting the overall laser power transmission through the device
Solution Approach 2:
The filter layer converts the harmful substrate light emission into a beneficial situation by selectively absorbing only the scattered light and spontaneous emission, while allowing the coherent laser light to pass through, thus improving beam quality without reducing laser power
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
Significantly enhances beam quality by minimizing substrate light emission, reducing image aberrations and maintaining the desired laser mode emission, thus improving the performance of laser diodes in projection applications.
Implementation Method 1
a filter layer...which is designed to scatter and/or absorb light which propagates in the semiconductor layer sequence and/or the substrate
Implementation Method 2
a filter layer...which is designed to scatter and/or absorb light which propagates in the semiconductor layer sequence and/or the substrate
Data Source
AI summary
A semiconductor laser diode includes a substrate. A semiconductor layer sequence on the substrate has at least one active layer designed for generating laser light that is emitted along an emission direction during operation. At least one filter layer has a main extension plane that is parallel to a main extension plane of the active layer and that is designed to scatter and/or absorb light that propagates in the semiconductor layer sequence and/or the substrate in addition to the laser light.