Patterned Substrate for Laser Diode Thermal Lensing
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Solution Overview
Problem
High-power laser diode arrays experience significant beam divergence due to thermal lensing caused by waste heat, leading to decreased brightness and efficiency in diode-pumped lasers.
Innovation Solution
The implementation of a laser diode array design that incorporates a semiconductor multilayer with emission regions separated by non-emitting regions, a metal layer, and a patterned substrate serving as a heat sink, with air gaps or open spaces created to restrict heat flow and reduce thermal gradients, thereby minimizing thermal lensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If laser diodes are operated at high power output, then the optical output of diode pumped lasers is enhanced, but beam divergence increases due to thermal lensing
Solution Approach 1:
The substrate is segmented into multiple regions with different thermal conductivities, including high thermal conductivity regions for heat dissipation and low thermal conductivity regions for thermal isolation. This segmentation allows different parts of the substrate to perform different thermal management functions, reducing thermal lensing while maintaining high power operation capability
Solution Approach 2:
Different regions of the substrate are assigned different thermal properties locally. The region beneath the laser diode has high thermal conductivity to conduct heat away, while surrounding regions have low thermal conductivity to minimize heat spread and reduce thermal gradients. This local differentiation of thermal properties addresses the beam divergence problem while preserving power output
2Temperature
If thermal isolation is implemented via air gaps or open spaces, then temperature falloff and thermal gradients are reduced, but device complexity increases
Solution Approach 1:
The substrate incorporates a porous layer with controlled porosity between 0.3 and 0.7, which provides thermal isolation through the porous structure itself. This approach achieves temperature uniformity reduction without requiring complex air gap structures, as the porous material inherently provides thermal resistance while maintaining structural integrity
Solution Approach 2:
The substrate is designed as a composite structure combining materials with different thermal conductivities in a single integrated component. This composite approach achieves both heat dissipation and thermal isolation functions without requiring multiple separate parts, thereby reducing device complexity while maintaining temperature uniformity
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 reduces beam divergence, enhances the brightness and efficiency of laser diode arrays by controlling temperature distribution and refractive index gradients, leading to improved optical power delivery to the gain media of diode-pumped lasers.
Implementation Method 1
a substrate disposed with respect to said semiconductor multilayer such that said metal layer is between said semiconductor multilayer and said substrate, said substrate providing a heat sink for at least portions of said semiconductor multilayer
Implementation Method 2
air gaps or open spaces or open regions are created to provide thermal isolation and curtail the temperature falloff and thermal gradients
Implementation Method 3
This divergence is believed to be caused by thermal lensing, which is induced by waste heat in the semiconductor laser that spreads and creates a thermal gradient. Variation in the semiconductor temperature with location in the semiconductor causes a change in refractive index with position that forms a thermal lens
Data Source
AI summary
Thermal management may in some cases improve the optical output of a semiconductor laser diode array. For example, providing gaps such as air gaps, at suitable locations may influence the temperature distribution of laser diodes in a laser diode array and curtail thermal lensing, which may in turn decrease beam divergence and increase delivered power.