Active Mirror VECSEL Architecture for kW-Level Thermal Management

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Solution Overview

Problem

The output power of optically pumped semiconductor lasers (OPSLs) is limited by thermal management issues, particularly due to high thermal resistance in distributed Bragg reflectors (DBRs) and heat transport limitations in DBR-free designs, restricting them to around 100 W, whereas fiber and disk lasers can achieve several kW.

Innovation Solution

A vertical-external-cavity surface-emitting laser (VECSEL) design featuring a heat sink, a heat spreader with a high thermal conductivity material, and a high contrast grating integrated into the active region, where the heat spreader is bonded to the heat sink and the active region, allowing for improved heat sinking and higher power operation by minimizing zero-order diffraction and optimizing grating parameters for total internal reflection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a distributed Bragg reflector (DBR) is used in the VECSEL design, then high reflectivity is achieved, but thermal resistance increases significantly limiting output power to around 100 W

Engineering Contradiction:

ImprovereflectivityVSAvoidthermal resistance

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent removes the distributed Bragg reflector (DBR) from the VECSEL design, extracting the problematic thermal resistance component while maintaining laser functionality through an alternative cavity configuration that uses the heat spreader surface as the reflecting element

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The heat spreader is given a dual function: it continues to perform its primary thermal management role while also serving as the optical cavity mirror, eliminating the need for a separate DBR structure and reducing overall thermal resistance

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Temperature

If the heat spreader is placed inside the laser cavity (DBR-free design), then thermal management is improved, but lateral heat transport limitations and optical purity requirements restrict power scalability

Engineering Contradiction:

Improveheat transportVSAvoidpower scalability

Core Design Contradiction:

TemperatureVSProductivity

Solution Approach 1:

The patent transitions from lateral heat transport in the cavity plane to vertical heat transport through the heat spreader surface, utilizing the third dimension (depth) to improve thermal management without compromising optical performance or power scalability

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If High Contrast Gratings are used as mirrors, then reflectivity is achieved with thin high-index material, but the heat spreader must be inside the cavity causing optical loss concerns

Engineering Contradiction:

ImprovereflectivityVSAvoidoptical losses

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent extracts the High Contrast Grating from the laser cavity and places it on the external heat spreader surface, removing the source of optical losses while maintaining the reflectivity function through the modified cavity geometry

Inventive Principle:

Principle #2Taking out (Extraction)

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 enables kW-level continuous-wave operation, outperforming standard VECSELs by nearly a factor of 5 in dissipated power, making multi-kW semiconductor disk lasers feasible by addressing thermal management challenges.

Implementation Method 1

heat spreader attached or bonded to a heat sink, where the heat spreader comprises a first material having a first refractive index

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

optimizing grating parameters for total internal reflection

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 3

minimizing zero-order diffraction and optimizing grating parameters

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 4

active region attached or bonded to the heat spreader, wherein the active region comprises a second material (or combination of materials) having a second refractive index

Methodology Applied

Scientific EffectOptical amplification:

Data Source

PatentUS11949211B2Broadband active mirror architecture for high power optically pumped semiconductor disk lasers

Publication Date: 2024.04.02 UNM RAINFOREST INNOVATIONS

AI summary

A vertical-external-cavity surface-emitting laser (VECSEL) and a method of forming the VECSEL is disclosed. The VECSEL includes a heat sink; a heat spreader or heat spreader formed on a top surface of the heat sink, where the heat spreader comprises a first material having a first refractive index; and a high contrast grating formed on a top surface of the heat spreader or active region, wherein the high contrast grating comprises an active region and the high contrast grating comprising a second material having a second refractive index, the second refractive index is greater than the first refractive index.