External-Cavity Semiconductor Lasers With Diamond Heat-Spreaders
Solution Overview
Problem
Optically pumped semiconductor lasers face limitations in power output due to heat extraction issues, particularly with the mirror structure impeding heat removal, and deformation of chips in multi-chip resonators leading to misalignment and reduced efficiency, especially at longer wavelengths.
Innovation Solution
A laser resonator design featuring an epitaxially grown semiconductor gain-structure with a diamond heat-spreader bonded to the gain-structure's second surface, allowing heat removal only through this surface while maintaining access for laser radiation, and a transparent mirror structure for pump radiation delivery, enabling efficient heat management and alignment in both standing-wave and traveling-wave configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a mirror structure is used to provide high reflectivity at the gain structure, then laser radiation is effectively confined in the resonator, but the mirror structure impedes heat extraction from the gain structure
Solution Approach 1:
The invention extracts the heat removal function from the mirror structure by bonding a diamond heat spreader to the rear surface of the gain structure. This separates the optical function (mirror reflection) from the thermal management function (heat extraction), allowing the mirror structure to provide high reflectivity while the diamond heat spreader provides efficient heat extraction path.
Solution Approach 2:
The diamond heat spreader acts as an intermediary between the gain structure and the heat sink substrate. It provides a low thermal impedance path for heat extraction while allowing the mirror structure to maintain its optical function. The diamond layer mediates between the thermal management requirements and the optical resonance requirements.
2Power
If pump power is increased to raise output power, then laser power output increases, but thermal roll-off occurs and power output drops dramatically
Solution Approach 1:
The invention converts the harmful heat that causes thermal roll-off into a manageable parameter by providing an efficient heat extraction path through the diamond heat spreader. The heat that would otherwise cause performance degradation is now effectively removed, allowing continuous operation at high pump powers without thermal roll-off.
3Power
If multiple OPS-chips are used in a resonator to overcome power limitations, then power output can be increased, but chip deformation causes misalignment between lasing mode and pump radiation
Solution Approach 1:
The invention changes the thermal management parameters by bonding diamond heat spreaders to all OPS-chips. This provides uniform thermal expansion characteristics across all chips, reducing differential deformation and maintaining alignment precision between lasing modes and pump radiation in multi-chip configurations.
4Device complexity
If the gain structure is cooled through the rear surface only, then heat extraction is simplified, but thermal impedance increases compared to dual-sided cooling
Solution Approach 1:
The invention uses a composite structure consisting of the gain structure bonded to a diamond heat spreader, which is then bonded to a heat sink substrate. This composite material approach provides efficient heat extraction through the rear surface while maintaining relatively low thermal impedance, as diamond has extremely high thermal conductivity.
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 thermal resistance and maintains alignment of pump radiation with circulating laser radiation, increasing power output and efficiency by optimizing heat removal and reducing thermal impedance, particularly beneficial for longer wavelengths.
Implementation Method 1
A diamond heat-spreader has first and second opposite surfaces with the first surface of the diamond heat-spreader bonded to the second surface of the gain-structure
Implementation Method 2
a residual portion of the pump-radiation being converted to heat in the gain-structure
Data Source
AI summary
A semiconductor gain-structure functions as a gain-element in a laser-resonator. The gain-structure is bonded to a diamond heat-spreader that is peripherally cooled by a heat-sink configured to allow access to the gain-structure by laser-radiation circulating in the laser-resonator. In one example, the gain-structure is used as a transmissive gain-structure in a traveling-wave ring-resonator. In another example, the gain-structure surmounts mirror-structure which functions as an end-mirror of a standing-wave laser-resonator.