Offset High-Reflectivity Region in Surface-Emitting Laser Mesa
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Solution Overview
Problem
Surface emitting lasers face challenges in maintaining single transverse mode operation while maintaining a large light-emitting region, leading to increased lasing threshold current when using off-orientation substrates and surface-relief structures, as the center of the high-reflectivity region often coincides with the center of the mesa structure, disrupting fundamental mode oscillation.
Innovation Solution
A surface emitting laser design featuring a mesa structure with a current confinement layer and a surface-relief structure where the center of the high-reflectivity region is intentionally offset from the center of the mesa structure, taking into account the anisotropy of the oxidation rate, to suppress the increase in lasing threshold current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surface-relief structure with high-reflectivity region is formed on the top reflection mirror to suppress high-order transverse mode oscillation, then single transverse mode operation is achieved, but the lasing threshold current increases when the center of the high-reflectivity region coincides with the center of the mesa structure
Solution Approach 1:
The patent applies asymmetry by intentionally offsetting the center of the high-reflectivity region from the center of the mesa structure. This asymmetric positioning prevents the high-reflectivity region from disrupting the fundamental transverse mode oscillation while still suppressing high-order transverse modes, thereby reducing the lasing threshold current compared to symmetric configurations where the centers coincide.
Solution Approach 2:
The patent applies local quality by creating different reflectivity regions (high-reflectivity and low-reflectivity regions) within the surface-relief structure. The high-reflectivity region is positioned at a specific location offset from the mesa center to provide localized optical feedback that suppresses high-order modes without disrupting the fundamental mode, while other regions have different reflectivity characteristics.
2Ease of manufacture
If the center of the high-reflectivity region coincides with the center of the mesa structure, then the surface-relief structure is symmetric and easy to manufacture, but the fundamental transverse mode oscillation is disrupted and lasing threshold current increases
Solution Approach 1:
The patent deliberately introduces asymmetry by offsetting the high-reflectivity region from the mesa center. This asymmetric design prioritizes optical performance (maintaining fundamental mode oscillation) over manufacturing simplicity, accepting that precise alignment is needed but achieving better overall device performance through the asymmetric configuration.
3Reliability
If a current confinement layer is formed by selective oxidation to limit the light-emitting region and achieve single transverse mode operation, then transverse mode control is improved, but the light-emitting region size is reduced making it difficult to obtain large laser output
Solution Approach 1:
The patent addresses the trade-off between mode control and emission area by introducing a surface-relief structure on the top reflection mirror, which is a different dimension from the current confinement layer. This surface-relief structure provides transverse mode control through optical feedback mechanisms rather than physical confinement, allowing the current confinement layer to maintain a larger light-emitting region while still achieving single transverse mode operation.
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 effectively lowers the lasing threshold current by ensuring the center of the high-reflectivity region is positioned to optimize the fundamental transverse mode operation, maintaining a large light-emitting region and reducing power loss.
Implementation Method 1
a current confinement layer is formed inside the element of the surface emitting laser by selective oxidation
Implementation Method 2
a surface-relief structure that is formed on a light-emitting region of the top reflection mirror and has a stepped structure including a low-reflectivity region and a high-reflectivity region
Data Source
AI summary
A surface emitting laser having a mesa structure includes an off-orientation substrate, a bottom reflection mirror, an active layer, a current confinement layer, a top reflection mirror, and a surface-relief structure. The central axis of a high-reflectivity region of the surface-relief structure and the central axis of the mesa structure do not coincide with each other.