Surface-Emitting Laser Stabilizes Polarization via Inclined Substrate
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Solution Overview
Problem
Vertical-cavity surface-emitting lasers (VCSELs) face challenges in maintaining stable light polarization direction and achieving a circular cross-sectional shape of the output light beam, which is crucial for high-definition applications like optical writing systems, due to variations in oxidation rates and symmetry issues with substrate orientations.
Innovation Solution
A surface-emitting laser element with a substrate having a principal plane inclined at 15 degrees to a crystallographic orientation, featuring a mesa structure with an oxidized aluminum layer surrounding the current passage area, ensuring a nearly circular cross-sectional shape and stable polarization direction without increasing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a non-inclination substrate with 4-fold symmetry is used, then the oxidation rate has predictable symmetry, but the electric current passage area cannot achieve sufficient circular symmetry due to oxidation rate variations
Solution Approach 1:
The patent applies asymmetry by using an inclination substrate with asymmetric crystallographic orientation (e.g., (311)B or (220) orientation) that breaks the 4-fold symmetry of non-inclination substrates. This asymmetric substrate orientation creates uniform oxidation rates in all radial directions, enabling the electric current passage area to achieve circular symmetry (roundness ratio of 0.95 or more) without requiring complex oxidation process control.
2Reliability
If an inclination substrate is used to control polarization mode, then polarization can be controlled, but the oxidation rate symmetry is broken causing elliptic FFP and degraded writing fineness
Solution Approach 1:
The patent applies local quality by selectively combining substrate inclination (for polarization control) with specific crystallographic orientation (311)B or (220) that provides uniform oxidation characteristics. This localized optimization allows the substrate to simultaneously achieve both polarization mode control and circular FFP, with the active layer and DBR mirrors providing polarization control while the inclined substrate orientation ensures uniform oxidation and circular current passage area.
3Manufacturing precision
If the mesa outline is adjusted to compensate for oxidation rate variations, then circular FFP can be achieved, but the manufacturing process becomes complex and costly
Solution Approach 1:
The patent applies parameter changes by modifying the substrate orientation parameter from standard (100) or (110) to inclined (311)B or (220) orientation. This parameter change fundamentally alters the oxidation characteristics, making the oxidation rate uniform in all radial directions. As a result, a simple circular mesa structure naturally produces a circular FFP without requiring complex outline adjustments, reducing manufacturing complexity while maintaining high precision.
4Reliability
If selective oxidation is used to confine current, then current confinement is achieved, but the electric current passage area shape varies due to oxidation rate anisotropy
Solution Approach 1:
The patent applies composite materials by using a combination of the inclined substrate (提供各向同性氧化特性) and the AlAs oxidation layer (提供选择性氧化和电流限制). This composite structure leverages the substrate's uniform oxidation characteristics to ensure that the oxidized layer forms a circular pattern, creating a symmetric electric current passage area that maintains both effective current confinement and circular geometry.
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 configuration stabilizes the light polarization direction and achieves a nearly circular output light beam, enabling high-precision optical scanning and high-quality image formation without cost increments.
Implementation Method 1
an oxidized aluminum layer which surrounds an electric current passage area in a plan view
Data Source
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AI summary
Disclosed is a surface-emitting laser element configured to emit light in a direction perpendicular to a substrate, including a substrate with a normal direction of a principal plane inclining toward one direction of a crystallographic orientation of <1 1 1> with respect to one direction of a crystallographic orientation of <1 0 0> and a mesa structure being formed on the substrate and having a narrowed structure with an oxide including at least an oxide produced by oxidizing a part of a layer to be oxidized selectively, the oxide containing aluminum and surrounding an electric current passage area, wherein a cross-section of the mesa structure being parallel to the substrate is parallel to a surface of the substrate and orthogonal to both the one direction of a crystallographic orientation of <1 0 0> and the one direction of a crystallographic orientation of <1 1 1> and a length in a first direction passing through a center of the electric current passage area is more than a length in a second direction parallel to a surface of the substrate and orthogonal to the first direction.