VCSEL Oxide Aperture Shaping for Circular Beam Profiles
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Solution Overview
Problem
Anisotropic oxidation in the fabrication of VCSELs leads to non-circular oxide apertures, resulting in non-circular output beams, which deviate from the preferred circular beam profile.
Innovation Solution
A method to determine the shape of the as-fabricated oxide aperture and calculate the necessary compensation to modify the mesa structure, ensuring it forms a target-shaped aperture by adjusting its geometry to match the desired shape through etching, thereby correcting for anisotropic oxidation effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a circular mesa structure is used with the presumption of isotropic oxidation, then the fabrication process is simple and straightforward, but anisotropic oxidation causes the oxide aperture to become non-circular, resulting in non-circular output beams
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-distorting the mesa structure geometry before oxidation to compensate for the known anisotropic oxidation effects. The mesa is intentionally shaped with different dimensions along x and y directions based on predicted oxidation rates, so that after oxidation, the aperture achieves the desired circular shape. This proactive compensation resolves the contradiction by maintaining fabrication simplicity while ensuring aperture precision.
Solution Approach 2:
The patent changes the geometric parameters of the mesa structure based on directional oxidation rate variations. By adjusting the mesa dimensions (width, length, curvature) along different axes according to the anisotropic oxidation characteristics, the final aperture shape is controlled to be circular despite the asymmetric oxidation process. This parameter adjustment resolves the contradiction between simple circular mesa fabrication and precise circular aperture formation.
2Productivity
If the oxidation process is allowed to proceed naturally without compensation, then the process is fast and efficient, but the resulting aperture shape deviates from the target circular shape due to anisotropic oxidation
Solution Approach 1:
The patent performs preliminary calculation and design of the mesa geometry to anticipate and compensate for anisotropic oxidation effects. By pre-configuring the mesa shape with appropriate dimensional variations along x and y directions, the natural fast oxidation process produces the desired circular aperture without requiring slow iterative adjustments or post-processing corrections. This resolves the contradiction by maintaining high oxidation speed while ensuring shape precision.
3Manufacturing precision
If the mesa structure is modified to compensate for anisotropic oxidation, then the oxide aperture achieves the desired circular shape, but the mesa fabrication becomes more complex requiring precise geometric control
Solution Approach 1:
The patent intentionally introduces asymmetry into the mesa structure design to counterbalance the asymmetry caused by anisotropic oxidation. The mesa is configured with different dimensional characteristics along x and y directions, creating a deliberately asymmetric geometry that, when subjected to asymmetric oxidation, produces a symmetric circular aperture. This asymmetric design resolves the contradiction by achieving high aperture precision while keeping the complexity manageable through purposeful geometric variation.
4Ease of manufacture
If conventional circular mesa etching is used, then the fabrication process is straightforward, but the resulting aperture shape is non-circular leading to non-circular beam output
Solution Approach 1:
The patent applies preliminary design of the mesa geometry to pre-compensate for anisotropic oxidation effects. By calculating the required dimensional variations before etching and incorporating them into the mesa pattern design, the subsequent straightforward etching process produces a mesa shape that, after oxidation, yields the desired circular aperture and circular beam profile. This resolves the contradiction by maintaining etching simplicity while ensuring beam quality.
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 approach ensures the formation of a predetermined target-shaped oxide aperture, even under anisotropic oxidation conditions, maintaining a circular or other desired beam profile, enhancing the consistency and quality of the VCSEL output.
Implementation Method 1
the aperture is typically created by oxidizing the exposed mesa structure of a distributed Bragg reflector (DBR) portion of the VCSEL
Implementation Method 2
the oxidation rates may differ for different directions across the x-y plane of the aperture layer, commonly referred to as direction-dependent, or 'anisotropic' oxidation
Data Source
AI summary
A corrected mesa structure for a VCSEL device is particularly configured to compensate for variations in the shape of the created oxide aperture that result from anisotropic oxidation. In particular, a corrected mesa shape is derived by determining the shape of an as-created aperture formed by oxidizing a circular mesa structure, and then ascertaining the compensation required to convert the as-created shape into a desired (“target”) shaped aperture opening. The compensation value is then used to modify the shape of the mesa itself such that a following anisotropic oxidation yields a target-shaped oxide aperture.