VCSEL High-Order Mode Suppression via Layer Thickness
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Solution Overview
Problem
Existing vertical-cavity surface-emitting lasers (VCSELs) face challenges in suppressing high-order transverse mode lasing across a wide temperature range, with existing methods either increasing the lasing threshold of low-order modes or reducing optical output at high temperatures, and these methods often require complex processing steps or etching variations that are difficult to reproduce accurately.
Innovation Solution
A VCSEL design with a substrate, semiconductor multilayers, and a metal layer where the optical thickness of the contact layer and the top layer of the second semiconductor multilayer is less than λ/4, combined with a current confining layer and an oxidized region, effectively suppresses high-order transverse mode lasing by optimizing the reflectivity and bandgap energy difference, allowing for consistent output across temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reflectivity adjusting layer with Bragg reflection condition is used to suppress high-order transverse mode, then high-order transverse mode suppression is improved, but manufacturing precision deteriorates due to etching variations and thickness control difficulties
Solution Approach 1:
The patent changes the key parameter from reflectivity adjusting layer thickness (which requires precise etching control) to top layer thickness and bandgap energy difference (which can be controlled during epitaxial growth). By making the top layer thickness smaller than λ/4 and optimizing the bandgap energy difference between the top layer and active layer, the patent achieves high-order transverse mode suppression without relying on precise etching of a reflectivity adjusting layer.
2Reliability
If existing methods are used to suppress high-order transverse mode, then mode suppression is improved, but optical output deteriorates at high temperatures
Solution Approach 1:
The patent optimizes the bandgap energy difference parameter between the top layer and active layer to maintain both high-order transverse mode suppression and high optical output at elevated temperatures. By carefully selecting materials and thicknesses to achieve the proper bandgap energy difference, the patent ensures that the VCSEL maintains stable performance across a wide temperature range without the trade-off seen in existing methods.
3Reliability
If the shape of the upper electrode is processed to match the dark portion of emission pattern to suppress high-order transverse mode, then mode suppression is improved, but device complexity increases due to complicated processing
Solution Approach 1:
The patent replaces the complex geometric shaping of the upper electrode with a simpler parameter-based approach. Instead of processing the upper electrode into specific shapes to match emission patterns, the patent achieves mode suppression by optimizing the top layer thickness and bandgap energy difference, which are controlled during the epitaxial growth process and require no additional complex processing steps.
4Reliability
If etching process is used to form reflectivity adjusting layer to suppress high-order transverse mode, then mode suppression is improved, but manufacturing precision deteriorates due to difficulty in forming accurate thickness with high reproducibility
Solution Approach 1:
The patent replaces the mechanical etching process with an epitaxial growth process. Instead of using etching to create the top layer with the required thickness characteristics, the patent forms the top layer with precise thickness control directly during epitaxial growth. This substitution eliminates the reproducibility issues associated with etching while maintaining the ability to achieve the necessary optical properties for high-order transverse mode suppression.
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 suppresses high-order transverse mode lasing while maintaining high optical output and reducing the complexity of manufacturing processes, ensuring consistent performance from low to high temperatures without the need for additional processing steps.
Implementation Method 1
a first mirror portion 12a having a thickness (thickness of λ/4) that meets the Bragg reflection condition
Implementation Method 2
a second mirror portion 12b having a thickness (thickness of λ/2) that meets the anti-Bragg reflection condition
Implementation Method 3
VCSELs have excellent characteristics which edge-emitting semiconductor lasers do not have
Implementation Method 4
vertical-cavity surface-emitting laser diode (hereinafter referred to as VCSEL)
Data Source
AI summary
A VCSEL includes a substrate, a first semiconductor multilayer of a first conductivity-type, an active layer, a second semiconductor multilayer of a second conductivity-type, a contact layer, each of the layers stacked on the substrate. The second semiconductor multilayer constitutes a resonator together with the active layer and the first semiconductor multilayer. A metal layer is formed on the contact layer. The metal layer includes an opening portion that defines a region that emits laser light. When oscillation wavelength of the laser light is λ, optical thickness T of the contact layer and a top layer of the second semiconductor multilayer that contacts with the contact layer is smaller than λ/4.