Multi-Junction VCSEL Low-Contrast DBR Beam Divergence
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Solution Overview
Problem
Multi-junction VCSELs face challenges in controlling beam divergence due to higher total gain, which promotes high-order and higher angle transverse modes, and in managing current injection profiles, especially for large aperture designs required in high-power LIDAR systems with narrow beam divergence.
Innovation Solution
Incorporating low-contrast DBR mirrors closer to the cavity to extend the effective length of the cavity, filter out higher-order modes, and improve current injection profiles, thereby reducing beam divergence and enhancing light-current-voltage characteristics and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multi-junction VCSEL structure is used to increase total gain, then laser output power is improved, but beam divergence increases due to promotion of high-order and higher angle transverse modes
Solution Approach 1:
A low-contrast DBR mirror is introduced as an intermediary element between the cavity and the high-contrast DBR mirror. This low-contrast mirror serves as a mediator that selectively filters high-order and higher angle transverse modes while allowing fundamental modes to pass through, thereby reducing beam divergence without compromising the high output power provided by the multi-junction structure.
Solution Approach 2:
The patent applies different contrast characteristics to different parts of the DBR mirror structure. The inner DBR mirror has low contrast to selectively filter specific modes, while the outer DBR mirror maintains high contrast for overall reflectivity. This local differentiation of optical properties enables mode control while preserving power output.
2Power
If large aperture design is used for high-power LIDAR systems, then power output is improved, but beam divergence control becomes more difficult
Solution Approach 1:
The low-contrast DBR mirror acts as an intermediary optical element that compensates for the increased beam divergence tendency in large aperture designs. By positioning this mirror close to the cavity, it provides localized mode filtering that maintains beam quality even when the aperture size is increased for high power output.
3Ease of manufacture
If conventional DBR mirror structure is used, then manufacturing is simplified, but current injection profiles are not optimized
Solution Approach 1:
The DBR mirror structure is segmented into two distinct parts: an inner low-contrast DBR mirror and an outer high-contrast DBR mirror. This segmentation allows each part to perform its specific function - the inner mirror optimizes current injection and mode filtering, while the outer mirror provides high reflectivity - thereby improving overall device performance without significantly complicating manufacturing.
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
The solution effectively reduces laser beam divergence, promotes lower order modes, and optimizes power and efficiency for multi-junction VCSELs in applications like LIDAR and 3D sensing, improving performance across temperature variations and short pulse durations.
Implementation Method 1
a low-contrast n-DBR disposed between the high-contrast n-DBR and the cavity
Implementation Method 2
a VCSEL is a semiconductor laser, more specifically a diode laser with a monolithic laser resonator, where light is emitted in a direction perpendicular to a chip surface
Implementation Method 3
a tunnel junction connecting the first active region and the second active region
Data Source
AI summary
A multi junction vertical cavity surface emitting laser (VCSEL) may comprise a substrate, a top contact, and a stack comprising a set of layers formed between the substrate and the top contact. In some implementations, the set of layers formed between the substrate and the top contact may comprise a cavity comprising a first active region, a second active region, and a tunnel junction connecting the first active region and the second active region, a first distributed Bragg reflector (DBR) pair comprising a high-contrast p-type DBR (p-DBR) and a low-contrast p-DBR between the cavity and the top contact, and a second DBR pair comprising a high-contrast n-type DBR (n-DBR) and a low-contrast n-DBR between the cavity and the substrate. The low-contrast p-DBR and the low-contrast n-DBR are located on an inner side of the stack, and the high-contrast p-DBR and the high-contrast n-DBR are located on an outer side of the stack.