Backside-Emitting VCSEL Mode Filter for Single-Mode Output
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Solution Overview
Problem
Conventional methods for achieving single mode operation in backside emitting vertical-cavity surface-emitting lasers (VCSELs) often reduce output power and manufacturability by decreasing the oxide aperture size, which is not desirable.
Innovation Solution
Incorporating a mode filter (MF) structure with a dielectric layer and a second mirror structure to suppress higher order transverse modes and increase reflectivity, allowing for single mode operation with improved performance uniformity and controllability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the oxide aperture size is decreased to achieve single mode operation, then mode purity is improved, but output power is reduced
Solution Approach 1:
The VCSEL structure is segmented into distinct functional regions: a first mirror structure with higher reflectivity, a cavity region with active layers, and a second mirror structure with lower reflectivity. This segmentation allows each region to be optimized independently, enabling single mode operation through the reflectivity differential without requiring aperture reduction that would limit output power.
Solution Approach 2:
Different reflectivity characteristics are applied locally to different parts of the VCSEL structure. The first mirror structure has higher reflectivity than the second mirror structure, creating a localized quality difference that enables mode selection. This local quality differentiation achieves single mode operation without the need to reduce the overall oxide aperture size, thereby maintaining output power.
2Measurement precision
If the oxide aperture size is decreased to achieve single mode operation, then mode purity is improved, but manufacturability is reduced
Solution Approach 1:
The invention segments the VCSEL into distinct mirror structures with different reflectivities, which can be fabricated using standard semiconductor processing techniques. This segmentation approach avoids the need for precise oxide aperture formation at small dimensions, simplifying the manufacturing process while achieving single mode operation.
Solution Approach 2:
The invention changes the reflectivity parameter of the mirror structures to achieve mode selection. By adjusting the reflectivity of the first and second mirror structures, single mode operation can be achieved without modifying the oxide aperture size, thereby maintaining ease of manufacture through conventional fabrication processes.
3Measurement precision
If a mode filter structure with dielectric layer and second mirror structure is added, then single mode operation is achieved, but device complexity is increased
Solution Approach 1:
The mode filter functionality is merged with the existing VCSEL mirror structures. The first and second mirror structures are integrated into the VCSEL cavity, combining the laser generation and mode filtering functions in a single unified structure. This merging approach achieves single mode operation without adding separate, complex filtering components.
Solution Approach 2:
The mirror structures serve multiple functions: they provide optical feedback for lasing, define the cavity resonances, and simultaneously act as the mode filter through their differential reflectivity. This multi-functionality reduces the need for additional dedicated filtering components, thereby limiting the increase in device complexity while achieving single 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
The MF structure enables reliable single mode operation with high reliability and low input power, maintaining performance uniformity and output power, unlike smaller oxide aperture approaches.
Implementation Method 1
an MF layer in a first region of the MF structure to at least partially suppress a higher order transverse mode (HOM) of the light, the MF layer comprising a dielectric layer
Implementation Method 2
a grating associated with polarizing light emitted by the VCSEL
Implementation Method 3
a grating associated with polarizing light emitted by the VCSEL
Implementation Method 4
a second mirror structure in at least a second region of the MF structure to increase reflectivity on a side of the VCSEL comprising the first mirror structure
Data Source
AI summary
A vertical-cavity surface-emitting laser (VCSEL) may include a first mirror structure over a cavity region. The VCSEL may include a grating associated with polarizing light emitted by the VCSEL. The grating may be over the first mirror structure. The VCSEL may include a mode filter (MF) structure over the grating. The MF structure may comprise an MF layer in a first region of the MF structure to at least partially suppress a higher order transverse mode (HOM) of the light, the MF layer comprising a dielectric layer. The MF structure may include a second minor structure in at least a second region of the MF structure to increase reflectivity on a side of the VCSEL comprising the first minor structure.