Extended-Cavity VCSEL Structure for Low-Divergence Proximity Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current VCSELs have relatively high divergence, limiting the sensitivity and accuracy of proximity sensors, especially in compact devices like mobile phones, where reflections from protective windows interfere with distance detection, and the divergence restricts the measurable distance.
Innovation Solution
Incorporating an additional epitaxial layer into the VCSEL structure to increase the cavity length, reducing beam divergence to as low as 0.5 to 5 degrees, achieved by placing the epitaxial layer between mirrors in the resonant cavity, allowing for higher power and fewer transverse modes, and using transparent materials for the epitaxial layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an additional epitaxial layer is added to increase cavity length, then beam divergence is reduced and measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent changes the physical parameter of cavity length by adding an additional epitaxial layer between the mirrors. This structural modification directly reduces beam divergence from typical values to below 10 degrees, thereby improving distance measurement precision without requiring external optical components.
Solution Approach 2:
The patent extends the VCSEL cavity in the vertical dimension by adding an epitaxial layer, transforming the original two-mirror cavity into a three-section structure. This dimensional extension enables better beam collimation and reduces divergence in the lateral direction, improving measurement precision.
2Measurement precision
If VCSEL beam divergence is reduced for better sensor sensitivity, then measurement precision improves, but the device footprint cannot be reduced further
Solution Approach 1:
The patent modifies the VCSEL's internal cavity length parameter to achieve low divergence (<10 degrees) directly from the laser source. This eliminates the need for external collimating lenses or optical systems, allowing high-precision proximity sensing in a miniaturized footprint suitable for mobile phones.
3Device complexity
If standard VCSEL divergence of fifteen degrees is used, then device complexity remains low, but sensitivity of proximity sensors is limited
Solution Approach 1:
The patent changes the cavity length parameter by inserting an additional epitaxial layer, which reduces beam divergence from the standard fifteen degrees to below ten degrees. This parameter change directly improves sensor sensitivity and reliability while maintaining a relatively simple VCSEL structure.
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 narrower beam divergence enhances the sensitivity and accuracy of proximity sensors, enabling longer distance measurements and improved performance in compact devices by reducing interference from protective windows and ambient light.
Implementation Method 1
The VCSEL includes a resonant cavity, including a gain region, disposed between a bottom mirror and a partially reflecting middle mirror... an additional epitaxial layer disposed between the partially reflecting middle mirror and a top mirror
Implementation Method 2
vertical cavity surface emitting laser (VCSEL) that includes a substrate, and an epitaxial VCSEL structure on the substrate... a gain region, disposed between a bottom mirror and a partially reflecting middle mirror
Data Source
AI summary
The disclosure describes VCSELs operable to produce very narrow divergent light beams. The narrow divergent beam can be obtained, in part, by incorporating an additional epitaxial layer so as to increase the cavity length of the VCSEL. The increased cavity length can result in higher power in fewer larger diameter transverse modes, which can significantly reduce the output beam divergence. The additional epitaxial layer can be incorporated, for example, into a top-emitting VCSEL or bottom-emitting VCSEL.