Thinned VCSEL for Near-Field Eye Illumination
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Solution Overview
Problem
Conventional VCSEL structures are not optimally designed for eye-tracking applications, leading to suboptimal performance when used in head-mounted devices for illuminating eyes, as they are typically suited for other applications like fiber optic communications and laser printers.
Innovation Solution
A customized VCSEL structure with a semiconductor substrate thinned to reduce size, a diverging infrared beam emission, and integration with a wafer-level optic to achieve near-field illumination, along with a compact footprint to minimize noticeability, is developed for eye-tracking systems in head-mounted devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional VCSEL structures are used for eye-tracking illumination, then the device can perform basic illumination function, but the performance is suboptimal and the structure is not effective for near-field eye illumination
Solution Approach 1:
The patent applies local quality by creating a diverging beam profile specifically at the eye illumination location rather than using a conventional collimated beam. The VCSEL structure is modified to produce a diverging beam that expands as it travels through the waveguide, ensuring optimal illumination coverage of the eye pupil area while maintaining a compact form factor suitable for HMD integration.
Solution Approach 2:
The patent changes key optical parameters of the VCSEL including the beam divergence angle, wavelength (850nm or 940nm infrared), and cavity structure to optimize performance for near-field eye illumination. The distributed feedback (DFB) VCSEL design allows precise control of these parameters to achieve the desired diverging beam pattern that conventional VCSELs do not provide.
2Area of stationary object
If the VCSEL structure is thinned to reduce size, then the footprint is minimized for compact HMD integration, but manufacturing complexity increases
Solution Approach 1:
The patent segments the VCSEL structure into distinct functional layers including the active region, distributed Bragg reflectors (DBRs), and contact layers. This segmentation allows selective thinning of non-essential substrate portions while preserving the critical laser cavity and optical emission regions, thereby reducing overall footprint without compromising manufacturing feasibility.
Solution Approach 2:
The patent transitions from a conventional planar VCSEL layout to a thinned three-dimensional structure where the substrate is selectively removed from the backside. This dimensional change allows the VCSEL to achieve a smaller projected area footprint while maintaining structural integrity through the thinned substrate regions, enabling compact HMD integration.
3Reliability
If a diverging infrared beam is emitted for near-field illumination, then eye-tracking performance is enhanced, but the beam divergence may reduce optical efficiency
Solution Approach 1:
The patent introduces a waveguide as an intermediary optical element that couples the DFB VCSEL to the eye illumination optics. The waveguide captures and guides the diverging infrared beam from the VCSEL, maintaining beam quality and reducing stray light losses. This intermediary structure enables the diverging beam to effectively illuminate the eye while minimizing optical energy loss through controlled total internal reflection at the waveguide interfaces.
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 customized VCSEL structure provides effective near-field illumination for eye-tracking, enhancing the performance and user experience by ensuring the illumination is unnoticeable to both the wearer and outside observers while maintaining optical efficiency.
Implementation Method 1
a vertical-cavity surface-emitting laser (VCSEL) may be utilized as the illumination source
Implementation Method 2
a diverging infrared beam emission
Data Source
AI summary
A vertical-cavity surface-emitting laser for near-field illumination of an eye includes a semiconductor substrate, a first reflector, a mesa region, a first electrical contact, and a second electrical contact. The first reflector is disposed on a first side of the semiconductor substrate and the mesa region is disposed on the first reflector. The mesa region includes a second reflector and an active region, where the mesa region is configured to generate a diverging infrared beam. The first electrical contact is disposed on a second side of the semiconductor substrate, opposite the first side, for electrically coupling to the first reflector. The second electrical contact is also disposed on the second side of the semiconductor substrate for electrically coupling to the second reflector.