Waveguide Eye Imaging System for HMD Gaze Tracking
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Solution Overview
Problem
Conventional eye tracking systems in head-mounted devices (HMDs) face challenges in capturing direct images of the cornea and pupil due to the form factor, which prevents effective use of PCCR gaze tracking processes.
Innovation Solution
Incorporating a waveguide with a narrow input coupler and output coupler in the HMD's display lens, utilizing diffraction or reflection to redirect light rays from the eye to an eye tracking camera, allowing for a more direct and in-focus imaging of the eye's surface, even when the camera is positioned outside the user's field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the eye tracking camera is mounted on the HMD frame to capture eye images, then the camera can obtain eye images for gaze tracking, but the camera cannot be positioned directly in front of the eye due to form factor constraints, resulting in angled imaging that degrades image quality
Solution Approach 1:
The patent introduces a waveguide as an intermediary optical element between the eye and the camera. The waveguide collects light from the eye through its input coupler and redirects it to the camera via total internal reflection, enabling the camera to capture eye images without being positioned directly in front of the eye. This resolves the contradiction by providing an indirect optical path that maintains imaging accuracy while accommodating form factor constraints.
Solution Approach 2:
The waveguide redirects light rays from a direct frontal path to an angled path by utilizing total internal reflection at specific angles. This dimensional change in the optical path allows the camera to be positioned on the HMD frame rather than directly in front of the eye, solving the positioning constraint while maintaining image quality through proper optical geometry.
2Adaptability or versatility
If conventional display waveguides are used to relay eye images, then the waveguide can image objects at infinity, but the display is too close to the eye's cornea for effective PCCR gaze tracking
Solution Approach 1:
The patent applies local quality by designing the waveguide with specific optical properties tailored for close-proximity eye imaging. The input coupler is positioned close to the cornea and designed with specific geometry to capture corneal reflections, while the waveguide itself is optimized to maintain image quality over the short distance. This localized optimization enables effective PCCR gaze tracking unlike conventional display waveguides.
Solution Approach 2:
The patent changes key parameters of the waveguide system, including the input coupler geometry, waveguide length, and internal reflection angles, to optimize performance for close-proximity eye imaging. These parameter adjustments allow the waveguide to effectively capture corneal reflections while maintaining the ability to relay images, resolving the contradiction between general waveguide capability and specific gaze tracking requirements.
3Manufacturing precision
If the input coupler is made narrow to maintain mapping between object points and propagation angles, then the waveguide can effectively focus at all distances, but the coupling efficiency may be reduced
Solution Approach 1:
The patent employs composite optical design combining the narrow input coupler with specific waveguide materials and reflective surfaces. The narrow coupler maintains angular mapping precision while the waveguide's total internal reflection and optimized geometry compensate for potential energy loss, achieving both focus precision and adequate coupling efficiency through composite optical elements.
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
Enables the use of mature PCCR algorithms with an opto-mechanical design that fits HMD form factors, providing a more accurate and direct image of the cornea, iris, and pupil for gaze tracking applications.
Implementation Method 1
The in-coupling may use diffraction or reflection to redirect light rays received from the eye at an angle
Implementation Method 2
The in-coupling may use diffraction or reflection to redirect light rays received from the eye at an angle
Implementation Method 3
redirect the light rays to an out-coupling using total internal reflection (TIR) or other reflective treatments
Implementation Method 4
The out-coupling may then use reflection or diffraction to redirect the light rays from the waveguide to the eye tracking camera's lens
Implementation Method 5
The out-coupling may then use reflection or diffraction to redirect the light rays from the waveguide to the eye tracking camera's lens
Data Source
AI summary
A waveguide with an input coupler and an output coupler that redirects reflected light to a camera. The waveguide may be integrated in a lens of a wearable device such as a pair of glasses. Light sources emit light beams towards the eye. A portion of the light beams are reflected by the surface of the eye towards the input coupler located in front of the eye. The input coupler may be implemented according to diffractive or reflective technologies, and may be a straight or curved line of narrow width to focus at close distances but of a length long enough to sufficiently image the eye. The input coupler changes the angles of the light beams so that the light beams are relayed using total internal reflection and focused towards an output coupler of the waveguide. The light beams are redirected by the output coupler to the camera.