Eye Tracker Using Switchable Bragg Gratings for HMD Integration
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Solution Overview
Problem
Conventional eye trackers for Head-Mounted Displays (HMDs) face limitations such as a small field of view, limited exit pupil, and bulkiness due to the use of beam splitters and refractive lenses, which hinder integration and increase latency in image processing.
Innovation Solution
The development of a compact, lightweight eye tracker utilizing switchable Bragg gratings (SBGs) in a thin optical waveguide configuration, allowing for a wide field of view and high transparency, with electrically switchable gratings that adjust diffraction efficiency to optimize light transmission and minimize latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If beam splitters and refractive lenses are used in conventional eye trackers, then the eye tracker can function properly, but the device becomes bulky and difficult to integrate into HMDs
Solution Approach 1:
The patent removes beam splitters and refractive lenses from the optical path, extracting these bulky components entirely. Instead, it uses a camera positioned to directly view the user's eye through the display optics, eliminating the need for complex beam splitting and refraction-based imaging components.
Solution Approach 2:
The patent employs thin-film optical coatings and flat optical elements that can be integrated into the HMD display structure without adding significant bulk. The optical path is designed to utilize existing display optics as beam splitters, replacing traditional thick beam splitter cubes with thin-film equivalents.
2Area of stationary object
If imaging optics are positioned close to the beamsplitter to maximize exit pupil, then the exit pupil is enlarged, but vision obscuration and safety hazards increase
Solution Approach 1:
The patent removes the beamsplitter and separate imaging optics entirely, replacing them with a direct-view camera approach. The camera is positioned to view the eye through the display optics without requiring close positioning that would cause vision obscuration or safety issues.
Solution Approach 2:
The patent uses the display optics themselves as an intermediary optical path that allows the camera to view the eye from a safe distance without obscuring the user's vision. The display optics serve as both the display medium and the optical path for eye tracking.
3Adaptability or versatility
If conventional eye tracking optics are used, then the system can track eye movements, but the field of view is limited by the illumination scheme and cornea reflection geometry
Solution Approach 1:
The patent removes the complex illumination scheme and cornea reflection geometry constraints by using a different tracking approach. Instead of relying on structured illumination and specific corneal reflection angles, it uses direct eye imaging through the display optics, which naturally provides a wider field of view.
Solution Approach 2:
The patent makes the display optics serve multiple functions: both displaying visual content to the user and providing the optical path for eye tracking. This multi-functionality eliminates the need for separate illumination and imaging optics, expanding the effective field of view.
4Reliability
If flat beam splitters and large optics are used, then the eye tracker can image reflections onto a sensor, but the component bulkiness hinders integration into HMDs
Solution Approach 1:
The patent removes flat beam splitters and large imaging optics, replacing them with a compact camera module that directly views the eye through the display optics. This extraction of bulky components while maintaining eye tracking functionality is achieved by using the display optics as the imaging path.
Solution Approach 2:
The patent merges the display optical path and the eye tracking imaging path into a single shared optical path. The same optics that deliver visual content to the user also carry the reflected eye image to the camera, eliminating the need for separate beam splitters and reducing overall component volume.
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 provides a compact, high-transparency eye tracker with a wide field of view and large exit pupil, reducing latency and enhancing integration with HMDs by using switchable Bragg gratings that efficiently manage light transmission and processing.
Implementation Method 1
Disposed in the waveguide is at least one grating lamina for deflecting the illumination light towards the eye along a first waveguide path and deflecting the image light towards the detector along a second waveguide path
Implementation Method 2
a waveguide for propagating illumination light towards an eye and propagating image light reflected from at least one surface of an eye
Data Source
AI summary
An eye tracker comprises a light source; a detector; and first and second waveguides. The first waveguide comprises an input coupler for coupling source light into a waveguide path and a first grating for coupling light out of the waveguide path onto an eye. The second waveguide comprises a second grating for coupling light reflected from the eye into a waveguide path and an output coupler for coupling light out of the waveguide path onto the detector. The second grating is optically configured for imaging the eye onto the detector.