Light Guide Eyeball Tracker for HMDs
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Solution Overview
Problem
Conventional head-mounted display (HMD) systems face challenges with compactness and manufacturability, resulting in limited field-of-view and eye-motion-box, making them impractical for wide applications, and existing eye-tracking technologies suffer from inaccuracies due to head position approximations.
Innovation Solution
The integration of a compact light-guide optical system with selectively reflecting surfaces for total internal reflection, allowing for wide field-of-view and large eye-motion-box, combined with eyeball tracking using a miniature CCD camera and infrared LED for accurate gaze direction measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If conventional free-space optical modules are used in HMDs, then the system can achieve basic imaging function, but the system becomes larger, heavier and bulkier
Solution Approach 1:
The patent combines multiple optical functions (imaging, beam combining, eye tracking) into a single integrated optical module. The light guide plate serves simultaneously as an imaging element, a beam combiner for displaying images to the user, and a platform for mounting eye tracking components, thereby reducing the overall system size and weight while maintaining functionality
Solution Approach 2:
The light guide plate is designed to perform multiple functions: it acts as an imaging lens to focus light, a beam combiner to superimpose virtual images with the real world, and a mounting substrate for eye tracking sensors. This multi-functionality eliminates the need for separate optical modules, directly addressing the weight and size issues
2Adaptability or versatility
If the field-of-view of HMD system is increased, then the viewing angle is improved, but the optical module becomes larger and bulkier
Solution Approach 1:
The patent utilizes the third dimension (depth/thickness of the light guide plate) to achieve wide field-of-view. By controlling light propagation and extraction angles through the thickness of the plate, the system can provide expanded viewing angles without increasing the lateral dimensions of the optical module
Solution Approach 2:
The patent adjusts optical parameters such as the refractive index of the light guide plate material, the angle of light injection, and the position of extracting surfaces to optimize field-of-view. By changing these parameters, the system achieves wider viewing angles while maintaining a compact form factor
3Volume of moving object
If compact optical solutions are implemented, then the system size is reduced, but the eye-motion-box becomes very small and the system becomes sensitive to optical movements
Solution Approach 1:
The patent embeds multiple functional layers within the light guide plate structure. The eye tracking sensors are integrated into the plate itself, and multiple extracting surfaces are nested within the plate thickness, allowing the system to maintain compact dimensions while providing sufficient eye motion tolerance through the distributed optical paths
Solution Approach 2:
The light guide plate acts as an intermediary element that decouples the relationship between small physical displacements and large optical field shifts. By using total internal reflection and controlled light extraction, the plate converts small physical movements into manageable optical path changes, providing a virtual eye-motion-box that is larger than the physical device dimensions
4Ease of manufacture
If separate HMD and eyeball tracker units are used, then each component can be optimized independently, but the overall system complexity increases
Solution Approach 1:
The patent merges the HMD optical path and eye tracking optical path into a single light guide plate structure. The same plate that guides display light to the user's eye also guides infrared light from the eye tracker to the sensor, eliminating the need for separate optical components and reducing integration complexity
Solution Approach 2:
The patent applies different optical properties to different regions of the light guide plate. Specific areas have different refractive indices or surface treatments to handle display light differently from eye tracking light, allowing independent optimization of each function while maintaining a unified 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 solution provides a compact, high-quality image display system with improved eye-tracking accuracy, accommodating large eye movements and reducing the need for off-axis optics, while ensuring ghost-free images and high brightness with low-power consumption.
Implementation Method 1
at least one optical means for coupling light waves into the substrate by total internal reflection
Implementation Method 2
at least two partially reflecting surfaces carried by the substrate wherein the partially reflecting surfaces are not parallel to the main surfaces of the substrate
Implementation Method 3
A typical eye tracker will combine a miniature CCD camera and an infrared LED to illuminate the pupil
Data Source
AI summary
Head-mounted display with an eye-tracking system and including a light-transmitting substrate (20) having two major surfaces and edges, optical means for coupling light into said substrate (20) by total internal reflection, partially-reflecting surfaces (22a-22c) carried by the substrate (20) that are not parallel with the major surfaces of the substrate (20), a near-infrared light source (78) and a display source (92) projecting within the photopic spectrum, wherein light from the light source (78) and light from the display source (92) are coupled into the substrate (20) by total internal reflection.