Light-Guide Eye Imaging for Compact Off-Axis Gaze Tracking
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Solution Overview
Problem
Existing optical systems for near-eye displays and head-up displays face challenges in efficiently tracking the gaze direction of the observer's eye due to the need for large apertures and the limitations of small, off-axis cameras, which result in low performance and user discomfort.
Innovation Solution
An optical system utilizing a light-guide optical element for eye tracking, which includes a light-transmitting substrate with internal reflection, optical coupling configurations for collimating and coupling light from the eye, and an optical sensor to derive the gaze direction, particularly suitable for augmented and virtual reality systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If off-axis cameras are used for eye tracking, then device size is reduced, but eye tracking performance deteriorates
Solution Approach 1:
The patent introduces a light-guide optical element as an intermediary between the eye and the camera. This optical element captures light from the eye motion box and guides it through internal reflection to the camera, enabling small off-axis cameras to achieve high-quality eye tracking images without requiring large aperture cameras positioned directly in the eye motion box
Solution Approach 2:
The patent transitions from direct optical path imaging to indirect imaging through the light-guide substrate. By using the substrate's internal reflection properties, the system effectively adds an optical dimension that allows light from the eye to be captured and redirected to the camera, overcoming the limitations of off-axis positioning
2Measurement precision
If large aperture is used to cover the eye motion box, then eye tracking performance is improved, but device size increases
Solution Approach 1:
The patent segments the optical function between the light-guide optical element and the camera. The optical element handles light collection and guidance from the eye motion box, while the camera handles image detection. This segmentation allows the use of a small camera with a light-guide substrate that collectively provides the equivalent performance of a large aperture system
Solution Approach 2:
The light-guide optical element creates an optical copy of the eye motion box scene by capturing light from the eye and guiding it through the substrate to the camera. This optical copying mechanism allows the small camera to receive information equivalent to what a large aperture camera would capture directly
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 system provides high-performance eye tracking with reduced user discomfort by using a light-guide optical element to collimate and guide light from the eye, enabling accurate gaze direction derivation.
Implementation Method 1
a light-transmitting substrate having at least two major surfaces for guiding light by internal reflection between the two major surfaces of the light-transmitting substrate
Implementation Method 2
a first optical coupling configuration associated with the light-transmitting substrate configured to: collimate light from the eye to produce collimated light
Implementation Method 3
optical coupling configurations for collimating and coupling light from the eye
Data Source
AI summary
A light-transmitting substrate is deployed with a first of two major surfaces in facing relation to an eye of a viewer and guides light by internal reflection between the two major surfaces. An optical coupling-out configuration couples image light, that corresponds to a collimated image and that is guided by internal reflection between the two major surfaces, out of the light-transmitting substrate. A first optical coupling configuration collimates light from the eye to produce collimated light, and couples the collimated light into the light-transmitting substrate for guiding by internal reflection. A second optical coupling configuration couples the collimated light out of the light-transmitting substrate toward an optical sensor that senses the coupled-out light. A processing system derives current gaze direction of the eye by processing signals from the optical sensor.