Eye Tracker LOE Retinal Reflection Isolation
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Solution Overview
Problem
Existing eye tracking technologies face challenges in accurately determining gaze direction using light-guide optical elements due to the one-to-many relationship in aperture multiplication, which results in superposition of light rays and difficulty in resolving images from scattered light sources in the field of view.
Innovation Solution
An eye tracking apparatus utilizing a light-guide optical element with partially-reflective surfaces or diffractive optical elements, coupled with focusing optics and an optical sensor, processes signals to derive the gaze direction by isolating retinal reflections and reducing background noise through selective illumination and spectral filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If aperture multiplication is implemented using light-guide optical elements, then the device aperture is expanded to cover the eye motion box area, but light rays from different directions superpose and create difficulty in resolving images from scattered light sources
Solution Approach 1:
The patent segments the aperture multiplication process into two distinct functional paths: a first light-guide optical element for delivering the displayed image to the user's eye, and a second light-guide optical element for directing retinal reflection light to the eye tracker. This segmentation prevents superposition of light rays between the display path and tracking path, enabling both large aperture coverage and precise gaze direction measurement.
Solution Approach 2:
The patent extracts the eye tracking function from the main display function by using a separate second light-guide optical element dedicated to guiding retinal reflection light to the eye tracker. This extraction isolates the tracking optical path from the display optical path, eliminating interference and enabling accurate gaze direction determination despite the presence of aperture multiplication in the display system.
2Volume of moving object
If a small aperture optical image generator is used to achieve compact device size, then the device form factor is reduced, but the aperture must be multiplied to cover the eye motion box area
Solution Approach 1:
The patent applies multi-functionality by having the light-guide optical elements serve dual purposes: the first LOE delivers display images while the second LOE captures retinal reflections for tracking. Both functions are achieved through integrated optical elements rather than separate systems, reducing overall device complexity while maintaining compact size and covering the eye motion box area.
3Area of stationary object
If partially-reflective surfaces are used for coupling light in and out of the light-guide element, then aperture multiplication is achieved, but background noise from scattered light increases
Solution Approach 1:
The patent introduces spectral filters as intermediary elements in the optical path of the second light-guide optical element. These filters selectively transmit wavelengths corresponding to retinal reflection light while blocking scattered light from the display, thereby reducing background noise and improving signal-to-noise ratio for gaze direction measurement.
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
Effectively determines the gaze direction by isolating retinal reflections from scattered light, enhancing image clarity and accuracy despite the challenges of aperture multiplication, and maintaining continuous tracking with reduced disruption to the user's perception.
Implementation Method 1
a light-guide optical element (LOE) formed from transparent material and having pair of parallel faces for guiding light by internal reflection
Implementation Method 2
A first reflecting surface 16 couples the projected image 18 into the light-guide optical element 20
Implementation Method 3
another diffractive optical element 17 for coupling in of image 18
Implementation Method 4
an optical sensor deployed for sensing the captured light
Data Source
AI summary
An apparatus (100) for deriving a gaze direction of a human eye (150) includes a light-guide optical element (LOE) (120) having pair of parallel faces (104a), (104b) deployed in facing relation to the eye (150). A coupling-in configuration, such as a set of partially-reflective surfaces (145), is associated with LOE (120) and configured for coupling-in a proportion of light incident on face (104a) so as to propagate within the LOE. Focusing optics (106) associated with LOE (120) converts sets of parallel light rays propagating within the LOE into converging beams of captured light which are sensed by an optical sensor (125). A processing system (108) processes signals from the optical sensor (125) to derive a current gaze direction of the eye. Despite the aperture-combining effect of the LOE, retinal images can be effectively recovered as the only image information brought to focus on the optical sensor.