Eye Tracking Waveguide With Curved Grating Input-Coupler
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing see-through mixed reality display devices face challenges in implementing eye tracking without impairing their see-through properties, particularly when used with prescription eyewear, and in covering the entire eye movement range and inter-pupillary distance range.
Innovation Solution
The use of a planar waveguide with an input-coupler and output-coupler, where the input-coupler comprises curved grating lines with a radially varying pitch, and the output-coupler is positioned to direct infrared reflections from the eye to an eye tracking IR sensor, allowing for flexible placement and operation without obstructing the user's view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a camera is directly focused on the user's eye with a direct line of sight, then the eye tracking implementation is simple and inexpensive, but the camera position close to eye level causes at least partial obstruction of the see-through properties of the mixed reality display device system
Solution Approach 1:
The patent introduces a beam splitter positioned at a 45-degree angle to redirect the camera's line of sight. This dimensional change in the optical path allows the camera to view the eye from the side rather than directly from the front, eliminating obstruction of the see-through display while maintaining simple eye tracking functionality
Solution Approach 2:
The beam splitter acts as an intermediary optical element that transfers the eye image to the camera without requiring direct line of sight. This mediator component enables the camera to be positioned in a location that does not obstruct the user's view through the mixed reality display
2Ease of manufacture
If a partial reflector is used to fold the camera view path to the user's temple, then the camera can be positioned outside the see-through field, but implementation is problematic if the eye tracking needs to work with prescription eyewear
Solution Approach 1:
The beam splitter configuration creates a universal eye tracking system that works with both prescription and non-prescription eyewear. By positioning the camera to view through the beam splitter at an angle, the system can track eyes regardless of whether corrective lenses are present, as the optical path is not blocked by the temple area where prescription glasses typically sit
3Device complexity
If reverse optical path imaging is used in a free form prism based mixed reality display device system, then the actual display optics provide the imaging functionality for eye tracking, but components of a free form prism tend to be rather large in size making this approach not always practical
Solution Approach 1:
The patent extracts the eye tracking imaging function from the main free form prism display optics by introducing a separate, dedicated beam splitter and camera subsystem. This extraction allows eye tracking to be implemented independently without requiring modification or enlargement of the primary display optical components
Solution Approach 2:
The eye tracking system is segmented as a separate functional module with its own beam splitter and camera, independent from the main display optics. This segmentation allows the eye tracking components to be miniaturized and positioned separately, avoiding the size constraints of free form prism components
4Adaptability or versatility
If a free form optical is added for eye tracking only, then eye tracking functionality is achieved, but this would be expensive and would add significant weight and size to the system
Solution Approach 1:
The patent employs inexpensive, compact optical components (beam splitter and camera) for eye tracking rather than expensive, heavy free form prism optics. The beam splitter can be a simple coated glass or plastic element, and the camera can be a small infrared sensor, significantly reducing weight and cost while maintaining eye tracking functionality
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
This solution enables effective eye tracking without compromising the see-through functionality of the mixed reality display device, even with prescription eyewear, and covers the entire eye movement and inter-pupillary distance range, providing accurate gaze direction tracking.
Implementation Method 1
curved grating lines of the input-coupler cause infrared light beams that are incident on the input-coupler to be diffracted towards a common region of the waveguide at which is located an output-coupler
Implementation Method 2
infrared light beams reflected from the eye and incident on the input-coupler enter the waveguide, propagate through the waveguide from the input-coupler to the output-coupler
Implementation Method 3
infrared light beams that exit the waveguide proximate the output-coupler are converted from angularly encoded infrared light beams to two-dimensional spatially encoded infrared light beams
Data Source
Figure 1
Figure 2A~2B
Figure 3A
AI summary
A transparent waveguide for use in eye tracking includes an input-coupler and an output-coupler. The input-coupler comprises a plurality of curved grating lines having a radially varying pitch. When positioned in front of an eye illuminated with infrared light, infrared light beams reflected from the eye and incident on the input-coupler enter the waveguide at the input-coupler, propagate through the waveguide by way of total internal reflections, and exit the waveguide proximate the output-coupler. The radially varying pitch of the curved grating lines of the input-coupler provides angular encoding of infrared light incident on the input-coupler, and more specifically, causes different beams of infrared light incident on respective different horizontal and vertical positions of the input-coupler to propagate through the waveguide at respective different angles of reflection and exit the waveguide at respective different angles of incidence relative to a surface of the waveguide through which infrared light beams exit.