Holographic Waveguide Eye Tracker Using Grating Lamina
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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 user safety, while also suffering from high latency and complexity in image processing.
Innovation Solution
A compact, lightweight eye tracker utilizing switchable Bragg gratings (SBGs) in a thin optical waveguide design, which deflects illumination and image light through grating lamina to enable a wide field of view and high transparency, using a waveguide system with input and output gratings to direct light efficiently and minimize cross-talk between illumination and image paths.
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 field of view and exit pupil can be achieved, but the device becomes bulky and difficult to integrate into HMDs
Solution Approach 1:
The patent replaces conventional beam splitters and refractive lenses with diffractive optical elements (DOEs), specifically transmission gratings and waveguide-based diffractive structures. This substitution eliminates the need for bulky mechanical optical components while achieving the same light manipulation functions, thereby reducing device size and enabling integration into compact HMDs without compromising field of view performance
Solution Approach 2:
The invention changes the fundamental optical parameters by using diffractive optics with specific grating periods and efficiencies optimized for eye tracking. The transmission gratings are designed with specific line densities (e.g., 600 lines/mm) and diffraction efficiencies that enable wide field of view and large exit pupil in a thin profile, fundamentally altering how light is manipulated compared to conventional refractive systems
2Adaptability or versatility
If beam splitters and refractive lenses are used in conventional eye trackers, then the field of view can be achieved, but the device complexity increases
Solution Approach 1:
The patent merges multiple optical functions into single diffractive components. The transmission gratings simultaneously perform beam splitting, light steering, and imaging functions that would traditionally require separate beam splitters, mirrors, and lenses. The waveguide-based diffractive structures integrate light delivery and collection paths, reducing the number of discrete components and simplifying the overall system architecture
Solution Approach 2:
The diffractive optical elements serve multiple functions: they act as beam splitters for illumination light, steer light to create wide field of view, and form images for eye tracking detection. This multi-functionality eliminates the need for specialized components for each function, reducing device complexity while maintaining or enhancing field of view performance
3Duration of action of stationary object
If imaging optics are positioned close to the beamsplitter to maximize exit pupil, then the exit pupil is improved, but vision obscuration and safety hazards increase
Solution Approach 1:
The patent replaces the conventional arrangement of beam splitters and close-positioned imaging optics with diffractive optical elements that can achieve large exit pupils at greater distances from the user's eye. The transmission gratings and waveguide-based diffractive structures manipulate light through diffraction rather than refraction, enabling exit pupil maximization without the need to position components in hazardous proximity to the user's vision path
Solution Approach 2:
The waveguide-based diffractive structures act as intermediaries that couple light into and out of the waveguide at optimized angles and positions. This intermediary approach allows the system to achieve large exit pupils while maintaining safe distances from the user's eye, as the waveguide structures mediate the light delivery and collection processes without requiring components to be positioned in obscuring or hazardous locations
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 slim, wide field of view, large exit pupil, and high transparency, reducing latency and complexity in image processing, while ensuring eye safety and ease of integration into HMDs, with the ability to track eye movements using low-resolution high-speed sensors and speckle patterns.
Implementation Method 1
At least one grating lamina for deflecting the illumination light out of the first waveguide path towards the eye and deflecting the image light into the second waveguide path towards the detector
Implementation Method 2
a first waveguide for propagating illumination light along a first waveguide path and propagating image light reflected from at least one surface of an eye along a second waveguide path
Data Source
AI summary
An eye tracker having a first waveguide for propagating illumination light along a first waveguide path and propagating image light reflected from at least one surface of an eye along a second waveguide path. At least one grating lamina for deflecting the illumination light out of the first waveguide path towards the eye and deflecting the image light into the second waveguide path towards a detector is disposed adjacent an optical surface of the waveguide.