Waveguide Eye Tracker with Switchable Bragg Gratings
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Solution Overview
Problem
Implementing eye tracking technology in virtual, augmented, and mixed reality systems is challenging due to the need for a small form-factor package that maintains stability and calibration, as traditional methods like the 'hot mirror' approach are inefficient and difficult to integrate effectively.
Innovation Solution
A waveguide-based eye tracker using switchable Bragg gratings (SBGs), an array of infrared light sources, and a detector array, where light is coupled into a waveguide, selectively out-coupled towards the user's eye, and reflected signals are used to determine the eye's position and orientation, allowing for precise tracking while minimizing package size and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional hot mirror based eye tracking is used, then eye tracking functionality is achieved, but device size and complexity increase making it difficult to integrate into small form-factor packages
Solution Approach 1:
The patent combines the eye tracking functionality with the waveguide display structure by integrating optical out-couplers into the waveguide. The same waveguide that delivers augmented reality images also serves as the optical path for eye tracking, eliminating the need for separate hot mirror assemblies and reducing overall device complexity and size.
Solution Approach 2:
The waveguide structure performs multiple functions: it delivers virtual reality images to the user's eye and simultaneously serves as the optical pathway for eye tracking detection. The out-couplers embedded in the waveguide both extract display images and detect reflected light from the user's eye, making the system more compact by eliminating dedicated components for each function.
2Measurement precision
If hot mirror based imaging approach is used, then eye position and orientation can be determined, but power consumption and computing requirements increase
Solution Approach 1:
The patent extracts only the essential eye tracking information (eye position and orientation) directly from the reflected light pattern detected by the waveguide, rather than capturing and processing full images. This selective extraction of needed parameters reduces computational burden and power consumption while maintaining measurement precision.
Solution Approach 2:
Instead of processing complete eye images, the system uses a simplified detection approach that captures only the necessary optical signals for determining eye position and orientation. This partial action approach reduces computational requirements and power consumption while achieving the required measurement accuracy for foveated rendering.
3Illumination intensity
If full resolution is provided across the entire display, then complete visual quality is maintained, but power consumption increases significantly
Solution Approach 1:
The patent implements variable pixel density across different regions of the display based on eye tracking data. The foveal region (center of gaze) receives high-resolution content with maximum pixel density, while peripheral regions use lower pixel density. This local quality adjustment reduces overall power consumption while maintaining visual quality where the user is actually looking.
Solution Approach 2:
The system dynamically adjusts pixel density distribution across the display in real-time based on the user's eye position and gaze direction. As the user moves their eyes, the high-resolution region moves accordingly, ensuring that maximum computational resources are allocated to the foveal region while minimizing power consumption in non-foveal areas.
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 waveguide-based eye tracker provides accurate eye tracking with improved performance compared to traditional methods, enabling efficient power consumption and computing cycle savings by focusing maximum pixel density on the foveal region while reducing it in non-foveal areas, thus enhancing the user's visual experience.
Implementation Method 1
The waveguide(s) couple in/out approximately collimated light which has spatially distributed angular samples across the eye-box
Implementation Method 2
The light can be selectively out coupled from the waveguide toward the user's eye via one or more of the SBGs along a length of the waveguide
Implementation Method 3
Depending on an orientation of the user's eye relative to the emitted IR light, some of the IR light is reflected back towards the waveguide
Data Source
AI summary
An eye tracker for determining a position of an eye, which may be integrated into a head-mounted display. The eye tracker includes a waveguide, switchable Bragg gratings (SBGs) that selectively out couple light from the waveguide, light sources coupled to the waveguide, a detector coupled to a return path of the waveguide, and a controller. The controller instructs at least one light source to emit at least one light beam propagating through the waveguide, and activates at least one SBG to out-couple the at least one light beam from the waveguide toward the eye. The waveguide in-couples at least one reflected light signal reflected from the eye that originates from the at least one light beam out-coupled from the waveguide. The detector detects the at least one reflected light signal. The controller determines a position of the eye using the detected at least one reflected light signal.