Eye Tracking Using Polarization Volume Grating
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Solution Overview
Problem
Conventional head-mounted display devices face challenges in effectively tracking a user's eye without obstructing their view, as they require both illumination and detection components that need to be positioned in a way that does not interfere with the display, while also being lightweight and compact to avoid user discomfort.
Innovation Solution
The use of a polarization volume hologram (PVH) in the eye-tracker allows for sufficient eye illumination and light reflection detection without obstructing the user's view, enabling the placement of detection components out of the user's field of vision, and includes a waveguide to transmit display light to the user's eyes while redirecting eye-tracking light for detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional eye-tracking components (illumination source and camera) are placed in front of the user's eyes to sufficiently illuminate and detect light, then eye-tracking functionality is achieved, but the user's view of the display is obstructed
Solution Approach 1:
The patent relocates the camera from the front view path to a side position on the head-mounted display frame, utilizing a different spatial dimension. The PVH optical element acts as an intermediary to redirect light from the eye at an angle, allowing the camera to capture eye images without being positioned in front of the user's eyes, thus eliminating view obstruction while maintaining eye-tracking functionality
Solution Approach 2:
The polarization volume hologram (PVH) serves as an optical intermediary between the eye and the camera. It selectively redirects light based on polarization properties, enabling the camera to receive reflected light from the eye at an angled position rather than requiring direct front-facing alignment, thereby resolving the conflict between detection capability and view obstruction
2Measurement precision
If illumination source and camera are positioned to sufficiently illuminate and detect the eye, then eye-tracking accuracy is improved, but the device becomes bulkier and heavier
Solution Approach 1:
The patent integrates the PVH optical element into the existing head-mounted display structure, combining multiple functions (display optics and eye-tracking optics) into a unified system. This integration eliminates the need for separate bulky mounting structures for the camera and illumination source, reducing overall device weight while maintaining precise eye-tracking capability
Solution Approach 2:
By positioning the camera and illumination source along the side frame rather than in front of the eyes, the system utilizes lateral space more efficiently. This dimensional reconfiguration reduces the need for forward-protruding components, resulting in a more compact and lighter device structure that achieves the same measurement precision
3Reliability
If illumination source and camera are positioned to sufficiently detect light reflected off the eye, then eye-tracking detection capability is improved, but the device complexity increases
Solution Approach 1:
The PVH optical element serves multiple functions simultaneously: it acts as a beam splitter, a polarizer, and a light redirector for both the display system and the eye-tracking system. This multi-functionality reduces the number of separate optical components needed, simplifying the overall device structure while maintaining robust eye-tracking detection capability
Solution Approach 2:
The PVH serves as a universal intermediary that manages light paths for both display and eye-tracking functions. By using this single optical element to handle multiple light routing tasks, the system reduces component placement complexity compared to using separate optical elements for each function
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 provides a lightweight and compact eye-tracker that effectively illuminates and detects eye light without obstructing the user's view, allowing for improved user comfort and functionality in head-mounted display devices.
Implementation Method 1
The optical element is configured to receive first light reflected off the eye on the first side and redirect a portion of the first light in a spectral range and a first circular polarization toward the detector. The optical element is also configured to transmit second light. The second light includes a second portion of the first light outside the spectral range and a third portion of the first light having a second circular polarization opposite to the first circular polarization.
Data Source
AI summary
An eye-tracker for determining a position of the pupil of an eye includes a detector and an optical element. The optical element is configured to receive first light reflected off the eye and reflectively diffract a portion of the first light that has a first polarization toward the detector. The optical element is also configured to transmit second light. The second light includes a second portion of the first light that has a second polarization that is different from the first polarization. A head-mounted display device that includes a display system and the eye-tracker is also disclosed. A method for determining the location of a pupil of an eye is also disclosed herein.