Freeform Prism Near-Eye Display Gaze Tracking
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Solution Overview
Problem
Near-eye display systems that utilize waveguides are sensitive to eye movement, leading to distortion in gaze-tracking accuracy due to changes in the distance between the eye and the display components, as the gaze-tracking system is not object-space telecentric.
Innovation Solution
The implementation of a freeform prism in the near-eye display system allows the display and gaze-tracking system to share optics, positioning the gaze-tracking system at the back focal plane of the freeform prism, which maintains accuracy by keeping the eye image collimated and focused without magnification, thereby reducing sensitivity to eye movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the gaze-tracking system uses separate optics from the display system, then the system can maintain simple optical paths, but the device size increases and compactness is reduced
Solution Approach 1:
The patent combines the display optical path and gaze-tracking optical path by positioning both the display device and imaging device to share the freeform prism. The display device emits display light through the freeform prism to the user's eye, while the imaging device receives gaze-detection light reflected from the eye and directed through the same freeform prism, merging two separate optical systems into one compact structure.
Solution Approach 2:
The freeform prism serves multiple functions: it acts as an optical element for the display system to direct display light to the user's eye, and simultaneously serves as an optical element for the gaze-tracking system to direct gaze-detection light to the eye and collect reflected light. This multi-functionality reduces the overall device volume by eliminating the need for separate optics.
2Measurement precision
If the imaging device is positioned away from the back focal plane, then the optical design becomes simpler, but gaze direction accuracy decreases due to perspective errors
Solution Approach 1:
The patent positions the imaging device at the back focal plane of the freeform prism to create an object-space telecentric imaging system. This telecentric configuration ensures that the principal rays are parallel to the optical axis, eliminating perspective errors and magnification changes that occur with eye movement. The system maintains constant image scale and accurate gaze direction determination regardless of changes in the distance between the eye and display components.
3Reliability
If the system uses traditional optics separate from the waveguide, then the optical paths remain simple, but the system becomes sensitive to eye movement causing distortion
Solution Approach 1:
The patent merges the display optics and gaze-tracking optics through the freeform prism, creating a unified optical system where both functions share the same optical path. This integration ensures that the gaze-tracking system moves with the display system, maintaining consistent optical relationships and reducing sensitivity to eye movement while eliminating the need for separate, complex optics.
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 configuration ensures accurate gaze direction determination regardless of changes in the distance between the eye and the display system, reducing perspective errors and distortions, and maintaining accurate edge and feature detection.
Implementation Method 1
a freeform prism, a display device configured to emit display light through the freeform prism to an eye of a user, and an imaging device configured to receive gaze-detection light reflected from the eye and directed through the freeform prism
Data Source
AI summary
An example see-through head-mounted display system includes a freeform prism and a display device configured to emit display light through the freeform prism to an eye of a user. The see-through head-mounted display system may also include an imaging device having an entrance pupil positioned at a back focal plane of the freeform prism, the imaging device configured to receive gaze-detection light reflected from the eye and directed through the freeform prism.