Eye Tracker Diffractive Beam Expander for Distance-Independent Gaze
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Solution Overview
Problem
Existing eye tracker devices face challenges in accurately determining gaze direction independently of the distance between the eye and the tracker device, and in efficiently illuminating the eye for reflection spot detection.
Innovation Solution
A device and method utilizing a substantially planar waveguiding substrate with in-coupling and out-coupling gratings to split a single collimated light beam into two beams, providing distinct reflection spots on the eye's surface for image analysis, allowing for gaze direction determination based on the positions of these spots and the pupil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single illuminating beam is used to illuminate the eye, then the device complexity is reduced, but the measurement precision of gaze direction deteriorates due to distance variations
Solution Approach 1:
The single illuminating beam is segmented into multiple beams (first and second illuminating beams) by using a beam splitting optical system comprising a beam splitter and reflective elements. This segmentation allows creation of multiple distinct reflection spots on the cornea, enabling more accurate gaze direction determination through geometric relationships between spots, thereby resolving the contradiction between simple illumination and precise measurement.
2Measurement precision
If multiple illuminating beams are used to improve gaze direction accuracy, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The optical components (beam splitter, reflective elements, waveguiding substrate) are designed to serve multiple functions: they both illuminate the eye for gaze tracking and can display virtual images. This multi-functionality reduces the need for separate systems, thereby improving measurement precision without proportionally increasing device complexity.
3Adaptability or versatility
If the distance between the eye and tracker device varies, then the adaptability of the device improves, but the measurement precision deteriorates
Solution Approach 1:
The system captures images of the eye showing multiple reflection spots at different positions, and uses data processing to calculate gaze direction based on the geometric relationships between these spots and the pupil. This feedback mechanism allows the system to compensate for distance variations, maintaining measurement precision across different eye-device distances.
4Productivity
If a planar waveguiding substrate with multiple gratings is used, then the illumination efficiency improves by creating distinct reflection spots, but the manufacturing precision requirements increase
Solution Approach 1:
The waveguiding substrate incorporates multiple gratings with different orientations and periods (first grating with period d1, second grating with period d2) to diffract light into specific directions. By carefully selecting and controlling these grating parameters during manufacturing, the system achieves efficient illumination with distinct reflection spots while managing the manufacturing precision requirements through standardized grating design.
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 approach provides a simple and stable method for determining gaze direction, minimizing the impact of distance variations and optimizing illumination to enhance accuracy and independence from distance, while also allowing for the display of virtual images.
Implementation Method 1
an in-coupling grating to diffract light of said light beam into said substrate and to form a first in-coupled beam and a second in-coupled beam propagating in different directions within said substrate
Implementation Method 2
a first expanding grating portion to provide a first expanded internal beam by diffracting light of said first in-coupled beam, a second expanding grating portion to provide a second expanded internal beam by diffracting light of said second in-coupled beam
Implementation Method 3
a first out-coupling grating portion to form a first substantially collimated illuminating beam by diffracting light of said first internal beam out of said substrate, a second out-coupling grating portion to form a second substantially collimated illuminating beam by diffracting light of said second internal beam out of said substrate
Implementation Method 4
a substantially planar waveguiding substrate
Data Source
Figure 1a~1b
Figure 2
Figure 3~4
AI summary
An eye tracker device (200) comprises a diffractive beam expander (207) to provide two substantially collimated illuminating light beams (B11, B12). The collimated light beams (B11, B12) provide two reflection spots (G1, G2) appearing in the image of the eye. The gaze direction (GZD) is calculated from the positions of the reflection spots (G1, G2) with respect to the pupil (P) of the eye (E1). The two illuminating beams (B11, B12) are provided by splitting an infrared laser beam (B4) into two in-coupled beams (B5, B6), which propagate in different directions in the substrate (7) of the beams expander. The in-coupled beams (B5, B6) are expanded and their light is subsequently coupled out of the substrate (7) by an out-coupling grating (230) to illuminate the eye (E1). The same substrate (7) may also be used to implement a virtual display device (100) for displaying virtual images to said eye (E1).