Eyepiece Diffraction Gratings for Accurate HMD Eye Tracking
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Solution Overview
Problem
Existing eye tracking systems in virtual and mixed reality headsets suffer from reduced detection accuracy and increased spacing due to direct viewing through eyepieces, which cause distortion and require larger distances between eyepieces and display panels.
Innovation Solution
Integrating transmissive or reflective diffraction gratings in the eyepieces of head-mounted displays (HMDs) to redirect infrared light towards eye tracking cameras, allowing for improved viewing angles and reduced spacing, while minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If diffraction gratings are integrated in the eyepieces to redirect infrared light towards eye tracking cameras, then eye tracking accuracy is improved, but device complexity increases
Solution Approach 1:
The diffraction grating is integrated directly into the eyepiece structure, merging the optical function of the eyepiece with the light redirection function. This combination eliminates the need for separate components and reduces overall device complexity while maintaining eye tracking accuracy.
Solution Approach 2:
The eyepiece is designed to serve multiple functions: it acts as both the optical element for viewing virtual content and as a light redirector for infrared eye tracking. This multi-functionality reduces the total number of components needed in the system.
2Adaptability or versatility
If diffraction gratings are used to redirect infrared light, then viewing angle is improved, but manufacturing precision requirements increase
Solution Approach 1:
The diffraction grating is designed with specific periodic structures that control the redirection of infrared light at different angles. By adjusting the grating parameters (period, depth, orientation), the system achieves wide viewing angles while maintaining manufacturability through standardized fabrication processes.
3Length of stationary object
If diffraction gratings are integrated in the eyepieces, then spacing between eyepieces and display panels is reduced, but optical quality may deteriorate
Solution Approach 1:
The diffraction grating is integrated as part of the eyepiece optical system, combining the spacing reduction function with the optical quality maintenance function. This integration ensures that the grating does not compromise the optical path while achieving compact design.
Solution Approach 2:
The diffraction grating acts as an intermediary element that redirects infrared light without significantly affecting visible light transmission. This allows the system to maintain optical quality for both eye tracking and virtual content viewing while reducing spacing.
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
Enhances eye tracking accuracy by improving the viewing angle and reducing distortion, enabling precise gaze detection even at extreme angles and minimizing the distance between eyepieces and display panels.
Implementation Method 1
The diffraction gratings may, for example, be a holographic layer or film sandwiched between two optical lenses in the eyepieces
Implementation Method 2
an illumination source (e.g., an IR light source) that emits light (e.g., IR light) towards the user's eyes
Implementation Method 3
A portion of the IR light is reflected off the user's eyes to the eye-facing surfaces of the eyepieces of the HMD
Data Source
AI summary
An eye tracking system for detecting position and movements of a user's eyes in a head-mounted display (HMD). The eye tracking system includes at least one eye tracking camera, an illumination source that emits infrared light towards the user's eyes, and diffraction gratings located at the eyepieces. The diffraction gratings redirect or reflect at least a portion of infrared light reflected off the user's eyes, while allowing visible light to pass. The cameras capture images of the user's eyes from the infrared light that is redirected or reflected by the diffraction gratings.