Diffraction Grating Eyepiece for Accurate Eye Tracking
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Solution Overview
Problem
Current eye tracking systems in virtual and mixed reality (VR/AR) applications face challenges in accurately detecting eye position and movement, especially at extreme gaze angles, due to distortion and the need for increased spacing between eyepieces and display panels, which affects detection accuracy and viewing angle.
Innovation Solution
Incorporating transmissive or reflective diffraction gratings in the eyepieces of head-mounted displays (HMDs) to redirect or reflect infrared light towards cameras, allowing for improved viewing angles and reduced distortion, enabling more accurate eye tracking without the need for hot mirrors and allowing cameras to be placed at the sides of the face.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hot mirrors are used to reflect IR light towards cameras, then eye tracking is enabled, but the spacing between eyepieces and display panels must be increased
Solution Approach 1:
The patent removes the hot mirror component from the optical path and extracts only the necessary diffraction grating functionality directly into the eyepiece assembly. This eliminates the need for increased spacing while maintaining eye tracking capability through direct integration of the diffraction grating in the eyepiece.
Solution Approach 2:
The diffraction grating is merged with the eyepiece optical elements, combining the functions of the eyepiece and the IR light redirecting component into a single integrated structure. This merging eliminates the need for separate hot mirrors and reduces the overall spacing requirements.
2Device complexity
If IR cameras view eyes directly through eyepieces, then system is simpler, but distortion increases and viewing angle is limited
Solution Approach 1:
The diffraction grating acts as an intermediary element within the eyepiece that selectively redirects IR light while allowing visible light to pass through. This intermediary structure enables the camera to capture eye images through the eyepiece with reduced distortion and improved viewing angle without requiring a completely different optical path.
3Length of stationary object
If diffraction gratings are integrated in eyepieces, then spacing is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent employs thin film diffraction grating technology that can be laminated or coated onto the eyepiece optical surfaces. This thin film approach allows for integration of the diffraction grating function without requiring complex mechanical structures, thereby reducing manufacturing complexity while achieving the desired optical effects.
4Ease of operation
If reflective gratings are used, then cameras can be placed at sides of face, but optical path complexity increases
Solution Approach 1:
The reflective grating is designed with asymmetric optical properties that redirect IR light at specific angles toward side-mounted cameras. This asymmetric design allows the camera to be positioned at the side of the user's face while maintaining a relatively simple optical path within the eyepiece, avoiding the need for complex multi-element optical systems.
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 enhances eye tracking accuracy and reduces distortion, enabling gaze-based interactions and improved image quality, while also allowing for a more compact design by reducing the spacing 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, or alternatively a holographic layer or film laminated to an image side (eye-facing) or object side (display-facing) surface of an optical lens 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.