Apodized Reflective Holographic Grating for Eye Tracking
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Solution Overview
Problem
Current eye-tracking systems in artificial reality systems suffer from optical artifacts such as rainbow ghost images due to the diffraction and dispersion of light by holographic gratings, which disrupt the user's immersive experience.
Innovation Solution
The implementation of an apodized reflective holographic grating with a refractive index modulation that follows a bell-shaped curve along its thickness direction, reducing optical artifacts by minimizing sidelobes and improving the accuracy of eye tracking while allowing visible light to pass through without obstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reflective holographic grating is used to track eye movement, then eye tracking capability is enabled, but optical artifacts such as rainbow ghost images are generated due to diffraction and dispersion of light
Solution Approach 1:
The patent applies apodization to create a non-uniform refractive index modulation profile within the holographic grating structure. Specifically, the refractive index modulation amplitude varies along the thickness direction of the grating, being stronger at certain depths and weaker at others. This local variation in optical properties reduces the generation of sidelobes and optical artifacts while maintaining the primary diffraction function for eye tracking, thereby resolving the contradiction between tracking accuracy and artifact reduction.
2Measurement precision
If the refractive index modulation of the holographic grating is increased to improve eye tracking signal strength, then tracking sensitivity improves, but optical artifacts are intensified
Solution Approach 1:
The patent changes the parameter distribution of refractive index modulation from uniform to non-uniform (apodized) along the thickness direction of the holographic grating. By controlling the amplitude profile of refractive index modulation—making it vary spatially rather than remain constant—the system achieves optimized diffraction efficiency for eye tracking while simultaneously suppressing the formation of optical artifacts. This parameter transformation resolves the contradiction between tracking precision and artifact reduction.
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
The solution effectively reduces optical artifacts, enhancing the accuracy and reliability of eye tracking and providing a more immersive experience by minimizing rainbow ghost images and other optical distortions.
Implementation Method 1
The reflective holographic grating is configured to transmit the visible light and reflectively diffract infrared light in a first wavelength range for eye tracking
Implementation Method 2
A refractive index modulation of the reflective holographic grating is apodized in a direction along a thickness direction of the reflective holographic grating to reduce optical artifacts in the visible light
Data Source
AI summary
Techniques disclosed herein relate to a near-eye display system. One example of an eye-tracking system includes a substrate transparent to visible light and infrared light and a reflective holographic grating conformally coupled to a surface of the substrate. The reflective holographic grating is configured to transmit the visible light and reflectively diffract infrared light in a first wavelength range for eye tracking. The refractive index modulation of the reflective holographic grating is apodized in a direction along a thickness of the reflective holographic grating to reduce optical artifacts in the visible light.