Birefringent Grating Reduces Rainbow Effect in Eye-Tracking
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Solution Overview
Problem
Near-eye displays used in virtual, augmented, and mixed reality applications face a 'rainbow effect' due to diffraction artifacts in eye-tracking devices, which degrade the image quality of the see-through view by diffracting visible light and reducing brightness.
Innovation Solution
An optical system with a grating structure, including a polarization volume hologram film with uniform birefringence or a birefringence gradient, is used to diffract infrared light while minimizing the diffraction of visible light, allowing for effective eye-tracking and maintaining image brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional dimming elements are used to suppress the rainbow effect, then the rainbow effect is reduced, but the brightness of the see-through image is reduced simultaneously
Solution Approach 1:
The patent applies local quality by using a wavelength-selective diffractive structure that treats different wavelengths differently. The grating is designed to have high diffraction efficiency for infrared light (for eye tracking) while maintaining low diffraction efficiency for visible light, thereby locally suppressing the harmful rainbow effect without globally dimming the see-through image.
Solution Approach 2:
The patent utilizes parameter changes by controlling the diffraction efficiency as a function of wavelength. By optimizing the grating parameters (pitch, depth, material properties) to achieve wavelength-dependent diffraction characteristics, the system suppresses visible light diffraction (rainbow effect) while preserving infrared light diffraction for eye tracking functionality.
2Adaptability or versatility
If a diffractive structure is used for eye-tracking, then eye-tracking function is achieved, but visible light diffraction causes rainbow effect degrading image quality
Solution Approach 1:
The patent introduces an intermediary approach by using a wavelength-selective diffractive structure that acts as a mediator between the infrared light source and the visible light path. The grating structure selectively interacts with different wavelengths, enabling eye-tracking through infrared diffraction while minimizing visible light diffraction that causes the rainbow effect.
Solution Approach 2:
The patent employs parameter changes by designing the diffractive structure with wavelength-dependent characteristics. By optimizing parameters such as grating pitch, duty cycle, and material refractive index to create wavelength-selective diffraction, the system achieves eye-tracking functionality while suppressing the harmful rainbow effect in the visible spectrum.
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 significantly reduces the 'rainbow effect' while preserving the brightness of the see-through image, enhancing the image quality in augmented and mixed reality applications by efficiently diffracting infrared light and transmitting visible light with minimal diffraction.
Implementation Method 1
The grating is configured to diffract the infrared light reflected from the eye, and transmit a visible light from a real world environment toward the eye
Implementation Method 2
including a birefringent material film configured with a uniform birefringence lower than or equal to 0.1
Data Source
AI summary
A system is provided. The system includes a light source configured to emit an infrared light to illuminate an eye of a user. The system includes a grating disposed facing the eye and including a birefringent material film configured with a uniform birefringence lower than or equal to 0.1. The grating is configured to diffract the infrared light reflected from the eye, and transmit a visible light from a real world environment toward the eye, with a diffraction efficiency less than a predetermined threshold. The system includes an optical sensor configured to receive the diffracted infrared light and generate an image of the eye based on the diffracted infrared light.