Crystalline Waveguide Eyepieces for Low-Artifact AR Depth Cues
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Solution Overview
Problem
Augmented reality systems face challenges in providing a comfortable and natural presentation of virtual image elements due to optical artifacts caused by birefringent materials with high indices of refraction, which affect the orientation and efficiency of diffractive optical coupling elements, and the mismatch between accommodative and vergence states in conventional 3-D displays leads to user discomfort.
Innovation Solution
The use of high-index materials like Li-based oxides for waveguides with blazed geometries to form polarization-insensitive diffraction gratings, and a stacked waveguide assembly that provides continuous vergence cues and discrete accommodation cues to align with the human visual system's accommodation-vergence reflex.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If high-index birefringent materials are used for waveguides to achieve large field of view, then the field of view is improved, but optical artifacts increase due to birefringence
Solution Approach 1:
The patent changes the physical parameters of the waveguide by using materials with progressively higher indices of refraction (from 1.5 to 2.5 or higher) and adjusting their birefringence properties. This allows achieving large field of view while managing optical artifacts through careful parameter selection and optimization of the waveguide structure.
Solution Approach 2:
The patent employs composite material structures where birefringent materials are combined with other optical materials in layered configurations. The birefringent waveguide is integrated with diffractive optical elements and other optical components to achieve both large field of view and reduced optical artifacts through the synergistic properties of the composite structure.
2Loss of energy
If diffractive optical coupling elements are used to couple light into waveguides, then light coupling efficiency is improved, but polarization sensitivity increases causing artifacts
Solution Approach 1:
The patent applies different local properties to different parts of the optical system. The diffractive optical coupling elements are designed with specific local geometries and material properties that optimize light coupling for different polarization states, reducing overall polarization sensitivity while maintaining high coupling efficiency at each interface.
Solution Approach 2:
The patent employs dynamic or adjustable optical elements that can adapt their properties to compensate for polarization effects. The system may include adjustable couplings or adaptive optics that dynamically adjust to minimize polarization-induced artifacts while maintaining efficient light coupling.
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 reduces optical artifacts and enhances the user experience by providing a realistic and comfortable perception of depth, aligning accommodative and vergence states, thus improving the overall AR display quality.
Implementation Method 1
a diffractive grating formed directly in the waveguide, wherein the diffractive grating has a blazed geometry
Implementation Method 2
substrates with high indices of refraction can advantageously provide large field of views (FOVs)
Implementation Method 3
propagate within the waveguide by total internal reflection
Implementation Method 4
Certain materials with high indices of refraction, however, are optically anisotropic (also known as birefringent), e.g., the index of refraction depends on the direction of light propagation relative to the optic axis of the material
Data Source
AI summary
A head-mounted display system includes: a head mounted display frame; a first eyepiece supported by the frame, the first eyepiece including a first substrate composed of a crystalline, transparent material having crystallographic axes in a first orientation with respect to the frame, the substrate having a first surface and a second surface opposite the first surface, the first eyepiece further including a first in-coupling element including a grating on the first surface, and a first out-coupling element including a grating on the first surface and/or a grating on the second surface; and a second eyepiece including a second substrate composed of the crystalline, transparent material having crystallographic axes in a second orientation with respect to the frame different from the first orientation, a second in-coupling element on either surface of the second substrate, and a second out-coupling element on either surface of the second substrate.