Buried Diffractive Gratings for Durable, Compact AR/VR Waveguides
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Solution Overview
Problem
Existing head-mounted displays for augmented and virtual reality are bulky due to the fragility and bulkiness of surface relief gratings, which are difficult to protect and integrate with additional optical elements or coatings, especially for AR applications requiring corrective lenses.
Innovation Solution
The use of buried diffractive gratings within optical elements, composed of high- and low-refractive index materials, allows for fabrication methods that protect the gratings from surface damage and enable integration with additional optical elements, coatings, and stacking, using techniques such as patterning sacrificial materials, laser bonding, and lithographic processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surface relief gratings are used in waveguides, then light diffraction function is achieved, but the optical elements become extremely fragile and difficult to protect
Solution Approach 1:
The diffractive grating is embedded within the bulk of the optical element rather than being placed on the surface. The grating structure is nested inside the waveguide material, surrounded by protective optical material that prevents direct contact and damage to the grating surfaces.
Solution Approach 2:
The patent introduces an intermediate protective layer of optical material between the diffractive grating and the external environment. This intermediary layer protects the fragile grating surfaces from direct contact with other optical elements while still allowing the grating to perform its light diffraction function.
2Adaptability or versatility
If surface relief gratings are used, then light refraction is achieved, but additional coatings or corrective lenses cannot be easily integrated
Solution Approach 1:
The diffractive grating is nested within the optical element, allowing additional coatings and corrective lenses to be applied to the external surfaces without risking damage to the grating structure. The grating is protected inside while coatings are applied outside.
Solution Approach 2:
The patent separates the diffractive grating function from the surface of the optical element. The grating is positioned at a different location (embedded within the bulk) than the surfaces that receive coatings or corrective lenses, allowing independent treatment of each component without mutual interference.
3Reliability
If multiple waveguides are mounted in a housing with protective spacing, then surface relief gratings are protected, but the head-mounted display becomes bulky and cumbersome
Solution Approach 1:
The diffractive grating is nested within each waveguide, eliminating the need for additional protective housings or spacing between waveguides. The protective structure is integrated into the waveguide itself, reducing overall device volume.
Solution Approach 2:
The protective function and the waveguide structure are merged into a single integrated component. The waveguide material itself provides protection to the embedded grating, eliminating the need for separate protective housings and reducing the number of discrete components.
4Reliability
If volume Bragg gratings are used, then refractive index modulation is achieved, but fabrication becomes difficult requiring ultraviolet light irradiation
Solution Approach 1:
The patent extracts the diffractive grating structure from the complex volume Bragg grating fabrication process. Instead of requiring ultraviolet light irradiation and photosensitive glass processing, the grating is formed using simpler lithographic techniques on standard optical materials.
Solution Approach 2:
The patent changes the fabrication parameters from requiring ultraviolet light irradiation and specialized photosensitive materials to using standard lithographic processes with conventional optical materials. This simplifies the manufacturing process while maintaining the refractive index modulation function.
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 buried diffractive gratings provide a compact and durable solution that allows for integration with corrective lenses and other optical elements, enabling a more compact and versatile head-mounted display design.
Implementation Method 1
The optical element comprises a first flat surface, a second flat surface, and a buried diffractive grating spaced from and disposed between the first surface and the second surface. The buried diffractive grating comprises a high-refractive index material interspersed with a low-refractive index material or non-solid pockets
Implementation Method 2
head-mounted displays include waveguides made from glass or plastic which diffract light from an image source to an eye of the user. The waveguides may be implemented in lenses of glasses that are attached to the image source. To diffract the light, waveguides include diffractive gratings
Implementation Method 3
Volume Bragg gratings are useful in that they provide refractive index modulation
Data Source
AI summary
Head-mounted displays with waveguides comprising buried diffractive gratings and methods for fabricating said waveguides are described herein. In an embodiment, a head-mounted display comprises an optical element and an image source that provides an image beam to an optical element. The optical element comprises a first flat surface, a second flat surface, and a buried diffractive grating spaced from and disposed between the first surface and the second surface. The buried diffractive grating comprises a high-refractive index material interspersed with a low-refractive index material or non-solid pockets, such as gas, air or vacuum.