Buried Diffractive Gratings for Compact, Durable 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 like corrective lenses.
Innovation Solution
The use of buried diffractive gratings within optical elements, fabricated using high and low-refractive index materials, allows for protected, flexible, and versatile integration with other optical components, enabling compact and durable displays.
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 on the surface. The grating structure is nested inside the waveguide material, surrounded by protective material on all sides, eliminating the fragility of surface-exposed gratings while maintaining the diffraction function.
Solution Approach 2:
A sacrificial material layer is used as an intermediary during fabrication. This layer is deposited, patterned, and then removed to create the buried grating structure. The intermediary enables the creation of the protected buried grating without directly exposing the final grating structure to damage risks.
2Ease of manufacture
If surface relief gratings are used, then mass production with lithographic techniques is enabled, but additional coatings or optical elements damage the gratings or ruin their refraction ability
Solution Approach 1:
The grating structure is created in advance within the bulk material before any coatings or additional optical elements are added. By performing the grating fabrication early in the manufacturing process and burying it, subsequent manufacturing steps can proceed without risk of damaging the grating structure.
Solution Approach 2:
The grating is nested within the optical element bulk, allowing subsequent coatings and elements to be added without exposing or touching the grating structure. This nesting protects the grating from damage during assembly and use while maintaining manufacturability.
3Reliability
If multiple waveguides are mounted in a housing with protective measures, then surface relief gratings are protected, but the head-mounted display becomes bulky and cumbersome
Solution Approach 1:
The grating structure is nested within each waveguide, eliminating the need for external protective housings or spacing structures. This integration reduces the overall volume required for protection while maintaining the protective effect, enabling more compact head-mounted display designs.
4Adaptability or versatility
If corrective lenses are added to waveguides with surface relief gratings, then vision correction is provided, but the non-flat surfaces and total internal reflection requirements make integration difficult
Solution Approach 1:
The buried grating is nested within the waveguide, providing flat external surfaces that are compatible with standard corrective lens mounting. This eliminates the complexity of integrating with non-flat surface gratings while maintaining the optical functionality.
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
Buried diffractive gratings provide a solution to the fragility and bulkiness issues, allowing for protected integration with additional optical elements and enabling compact, durable, and versatile head-mounted displays.
Implementation Method 1
waveguides include diffractive gratings, such as an input coupler (incoupling) grating and an output coupler (outcoupling) grating. Approaches of gratings used in waveguides include volume Bragg gratings and surface relief gratings.
Implementation Method 2
As waveguides with surface relief gratings include fragile non-flat surfaces, and rely on total internal reflection, the addition of lenses or coatings is not a straightforward process.
Implementation Method 3
Volume Bragg gratings are useful in that they provide refractive index modulation. 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.
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.