Display devices having grating substrates with sub-wavelength patterns
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical systems in electronic devices, such as virtual or augmented reality headsets, suffer from unsightly cosmetic artifacts due to variations in optical elements, which can detract from the appearance of displayed images.
Innovation Solution
A display system with a waveguide that includes a substrate with surface relief gratings and non-diffractive microstructures, where a capping layer is disposed over the substrate with anti-reflective coating, and microstructures are cut in non-SRG regions to maintain a uniform thickness and prevent visible artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surface relief gratings are used in the substrate for optical coupling, then optical performance is improved, but variations in the substrate thickness cause cosmetic artifacts
Solution Approach 1:
The patent applies local quality by introducing non-diffractive microstructures only in specific non-SRG regions of the substrate, rather than uniformly across the entire substrate. These localized microstructures have different properties (sub-wavelength dimensions, non-diffractive) compared to the SRG regions, allowing them to compensate for thickness variations without interfering with optical coupling. This localized application resolves the contradiction by addressing cosmetic artifacts only where they occur without compromising optical performance in SRG regions.
Solution Approach 2:
The non-diffractive microstructures act as an intermediary element between the substrate and the capping layer. They provide a mechanical foundation that compensates for substrate thickness variations, enabling the capping layer to achieve uniform thickness despite underlying SRG variations. The microstructures mediate between the optical requirements (preserving SRG functionality) and the cosmetic requirements (achieving uniform surface appearance).
2Object-affected harmful factors
If the capping layer thickness is made uniform across the substrate, then cosmetic appearance is improved, but the substrate variations prevent uniform deposition
Solution Approach 1:
The patent introduces non-diffractive microstructures with specific local properties (sub-wavelength dimensions, non-diffractive characteristics) in non-SRG regions to create localized compensation for thickness variations. These microstructures have different properties from the SRG regions, allowing selective correction of cosmetic issues without affecting optical performance. This enables uniform capping layer deposition by providing a mechanically uniform foundation in critical areas while preserving optical functionality in SRG areas.
Solution Approach 2:
The patent changes the dimensional parameters of the microstructures to be sub-wavelength (at least 5-10 times less than visible wavelength) while maintaining a similar filling factor to SRGs. This parameter change allows the microstructures to be invisible to optical wavelengths while still providing mechanical support for uniform capping layer deposition. The filling factor parameter is specifically tuned to match SRG regions, ensuring uniform material distribution during deposition processes.
3Object-affected harmful factors
If microstructures are added to compensate for substrate variations, then cosmetic artifacts are reduced, but the device complexity increases
Solution Approach 1:
The patent minimizes device complexity by applying microstructures only locally in non-SRG regions rather than across the entire substrate. This localized approach adds structural complexity only where needed for cosmetic correction, preserving the simplicity of the overall device design. The microstructures are confined to specific areas where thickness variations cause cosmetic issues, avoiding unnecessary complexity in optical coupling regions.
Solution Approach 2:
The non-diffractive microstructures are designed to have a similar filling factor to the SRGs, creating a visual and structural copy that mimics the SRG pattern without replicating their optical functionality. This copying approach allows the microstructures to blend seamlessly with the overall substrate design, reducing the visual impact of added complexity while maintaining cosmetic uniformity.
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 prevents the formation of cosmetic artifacts by ensuring a uniform thickness of the capping layer, enhancing optical performance and image fidelity without affecting the propagation of image light.
Implementation Method 1
The input coupler may include a first surface relief grating (SRG) in a substrate on the waveguide. The cross-coupler may include a second SRG in the substrate. The output coupler may include a third SRG in the substrate.
Implementation Method 2
The microstructures may be non-diffractive to visible wavelengths and/or the image light. The microstructures may, for example, include sub-wavelength grooves or structures having dimensions that are at least 5-10 times less than a visible wavelength.
Implementation Method 3
This may cause portions of the capping layer over the microstructures to sink into the sub-wavelength grooves, thereby providing the capping layer with a relatively uniform thickness across a lateral area of the waveguide
Implementation Method 4
An anti-reflective coating may be disposed over the capping layer.
Data Source
AI summary
A display may include a waveguide, an input coupler having a first surface relief grating (SRG) in a substrate on the waveguide, a cross-coupler having a second SRG in the substrate, and an output coupler having a third SRG in the substrate. The display may direct light to an eye box. A capping layer may be disposed over the substrate. An anti-reflective coating may be disposed over the capping layer. Microstructures may be disposed in non-SRG regions of the substrate and may be non-diffractive at visible wavelengths. The microstructures may include grooves and may have a similar filling factor to the SRGs. This may cause portions of the capping layer over the microstructures to sink into the grooves, thereby providing the capping layer with a relatively uniform thickness across a lateral area of the waveguide, without the microstructures producing visible artifacts or interacting with the light.