Regional AR Coating for Waveguides Without Grating Interference
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Solution Overview
Problem
Existing anti-reflective coatings in HMDs compromise the performance of optical gratings, leading to reduced efficiency and uniformity of image projection due to interference with their targeted coating thicknesses.
Innovation Solution
Selective application of a multi-layer dielectric anti-reflective coating to specific regions of the waveguide, excluding areas with gratings, to optimize both anti-reflection and grating performance without compromise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a multi-layer dielectric anti-reflective coating is applied to the waveguide, then stray light is reduced and image contrast is improved, but the performance of optical gratings is compromised due to interference with their targeted coating thicknesses
Solution Approach 1:
The waveguide surface is divided into distinct regions: regions with optical gratings and regions without gratings. The anti-reflective coating is selectively applied only to the non-grating regions, thereby eliminating stray light reflections from those areas while preserving the optimal performance of optical gratings in their dedicated regions.
Solution Approach 2:
Different regions of the waveguide are assigned different coating properties. Regions containing optical gratings maintain their specific coating thicknesses required for grating functionality, while regions without gratings receive the anti-reflective coating to minimize stray light. This local differentiation resolves the contradiction by optimizing each region for its specific function.
2Object-affected harmful factors
If anti-reflective coating is applied uniformly across the waveguide, then stray light is minimized, but the efficiency and uniformity of image projection are reduced due to interference with grating functions
Solution Approach 1:
The waveguide is segmented into grating regions and non-grating regions. The anti-reflective coating is applied selectively to non-grating regions only, thereby reducing stray light without interfering with the optical grating functions that are critical for efficient and uniform image projection.
Solution Approach 2:
The coating application is localized to specific regions based on their functional requirements. Non-grating regions receive anti-reflective coating to minimize reflections, while grating regions maintain their original coating characteristics to preserve image projection efficiency and uniformity.
3Object-affected harmful factors
If the coating thickness is optimized for anti-reflection, then stray light is reduced, but the performance of optical gratings that require specific coating thicknesses is compromised
Solution Approach 1:
The waveguide manufacturing process is segmented into two distinct coating operations: one for grating regions with specific thickness requirements, and another for non-grating regions with anti-reflective optimization thickness. This segmentation allows each region to achieve its optimal coating thickness without compromising the other.
Solution Approach 2:
Different coating thicknesses are applied to different regions of the waveguide based on local functional requirements. Grating regions receive coating at thicknesses optimized for grating performance, while non-grating regions receive coating at thicknesses optimized for anti-reflection, thereby achieving both manufacturing precision and stray light reduction.
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
Enhances the efficiency and uniformity of image projection by balancing anti-reflection and grating functions, reducing stray light and improving the clarity and quality of displayed images.
Implementation Method 1
Anti-reflective coatings are generally formed by one or more thin layers of stacked dielectric material, with specifically chosen thickness(es) such that interference effects within the coating stack result in destructive interference towards zero net reflected energy.
Implementation Method 2
a waveguide that receives the light from the micro-display and transmits the light to a user's eye via a plurality of reflections, refractions, diffractions, and/or changes in polarization
Data Source
AI summary
Improving the performance and efficiency of waveguide gratings while also improving the anti-reflection performance of the waveguide can be achieved by selective application of a dielectric anti-reflective coating (or coatings) to distinct regions of the waveguide. For example, a multi-layer dielectric anti-reflective coating is selectively applied to the region of the waveguide between an exit pupil expander grating and an outcoupler grating wherein light is transmitted within the waveguide via instances of total internal reflection (TIR) and where no gratings are typically present. By selectively excluding the regions of the waveguide containing gratings from receiving the anti-reflective coating, such as the incoupler and outcoupler regions, the performance of the gratings can be improved for their respective functions without compromising the anti-reflection performance of the waveguide overall.