Multilayer Out-Coupling Grating for Uniform AR Waveguide Brightness
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Solution Overview
Problem
Multilayer waveguides in augmented reality devices experience non-uniform brightness due to varying intensity of imaging light propagation based on incidence angles, leading to distorted virtual images.
Innovation Solution
A multilayer waveguide system with diffractive out-coupling elements featuring multiple grating layers with varying refractive indices and diffraction efficiencies to compensate for intensity variations at different angles of incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If a multilayer waveguide is used to reduce weight, then weight is reduced, but brightness uniformity deteriorates due to varying light intensity at different propagation angles
Solution Approach 1:
The patent applies local quality by creating different grating structures at different locations within the waveguide. Specifically, the waveguide includes a first region with a first grating and a second region with a second grating, where the gratings have different characteristics (such as different periods, depths, or orientations) to compensate for the angle-dependent intensity variations at different propagation angles. This localized differentiation allows each region to optimize light extraction for its specific angular range, thereby improving overall brightness uniformity while maintaining the lightweight multilayer structure.
Solution Approach 2:
The patent employs parameter changes by systematically varying grating parameters (such as grating period, depth, width, or orientation angle) across different regions of the waveguide. These parameter modifications are designed to counteract the intensity variations that occur at different propagation angles. For example, gratings in regions with higher intensity may have different parameters compared to those in regions with lower intensity, thereby equalizing the overall light extraction efficiency across all angles and improving brightness uniformity.
2Adaptability or versatility
If a single-layer waveguide with high-index material is used to achieve wide field of view, then field of view is improved, but weight increases due to high density materials
Solution Approach 1:
The patent applies composite materials by constructing the waveguide as a multilayer structure comprising multiple layers with different refractive indices and densities. Instead of using a single high-index material throughout, the waveguide combines layers such as a high-index core layer with lower-index cladding layers or buffer layers. This composite approach allows the optical design to achieve the necessary light guidance and wide field of view through careful refractive index profiling, while the overall density and weight are reduced by incorporating lighter materials in non-critical regions.
Solution Approach 2:
The patent employs segmentation by dividing the waveguide into multiple functional layers, each with specific optical properties. The waveguide is segmented into a high-index core layer that provides the primary light guidance capability for wide field of view, and additional lower-index layers that provide mechanical support, optical confinement, or weight reduction. This segmentation allows the high-index material to be used only where necessary for optical performance, thereby achieving wide field of view with minimized weight.
3Adaptability or versatility
If imaging light is coupled into the waveguide over a range of incidence angles, then field of view is improved, but brightness uniformity deteriorates due to intensity variation with incidence angle
Solution Approach 1:
The patent applies local quality by designing different grating structures in different angular regions of the waveguide. The waveguide is divided into multiple regions corresponding to different incidence angle ranges, with each region having gratings optimized for its specific angular range. For example, gratings in regions receiving light at steeper angles may have different characteristics than those receiving light at shallower angles, thereby compensating for the intensity variations and achieving uniform brightness across the entire field of view.
Solution Approach 2:
The patent employs parameter changes by systematically adjusting grating parameters (such as period, depth, width, or orientation) as a function of position within the waveguide to compensate for incidence angle-dependent intensity variations. These parameter modifications are calculated to equalize the light extraction efficiency across different incidence angles, thereby maintaining brightness uniformity while preserving the wide field of view enabled by multi-angle 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
The solution enhances brightness uniformity across a wide range of incidence angles, improving the quality of virtual images by equalizing light intensity distribution.
Implementation Method 1
The diffractive out-coupling element features two or more layers that differ in refractive index and is configured to include a variability in diffraction efficiency that acts to improve the uniformity in diffracted brightness of imaging light received at different angles of incidence
Implementation Method 2
The coupled light propagates within the waveguide by total internal reflection to the diffractive out-coupling element
Data Source
AI summary
An optical element for augmented reality and other devices is described. The optical element includes a multilayer waveguide, an in-coupling element for directing imaging light into the multilayer waveguide, and an out-coupling element spaced apart from the in-coupling element for directing light out of the multilayer waveguide to form a virtual image in the viewing field of an observer. The out-coupling element is a diffractive optical element that includes two or more diffractive grating layers that differ in refractive index. Inclusion of multiple diffraction grating layers in the out-coupling element leads to an improvement in the brightness uniformity of virtual images produced by imaging light spanning a wide range of incidence angle.