Curved AR Waveguide Grating Layout for Distortion-Free Imaging
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Solution Overview
Problem
Existing augmented reality glasses with curved waveguides face challenges in maintaining image quality and compactness due to distortions caused by the curvature of the waveguide, and issues with external visibility of virtual images.
Innovation Solution
A curved waveguide-based augmented reality device using a concentric cylindrical meniscus with in-coupling and out-coupling diffractive optical elements, where the grating periods are designed to maintain consistent angles of incidence and reflection, ensuring distortion-free image formation and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a curved waveguide is used as an optical combiner to make the device compact and ergonomic, then the device size and weight are reduced, but image distortion occurs and image quality deteriorates
Solution Approach 1:
The waveguide surface is designed with different curvatures in different regions: a first curved surface with a first radius of curvature for the input face, and a second curved surface with a second radius of curvature for the output face. This local differentiation of geometric properties allows the waveguide to maintain compactness while compensating for image distortion through optimized light propagation paths in different zones.
Solution Approach 2:
The waveguide employs curved surfaces with specific radii of curvature to achieve both compact form factor and image quality. The first curved surface has a first radius of curvature and the second curved surface has a second radius of curvature, where the ratio between these radii is optimized to maintain parallel light propagation and prevent image distortion while keeping the device compact.
2Volume of moving object
If a curved waveguide is used to reduce device dimensions, then compactness is improved, but the field of view is limited
Solution Approach 1:
The waveguide utilizes curved surfaces with optimized radii of curvature to expand the field of view while maintaining compact dimensions. The specific curvature ratios enable wider angular coverage for virtual image observation without increasing device size, resolving the trade-off between compactness and field of view.
3Ease of operation
If a curved waveguide is used to make the device ergonomic, then ease of operation is improved, but virtual images become visible to external observers
Solution Approach 1:
The asymmetric curved surface design with different radii of curvature creates directional light propagation characteristics. The first curved surface and second curved surface are optimized to direct virtual images exclusively toward the user's eye position, preventing external observers from viewing the virtual images while maintaining ergonomic comfort.
4Volume of moving object
If a curved waveguide is used to reduce device size, then compactness is improved, but image distortion occurs due to non-parallel light propagation
Solution Approach 1:
The waveguide employs specifically designed curved surfaces with a optimized ratio of radii of curvature to maintain parallel light propagation throughout the curved path. The first curved surface and second curved surface are configured such that light rays entering parallel to the optical axis remain parallel after propagation, eliminating image distortion while preserving compact device size.
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 provides a compact, ergonomic, and aesthetically pleasing AR device with a wide field of view and high image quality, preventing external visibility of virtual images.
Implementation Method 1
a beam of parallel rays falling (incident) on the waveguide will turn into a non-parallel beam inside the waveguide, the rays of which will propagate at different angles within the waveguide
Implementation Method 2
the curved waveguide is configured to propagate the rays of the initial image from the in-coupling diffractive optical element to the out-coupling diffractive optical element based on total internal reflection from surfaces of the curved waveguide, wherein, when propagating the rays of the initial image, angles of incidence on and of reflection from a concave surface of the curved waveguide within the curved waveguide are equal to each other and constant
Implementation Method 3
the out-coupling diffractive optical element is configured to form a virtual image on a user retina by converting the rays passed through the curved waveguide and falling on the out-coupling diffractive optical element into parallel beams of rays
Data Source
AI summary
A curved waveguide-based augmented reality device is provided. The device includes a projector, and a curved waveguide. The waveguide has a shape of a concentric cylindrical meniscus and includes an in-coupling diffractive optical element and an out-coupling diffractive optical element, a grating period of a diffraction grating of the in-coupling diffractive optical element at each point of the in-coupling diffractive optical element is such that rays from one point of an initial image are input into the curved waveguide in each point of the in-coupling diffractive optical element at the same angle relative to a normal to a surface of the curved waveguide at a point of ray incidence, and at least at one point on each of the diffractive optical elements a diffraction grating period of the in-coupling diffractive optical element is equal to a diffraction grating period of the out-coupling diffractive optical element.