Waveguide Display Grating Design for Large Field of View
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Solution Overview
Problem
Conventional near-eye displays (NEDs) face challenges in achieving a small form factor, large field of view, and large eyebox due to the need for high refractive index materials and complex diffraction grating designs, which result in increased weight and cost.
Innovation Solution
A waveguide display system comprising a light source assembly, an output waveguide with diffraction gratings, and a controller that expands image light to provide a diagonal field of view of at least 60 degrees and an eyebox of 20 mm by 10 mm, using a single projector or multiple projectors with strategically positioned diffraction gratings to minimize the form factor and enhance the field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional diffraction grating designs with high refractive index materials are used to achieve a large field of view, then the field of view increases, but the weight and cost increase significantly
Solution Approach 1:
The patent changes the physical parameters of the diffraction grating by using a low refractive index material (acrylic with n≈1.49) instead of conventional high refractive index materials. This parameter change allows achieving a large field of view (≥60 degrees diagonal) while significantly reducing the weight and cost of the waveguide display system.
Solution Approach 2:
The patent employs a composite structure combining a low refractive index waveguide material (acrylic) with specifically designed diffraction grating patterns. This composite approach allows the system to achieve high field of view performance without relying on heavy high-index materials, thus reducing overall weight while maintaining optical performance.
2Illumination intensity
If conventional diffraction grating designs with high refractive index materials are used to achieve a large field of view, then the field of view increases, but the cost increases significantly
Solution Approach 1:
The patent changes the material parameter from high refractive index to low refractive index (acrylic), which is a more cost-effective material. This parameter change reduces manufacturing cost while still achieving the required large field of view through optimized grating design and configuration.
Solution Approach 2:
The patent adopts inexpensive acrylic material for the waveguide and diffraction gratings, replacing expensive high-index optical materials. This substitution significantly reduces the cost of manufacturing the waveguide display system while maintaining the required optical performance for large field of view.
3Illumination intensity
If two different output grating elements that are spatially separated are used for two-dimensional expansion, then the field of view expands, but the form factor increases
Solution Approach 1:
The patent merges the two-dimensional expansion function into a single integrated output grating element rather than using two spatially separated grating elements. This integration achieves the same two-dimensional field of view expansion (horizontal and vertical) while significantly reducing the overall form factor and making the device more compact.
Solution Approach 2:
The patent uses a single grating element with a two-dimensional grating pattern (combining horizontal and vertical grating vectors) to achieve two-dimensional field of view expansion. This approach effectively uses the grating's spatial frequency structure in multiple dimensions to expand the field of view without requiring physically separated components, thus reducing form factor.
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 enables a compact, lightweight, and cost-effective NED with a large field of view and eyebox, improving user experience in virtual and augmented reality applications while reducing material costs and complexity.
Implementation Method 1
The output waveguide includes at least an input diffraction grating on at least one of the opposite surfaces. The input diffraction grating in-couples the image light (propagating along an input wave vector) emitted from the light source assembly into the output waveguide
Implementation Method 2
Conventional near-eye displays (NEDs) have a design criteria to be compact and light weight, and to provide a two-dimensional expansion with a large eyebox and a wide field-of-view (FOV). In typical NEDs, the limit for the FOV is based on satisfying two physical conditions: (1) an occurrence of total internal reflection of image light coupled into a waveguide
Implementation Method 3
The output waveguide includes a second and third grating (that are associated with a second and third grating vector, respectively) that together direct and decouple the expanded image light from the output waveguide
Data Source
AI summary
A waveguide display is used for presenting media to a user. The waveguide display includes light source assembly, an output waveguide, and a controller. The light source assembly includes one or more projectors projecting an image light at least along one dimension. The output waveguide includes a waveguide body with two opposite surfaces. The output waveguide includes a first grating receiving an image light propagating along an input wave vector, a second grating, and a third grating positioned opposite to the second grating and outputting an expanded image light with wave vectors matching the input wave vector. The controller controls the scanning of the one or more source assemblies to form a two-dimensional image.