Interleaved Skewed Grating for AR Waveguide Eyebox
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Solution Overview
Problem
Existing diffractive waveguide combiners for augmented and virtual reality displays face challenges in achieving two-dimensional pupil replication and eyebox expansion while minimizing rainbow artefacts and manufacturing complexities, particularly with tightly constrained optical structures that can lead to undesirable scattering properties and increased device size.
Innovation Solution
A diffractive waveguide combiner utilizing an interleaved skewed rectangular grating with oblique unit cells, where the first and second periodic arrays of optical structures are spatially offset and differ in characteristics, allowing for controlled pupil replication and eyebox expansion, and reducing rainbow artefacts by varying the scattering properties and optimizing the design for improved luminance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If tightly constrained optical structures are used in existing diffractive waveguide combiners, then pupil replication and eyebox expansion can be achieved, but rainbow artefacts increase and manufacturing complexity increases
Solution Approach 1:
The diffractive optical element is segmented into multiple zones with different diffraction characteristics. Each zone is optimized to control specific diffraction orders, allowing selective suppression of rainbow artefacts while maintaining eyebox expansion functionality. This zoned approach enables independent optimization of different regions to address both the eyebox size and artefact reduction requirements
Solution Approach 2:
Different regions of the diffractive optical element are assigned different optical properties and structures. The local diffraction efficiency, period, and phase modulation are varied across the element to optimize performance for specific field-of-view regions while minimizing rainbow artefacts in critical viewing areas. This local quality variation allows tailored control of light distribution
2Area of stationary object
If tightly constrained optical structures are used in existing diffractive waveguide combiners, then pupil replication can be achieved, but manufacturing complexity increases
Solution Approach 1:
The invention varies key parameters of the diffractive structures including period, depth, shape, and material composition to optimize optical performance. By systematically adjusting these parameters across different zones, the design achieves superior eyebox expansion and artefact reduction while remaining compatible with existing manufacturing processes. The parameter optimization balances performance requirements with manufacturability
Solution Approach 2:
The diffractive optical element utilizes composite material structures combining different materials with complementary optical properties. This allows enhanced control over diffraction efficiency and artefact suppression while maintaining compatibility with standard fabrication techniques. The composite approach enables tailored optical characteristics without requiring overly complex single-material structures
3Illumination intensity
If conventional diffraction gratings are used, then light can be coupled out of the waveguide, but luminance uniformity across the eyebox is poor
Solution Approach 1:
The diffractive optical element incorporates dynamic phase modulation capabilities through varied structure depths and shapes. This allows adaptive control of diffraction efficiency across different spatial regions, enabling uniform light distribution across the eyebox while maintaining high overall coupling efficiency. The dynamic structural variation compensates for non-uniformities in light propagation through the waveguide
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 efficient two-dimensional expansion of light and improved luminance uniformity across the eyebox, reducing manufacturing complexities and minimizing rainbow artefacts, thus enhancing the user experience and display performance.
Implementation Method 1
light coupled into the waveguide is expanded in two dimensions by a diffractive optical element
Implementation Method 2
waveguide in which light coupled into the waveguide is expanded in two dimensions by a diffractive optical element as well as coupled out of the waveguide towards a viewer
Data Source
AI summary
A diffraction grating for use as an output element of a diffractive waveguide combiner for an augmented reality or virtual reality display. First and second periodic arrays of optical structures are arranged on a plane according to a common unit cell which is oblique, first and second periods, respectively, of the diffraction grating being defined by a spacing between neighbouring optical structures of one of the first and second periodic arrays along a first side and second side, respectively, of the common unit cell. The first periodic array of optical structures is overlaid on the second periodic array of optical structures in the plane such that the arrays are spatially offset from one another on the plane.