Modulated Surface Relief Gratings for Uniform Eye Box
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Solution Overview
Problem
Designing electronic devices with displays, such as virtual and augmented reality headsets, is challenging due to the need for components that are both unobtrusive and exhibit desired optical performance, often resulting in unsightly and bulky designs.
Innovation Solution
The use of a display system that includes a waveguide and a surface relief grating (SRG) structure, where the SRG performs both cross-coupling and output coupling operations to expand and redirect image light efficiently, with modulated grating strengths across its lateral area to maximize optical efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If traditional display components are used in virtual and augmented reality headsets, then the displays can present images to users, but the components become unsightly and bulky
Solution Approach 1:
The patent combines multiple optical functions (input coupling, cross-coupling, output coupling, and pupil expansion) into a single integrated waveguide structure with surface relief gratings, eliminating the need for separate bulky optical components and achieving a sleek, eyeglass-like form factor
Solution Approach 2:
The waveguide structure performs multiple functions simultaneously: it guides light from the display, expands the pupil, and couples light to and from the waveguide, allowing a single component to replace what would traditionally require multiple separate elements
2Area of stationary object
If the eye box area is increased to provide a wider field of view, then more light is required which increases system complexity
Solution Approach 1:
The patent uses diffractive surface relief gratings that operate in the spatial frequency domain to expand the pupil in both horizontal and vertical dimensions simultaneously, achieving a large eye box without requiring proportionally increased light output or additional optical elements
3Illumination intensity
If uniform light intensity across the eye box is achieved, then optical efficiency must be maximized which requires precise grating modulation
Solution Approach 1:
The patent implements spatially varying grating strengths across different regions of the waveguide surface, with each local area optimized to compensate for geometric factors and achieve uniform light distribution across the entire eye box, rather than using a uniform grating structure throughout
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
This configuration allows for a more compact and efficient optical system that fills a larger eye box with uniform-intensity image light, reducing manufacturing complexity and increasing throughput while maintaining a wide field of view.
Implementation Method 1
The image light may propagate down the waveguide via total internal reflection
Implementation Method 2
The SRG structure may perform a cross-coupling operation in which the SRG structure expands the image light in a direction perpendicular to the direction of propagation
Data Source
AI summary
A display may include a waveguide and a surface relief grating (SRG) structure on the waveguide. The SRG structure may perform expand image light propagating in the waveguide. The SRG structure may also couple the expanded image light out of the waveguide and towards an eye box. The SRG structure may include at least first and second SRGs that expand the image light in opposite directions. The first SRG may couple the image light expanded by the second SRG out of the waveguide and the second SRG may couple the image light expanded by the first SRG out of the waveguide. Modulation functions may be used to vary the grating strengths of the SRGs in the SRG structure between brow and cheek regions of the SRG structure. Diffraction efficiency of the SRG structure may additionally or alternatively be varied between nasal and temple regions of the SRG structure.