FTIR Diffractive Optical Structure for AR Waveguide Eye-Box Expansion
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Solution Overview
Problem
In augmented reality displays, the narrow space for output gratings on waveguides limits the monitoring area, making it difficult to expand the eye-box without enlarging the waveguide.
Innovation Solution
A diffractive optical structure is implemented on one face of the waveguide, featuring an extension grating and an overlapping output grating along a perpendicular axis, which enlarges the output grating size and expands the monitoring area without increasing the waveguide's dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diffraction gratings are separated and disposed on one face of the waveguide, then the structure is simple and easy to manufacture, but the monitoring area (eye-box) becomes narrow
Solution Approach 1:
The patent transitions from a two-dimensional arrangement of separated gratings on the waveguide face to a three-dimensional overlapping configuration. The extension grating and output grating are positioned at different depths (along the z-axis perpendicular to the waveguide face), allowing both gratings to coexist in the same planar footprint. This dimensional transition enables the output grating to be enlarged without increasing the waveguide's external dimensions, thereby expanding the monitoring area while maintaining manufacturing simplicity.
2Area of stationary object
If the waveguide is enlarged to expand the monitoring area, then the monitoring area increases, but the form factor and device compactness deteriorate
Solution Approach 1:
The patent implements a nested configuration where the output grating is positioned within the spatial footprint of the extension grating. Specifically, the output grating is disposed to overlap at least some area of the extension grating along the axis perpendicular to the waveguide face. This nesting arrangement allows the output grating to be enlarged without requiring additional external space, as it utilizes the vertical space within the existing waveguide structure. Consequently, the monitoring area is expanded while the waveguide's external dimensions and form factor remain unchanged.
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 enhances the monitoring area and improves the form factor of augmented reality displays by allowing a larger eye-box without enlarging the waveguide, increasing the user's eye location freedom.
Implementation Method 1
The diffraction gratings may be mounted on the waveguide and diffract received light. Accordingly, when the diffraction gratings output at least some of the received light, a user can monitor an image related to the received light.
Data Source
AI summary
Various embodiments relate to an FTIR-based diffractive optical structure, and a waveguide device and an augmented reality display each including same. The augmented reality display may comprise: a projector configured to provide light related to an image; and a waveguide device for outputting at least a part of the light, wherein: the waveguide device comprises a waveguide and a diffractive optical structure disposed on one surface of the waveguide; and the diffractive optical structure comprises an expansion grating disposed at the one surface of the waveguide and an output grating disposed along the axis perpendicular to the one surface of the waveguide and overlapping at least a partial area of the expansion grating.