Diffractive Waveguide Grating Layout for 180° Pupil Expansion
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Solution Overview
Problem
Conventional diffractive waveguide systems suffer from a limited eye box due to a small setup area of the output coupled grating, resulting in reduced utilization of the waveguide substrate and restricted eye movements, and the two-dimensional grating systems have inefficiencies in pupil expansion angles.
Innovation Solution
A diffractive waveguide apparatus with a grating structure featuring adjustable first and second periods in different directions, allowing for a two-dimensional pupil expansion angle of 180°, increasing the valid coupled grating area and improving utilization by eliminating invalid regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional two-dimensional grating with hexagonal lattice structure is used, then the grating can be manufactured with standard periodic structure, but the pupil expansion angle is limited to 120° causing reduced valid output coupled grating area
Solution Approach 1:
The patent changes the fundamental parameter of pupil expansion angle from 120° to 180° by redesigning the grating structure. This is achieved by using a rectangular lattice structure with orthogonal directions instead of hexagonal lattice, allowing the light to be coupled out in four directions (±x and ±y directions) rather than three directions, thereby maximizing the valid grating area utilization.
2Adaptability or versatility
If an orthogonal pupil expander is added to expand the pupil in two directions, then the field of view is improved, but the output coupled grating has small setup area due to the expander occupying waveguide substrate
Solution Approach 1:
The patent merges the functions of the orthogonal pupil expander and the output coupled grating into a single integrated grating structure. The rectangular lattice grating simultaneously performs pupil expansion in orthogonal directions and couples light out, eliminating the need for a separate orthogonal pupil expander component and thereby maximizing the available waveguide substrate area for the output coupled grating.
Solution Approach 2:
The output coupled grating is designed to perform multiple functions: it acts as both the pupil expander and the light coupling element. The rectangular lattice structure enables the grating to expand the pupil in both horizontal and vertical directions while simultaneously coupling the expanded light out of the waveguide, making the structure universal and eliminating wasted substrate area.
3Area of stationary object
If the waveguide substrate area is increased to accommodate larger output coupled grating, then the valid display area is improved, but the device size and weight increase
Solution Approach 1:
The patent changes the grating structure parameters from hexagonal lattice to rectangular lattice, which enables 180° pupil expansion. This parameter change allows the same waveguide substrate area to provide a larger valid display area by eliminating invalid grating regions, thereby improving display area without increasing substrate size, weight, or volume.
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 enhances the valid display area and utilization rate of the grating structure, enabling a wider range of eye movements and improved AR functionality by optimizing the pupil expansion angle to 180°.
Implementation Method 1
A diffractive waveguide apparatus with a grating structure featuring multiple grating units having adjustable first and second periods, allowing for a two-dimensional pupil expansion angle of 180°
Data Source
AI summary
A diffractive light waveguide apparatus, a near-eye display device, and a manufacturing method for a diffractive light waveguide apparatus are provided. The diffractive light waveguide apparatus includes a waveguide substrate and a grating structure. The grating structure is arranged on a surface of the waveguide substrate and includes multiple grating units, the multiple grating units have a first period in a first direction and a second period in a second direction, and the second direction is different from the first direction. The first period and the second period are adjustable to cause a two-dimensional pupil expansion angle of the grating structure to be 180°.