Two-Dimensional Grating for AR Pupil Expansion
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Solution Overview
Problem
Current augmented reality (AR) optical display systems face challenges in achieving uniform color and brightness across the field of view due to limitations in pupil expansion and out-coupling efficiency, particularly with one-dimensional gratings, which result in intensity differences and polarization imbalances.
Innovation Solution
The implementation of a two-dimensional grating with rhombus lattices and un-symmetric unit cells at the output end of the waveguide for pupil expansion and out-coupling, allowing for enhanced diffraction efficiency and uniformity by compensating polarization differences and improving manufacturing feasibility with a thinner design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one-dimensional gratings are used for pupil expansion and out-coupling, then the device structure is simpler, but the color uniformity and brightness uniformity across the field of view deteriorate due to intensity differences and polarization imbalances
Solution Approach 1:
The patent transitions from one-dimensional gratings to two-dimensional gratings with rhombus unit cells. This dimensional change enables the grating to manipulate light in multiple directions simultaneously, achieving both pupil expansion and out-coupling functions while maintaining uniform color and brightness across the field of view by compensating for polarization differences through the symmetric rhombus geometry.
Solution Approach 2:
The patent employs asymmetric orientation of the rhombus unit cells relative to the waveguide surface normal. The unit cells are rotated at a specific angle (e.g., 45 degrees) to optimize the diffraction efficiency for different polarization states, thereby achieving polarization compensation and uniform light output across the viewing area.
2Illumination intensity
If traditional pupil expansion components are added to AR devices, then the exit pupil expansion is achieved, but the device complexity and number of components increase
Solution Approach 1:
The patent combines the pupil expansion function and the out-coupling function into a single two-dimensional grating component. This merged design eliminates the need for separate pupil expansion optics, reducing the overall device complexity while achieving both functions simultaneously through the engineered diffraction pattern of the rhombus unit cells.
Solution Approach 2:
The two-dimensional grating with rhombus unit cells serves multiple functions: it acts as both an exit pupil expander and an out-coupler. The grating's periodic structure and geometric configuration enable it to perform multiple optical functions that traditionally required separate components, thereby simplifying the AR device architecture.
3Productivity
If thicker grating designs are used to improve diffraction efficiency, then the out-coupling efficiency improves, but the manufacturing feasibility and device compactness deteriorate
Solution Approach 1:
The patent optimizes the geometric parameters of the rhombus unit cells, including the side length, internal angles, and orientation, to achieve high diffraction efficiency in a thin grating structure. By carefully tuning these parameters, the design achieves effective light out-coupling without requiring a thick grating, thereby maintaining manufacturing feasibility and device compactness.
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 solution achieves improved exit-pupil expansion efficiency, uniform color output, and wider field of view while maintaining acceptable display performance, addressing the limitations of one-dimensional gratings by reducing polarization imbalances and intensity differences.
Implementation Method 1
a two-dimensional grating, which is provided at the output end of the waveguide, wherein the waveguide delivers the image light coupled by the input coupler to the two-dimensional grating, and the two-dimensional grating performs pupil expansion on the image light and out-couples the expanded image light
Implementation Method 2
The image light undergoes total internal reflection in the waveguide, and is finally out-coupled to the air using out-coupler gratings
Data Source
AI summary
An optical display system and an augmented reality electronic device are disclosed. The optical display system comprises: a waveguide; an input coupler, provided at the input end of the waveguide and couples an image light into it; and a two-dimensional grating, provided at the output end of waveguide. The waveguide delivers the image light to the two-dimensional grating, which performs pupil expansion on the image light and out-couples the expanded image light. The two-dimensional grating has rhombus lattices. Unit cells of the two-dimensional grating are un-symmetric along respective axes parallel with a propagation direction of the image light incident onto the two-dimensional grating, from a top view of the two-dimensional grating. The unit cells are oriented with the propagation direction of the image light and each of the unit cells has at least two vertexes at its end side.