Waveguide Fold and Output Gratings for Dual-Axis Pupil Expansion
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Solution Overview
Problem
Existing near-eye displays face challenges in preserving eye box size while reducing lens size, limiting the field of view and requiring multiple layers in waveguide systems.
Innovation Solution
A near-eye optical display system utilizing a waveguide with an input coupler, fold grating, and output grating for dual-axis pupil expansion, enabling light to travel via total internal reflection and exit the waveguide through these gratings for enhanced field of view without needing multiple layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If waveguide systems use multiple layers to preserve eye box size, then the field of view is limited and device complexity increases, but reducing lens size is achieved
Solution Approach 1:
The patent applies pupil expansion gratings that operate in both horizontal and vertical dimensions simultaneously, transitioning from single-axis to dual-axis expansion. This dimensional change allows the system to achieve larger effective eye box area without adding multiple waveguide layers, thereby reducing device complexity while maintaining the desired field of view
Solution Approach 2:
The invention changes the optical parameters by using gratings with specific diffraction efficiencies and geometries that enable pupil expansion in two dimensions. By adjusting grating parameters such as period, depth, and orientation, the system achieves enhanced eye box size without increasing the number of layers, thus resolving the contradiction between eye box preservation and device simplicity
2Area of stationary object
If waveguide systems use multiple layers to preserve eye box size, then the field of view is limited, but reducing lens size is achieved
Solution Approach 1:
The patent implements dual-axis pupil expansion by designing gratings that diffract light in both horizontal and vertical directions. This two-dimensional expansion capability significantly increases the effective eye box area and field of view without requiring multiple waveguide layers, thereby improving adaptability while maintaining a compact structure
Solution Approach 2:
The pupil expansion gratings serve multiple functions simultaneously: they expand the pupil in both axes, control light propagation directions, and define the field of view. This multi-functionality allows a single grating structure to achieve what would otherwise require multiple separate components, enhancing field of view without increasing system complexity
3Device complexity
If traditional waveguide systems are used, then lens size is maintained, but field of view is limited and multiple layers are required
Solution Approach 1:
The patent introduces dual-axis pupil expansion gratings that operate in both horizontal and vertical dimensions, enabling the system to achieve larger eye box size with fewer layers. This dimensional approach allows single-layer or reduced-layer waveguide structures to provide sufficient pupil expansion area that would otherwise require multiple stacked layers
Solution Approach 2:
By optimizing grating parameters including period, depth, fill factor, and orientation angles, the invention achieves maximum pupil expansion efficiency in two dimensions. These parameter adjustments enable a reduced number of layers to provide the same or greater effective eye box area compared to traditional multi-layer systems
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 system achieves a wider field of view with fewer layers by using fold gratings for dual-axis pupil expansion, allowing for smaller lenses and improved optical efficiency.
Implementation Method 1
The input coupler is configured to receive collimated light from a display source and to cause the light to travel within the waveguide via total internal reflection between the first surface and the second surface
Implementation Method 2
The fold grating is configured to provide pupil expansion in a first direction and to direct the light to the output grating via total internal reflection between the first surface and the second surface
Implementation Method 3
The output grating is configured to provide pupil expansion in a second direction different than the first direction and to cause the light to exit the waveguide from the first surface or the second surface
Data Source
AI summary
A near eye optical display includes a waveguide comprising a first surface and a second surface, an input coupler, a fold grating, and an output grating. The input coupler is configured to receive collimated light from a display source and to cause the light to travel within the waveguide via total internal reflection between the first surface and the second surface to the fold grating; the fold grating is configured to provide pupil expansion in a first direction and to direct the light to the output grating via total internal reflection between the first surface and the second surface; and the output grating is configured to provide pupil expansion in a second direction different than the first direction and to cause the light to exit the waveguide from the first surface or the second surface.