Two-Dimensional Pupil Expansion Waveguide for HUD Uniformity
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Solution Overview
Problem
Existing optical waveguides for head-up displays face challenges in providing uniform pupil expansion in two dimensions while maintaining suitable size and output brightness, leading to non-uniformities and reduced perceived brightness as the expansion ratio increases.
Innovation Solution
The optical waveguide design incorporates first and second input regions with optical gratings and beam splitters to expand the pupil in two dimensions, utilizing a compact configuration with two input locations and gratings to redirect light, ensuring uniformity and alignment with the user's eye, and an output grating to couple light out of the waveguide, allowing for increased luminance and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pupil expansion is performed in two dimensions using diffractive structures, then the exit pupil size is increased to accommodate eye position flexibility, but non-uniformities in luminance occur causing non-uniform output display and reduced perceived brightness as expansion ratio increases
Solution Approach 1:
The waveguide is divided into multiple discrete pupil regions (first, second, third, and fourth pupils) arranged in a two-dimensional array. Each pupil region is independently formed by specific combinations of beam splitters and diffractive structures, allowing separate control and optimization of luminance distribution across different spatial locations to achieve overall uniformity
Solution Approach 2:
Different regions of the waveguide are designed with locally optimized optical paths and beam splitter configurations. The first and second input regions have different optical path arrangements compared to the third and fourth input regions, allowing each local area to be optimized for its specific position in the expanded pupil array, thereby achieving uniform luminance across the entire two-dimensional expansion
2Area of stationary object
If the waveguide size is reduced to maintain compactness, then the device size is suitable for practical applications, but the ability to provide uniform two-dimensional pupil expansion is compromised
Solution Approach 1:
The patent transitions from traditional one-dimensional pupil expansion to two-dimensional pupil expansion by arranging multiple pupil regions in a grid pattern. This dimensional expansion allows the system to provide larger effective pupil size in both horizontal and vertical directions while maintaining a compact waveguide footprint through efficient spatial packing of the pupil regions
Solution Approach 2:
Multiple beam splitters and diffractive structures are nested within the compact waveguide volume. The beam splitters are positioned at different locations and orientations to create overlapping optical paths that form the two-dimensional pupil array, effectively nesting complex optical functionality within a small form factor
3Adaptability or versatility
If expansion ratio is increased to provide larger exit pupil, then eye position flexibility is improved, but luminance for each pupil decreases reducing perceived brightness
Solution Approach 1:
Multiple input regions (first, second, third, and fourth input regions) are combined to feed the expanded two-dimensional pupil array. The optical paths from these multiple inputs are merged through the beam splitter network to distribute light uniformly across all pupil regions, increasing the total light available to maintain brightness even as the pupil expansion ratio increases
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 design achieves pupil expansion in two dimensions with improved uniformity and brightness, accommodating various eye positions and enhancing the reliability and flexibility of the head-up display system.
Implementation Method 1
Input grating 13 may be a diffractive grating which diffracts ray 14 to an angle at which it is trapped within the waveguide 10 by total internal reflection
Implementation Method 2
trapped within the waveguide 10 by total internal reflection
Implementation Method 3
first and second beam splitters configured to expand the pupil of light propagating in the optical waveguide and received through the first and second input regions respectively
Data Source
AI summary
An optical waveguide for a head-up display having two optical input regions. Optical gratings direct light injected into the optical input regions toward an output region; the directed light is substantially trapped in the optical waveguide by total internal reflection. Beam splitters and other optical elements can be provided to expand the pupil in two dimensions. Light from each input region is directed to different areas of the output region.