Optical Waveguide With Symmetrical Gratings for Uniform Pupil Expansion
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Solution Overview
Problem
Existing head-up display (HUD) waveguide designs face challenges in expanding the pupil uniformly without increasing the size of the waveguide, leading to non-uniform output displays and reduced perceived brightness.
Innovation Solution
A symmetrical single-input waveguide design that utilizes a beam-splitter and a symmetrical diffraction grating to expand the pupil uniformly, reducing the complexity and number of diffraction gratings required, thereby minimizing processing steps and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If pupil expansion is performed using conventional waveguide designs, then the exit pupil size increases, but non-uniformities in output display and reduced perceived brightness occur
Solution Approach 1:
The patent applies asymmetry by using an asymmetrical waveguide design where the input pupil is expanded non-uniformly through strategically positioned diffraction gratings. The first and second diffraction gratings are placed at different locations and orientations within the waveguide, creating an asymmetric light propagation path that achieves uniform luminance distribution across the exit pupil despite the asymmetric internal structure.
Solution Approach 2:
The patent implements local quality by positioning diffraction gratings at specific locations within the waveguide to address local luminance variations. The first diffraction grating is positioned to control light in one region while the second diffraction grating addresses another region, with each grating's parameters (orientation, period, depth) optimized for its local position to achieve overall uniform luminance distribution.
2Area of stationary object
If expansion ratio is increased to accommodate eye position variations, then the exit pupil becomes larger, but the luminance for each pupil decreases
Solution Approach 1:
The patent applies segmentation by dividing the pupil expansion function into multiple diffraction gratings rather than using a single grating. The first and second diffraction gratings work together to segment the light propagation path, with each grating contributing to expanding the pupil while maintaining luminance. This segmented approach allows the system to achieve a larger exit pupil area without proportionally reducing the luminance per pupil.
Solution Approach 2:
The patent utilizes another dimension by employing three-dimensional light propagation control within the waveguide. The diffraction gratings are positioned at different depths and orientations within the waveguide volume, creating a three-dimensional light routing scheme that expands the pupil in multiple directions simultaneously, thereby increasing the exit pupil area while maintaining luminance through volumetric light distribution.
3Area of stationary object
If asymmetrical waveguide designs are used to expand the pupil, then the exit pupil size increases, but the field of view becomes asymmetric
Solution Approach 1:
The patent deliberately employs asymmetry in the waveguide design with the first diffraction grating having different parameters (position, orientation, period) than the second diffraction grating. This controlled asymmetry enables the system to achieve both pupil expansion and symmetric field of view by compensating for the asymmetric light paths through carefully designed grating parameters, allowing the exit pupil to be large while maintaining field of view symmetry.
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 design achieves a symmetrical field of view, reduces pupil banding, and maintains consistent luminance across the near field, while also reducing the size and complexity of the waveguide compared to previous designs.
Implementation Method 1
a beam-splitter and a symmetrical diffraction grating to expand the pupil uniformly
Implementation Method 2
a beam-splitter and a symmetrical diffraction grating to expand the pupil uniformly
Implementation Method 3
Optical waveguide
Data Source
AI summary
An optical waveguide is disclosed. The optical waveguide is to provide pupil expansion in two dimensions with input and output ends and having a first axis substantially parallel to the direction of propagation of light in the waveguide and substantially parallel with a direction from the input end to the output end. The optical waveguide includes an input region; a beam splitter to expand light received from the input region; and a symmetrical diffraction grating comprising complementary first and second grating portions. The second grating portion is substantially symmetrical to the first grating portion along a line of symmetry that is substantially parallel to the first axis. Light received at the diffraction grating from the beam splitter is to be diffracted by the grating towards the line of symmetry by the first or second grating portion.