Waveguide Display Structure with Two-Stage Pupil Expansion
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Solution Overview
Problem
Conventional waveguide-based displays using laser light sources suffer from brightness non-uniformities and image quality disturbances due to uneven light distribution and interference from replicated beams, which are exacerbated by the high temporal coherence of laser light sources.
Innovation Solution
A display structure comprising a waveguide with an in-coupling structure, diffractive primary and secondary exit pupil expansion structures, and an out-coupling structure to evenly distribute light and minimize interference by guiding beams through distinct light guiding directions, utilizing diffractive optical elements to manage k-vectors in k-space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional exit-pupil-expansion methods using pupil replication are used, then the size of output images is increased, but brightness non-uniformities occur due to uneven light distribution
Solution Approach 1:
The exit pupil expansion is divided into multiple stages: a first exit pupil expansion structure creates intermediate images, and a second exit pupil expansion structure further expands these to form final output images. This multi-stage segmentation allows for more controlled and uniform light distribution across the expanded output area, resolving the brightness non-uniformity problem while achieving large output image size.
2Area of stationary object
If pupil replication is used with laser light sources, then output image size is increased, but image quality deteriorates due to interference from replicated beams
Solution Approach 1:
The patent divides the pupil replication process into two separate structures: a first exit pupil expansion structure that creates intermediate images with controlled interference, and a second exit pupil expansion structure that further expands these intermediate images. By segmenting the expansion process and using laser light sources with appropriate coherence management, the patent achieves large output image size while minimizing interference-related image quality deterioration.
3Device complexity
If a single exit pupil expansion structure is used, then device complexity is reduced, but light distribution becomes uneven causing brightness non-uniformities
Solution Approach 1:
The patent employs a segmented approach with a first exit pupil expansion structure followed by a second exit pupil expansion structure. This segmentation allows each structure to perform a specific function in the light distribution process, achieving uniform brightness across the output image while maintaining manageable device complexity through functional division.
Solution Approach 2:
The patent extends the exit pupil expansion from a single-dimensional approach to a multi-dimensional process by using sequential expansion structures. The first structure expands in one dimensional aspect, and the second structure further expands in the same or complementary dimension, achieving comprehensive and uniform light distribution across the two-dimensional output image area.
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 effectively reduces brightness non-uniformities and image quality disturbances by evenly coupling light out of the waveguide, enhancing image quality and reducing optical losses.
Implementation Method 1
a waveguide; an in-coupling structure configured to couple a set of input beams into the waveguide
Implementation Method 2
a diffractive primary exit pupil expansion structure configured to receive the set of in-coupled beams and to diffract the set of in-coupled beams to form a first set of guided beams and a second set of guided beams
Implementation Method 3
a diffractive secondary exit pupil expansion structure configured to receive from the primary exit pupil expansion structure a set of transition beams and to diffract the set of transition beams to form a first secondary set of guided beams and a second secondary set of guided beams
Implementation Method 4
an out-coupling structure arranged towards the second light guiding direction and configured to couple light out of the waveguide
Data Source
AI summary
A display structure (1000), a display device, and a vehicle are disclosed. The display structure (1000) comprises a waveguide (1100), an in-coupling structure (1200), a diffractive primary exit pupil expansion structure (1300), a diffractive secondary exit pupil expansion structure (1400) configured to receive from the primary exit pupil expansion structure (1300) a set of transition beams (1040), and an out-coupling structure (1600) arranged towards a second light guiding direction (1002) from the primary exit pupil expansion structure (1300) and from the secondary exit pupil expansion structure (1400).