Optical Pupil Expander for Multi-Color Virtual Image Display
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Solution Overview
Problem
Existing optical expander devices fail to effectively display multi-color virtual images due to issues with total internal reflection, leading to missing colors at image corners, particularly red and blue, in the extended field of view.
Innovation Solution
The expander device employs a planar waveguide with diffractive elements to guide light through two separate routes, using distinct grating periods and orientations to ensure parallel propagation of light beams, thereby maintaining color fidelity across the expanded field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single route is used for light propagation in the waveguide plate, then the device structure is simple, but red or blue light at corner regions fails to fulfill total internal reflection criterion, causing color loss
Solution Approach 1:
The optical propagation route is segmented into two separate routes: a first route for red light and a second route for blue light. Each route has distinct diffractive optical elements with specific grating periods and orientations optimized for its wavelength, allowing both colors to fulfill total internal reflection criteria simultaneously in the waveguide plate.
2Area of moving object
If the field of view is expanded, then the viewing angle is increased, but corner regions exhibit color loss due to failed total internal reflection
Solution Approach 1:
Different diffractive optical elements are assigned different local qualities: the first diffractive optical element has a first grating period optimized for red light, while the second has a second grating period optimized for blue light. This local optimization ensures that each color maintains proper total internal reflection at its designated route, preserving color fidelity across the expanded field of view.
3Reliability
If diffractive elements with different grating periods are used for different colors, then color fidelity is maintained, but the device complexity increases
Solution Approach 1:
Both the first and second diffractive optical elements are integrated into a single waveguide plate structure. The plate serves as a common medium for both routes, combining multiple functional elements into one unified component. This merging approach maintains color fidelity through wavelength-specific grating periods while avoiding the complexity of separate discrete components.
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 ensures that all colors, including red and blue, are properly propagated and displayed across the expanded field of view, enhancing the quality and completeness of multi-color virtual images.
Implementation Method 1
The in-coupling element DOE01 forms first guided light B1 by diffracting input light B1
Implementation Method 2
red or blue light corresponding to a corner point of the virtual image VIMG1 does not fulfill the criterion of total internal reflection when propagating in the waveguide plate SUB01
Implementation Method 3
The expander element DOE02 forms expanded guided light B3 by diffracting the first guided light B1
Implementation Method 4
The out-coupling element DOE03 forms output light OUT1 by diffracting the expanded guided light B3
Data Source
Figure 1~2a
Figure 2b~2d
Figure 2e~2g
AI summary
An optical expander device comprises a waveguide plate, which in turn comprises: an in-coupling element to form first guided light and second guided light by diffracting input light, first expander element to form third guided light by diffracting the first guided light, second expander element to form fourth guided light by diffracting the second guided light, and an out-coupling element to form first output light by diffracting the third guided light, and to form second output light by diffracting the fourth guided light, wherein the out-coupling element is arranged to form combined output light by combining the first output light with the second output light, wherein the in-coupling element has a first grating period for forming the first guided light, and wherein the in-coupling element has a second different grating period for forming the second guided light.