Optical Expander Device for Uniform Color Distribution
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Solution Overview
Problem
Existing optical diffractive beam expanders for virtual display devices face challenges in maintaining uniform color distribution and preventing leakage of red and blue light at corner points of multi-color images, leading to incomplete images and non-uniform brightness due to failure in total internal reflection and diffraction equations.
Innovation Solution
The proposed optical device includes a waveguide plate with in-coupling and out-coupling elements and spectral filter regions optimized for red and blue light, using different grating periods and orientations to confine and direct light paths, and Bragg grating regions to enhance absorption and prevent ghost images, ensuring complete image display with uniform brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single diffractive beam expander is used to expand the viewing pupil, then the eye box is enlarged and virtual image display is enabled, but red or blue light at corner points fails to fulfill total internal reflection criteria, causing color deficiency in corner regions
Solution Approach 1:
The waveguide plate is divided into multiple functional regions: a first diffractive beam expander for expanding the viewing pupil, and a second diffractive beam expander specifically for red or blue light paths. This segmentation allows each region to be optimized for its specific function, enabling the overall system to achieve both large eye box and complete color display at corner points.
Solution Approach 2:
A spectral filter is introduced as an intermediary element between the light source and the diffractive beam expanders. This spectral filter selectively transmits red or blue light to the second diffractive beam expander while blocking other wavelengths, enabling precise control over which colors are expanded by which expander and preventing color mixing that would cause corner point color deficiency.
2Length of stationary object
If the diffractive expander element expands light in two transverse directions, then the output beam width is increased, but red or blue light leakage occurs at corner points due to failure in total internal reflection
Solution Approach 1:
The light expansion function is segmented between two separate diffractive beam expanders: the first expander handles general beam expansion in two transverse directions, while the second expander specifically handles red or blue light paths. This segmentation prevents the harmful effect of light leakage at corner points while maintaining the desired wide output beam width.
Solution Approach 2:
Different regions of the waveguide plate are assigned different optical properties: the first diffractive beam expander region is optimized for general beam expansion, while the second diffractive beam expander region is specifically optimized for red or blue light confinement. This local differentiation ensures that each region performs its specific function effectively, preventing light leakage at corner points.
3Reliability
If spectral filter regions are added to prevent red and blue light coupling to wrong expander elements, then color accuracy is improved, but device complexity increases
Solution Approach 1:
The spectral filter is merged with the waveguide plate structure, forming an integrated component rather than a separate element. This merging approach maintains color accuracy by preventing red and blue light from coupling to wrong expander elements, while avoiding the complexity increase that would result from adding a separate, standalone spectral filter component.
Solution Approach 2:
The waveguide plate is designed to serve multiple functions simultaneously: it acts as the substrate for the diffractive beam expanders, contains the spectral filter regions for color separation, and provides the optical path for light propagation. This multi-functionality reduces the need for additional separate components, thereby improving color accuracy without proportionally increasing device complexity.
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 displays a wide multi-color image with extended field of view by confining and combining red and blue light paths, preventing leakage and ensuring uniform brightness and color distribution across the image.
Implementation Method 1
an in-coupling element (DOE1) to form first guided light (B1a) and second guided light (B1b) by diffracting input light (IN1)... wherein the in-coupling element (DOE1) has a first grating period (d1a) for forming he first guided light (B1a), and wherein the in-coupling element (DOE1) has a second different grating period (d1b) for forming the second guided light (B1b)
Implementation Method 2
a first expander element (DOE2a) to form third guided light (B2a) by diffracting the first guided light (B1a)
Implementation Method 3
a second expander element (DOE2b) to form fourth guided light (B2b) by diffracting the second guided light (B1b)
Implementation Method 4
an out-coupling element (DOE3) to form first output light (OB3a) by diffracting the third guided light (B2a), and to form second output light (OB3b) by diffracting the fourth guided light (B2b)
Implementation Method 5
wherein the optical device (EPE1) comprises a first spectral filter region (C2a) to prevent coupling of red light from the in-coupling element (DOE1) to the out-coupling element (DOE3) via the first expander element (DOE2a), wherein the optical device (EPE1) comprises a second spectral filter region (C2b) to prevent coupling of blue light from the in-coupling element (DOE1) to the out-coupling element (DOE3) via the second expander element (DOE2b)
Implementation Method 6
wherein the optical device (EPE1) comprises a first Bragg grating region (BRGa), which at least partly overlaps the first spectral filter region (C2a) so as to enhance absorption of red light in the first spectral filter region (C2a), wherein the optical device (EPE1) comprises a second Bragg grating region (BRGb), which at least partly overlaps the second spectral filter region (C2b) so as to enhance absorption of blue light in the second spectral filter region (C2b)
Implementation Method 7
The expander device may expand a light beam in two transverse directions... An attempt to use the expander device EPE0 of FIG. 1 for displaying a multi-color virtual image VIMG1 may cause a situation where 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
Data Source
AI summary
A diffractive beam expander device (EPE1) includes a first spectral filter region (C2a) and a second spectral filter region (C2b) to provide a first optical route for blue and green light (B, G), and to provide a second optical router for red light (R). The expander device (EPE1) includes a first Bragg grating region (BRGa) to enhance optical absorption of red light (R) in the first spectral filter region (C2a). The expander device (EPE1) includes a second Bragg grating region (BRGb) to enhance optical absorption of blue light (B) in the second spectral filter region (C2b).