Stepped Lightguide Structure for AR Display Brightness Uniformity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional augmented reality optical devices are bulky and heavy due to their monolithic eyepiece and beam-splitter design, and they suffer from brightness non-uniformity and the need for expensive coatings with specific reflectance and transmittance properties.
Innovation Solution
A lightguide structure with a stepped configuration, comprising a first part, a second part, and an intermediate part, where the second part has a top surface with inclined portions and a compensating part for improved light propagation and polarization sensitivity, allowing for compact and efficient virtual image display against a background image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monolithic eyepiece and beam-splitter structure is used, then the optical device can display virtual images combined with background images, but the device becomes bulky and heavy
Solution Approach 1:
The patent divides the lightguide into multiple separate sections: a first lightguide for delivering virtual image light, a second lightguide for delivering background image light, and a beam combiner for merging them. This segmentation allows each component to be optimized independently and reduces the overall device weight compared to a monolithic structure.
2Ease of manufacture
If prism microstructures with flat surfaces are used for light extraction, then light can be extracted from the lightguide, but brightness non-uniformity occurs
Solution Approach 1:
The patent applies different surface characteristics to different regions of the lightguide. The first lightguide has a first surface with specific microstructures for virtual image extraction, while the second lightguide has a second surface with different microstructures for background image extraction. This local differentiation ensures uniform brightness distribution for each image type.
3Reliability
If expensive coatings with predefined reflectance and transmittance properties are used, then light can be controlled inside the substrate, but the device cost increases
Solution Approach 1:
The patent utilizes the natural total internal reflection property of the lightguide-substrate interface to control light propagation, eliminating the need for expensive reflective coatings. The lightguide structure itself serves the function of light control through its geometric design and refractive index differences.
4Volume of moving object
If a compact lightguide design is used, then device size is reduced, but brightness uniformity deteriorates
Solution Approach 1:
The patent transitions from a single-plane light extraction approach to a three-dimensional stepped structure with multiple extraction surfaces at different heights and angles. This dimensional expansion allows compact packaging while maintaining uniform brightness distribution through multiple extraction paths.
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 lightguide structure enhances compactness, reduces the need for expensive coatings, and improves brightness uniformity by using mirror coatings sensitive to polarization, enabling effective display of virtual objects against real-world backgrounds.
Implementation Method 1
the first part is configured to receive light rays emitted by an external display and, due to total internal reflection, provide the propagation of the light rays though the intermediate part to the second part
Implementation Method 2
the stepped structure is configured to output outwards the light rays which are reflected from the inclined portions of the top surface
Data Source
Figure 1~3
Figure 4~7
Figure 8~10a
AI summary
It is provided that a lightguide structure comprising: a first portion disposed to receive light rays emitted by an external display, a second portion disposed to provide, to a second surface facing a viewer, the light rays from the first portion and ambient light, wherein the second portion has a plurality of first surfaces for reflecting light rays and at least one second surface which the light rays and the ambient light perpendicularly enter into and pass through, an intermediate portion disposed to connect between the first portion and the second portion and reflect the light rays from the first portion for transferring the light rays to the second portion.