Variable Focus AR Display Using Polarization-Sensitive LC Lens
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Solution Overview
Problem
Conventional near-eye display systems for augmented reality often suffer from focus mismatch between virtual and real-world images, leading to image blur and eye stress due to the constant virtual image plane distance from the user's eyes, which existing solutions attempt to address with multiple lenses but are sub-optimal in terms of weight and cost.
Innovation Solution
A near-eye optical display system incorporating a waveguide with a polarizing filter and an electrically-modulated tunable liquid crystal (LC) lens, where the LC lens imparts variable focus only to virtual images by being sensitive to TE-polarized light, while real-world TM-polarized light is not affected, eliminating the need for a compensating lens.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a tunable lens is added to provide variable focus for virtual images, then focus adaptability is improved, but device complexity and weight increase due to requiring multiple lenses including compensating lenses
Solution Approach 1:
The patent segments the optical system into two distinct polarization channels: TE-polarized light for virtual images and TM-polarized light for real-world images. This segmentation allows the tunable LC lens to selectively focus only virtual images while leaving real-world images unaffected, eliminating the need for compensating lenses and reducing overall system complexity.
Solution Approach 2:
The patent applies local quality by making the LC lens polarization-sensitive, giving it different optical properties for different polarization states. The lens provides variable focus power for TE-polarized virtual images while maintaining zero or minimal power for TM-polarized real-world images, enabling selective focus control without affecting the entire optical path.
2Adaptability or versatility
If conventional multiple lens solutions are used to address focus mismatch, then focus control is improved, but weight increases due to additional lens components
Solution Approach 1:
The patent extracts the focus control function from the general optical path and applies it selectively only to virtual images through polarization discrimination. By removing the need for compensating lenses that would otherwise be required to maintain real-world image quality, the system reduces weight while preserving focus control capability.
Solution Approach 2:
The patent changes the optical parameter of the LC lens dynamically by adjusting its focal power through electrical control of the liquid crystal material. This allows continuous variation of focus for virtual images without mechanical movement or additional optical components, reducing weight while maintaining focus adaptability.
3Manufacturing precision
If variable focus is applied to all light paths, then virtual image focus is improved, but real-world image quality deteriorates due to unwanted focusing effects
Solution Approach 1:
Instead of trying to prevent the LC lens from affecting real-world images, the patent inverts the approach by designing the system so that real-world images (TM-polarized) are intentionally excluded from the focusing action. The out-coupling element is configured to direct only TE-polarized virtual images to the LC lens, while TM-polarized real-world images pass through unaffected.
Solution Approach 2:
The patent introduces polarization state as an intermediary property that mediates between virtual images and real-world images. By assigning different polarization states to different image types and using a polarization-sensitive LC lens, the system enables selective focus control without cross-interference, maintaining reliability for both virtual and real-world imagery.
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
This solution provides variable focus for virtual images without affecting real-world images, reducing focus mismatch and eye stress, and is more lightweight and cost-effective compared to conventional multiple lens solutions.
Implementation Method 1
A polarizing filter is located on the other side of the waveguide so that light from the real world enters the system with a particular polarization state, for example, TM-polarized
Implementation Method 2
An electrically-modulated tunable liquid crystal (LC) lens is located between the waveguide and the eyes of the user. The tunable LC lens is configured to impart variable focus on light that has an opposite polarization state, for example TE-polarized
Implementation Method 3
An electrically-modulated tunable liquid crystal (LC) lens
Implementation Method 4
a waveguide having optical elements configured for in-coupling, exit pupil expansion, and out-coupling
Data Source
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AI summary
A near-eye optical display system that may be utilized in augmented reality applications and devices includes a diffractive waveguide having diffractive optical elements (DOEs) configured for in-coupling, exit pupil expansion, and out-coupling. An electrically-modulated tunable liquid crystal (LC) lens is located between the diffractive grating and the eyes of the user. A polarizing filter is located on the other side of the diffractive grating so that light from the real world enters the system with a particular polarization state, for example, TM-polarized. The tunable LC lens is configured to impart variable focus on light that has an opposite polarization state, for example TE-polarized. The optical display system is arranged to be polarization-sensitive so that virtual images from an imager are out-coupled from the diffractive waveguide with TE-polarization. The tunable LC lens may thus impart variable focus to the virtual images due to the lens' sensitivity to TE-polarization.