A thin lens has a constant focal length. One day, the new lens could make visual fatigue a thing of the past.
The research team leader said that many of the 3D displays used in today's augmented and virtual reality devices are uncomfortable after long-term use. This problem can be alleviated with the use of our lens, known as anlvarez lens. It could provide a more comfortable and realistic 3D experience that would allow more widespread use of augmented and virtual reality headsets.
They describe their new lens in a paper. The liquid crystal elements can be moved in relation to each other to change the focal length. They put the new lens into an augmented reality display system that showed virtual images on a real-world view at different depths.
The thin formfactor of the lens is lightweight and can be made using a simple low-cost fabrication process. This type of compact tunable lens can be used for a lot of things.
The virtual experience could be improved.
The vergence-accommodation conflict occurs because the left and right eyes receive different images that the brain puts together to make a virtual 3D image. Each eye looks at the plane where the image is displayed. This causes the single eye focus at the 2D plane to be inconsistent, which leads to dizziness and visual fatigue.
A vari-focal display can change the depth of single-plane virtual objects so that they appear at different depths. A multi-focal display system renders multiple 2D cross-sections of a virtual object at multiple depths at the same time to reconstruct a 3D volume. The human eye can focus on the right depths of virtual objects.
A multi-focal display system needs a lens that can change focus continuously within a large range while also being small and lightweight. Li has been working on fatigue-free AR displays and liquid crystal devices for about 10 years and recently developed a way to fabricate a liquid crystal based diffractive optical component.
"Our method allows for the creation of an Alvarez lens with high precision, low cost and unprecedented convenience," said Li. We wanted to see if the ultracompact Alvarez tunable lens could offer a solution to the conflict problem in virtual reality and augmented reality displays.
A display demonstrating augmented reality.
The researchers used a new approach to create a lens. Each element has an ultrathin polymetric liquid crystal layer just a few hundred nanometers thick. The off-the-shelf optical elements on an optical table were used to build the augmented reality display system. They were able to continuously tune the depth of the virtual image by shifting the two elements of the Alvarez lens.
The virtual image exhibited the same in-and-out of focus effect as the real 3D objects in the real world. The human eye was able to focus on the depth of the virtual 3D image correctly because of this.
The researchers are trying to find a way to use the lens for a full-color display, even though it was designed for single-color operation. They would like to use an electronic method for controlling the displacement between the optical elements.
More information: Shuyi Chen et al, Planar Alvarez tunable lens based on polymetric liquid crystal Pancharatnam-Berry optical elements, Optics Express (2022). DOI: 10.1364/OE.468647 Journal information: Optics Express
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