Despite all the advances in consumer technology over the past decades, one component has remained frustratingly stagnant: the optical lens. Unlike electronic devices, which have gotten smaller and more efficient over the years, the design and underlying physics of today's optical lenses haven't changed much.
Researchers have developed the next generation of lenses that promises to replace bulky curved lenses with a simple, flat surface that uses nanostructures to focus light. The team created a two-millimeter achromatic metalens that can focus RGB (red, green, blue) colors without aberrations and developed a miniaturized display for virtual and augmented reality applications.
Like previous metalenses, this lens uses arrays of titanium dioxide nanofins to equally focus wavelengths of light and eliminate chromatic aberration. By engineering the shape and pattern of these nanoarrays, the researchers could control the focal length of RGB light. To incorporate the lens into a VR system, the team developed a near-eye display using a method called fiber scanning.
The display, inspired by fiber-scanning-based endoscopic bioimaging techniques, uses an optical fiber through a piezoelectric tube. When a voltage is applied onto the tube, the fiber tip scans left and right and up and down to display patterns, forming a miniaturized display. The display has high resolution, high brightness, high dynamic range, and wide color gamut.
In a VR or AR platform, the metalens would sit directly in front of the eye and the display would sit within the focal plane of the metalens. The patterns scanned by the display are focused onto the retina, where the virtual image forms with the help of the metalens. To the human eye, the image appears as part of the landscape in the AR mode, some distance from our actual eyes.
The team aims to scale up the lens even further, making it compatible with current large-scale fabrication techniques for mass production at a low cost.