High-tech material used to create a thin, flat fisheye lens
Ultra wide-angle fisheye lenses are typically thick, bulbous contraptions, that can't easily be incorporated into devices such as smartphones. That could be about to change, though, as engineers have now created one that's completely flat.
Designed via a collaboration between MIT and the University of Massachusetts at Lowell, the prototype device is what's known as a metalens. This means that it's made of an engineered material – a metamaterial – which exhibits properties not found in naturally occurring materials.
The lens consists of a single millimeter-thick piece of calcium fluoride glass, the back of which is coated with a thin film of lead telluride. Carved into that film is a pattern of nanoscale optical structures called meta-atoms. These are made in several different shapes, each one of which refracts light in a specific fashion.
When light passes through an aperture (such as the iris of a camera) and onto the lens, it goes through the glass and into the lead telluride film, where it's dispersed through the meta-atoms at a variety of angles. What results is a single crisp, clear image of the subject, with a 180-degree field of view.
The current version of the lens only works with infrared light, although the researchers state that by making the nanostructures smaller and using different materials, it could be adapted for use with visible light. Possible applications could then include not only camera lenses, but also lenses for items such as endoscopes, video projectors and virtual reality glasses.
"This design comes as somewhat of a surprise, because some have thought it would be impossible to make a metalens with an ultra-wide-field view," says MIT's Assoc. Prof. Juejun Hu. "The fact that this can actually realize fisheye images is completely outside expectation."
The research is described in a paper that was recently published in the journal Nano Letters.