Scientists at Harvard University on Monday unveiled a metalens that has the potential to shrink the size of any device that uses a camera while at the same time improving performance.
While traditional lenses are made from glass, metalenses use a flat surface peppered with nanostructures to focus light. One problem with metalenses has been their inability to focus the full spectrum of light.
That’s not the case any more, however, as a team at Harvard’s Paulson School of Engineering and Applied Science have developed a metalens that can focus the entire visible spectrum of light — including white light — at a focal point, with high resolution.
Rx for Thinner Phones
An advantage a metalens has over conventional lens systems is that multiple elements aren’t needed to correct for aberrations. Those multiple elements make lenses thick, and thick lenses mean thicker devices.
“Our lens is a flat lens, so it’s thinner than a conventional lens,” explained Federico Capasso, a professor of applied physics at Harvard and author of the research paper on the new metalens published Monday in Nature Nanotechnology.
“If this lens were used in a cellphone, the cellphone could be much thinner,” he told TechNewsWorld.
Two components of a cellphone continue to challenge designers driven to make the devices thinner: the battery and the camera.
“The lens is responsible for the bump on the back of the cell phone that the cell phone companies hate,” Capasso said. “Right now, a cellphone has six or seven regular lenses. Even if we can cut it down to three, it’ll be extremely significant.
Impact on VR, AR
By correcting chromatic aberration, the metalens developed by the Harvard researchers addresses an annoying problem facing virtual reality and augmented reality hardware developers.
“Chromatic Aberration — color focal point mismatch resulting from the propagation speed of different frequencies of light — is one of many visual artifacts causing lack of visual fidelity and realism in augmented and virtual reality,” explained Sam Rosen, a vice president at ABI Research.
To correct those artifacts, high-end VR or AR hardware will often use advanced computational techniques to adjust focal points on a color-by-color basis.
“That process is compute-intensive and must be tuned for every model of device,” Rosen told TechNewsWorld.
“An improved passive lens which solves this problem could make for better devices by resolving the problem in the underlying physical hardware, making systems simpler and easier to program,” he added.
To address the propagation problem found in both conventional and other metalenses, the scientists cooked up a clever fix.
“By combining two nanofins into one element, we can tune the speed of light in the nanostructured material to ensure that all wavelengths in the visible are focused in the same spot, using a single metalens,” explained Wei Ting Chen, a postdoctoral fellow at Harvard and member of the metalens team.
Another benefit of using an achromatic metalens in a camera is that it makes the production of the camera subsystem easier to produce.
Now, the subsystem is made up of a sensor, which is a piece of fabricated silicon, and a stack of lenses, which are produced by lens molding, a process dating back to the 19th century.
“With a metalens, we can have the same foundry that makes the sensor chip make the metalenses for the camera module,” Capasso said. “That’s why so many companies are excited about this. There is a chance to disrupt the business model anywhere cameras are used.”
The use of cameras with metalenses is still some time away, Capasso acknowledged.
“I’m not going to tell you that you’re going to see a cellphone with metalenses two years from now,” he said. “That would be ludicrous. This is in the research stages, but it’s still a big step forward.”