The pill-sized cameras in today’s mobile phones may seem miraculously tiny, given that a decade ago the smallest cameras available for retail sale were the size of a pack of cards. Ali Hajimiri of the California Institute of Technology will make far smaller cameras. His team plan to replace them with truly minuscule devices that spurn every aspect of current photographic technology. Not only do Dr Hajimiri’s cameras have no moving parts, they also lack lenses and mirrors—in other words, they have no conventional optics. That does away with the focal depth required by today’s cameras, enabling the new devices to be flat.
Caltech engineers developed the new camera design that replaces the lenses with an ultra-thin optical phased array (OPA). The OPA does computationally what lenses do using large pieces of glass: it manipulates incoming light to capture an image.
The new system can selectively look in a desired direction and at a very small part of the picture in front of you at any given time, by controlling the timing with femto-second—quadrillionth of a second—precision.
Last year, Hajimiri’s team rolled out a one-dimensional version of the camera that was capable of detecting images in a line, such that it acted like a lensless barcode reader but with no mechanically moving parts. This year’s advance was to build the first two-dimensional array capable of creating a full image. This first 2D lensless camera has an array composed of just 64 light receivers in an 8 by 8 grid. The resulting image has low resolution. But this system represents a proof of concept for a fundamental rethinking of camera technology, Hajimiri and his colleague.
The processed optical signal will be passed down the waveguide to further photodiodes. These convert it into an electrical signal, which is used to create the final photo. Crucially, all this can be achieved in a stack of electronics five microns thick—about a fifteenth of the diameter of a human hair.
The exact size of any production version will depend on the job to be done. The prototype can manage fuzzy images of barcodes, but not much else. To achieve the same resolution as the camera in a modern Apple iPhone, Dr Hajimiri reckons an array of about 1 million grating couplers will be needed. Allowing for the space between these, the result would, at the moment, have an area of square centimeter. This is similar to the area of an iPhone’s camera, but that camera is 1,000 times thicker. Dr Hajimiri thinks, moreover, that a production version of the new device would be smaller.
Tiny cameras might be deployed, Fantastic Voyage-like, to take pictures inside blood vessels. They could be combined into massive arrays to create lightweight but extremely large-aperture telescopes able to resolve images from the deepest parts of the universe. They might even be strewn to the winds, photographic dust particles scavenging the energy they need from stray radio signals, and broadcasting what they see.
This paper presents an 8×8 optical phased array (OPA) receiver that operates as a lens-less camera using a heterodyne architecture on a thin silicon-photonics integrated SOI substrate. It has a receiving beam width of 0.75° and beam steering range of 8°.