Researchers at Caltech have developed an ultrathin camera sensor that doesn't need a lens to provide focus, opening up the possibility of dramatically thinner embedded designs.
The key to the sensor is an optical phased array (OPA) that computationally does what lenses do using shaped pieces of glass or plastic.
The OPA has an 8x8 array of light receivers, each of which can individually add a tightly controlled time delay (or phase shift) to the light it receives, enabling the camera to selectively look in different directions and focus on different things with large amounts of digital signal processing (DSP).
"Here, like most other things in life, timing is everything," said Ali Hajimiri, Bren Professor of Electrical Engineering and Medical Engineering in the Division of Engineering and Applied Science at Caltech, and the principal investigator. "With our new system, you 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,"
"We've created a single thin layer of integrated silicon photonics that emulates the lens and sensor of a digital camera, reducing the thickness and cost of digital cameras. It can mimic a regular lens, but can switch from a fish-eye to a telephoto lens instantaneously -- with just a simple adjustment in the way the array receives light," he said.
A similar principle to a phased array antenna is used in reverse in an optical phased array receiver. Light waves that are received by each element across the array cancel each other from all directions, except for one. In that direction, the waves amplify each other to create a focused image.
"What the camera does is similar to looking through a thin straw and scanning it across the field of view. We can form an image at an incredibly fast speed by manipulating the light instead of moving a mechanical object," says graduate student Reza Fatemi.
Last year, Hajimiri's team developed 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 first 2D lensless camera has an array composed of just 64 light receivers, limiting the resolution, but represents a proof of concept for a fundamental rethinking of camera technology says Hajimiri.
"The applications are endless," says graduate student Behrooz Abiri. "Even in today's smartphones, the camera is the component that limits how thin your phone can get. Once scaled up, this technology can make lenses and thick cameras obsolete. It may even have implications for astronomy by enabling ultra-light, ultra-thin enormous flat telescopes on the ground or in space."
"The ability to control all the optical properties of a camera electronically using a paper-thin layer of low-cost silicon photonics without any mechanical movement, lenses, or mirrors, opens a new world of imagers that could look like wallpaper, blinds, or even wearable fabric," said Hajimiri.
Naturally the team is now working on scaling up the camera by designing chips that enable much larger receivers with higher resolution and sensitivity.
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