No matter how small today’s cameras may seem, the analog nature of lenses, which need to be of a certain size and shape to function properly, puts a limit on the extent to which they can miniaturised even further.
Unless, that is, lenses were to be replaced by an altogether different system that would allow cameras to be made almost entirely flat – and that’s exactly what researchers at Caltech had proposed in a paper published online in the OSA Technical Digest.
The new camera design does away with lenses and relies instead on an ultra-thin optical phased array (OPA), which contains a number of light receivers capable of adding a tightly controlled time delay to the incoming light – a feat that allows the camera to selectively look in different directions and focus on different objects.
“Here, like most other things in life, timing is everything. 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,” said principal investigator Ali Hajimiri, Bren Professor of Electrical Engineering at Caltech.
Just like phased arrays, used in wireless communication and radar, and comprised of individual transmitters which send the same signal as waves that interfere with each other depending on the timing of transmissions, thereby amplifying the signal in one direction but not in others, OPA employs the same process – only in reverse.
Light waves received by each element across the array cancel each other out in all directions, except one – allowing the camera to focus its “gaze” on a specific object or scene.
“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,” said study lead author Reza Fatemi.
While the camera, such as it is at the moment, is only a proof of concept and can only produce low-resolution 2D images, it could become immensely useful once improved and scaled-up, potentially even leading to ultra-light, ultra-thin 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,” concluded Hajimiri.
The next step will be to build larger receivers with higher resolution and sensitivity.
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