Traditional cameras — even those on the thinnest cellphones — cannot be truly flat due to their optics. The lenses require a certain shape and size in order to function. A new camera design replaces the lenses with an ultra-thin optical phased array (OPA) that does, computationally, what lenses do using large pieces of glass, manipulating incoming light to capture an image.
Lenses have a curve that bends the path of incoming light and focuses it onto a piece of film or, in the case of digital cameras, an image sensor. The OPA has a large 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 the new system, a user can selectively look in a desired direction and at a very small part of the picture in front of them at any given time by controlling the timing with femtosecond precision. A single thin layer of integrated silicon photonics 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 fisheye to a telephoto lens instantaneously with a simple adjustment in the way the array receives light.
Phased arrays, which are used in wireless communication and radar, are collections of individual transmitters, all sending out the same signal as waves. These waves interfere with each other constructively and destructively, amplifying the signal in one direction while canceling it out elsewhere. Thus, an array can create a tightly focused beam of signal, which can be steered in different directions by staggering the timing of transmissions made at various points across the array. A similar principle is used in reverse in an OPA receiver, which is the basis for the new camera. 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 “gaze” that can be electronically controlled. Images can be formed at fast speed by manipulating the light instead of moving a mechanical object.
The 2D lens-less camera has an array composed of 64 light receivers in an 8 × 8 grid. The resulting image has low resolution, but the system represents a proof of concept for future camera technology. Once scaled up, the technology can make lenses and thick cameras obsolete, and may have implications for astronomy by enabling ultralight, ultra-thin, large, 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 could lead to imagers that look like wallpaper, blinds, or wearable fabric.