Grating coupler arrays as cameras


in Photography, Politics, Rants, Science, Security

A recent Economist article describes a novel camera design with the promise to be far thinner than those that exist now, with some novel features:

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.

To mimic the image-making role of the optics in conventional cameras, the OPA manipulates incoming light using electrons. Dr Hajimiri compares the technique to peering through a straw while moving the far end swiftly across what is in front of you and recording how much light is in each strawful. In the OPA this scanning effect is created by manipulating the light collected by the grating couplers electronically, using devices called photodiodes. These place varying densities of electrons into the amplified light’s path through the OPA, either slowing it down or speeding it up as it travels. That shifts the arrival times of the peaks and troughs of the lightwaves. This “phase shifting” results in constructive interference between waves arriving from the desired direction, which amplifies them. Light coming from other directions, by contrast, is cancelled through destructive interference. Change the pattern of electrons and you change the part of the image field the OPA is looking at. Scanning the entire field in this way takes about ten nanoseconds (billionths of a second).

To zoom in for a close-up, the device selects a specific part of the image and scans it more thoroughly. To zoom out for a fish-eye, it scans the entire optical field, including light from the edges of that field. To change from zoom to fish-eye takes nanoseconds.

Doubtless, such cameras will have some interesting applications. Unfortunately, that will certainly include further entrenching the surveillance state — increasingly using devices too small to see.

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