Looking Around Corners With SPAD

Researchers  from Heriot-Watt University in Edinburgh published an article about a clever technique to see around corners analyzing reflected light. Pretty cool!

I’m no expert in photonics, so I’ll quote Prachi Patel from IEEE Computer who explains,

To detect an object around a blind corner, the system fires millions of very short laser pulses at the floor just past the corner. The light hits the floor and scatters in every direction as a spherical light wave. When the photons bounce off the object, they again scatter and some of them reach the field-of-view of the camera, which is also pointed at the spot where the laser was aimed. The system then calculates the object’s position with centimeter precision by looking at two things: how long it takes for light to go from the laser to the object and back, and at the shape and direction of the returning spherical wave.

It seems so obvious, when you say it this way!

This technique uses a single-photon avalanche diode (SPAD) camera, which I don’t know anything about. As with many advances these days, it is possible only with the aid of lots of computing power packed into a small space, combined with absurdly sensitive sensors. This combination lets us apply “simple” ideas all the way down to a single photon.

If you let me fiddle around with individual photons, I can perform black magic!

For details, ask your library to help you get the paper and associated materials.


  1. Genevieve Gariepy, Francesco Tonolini, Robert Henderson, Jonathan Leach, and Daniele Faccio, Detection and tracking of moving objects hidden from view. Nat Photon, advance online publication 12/07/online 2015. http://dx.doi.org/10.1038/nphoton.2015.234

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