The MIT Camera Culture group present a new approach to time-of-flight imaging that increases its depth resolution 1,000-fold. That’s the type of resolution that could make self-driving cars practical.
The new approach could also enable accurate distance measurements through fog, which has proven to be a major obstacle to the development of self-driving cars.
At a range of 2 meters, existing time-of-flight systems have a depth resolution of about a centimeter. That’s good enough for the assisted-parking and collision-detection systems on today’s cars.
But as Achuta Kadambi, a joint PhD student in electrical engineering and computer science and media arts and sciences and first author on the paper, explains, “As you increase the range, your resolution goes down exponentially. Let’s say you have a long-range scenario, and you want your car to detect an object further away so it can make a fast update decision. You may have started at 1 centimeter, but now you’re back down to [a resolution of] a foot or even 5 feet. And if you make a mistake, it could lead to loss of life.”
At distances of 2 meters, the MIT researchers’ system, by contrast, has a depth resolution of 3 micrometers. Kadambi also conducted tests in which he sent a light signal through 500 meters of optical fiber with regularly spaced filters along its length, to simulate the power falloff incurred over longer distances, before feeding it to his system. Those tests suggest that at a range of 500 meters, the MIT system should still achieve a depth resolution of only a centimeter.
Many ranging systems work by amplitude modulating the power of an integrated laser at MegaHertz (MHz) frequencies and demodulating it using a specialized imaging sensor to obtain sub-cm range precision. To extend a similar architecture to micron range precision, this paper incorporates beat notes. We study a form of cascaded light ranging which uses a Hertz-scale intermediate frequency to encode high-frequency pathlength information. We show synthetically and experimentally that a bulk implementation of opto-electronic mixers offers: (a) robustness to environmental vibrations; (b) programmability; and (c) stability in frequency tones. A fiberoptic prototype is constructed, which demonstrates 3 micron range precision over a range of 2 meters. We study and evaluate the cascaded architecture for use in machine vision, where vibrations and sampling rate are constraints.
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