This illustration (not to scale) simulates the process
by which an incoming complex wave can be
identified and transmitted to a photodetector.
(Image courtesy of Patrice Genevet.)

Counting the twists in a helical light beam

by Staff Writers
Boston MA (SPX) Jan 10, 2013

At a time when communication networks are scrambling for ways to transmit more data over limited bandwidth, a type of twisted light wave is gaining new attention. Called an optical vortex or vortex beam, this complex beam resembles a corkscrew, with waves that rotate as they travel. Now, applied physicists at the Harvard School of Engineering and Applied Sciences (SEAS) have created a new device that enables a conventional optical detector (which would normally only measure the light’s intensity) to pick up on that rotation.

The device, described in the journal Nature Communications, has the potential to add capacity to future optical communication networks.

“Sophisticated optical detectors for vortex beams have been developed before, but they have always been complex, expensive, and bulky,” says principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS.

In contrast, the new device simply adds a metallic pattern to the window of a commercially available, low-cost photodetector. Each pattern is designed to couple with a particular type of incoming vortex beam by matching its orbital angular momentum-the number of twists per wavelength in an optical vortex.

Read more: Counting the twists in a helical light beam — Space Daily.

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