Twisted light on a silicon chip

(In honor of Terry Pratchett, I almost wrote that “Twisted light? Onna chip?”, but that would probably confuse 90% of my readers.)

Light is used to carry data, but mostly we don’t use the properties of the photons themselves to convey information. Quantum communication, among other applications, could use the state of the photon to encode data. In particular, the orbital angular momentum (OAM) state of a photon, where the photon describes a helix as it travels, can carry a lot of bits. Now researchers have fabricated a silicon chip to make twisted light.

Photons possess a number of quantum properties that can be used to encode information. You can think of photon polarization as like the rotation of a planet on its axis. In this view, the helical shape of the light wave—known as its orbital angular momentum (OAM)—is akin to the planet’s orbit around the Sun. These properties are independent of each other, and of the wavelength of light, so they can be manipulated separately. Whereas polarization occurs as a combination of two possible orientations, the OAM theoretically can have infinite values, though in practice far fewer states are available. Nevertheless, exploiting OAM greatly expands the potentially exploitable quantum states of photons we could put to use.

The researchers created helical OAM states using a ring-shaped chamber fabricated from silicon and mounted on a chip. [Read more….]

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