(Photonics.com) Researchers from the University of Padova have developed an all-fiber device to generate the quantum states necessary for quantum key distribution (QKD), a method of protecting data that uses properties of light, such as polarization, to encode data and send a random key needed to decrypt the encoded data. The fiber device can switch the polarization of light more than 1 billion times per second. It is insensitive to temperature and other environmental changes.
The Padova team’s new polarization encoder, called POGNAC for POlarization SaGNAC, can rapidly rotate the polarization of incoming laser light thanks to a fiber-loop Sagnac interferometer. This setup splits the light into two beams whose polarizations are at right angles relative to each other. The beams then travel through the fiber-loop in clockwise and counterclockwise directions.
The POGNAC could help simplify QKD for free-space communication, such as from satellites to Earth or between moving terminals. “Our goal is to develop a quantum encryption scheme to use between a satellite and the ground, where the keys are generated in orbit,” Vallone said.

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