The National Institute of Information and Communications Technology (NICT) is researching potential encryption methods for quantum communication that could be integrated into fiber optic networks. The research focuses on how to achieve secure communication using continuously variable quantum key distribution (QKD), which is the ongoing exchange of quantum keys for encrypting data that is being transferred between two or more parties.

The research team, which includes visiting researcher Tobias Eriksson, says that the primary stumbling block to achieving a QKD application over fiber optics is noise generated by fiber amplifiers on current generation single-mode fiber systems. It is investigating how to exploit multicore fiber optic technology, which it expects will be the primary technology used in future transmission networks.

The researchers measured the excess noise from crosstalk between the classical and the quantum channels using 19-core fiber. They found that this approach has the potential to support 341 QKD channels, with 5-GHz spacing between wavelengths of 1537 nm and 1563 nm.

“The question we asked ourselves is whether the spatial dimensions of multicore fibers can be exploited for co-propagation of classical and quantum signals,” Eriksson said. “What we found is that the classical channels can be transmitted completely oblivious of the quantum signals, which in single-mode fiber is not possible since the amplifier noise kills the quantum channels.”

The team’s technical results are outlined in a paper to be presented March 7 at the OFC: The Optical Fiber Communications Conference and Exhibition, March 3-7, in San Diego (https://doi.org/10.1364/OFC.2019.Th1J.1).