Quantum key distribution experiment through a PLC matrix switch

Quantum key distribution (QKD) is being studied as a way to provide unconditionally secure communications. Several experiments have shown its feasibility. However, most experiments have used a point-to-point occupied optical link. In order to use QKD for secure communications on a real network, it is preferable to be able to change parties on demand and to have quantum transmission and ordinary optical transmission share the optical network. In this work, QKD through a silica-based planar lightwave circuit (PLC) 8 × 8 non-blocking matrix switch was investigated. We found that an interferometer type switch can work even for a single-photon-level light and that a multi-user QKD network can be constructed using a silica-based PLC 8 × 8 non-blocking matrix switch. In addition, single-photon-level transmission and ordinary optical transmission can share the same 8 × 8 non-blocking matrix switch, so which shows the possibility of sending quantum signals through current optical networks.