Experimental investigation of quantum key distribution through transparent optical switch elements

Quantum key distribution (QKD) enables unconditional physical layer security for the distribution of cryptographic key material. However, most experimental demonstrations have relied on simple point-to-point optical links. In this paper we investigate the compatibility of QKD with reconfigurable optical networks. By performing the first tests of QKD transmission through optimal switches, we study if there are impairment mechanisms other than switch insertion loss that impact the sifted and error corrected secret bit yield. Three types of transparent optical switch elements are investigated including lithium niobate (LiNbO3), microelectromechanical systems (MEMS), and optomechanical. We show that QKD can be extended beyond point-to-point links to switched multinode architectures including protected ring networks to enhance quantum channel availability.