An application-oriented hierarchical quantum cryptography network test bed

A hierarchical metropolitan quantum cryptography network upon the inner-city commercial telecom fiber cables is reported in this paper. The techniques of the quantum router, optical switch and trusted relay are assembled here to divide the seven-user network into a four-node backbone net, a two-user subnet and a single-fiber access link. Secure keys distributed in this network can be utilized to encrypt the instant video, sound, text messages and confidential files transmitting between nodes. The whole implementation including the hierarchical quantum cryptographic communication links and the corresponding application software shows a big step toward the practical user-oriented network with a high security level.