  Quantum key distribution (QKD) network has recently attracted growing
attentions. Due to the special characteristics of quantum information, to build
a full-connectivity QKD network without trusted relays is a stimulating
challenge. In this letter, we report on the first realization of QKD network
without trusted relays which covers metropolis in the commercial backbone
optical fiber networks. The star topology four-user QKD network automatically
addresses the quantum signal with a quantum router (QR) and every user in the
network can receive and distribute quantum keys to any others simultaneously.
The longest and the shortest length of fibers between two geographically
separated nodes are 42.6km and 32km respectively, and the maximum average
quantum bit error rate (QBER) is below 8%. This result opens a new possibility
for the use of QKD into existing network.
