  In this paper, we present an efficient implementation method of physical
layer of Y-00 which can support a secure communication and a quantum key
distribution (more generally key expansion) by IMDD(intensity modulation/direct
detection) or FSK(frequency shift keying)optical fiber communication network.
Although the general proof of the security is not yet given, a brief sketch of
security analysis is shown, which involve an entanglement attack.

Quantum Physics