Abstract

In general, the reliability of optical communications is limited by the several noises in the optical and electrical regions. At present time, we can obtain the systems which are operated under the standard quantum limitation by the current technology. The standard quantum limited system means the system whose reliability is bounded by the Poisson shot noise based on the coherent state of the signal light. The quantum communication theory, however, has predicted the possibility of breaking of the standard quantum limitation by control of quantum state of light(1). This concept gave the strong impact to optical communications. Unfortunately, the advantage of such a novel quantum state is strongly degraded by energy loss in the transmission channels(2). Recently, we have proposed the concept of the received state control and showed some examples of these advantages, in which the system employs the coherent state as the transmitter state and the squeezer at the receiver to produce the two-photon coherent state from the received state.

© 1988 Optical Society of America