Fiber-optic local area networks (LANs) with Fiber Distributed Digital Interface (FDDI) protocol have come into use as backbones connecting other small LANs. This paper describes the current status of LANs, reviews a number of issues that stand in the way of further development and look at the future of LANs. Demands for wide-area networks (WANs) connecting LANs and multimedia LANs including voice and image capability has been extremely strong, spurring progress in geographical expansion and throughput increase, now over 100Mbit/s. The logical choice of transmission medium for next-generation systems is single-mode optical fiber, not only for backbone LANs but also, eventually, for floor LANs.

One of the limitation factors on the achievable distance for long-haul nonlinear Return-to-Zero (RZ)-Gaussian pulse transmission on optical fiber links is timing jitter. Although it is well known that the dispersion management technique is very effective to reduce the timing jitter, comparisons among some dispersion management methods based on the timing jitter reduction have not been reported yet. In this paper, timing jitter reduction by some dispersion management methods in nonlinear RZ-Gaussian pulse transmission systems are discussed. Moreover, we will report that the amount of timing jitter at the receiver side drastically changes depending on the configuration of dispersion managed optical fiber transmission line.

This letter clarifies properties of cutoff rate R0 of photon channels using coherent state and photon number state as quantum state of light. The relation between cutoff rate improvement and energy saving rate is found, when one uses the number state instead of coherent state.

The advantage of nonstandard quantum states such as two-photon coherent state (or squeezed states) and photon number state as transmitter state is strongly degraded by transmission loss in quantum communications. To cope with such a problem, a new application of these states is proposed, and it is shown that its system has infinite capacity.

It is well known that energy loss brings a serious problem in the optical information transmision systems with the quantum state control at transmitter. This letter presents proposal of a new system for the application of the quantum state control, which copes with the energy attenuation problem, and shows the numerical properties of performances.