Recently, a great deal of progress has been made in the area of optical amplifiers and many experiments using them have been conducted aiming at practical applications to various transmission systems. This paper reviews recent developments in optical amplifiers, focusing on Er-doped fiber amplifiers (EDFAs), and their prospective applications. Included are introductory amplification theory to clarify the features of optical amplifiers, comparison of optical amplifiers focusing on EDFAs and semiconductor laser amplifiers (SLAs), and recent typical system applications using EDFAs, including IM/DD transmission, analog transmission, coherent transmission, FDM transmission and other applications.

Two new technologies, coherent optical fiber communications and optical fiber amplifiers, are now combined together to bring forth a new era in optical fiber communications research. The purpose of this paper is to describe two topics in this innovative research area: various diversity techniques in coherent optical fiber communications, and combination of the coherent optical fiber communications with erbium-doped fiber amplifiers (EDFAs).

Prospects of photonic switching technologies are described from the viewpoint of an experienced switching system engineer. Photonic switching technologies are classified into five categories, and each of them has the explanation about basic device operation principles with the experimental switching system technologies. The author's view of present technologies is explained with comparison table about these five typical system technologies. Finally, the expectation to the photonic switching system is described that it will be introduced at the beginning of 21st century.

Introduction of fiber-optic systems to the subscriber network is the key issue for the next generation network. Fiber-optic systems have, so far, been limited to business applications. However, the large scale introduction of fiber-optic systems to all customers, especially to the home and to small business customers is indispensable for the smooth evolution of B-ISDN. Accordingly, NTT plans to introduce a fiberoptic subscriber network widely to the home from around 1995 and to achieve an all fiber subscriber network by 2015. This paper presents the development and deployment concept for a fiber-optic subscriber network. It also proposes the fiber-optic network services that should be offered upon fiber-optic system deployment. Near term system development and deployment strategies are also discussed.

In this letter, we present a channel access strategy with both downward and upward (thus called both-way) overflow mechanisms, which allocates channel bandwidth dynamically to multiple heterogeneous traffics with differing intensities, bit rates and holding times. Each input traffic has its own service channel and finite waiting room and can overflow to any other channels. The threshold parameter which limits overflow is also considered, and the performance of this channel access strategy is analyzed as an M/M/S/N system with state-dependent arrival rates.

The spherical electromagnetic wave backscattering from a random rough terrain is investigated. The incoherent backscattered power is computed to examine how the antenna beamwidth and wave sphericity influence the magnitude of copolarized terrain radar backscattering.