Optical transmission for high data rate telecommunications constitutes one of the most important applications of quantum electronics. The author describes the rapid development of this technology, the state of the art, and some projections for the future. In particular, the characteristics of the fiber transmission medium, the semiconductor laser sources, and the receivers are described along with the recent advances made possible by the development of practical optical amplifiers. The main challenges for the future are in development of practical broadband integrated-services digital networks and components for an all-photonic network.>

Three types of photonic switching networks have been proposed, namely, optical space-division switching, optical wavelength-division switching. Optional function devices required for each switching network are as follows: optical switch matrix for space-division switching; optical memory and optical write/read gate for time-division switching; and tunable wavelength filter and wavelength converter for wavelength-division switching. Recent progress in semiconductor functional devices such as modulators, switching devices, bistable devices, and wavelength control devices, which would be key devices to build switching networks, is reviewed.>

This paper reports the strategy for establishing the reliability assurance for LD's and APD's available for undersea transmission systems. On the basis of aging data during more than 104h and a statistical analysis for the reliability of semiconductor devices, the LD's and Ge-APD's lifetest plans for high reliability assurance are proposed.