SINGLE-MODE TRANSMISSION-SYSTEMS FOR CIVIL TELECOMMUNICATION

Owing to the low attenuation of optical fibers, transmission systems with repeater spacings of 10-20 km become feasible. For future high-capacity systems this imposes demands on the fiber bandwidth. Because of the inherent limitations of multimode fibers, single-mode fiber waveguides have to be taken into account. The transmission properties of single-mode fibers and their dependence on the fiber design are discussed, resulting in recommendations for practical fiber structures and statements of their production tolerances. For efficient coupling between two single-mode fibers the requirements are analysed and methods are described to achieve them in practice. As a transmitter for single-mode fiber systems mainly the GaAlAs-injection laser is considered. Its high speed modulation and spectral behavior are discussed with reference to high-capacity transmission systems. Also the problem of launching is treated in detail. Finally, fast avalanche-photodiodes are considered as receivers for single-mode fiber transmission systems.