Abstract

The recent enhancements made to coherent lightwave technology and erbium-doped-fiber amplifiers (EDFA’s) have suggested the possibility of realizing long-span high-speed transmission systems. Extensive efforts have been made to achieve such systems. As a result, coherent transmission has made it possible to realize the field-deployable transmission systems shown in Table 1.^1–4 Although the receiver sensitivity of direct-detection systems that use preamplifier EDFA’s pumped at 0.98 µm and narrow optical filters approaches that of coherent- detection systems,^5,6 long-span coherent-detection systems remain practical. This paper describes the initial application of coherent-optical-transmission technologies to synchronous digital hierarchy (SDH) and shows the practicality of nonrepeatered CPFSK transmission systems with EDFA booster amplifiers, as confirmed by a 1-yr field experiment.

© 1993 Optical Society of America