A Comparison of Direct and Coherent Detection Systems with Optical Amplifiers

Abstract : The use of fiber amplifiers in future lightwave systems now appears certain. Many experiments have been published demonstrating both the long-distance and multi-channel capability of fiber amplifier-based systems. Most experiments have used conventional on direct detection systems but some experiments, including a record transmission distance experiment, have used coherent detection systems and models of both systems have been developed. This paper will compare the two systems under the same conditions using both experiments and models. We will emphasize a practical comparison by using a direct detection regenerator from AT and T's commercial, 1.7 Gb/s system and a shelf-mounted, coherent detection regenerator from a recent AT and T field trial. We will also emphasize a direct comparison by using transmitters of the same wavelength and identical optical paths including erbium-doped fiber amplifiers.