Overview of coherent lightwave communications

Overview of coherent lightwave communicationsRoger C SteeleBritish Telecom Research Laboratories, Martlesham Heath,Ipswich, UK. 1P5 7RE.SummaryCoherent lightwave systems have now reached the stage where good performance hasbeen achieved in several field trial systems. To achieve this, many practical problemshave had to be overcome. Suitable laser sources have been developed, though the idealsource for coherent systems has still to be demonstrated. Polarisation control anddiversity schemes have been successfully implemented and shown to give good perform-ance. A number of different modulation and demodulation schemes have been proposed