Coherent optical communication

Activities associated with the development of coherent optical communication systems for application in future public broadband networks are reviewed. It is pointed out that the main future transmission medium, the optical single-mode fiber, provides an extremely high bandwidth which will have to be utilized when high-capacity-demanding digital broadband services are introduced. Attention is given to long-distance transmission systems where coherent multicarrier (CMC) techniques can be used for multiple utilization of the optical fiber and where, by using optical amplifiers, a high number of optoelectronic repeaters can be replaced. Developments concerning CMC customer access systems are reviewed. Attention is given to carrier number considerations, modulation schemes, power budget considerations, wavelength allocation aspects, and the OLO (optical line outlet) concept for optical interfaces. Two approaches for the application of CMC techniques to switching are mentioned: the optoelectronic approach, which offers the possibility of introducing a CMC transfer mode, and an approach with optically transparent transport paths. Key components required for the implementation of the discussed CMC systems are mentioned.