Techniques for multigigabit coherent optical transmission

It has been anticipated that the main roles for coherent optical techniques will be to provide increased capacity both for long-haul transmission and wide-band signal distribution. This could be achieved by the combination of high-data-rate transmission and fine-grain WDM. To this end, heterodyne detection experiments have recently been extended into the gigabit regime but difficulties not present at lower data rates have been encountered. This paper discusses a range of technical solutions to these problems, including broad-band receivers, homodyne detection, and phase diversity reception, and reviews their current status.