8. The Future of Optical Communications

Optical fiber communications systems have experienced a tremendous development over the past decades, enabling a steady exponential increase of data rates over short and long distances. Over the last 10 years, it became clear that using current fibers and/or spectral transmission bands won’t support a significant further increase. After introducing single-mode fiber-based optical transmission systems and the technological evolution that enabled current transmission systems, this chapter gives an overview on two distinct ongoing research directions for a drastic increase of data rates: (1) to further push the data rates limits in current single-mode fibers and (2) to explore a new multiplexing dimension, the spatial dimension of optical fibers to drastically increase the per-fiber data rates. The former topic focuses on approaches to increase the spectral efficiency and hence the amount of data that can be transported in a given bandwidth as well as adding further spectral bands where single-mode fibers guide at low loss. This approach is particularly interesting when maximizing data rates in existent fiber infrastructure. The second part describes novel optical fibers such as few-mode and multi-core fibers and related space-division multiplexing technologies that have been demonstrated to offer a strong per-fiber capacity increase of 2 orders of magnitude.