Space-Division Multiplexing in Optical Fibers

Optical communication over fiber networks are the backbone of our current communication infrastructure.. Fiber optic networks have scaled in capacity over the years by first adding multiple wavelength channels and most recently by increasing the spectral efficiency of the transmitted signals by using advanced modulation techniques made possible by the introduction of digital coherent transceivers. In particular by using pulse shaping to optimize the use of the optical spectrum, multilevel complex formats, and by transmitting individual signals over the two polarizations supported by the single-mode fibers (SMFs). This way, a single SMF is able to provide around 50 Tbit/s for distances up to 10,000~km. This high capacity, which was once considered as practically unlimited, is now becoming the bottleneck of the cloud-centric information-technology communication networks. It is therefore paramount to identify and develop new technologies to increase the capacity of fiber optic communications system by 2 to 3 orders of magnitude, while significantly reducing the cost per bit of the transmitted data. As current state-of-the-art fiber optic systems operate close to the theoretical limit, this can only be achieved by increasing the number of parallel spatial channels, which is exactly the aim of research in space-division multiplexing (SDM).