Advanced Space-division Multiplexing for Optical Communications

Single-mode optical fibers are widely used for data transmission, and form the backbone of our communications infrastructure. However, these fibers have a finite capacity, which we are approaching. The most promising solution to increase the capacity of optical fibers is the use of spacedivision multiplexing (SDM), where several spatial paths in a single optical fiber are used to enable simultaneous data transmission of several independent data streams for each carrier wavelength. This thesis examines SDM using orbital angular momentum (OAM) modes, and linearly polarized (LP) modes. A special air-core optical fiber supporting stable propagation of OAM modes is characterized, and used in a communications experiment. This resulted in simultaneous transmission of 12 OAM modes in the air-core fiber, without the need of multiple-input multiple-output signal processing. Raman amplification of OAM modes in the air-core fiber is explored, using different pumping schemes, and is found to be a solution in order to amplify OAM modes in the transmission fiber. Finally, the complexity of SDM systems is addressed, through a novel SDM receiver structure, which significantly reduces the number of components needed to receive an SDM signal. The receiver is demonstrated using a system based on LP mode multiplexing in a fiber supporting 3 modes.