Mimo Communications over Multi - Mode Optical Fibers

We consider multi-input multi-output (MIMO) communications over multimode fibers (MMFs). Current MMF standards, such as OM3 and OM4, use fibers with core radii of 50μm, allowing hundreds of modes to propagate. Unfortunately, due to physical and computational complexity limitations, we cannot couple and detect hundreds of data streams. In order to circumvent this issue, two solutions were presented in the literature. The first is to design new fibers with smaller radii so that they can support a desired number of modes. The second is to design multi-core fibers with a reasonable number of cores. However, both approaches are expensive as they necessitate the replacement of installed fibers. In our work, we consider input-output coupling schemes that allow the user to couple and extract a reasonable number of signals from a fiber with many modes. This approach is particularly attractive as it is scalable; i.e., the fibers do not have to be replaced every time the number of transmitters or receivers is increased (which is likely to happen in the near future). In addition, fibers with large radii can support higher peak powers, relative to fibers with small radii, while still operating in the linear regime. However, the only concern is that fibers with more modes suffer from increased mode-dependent losses (MDLs). Our work addresses this last concern. This thesis is divided into two parts. In the first part, we present a channel model that incorporates intermodal dispersion, chromatic dispersion, mode dependent losses, and mode coupling. We later extend this model to include the input and output couplers and provide an input-output coupling strategy that leads to an increase in the overall capacity. This strategy can be used whenever channel state information (CSI) is available at the transmitter and the designer has full control over the couplers. We show that the capacity of an Nt×Nt MIMO system over a fiber with M Nt modes can approach the capacity of an N -mode fiber with no loss. Moreover, we present a statistical