1MIMO Communications over Multi-Mode Optical Fibers: Capacity Analysis and Input-Output Coupling Schemes

We consider multi-input multi-output (MIMO) communications over multi-mode 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 into and out of the fiber. 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 currently installed fibers. Moreover, both approaches have limited future scalability. In our work, we present input-output coupling schemes that allow the user to couple and extract a reasonable number of signals from a fiber with many modes (such as those used in OM3 and OM4 standards). 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, a phenomenon that 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