Optical Fiber Communication with Vortex Modes

Abstract

Internet data traffic’s capacity is rapidly reaching limits imposed by optical fiber nonlinearities [5]. Optical vortices appear in high order fiber optical mode. In this thesis, we consider multimode fibers (MMFs) that are capable of transmitting a few vortex modes. Certain types of fibers have a spatial dimension leads to space-division-multiplexing (SDM), where information is transmitted with cores of multicore fibers (MCFs) or mode-division-multiplexing (MDM), where information is transmitted via different modes of multimode fibers (MMFs). SDM by employing few-mode fibers in optical networks is expected to efficiently enhance the capacity and overcome the capacity crunch owing to fast increasing capacity demand. For generation of vortex modes, we investigate computer-generated holograms (CGHs) that are fabricated by interference technique. These components constitute the potential backbone for the high-speed network of the future. To address the capacity crunch, we study the possibility of applying modes with OAM or helicity in optical fiber communication systems. First, novel fibers (known as vortex fibers) are investigated for their maximum transmission speed and energy guiding capacities. We study the mode properties of these fibers with wave transfer matrix (T-matrix) method such that the number of guided modes, material and waveguide dispersions are determined. We optimize these fibers by changing their sizes and structures with various concentrations and types of doping for the index profile. Then an optimized profile is determined for guiding of vortex or higher order modes with a minimum total dispersion and maximum bandwidth to address the capacity crunch. During this process, the waveguide dispersion is computed from numerical results that are applied for generating fitting equations. Similarly, fitting equations are formulated for estimation of number of modes in vortex fibers. Then, the use of computer generated hologram (CGH) technique for encoding vortex modes onto signals is investigated.