Doctorate thesis defense of Ameni Ben Khalifa

Committee

Abstract

Using the modes of a multimode fiber is considered as a frontier between what is achievable with current fiber technology and what is required for the remainder of the 21st century. Multimode fibers are of key importance for next-generation telecommunication systems. Also, they are used for the generation of white light sources and in sensing applications. Three major research trends have been investigated.

A new design of a multimode step index fiber using “the weakly coupled approach” is proposed. We investigate the propagation of six strongly coupled groups of modes, which are very important for mode division multiplexing (MDM) optical communications. Using the coupled Manakov equations, we find that the phenomenon known as soliton trapping occurs between co-propagated modes and is a consequence of the intermodal nonlinear coupling based on cross phase modulation. This fiber is very promising to increase the capacity of MDM systems by more than a tenfold factor compared to single mode systems.

Therefore, we have shown that multimode fibers composed from highly nonlinear glass of chalcogenide, are suitable for the development of high-energy supercontinuum light source. By solving the multimode generalized nonlinear Schrödinger equation (MM-GNLSE), we have predicted the generation of a very broadband mid-infrared supercontinuum in both polarizations of the fundamental mode and higher order modes spanning more than one octave. The proposed study confirms that the energy transfer occurs only between the optical degenerate modes when propagating in the multimode fiber in the mid-infrared region. We believe that the reported results will be relevant for researchers working on high power supercontinuum sources.

By investigating mode coupling between co-propagated modes, we find that multimode interference can be used for the design of fiber optic sensors in order to analyze the properties of the surrounding medium. By inserting a multimode fiber or thin core fiber between two single mode fibers, a highly sensitive refractive index sensor is proposed. The designed structures present the merits of high sensitivity and easy fabrication, which make them an excellent candidate for biochemical sensing applications.

Keywords

Multimode fibers, mode coupling, nonlinear optics, supercontinuum generation, optical sensing