Emerging microstructured fibers for linear and nonlinear optical applications in the mid-infrared and terahertz spectrum

The first research topic of my thesis was to design novel highly-nonlinear fibers (HNLFs) to be used in mIR light generation (e.g. supercontinuum generation) and mIR wavelength conversion schemes based on nonlinear optical effects. The efficiency of mIR light generation/conversion depends intimately on the precise control of the linear and nonlinear optical properties of the waveguide used in the optical setup. During the course of this work, we investigated various designs of both microstructured and nanostructured highly-nonlinear waveguides with great potential for end-user applications. In particular, we demonstrated two novel types of HNLFs: the hybrid chalcogenide-metal nanostructured optical fiber that supports a plasmonic mode enabling deep-subwavelength field confinement capabilities, and the chalcogenide microporous fiber that provides extensive design freedom for engineering the chromatic dispersion of nonlinear fibers. Furthermore, simulations of the nonlinear Schrodinger equation, assuming the latter type of HLNF, were performed and showed the potential for generating a broad mIR supercontinuum inside a chalcogenide microporous fiber seeded at long wavelengths (i.e. 10.5 microm) using short picosecond pulses.;Furthermore, the study of the hybrid chalcogenide-metal nanostructured optical fiber demonstrated subwavelength-size optical mode confinement beyond the classical diffraction limit. This feat was made possible by harnessing surface plasmon polaritons guided by the metallic nanowire arrays integrated within the core of the HNLF. This subwavelength-size modal confinement translates into an extremely large nonlinear optical enhancement that provides the key component towards the realisation of broadband mIR sources via supercontinuum generation, and highly-nonlinear and highly-integrated photonic components in general.;We designed, fabricated and characterized various types of THz waveguides based on polymer materials, and which demonstrated a high practical impact for the efficient delivery of terahertz radiation. In this regard, polymer optical fibers provide a versatile platform for guiding THz radiation. The key benefits of this technology include: the abundance of the low-cost and relatively low-absorption-loss polymers; the ease of fiber preform fabrication by molding, drilling, stacking and the use of other standard polymer processing techniques; and finally the convenience of simple fabrication method by fiber drawing at relatively low-forming temperatures.;We studied the performance of hollow-core Bragg fibers fabricated using a host polymer matrix with varying doping levels of high-index and high-loss titania microparticles. Our analysis revealed that the large absorption losses induced by the high concentration of dopants can effectively destroy the photonic bandgap guiding mechanism of Bragg fibers such that an appropriate trade-off between the high-refractive-index contrast and the large associated material losses is necessary. This finding is relevant to the design of THz optical components based on polymeric composite materials.;Several recent designs of terahertz waveguides have taken the approach of reducing the fraction of guided optical power in lossy materials regions so as to minimize the modal propagation losses of the THz signal. However the highly-delocalized modal fields in many of these designs hinders their practical use for THz waveguiding, because of their significant modal sensibility to external perturbations like simple hand manipulation of the fiber. A solution was proposed in this thesis via the suspended core dielectric fiber which enables a fully-encapsulated core-guided modal propagation inside an outer polymer tube cladding that provides protection against external pertubations and the accumulation of surface contaminants on the suspended core's surface. Experimental measurements of the output mode profiles, performed with THz near-field imaging (and confirmed by finite-element simulations), have indicated that the suspended core dielectric fiber guides in an effectively single-mode regime inside its main low-loss window. Owing to the large fraction of modal power that is guided in the holey cladding, experimental fiber propagation losses as low as 0.02 cm-1 have been demonstrated with the fabricated fiber. (Abstract shortened by UMI.)...