DESIGN AND MODELING OF SPECIALTY OPTICAL FIBERS FOR SUPERCONTINUUM GENERATION

Abstract

This thesis work aims to design and modeling of specialty optical fibers for supercontinuum generation. Some novel photonic crystal fiber designs have been explored for the study of supercontinuum generation using highly nonlinear materials such as silica, tellurite, chalcogenide, and organic liquids in shorter fiber length with low input peak power and also focused on the coherence property to enhance the bandwidth of the supercontinuum broadband in the visible, near and mid-infrared wavelength regions. Supercontinuum generation arises due to broadening of the high-intensity ultra-short pulses in a nonlinear optically active medium due to self-phase modulation, cross-phase modulation, solitons, high order dispersion, stimulated Raman scattering, self-steepening, and some optical losses. The various potential applications of supercontinuum sources include cancer detection, medical imaging, gas sensing, optical coherence tomography, wavelength-division multiplexing, spectroscopy, and metrology. In this thesis, some sincere efforts have been made to numerically design the dispersion engineered photonic crystal fiber designs for supercontinuum generation in the visible, near, and mid-infrared wavelength regions. The computational analysis of the proposed fiber designs is based on the finite element method. We have tried to optimize the dispersion characteristics to reduce the effect of dispersion at the pump wavelength by tweaking the respective geometrical parameters of the core and cladding and also by changing the material composition in the core region. We have numerically analyzed the influence of input peak power, pulse width, peak power, and coherence on the supercontinuum broadening. The proposed silica-based photonic crystal fibers can generate the broad supercontinuum spectrum of bandwidth 0.67 µm to 2.4 µm in the visible and the near-infrared wavelength region at low input power in shorter fiber length. Some newly reported chalcogenide glasses V have been numerically investigated for the ultra-broadband supercontinuum generation in the infrared wavelength region. We have attained the supercontinuum spanning, 1 µm to 14 µm and 2 µm to 11 µm in photonic crystal fibers composed of Ga-Sb-S and GAP-Se chalcogenides respectively. In a tellurite based photonic crystal fiber, we achieved a broadband supercontinuum ranging, 1 µm to 5.5 µm. We have also proposed a photonic crystal fiber based on liquid infiltration to increase the nonlinearity in silica fibers and able to produce highly coherent supercontinuum broadband of spanning, 1 µm to 2.6 µm in the near-infrared wavelength region by using a few centimeters fiber length with low peak power.