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Design and optimization of chalcogenide waveguides for supercontinuum generation

Karim, Mohammad (2015). Design and optimization of chalcogenide waveguides for supercontinuum generation. (Unpublished Doctoral thesis, City University London)


This research work presents numerical simulations of supercontinuum (SC) generation in optical waveguides based on Ge11.5As24Se64.5 chalcogenide (ChG) material. Rigorous numerical simulations were performed using finite-element and split-step Fourier methods in order to optimize the waveguides for wideband SC generation. Through dispersion engineering and by varying dimensions of the 1.8-cm-long ChG nanowires, we have investigated dispersion curves for a number of nanowire geometries and identified a promising one which can be used for generating a SC with 1300 nm bandwidth pumped at 1550 nm with a low peak power of 25 W. It was observed through successive inclusion of higher-order dispersion coefficients during SC simulations that there is a possibility of obtaining spurious results if the adequate number of dispersion coefficients is not considered.We then investigate MIR SC in dispersion-tailored, air-clad, ChG channel waveguide employing either Ge11.5As24S64.5 or MgF2 glass and ChG rib waveguide employing MgF2 glass for their lower claddings. We study the effect of waveguide parameters on the bandwidth of the SC at the output of 1-cm-long waveguides. Our results show that output can vary over a wide range depending on their design and the pump wavelength employed. At the pump wavelength of 2 μm the SC never extended beyond 4.5 μm for any of our designs. However, SC could be extended to beyond 5 μmfor a pump wavelength of 3.1 μm. A broadband SC spanning from 2 to 6 μm and extending over 1.5 octave could be generated with a moderate peak power of 500 W at a pump wavelength of 3.1 μm using an air-clad, all-ChG, channel waveguide. We show that SC can be extended even further covering the wavelength ranges 1.8-7.7 μm and 1.8-8 μm (> 2 octaves) when MgF2 glass is used for the lower claddings of ChG channel waveguide and rib waveguide, respectively. By employing the same pump source, we show that SC spectra can cover a wavelength range of 1.8-11 μm (> 2.5 octaves) in a channel waveguide and 1.8-10 μm in a rib waveguide employing MgF2 glass for their lower claddings with a moderate peak power of 3 kW. Finally we present microstrucured fibre based design made with same glass to generate SC spectra in the MIR region. Numerical simulations show that such a 1-cm-long fibre can produce a spectrum extending from 1.3 μm to beyond 11 μm (> 3 octaves) with the same pump and peak power applied before. We consider three fibre structures with microstrucured air-holes in their cladding and find their optimum designs through dispersion engineering. Among these, equiangular-spiral microstrucured fibre is found to be the most promising candidate for generating ultrawide SC in the MIR region.

Publication Type: Thesis (Doctoral)
Subjects: Q Science > QA Mathematics
Q Science > QC Physics
Departments: School of Science & Technology
Doctoral Theses
School of Science & Technology > School of Science & Technology Doctoral Theses
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