Full-vectorial study of light and sound interactions in low and high index contrast silica waveguides

Rahman, Mohammed Moseeur (2016). Full-vectorial study of light and sound interactions in low and high index contrast silica waveguides. (Unpublished Doctoral thesis, City University London)

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Abstract

A full-vectorial finite element based approach has been developed to find accurate modal solutions of acoustic modes in Ge-doped and un-doped planar silica waveguides. The structural symmetry is exploited and Aitken’s extrapolation is also used to improve the accuracy of the solutions. The spatial dependences of the dominant and non-dominant displacement vectors are shown for the fundamental and higher order shear and longitudinal modes for Ge-doped core. The modal hybridness and modal birefringence between the two fundamental shear modes are also presented for this low index contrast waveguide. Further, rigorous analyses of the interactions between the guided acoustic and optical modes are performed for higher Ge-doped planar, for this case 10% doping is used. The Stimulated Brillouin Scattering (SBS) frequency and the overlaps between the fundamental and the higher order shear and longitudinal acoustic modes and the fundamental quasi-TE optical mode are presented. Brillouin gain spectrum for this moderate index contrast waveguide is determined. Furthermore, for a high index contrast air-clad rectangular silica strip waveguide, this program is used to accurately study the evolution of the acoustic modes. The existing structural symmetry is also exploited to reduce modal degeneration and to enhance the accuracy of the solutions. The interactions between the guided acoustic and optical modes are calculated after considering the full-vectorial nature of the modal fields. The SBS frequency and the overlaps between the fundamental and higher order acoustic modes with the fundamental quasi-TE optical mode are presented. The peak Brillouin gain, Brillouin gain spectrum (BGS), strength of Bragg gratings and threshold SBS power for this air-clad silica guide are also evaluated. Further comments are added on figure of merit (FOM) and acoustic attenuation coefficient for this air-clad silica waveguide.

Item Type: Thesis (Doctoral)
Subjects: Q Science > QC Physics
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Divisions: School of Engineering & Mathematical Sciences > Engineering
URI: http://openaccess.city.ac.uk/id/eprint/15045

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