Rib waveguide Bragg grating based refractive index sensor with metal under clad layer

Abstract

This thesis aims at measurement and comparison of sensitivity of Rib waveguide with and without metal layer operating at 1550nm wavelength. The Bragg grating -based integrated device interact with the broad spectrum of light and transmit, reflect the input signal of specific wavelength. We have focused on enhancing the fractional modal power (FMP) in the ambient region as it would increase the evanescent field overlap in the ambient region. Evanescent field is important for the refractive index sensitivity. We have observed the relatively higher FMP in the ambient region with metal layer introduction based on rib waveguide. The single mode condition of rib waveguide is chosen for low intermodal losses. It is verified with the single mode equation and also with the COMSOL Multiphysics software. The modal profile of rib waveguide is checked with COMSOL. To analyse the behaviour of Bragg grating transfer matrix method is employed and solved by MATLAB programming language. After solving it resonance spectrum is obtained. Resonance peak shift is observed with the change of ambient refractive index. The period of grating was chosen such a way that we would get resonance peak at 1550nm wavelength. Finally, the slope between resonance wavelength and ambient refractive index is calculated to find the overall sensitivity of the structure. Sensitivity increment has been observed for metal under clad rib waveguide.