Low-index-material-based nano-slot waveguide with quasi-Bragg-reflector buffer

A low-index-material-based nano-slot waveguide based on a quasi-Bragg-reflector buffer is presented. This quasi-Bragg-reflector buffer includes alternating low and high refractive index dielectric layers. The thicknesses of these dielectric layers are chosen optimally by using a genetic algorithm so that the leakage loss of the present optical waveguide is minimised. An SiO₂-based slot-waveguide is designed as an example and the quasi-Bragg-reflector buffer is formed by using several Si/SiO₂ bilayers. The theoretical leakage loss for an SiO₂-based slot-waveguide with three optimised Si/SiO₂ bilayers is about 0.01 dB/mm (at 1550 nm). The modal analysis with a full-vectorial finite-difference method shows that the present slot waveguide has an enhancement of the field distribution in the nano-slot region.