Design of SiON-based grating-assisted vertical directional couplers

In this paper, we present the design of a SiON-based grating-assisted codirectional coupler for dissimilar waveguides, based on an accurate numerical method. All the design parameters, including coupling length and coupling efficiency, have been calculated at the free-space optical wavelength of lambda. = 1.54 mu m for both TE and TM polarisations as a function of grating height, thickness of the coupled slabs, gap thickness between the two coupled planar waveguides. It is shown that efficient ( up to 70%) and polarisation independent vertical couplers can be realised