Design of a buried grating structure for the optimization of Surface Plasmon Polariton wave excitation at the lower interface of a metallic nanostrip

Grating is the most suitable for the excitation of the SPP because the grating coupling is more compatible than prism coupling for active PIC devices. But traditional gratings are not able to selectively excite SPP waves at single interfaces of the metallic waveguides. Traditional gratings usually excite SPP wave at the interface where they are or, for thin metallic nanostrips, at both interfaces. But the reduction of the thickness of the metal layer in the presence of a grating has the handicap of increasing the tunnelling of the light towards the substrate, increasing the losses and reducing the coupling efficiency. Through numerical simulations, I optimized the effective parameters for the coupling of the SPP waves, such as the angle of incidence, the thickness of the metal layer in the grooves of the buried lattice and in the upper cover, as well as the width and depth of the grooves. As a result of the optimization process, the efficiency of light coupling in the SPP wave increased at the lower interface with the substrate and the transmitted tunnelling light was effectively suppressed compared to an equivalent conventional lattice. The attenuation of the transmitted tunnelling light favours the use of SPP for a nonlinear medium.