FINITE-DIFFERENCE TIME-DOMAIN MODELING OF NONPERFECTLY CONDUCTING METALLIC THIN-FILM GRATINGS

A simulation tool based on the finite-difference time-domain (FDTD) te chnique is developed to model the electromagnetic interaction of a foc used optical Gaussian beam in two dimensions incident on a simple mode l of a corrugated dielectric surface plated with a thin film of realis tic metal. The technique is a hybrid approach that combines an intensi ve numerical method near the surface of the grating, which takes into account the optical properties of metals, with a free-space transform to obtain the radiated fields. A description of this technique is pres ented along with numerical examples comparing gratings made with reali stic and perfect conductors. In particular, a demonstration is given o f an obliquely incident beam focused on a uniform grating and a normal ly incident beam focused on a nonuniform grating. The gratings in thes e two cases are coated with a negative-permittivity thin film, and the scattered radiation patterns for these structures are studied. Both T E and TM polarizations are investigated. Using this hybrid FDTD techni que results in a complete and accurate simulation of the total electro magnetic Geld in the near field as well as in the far field of the gra ting. It is shown that there are significant differences in the perfor mances of the realistic metal and the perfect metal gratings.