Optical spectra of periodically patterned dielectric surface simulated by finite-different time-domain method

A dielectric film imprinted with a hexagonal periodical pattern of nanosphere holes can be fabricated by a two-step process of depositing a dielectric thin film on a hexagonally patterned array of nanospheres fabricated by convective deposition, and then removing the nanosphere particles. In this work, the optical transmission through a dielectric slab with hexagonal pattern of half-sphere holes was simulated by finite-different time-domain (FDTD) methods. In the simulation, a short Gaussian pulse of electromagnetic waves was generated and propagated through the dielectric patterned slab and the near-field diffraction from the structure was collected as a function of time. Using a Fourier transformation, the optical spectra of the structure were evaluated. The far-field diffraction was also investigated by evaluating the analytical Green's function at given points. Several parameters of the optical response including full width at half maximum and relative intensities of high order diffraction peaks were examined for various structure sizes. The structures examined were composed of a periodic hexagonal pattern of half nanosphere holes (radius of 290 nm). In addition, the effect on the optical response of 10% elliptical shape deformation of the half-sphere holes was studied. Our calculations enable us to identify parameter schemes where the third order diffraction exceeds second order diffraction efficiency from gratings.