Optical Transmission Property Of Sub-Wavelength Metal Holes

Extraordinary optical transmission (EOT) was observed by Ebbesen at 1998, and the related mechanisms got more and more attention thereafter. In general, there are two independent theoretical models, i.e., surface plasmon polarition (SPP) and composite diffractive evanescent wave (CDEW). According SPP model, the transmission peaks depend on wavelength of SPP, it relates to the array periods, and dielectric constant of metal and medium. According to CDEW model, the transmission valley depends on Wood's abnormity, it relates to the array periods, These models could explain some EOT phenomenon under specific conditions, but there are deviations when explaining 2-dimentioanl array because they are deduced from 1-dimentional model and induced a lot of hypothesizes.In this paper, the transmission property of 2D array is simulated by 3D Finite Difference Time Domain, the material dielectric constant is defined, and no other simplified hypothesis induced. Experiment is used to validate the model accuracy. Au film was deposited on quartz substrate by magnetic sputter, and sub-wavelength hole array was prepared by focus ion beam. A micro spectroscopy system was designed to measure the optical transmission. The comparison between results from simulation and measurement validated the accuracy of FDTD model. The simulation model is used to analyze the influence of apparatus and material parameters on EOT, and the related mechanisms. The major conclusions are:EOT is induced by both of surface plasmon polarition and composite diffractive evanescent wave, both of them must be considered to explain the phenomenon;SPP wavelength corresponds to the transmission valley; the position of these valleys only depends on the materials of metal and medium and the array period; and there is transmission peak following these valley related to surface plasmon polarition. The simulation and experiment broaden the knowledge on EOT phenomenon, and remedying the limitations of exiting theory. It could help to predict the device response and optimize the performance.