Generalized circuit model for analysis of extraordinary transmission in multilevel slits

We propose a generalized circuit model for accurate analysis of the extraordinary transmission phenomenon in multilevel stepped slit structures. The multilevel stepped slit consists of some continuous sub-wavelength metal slits with different widths. By applying the proposed circuit model, we study the extraordinary transmission property of this structure for the two cases of ideal and real metal structures. The accuracy of the achieved results is validated by a full wave analysis based on the finite element method. Additionally, since the multilevel slit structure is adjustable by simply manipulating slit parameters such as widths and heights, various kinds of transmission spectra and a different number of resonance points are investigated by the circuit model and the numerical approach. Multilevel stepped slits can be used potentially as bandpass filters or optical attenuators in photonics integrated circuits.