Frozen mode from hybridized extraordinary transmission and Fabry-Perot resonances

Frozen modes arising in stacked subwavelength hole arrays are studied in detail. Their origin is proved to be connected with the interaction between the extraordinary transmission resonance and the Fabry–Perot cavity mode. The analysis is done for various situations that differ in metal plate thicknesses and sizes and shape of the holes. Dispersion results and finite-stack transmission spectra are in good agreement, both showing the features indicating hybridization. The boundaries of the hybridization are found in terms of the geometrical parameters. The effect of the number of stacked plates on the transmission has been demonstrated. Finally, it is shown that the group index of refraction ng in the considered finite structures can be larger than 200. The obtained estimates of ng, which are based on dispersion and transmission results, well coincide with each other.This work was supported in part by the Spanish Government under Contract Consolider Engineering Metamaterials CSD2008-00066 and Contract TEC2011-28664-C02-01. M.B. is sponsored by the Spanish Government via RYC-2011-08221. P.R.U. is sponsored by the Government of Navarre via program “Formación de Tecnólogos” 055/01/11. M.N.C. is supported by the Imperial College Junior Research Fellowship. A.E.S. thanks Deutsche Forschungsgemeinschaft for partial support of this work under Project No. SE1409/2-2. In memoriam of Mario Sorolla