Optimized effective permittivity to improve imaging resolution of multilayered structures in the infrared

Two periodic structures with different effective impedances, both comprising alternate layers of a positive and a negative permittivity material, are considered in the infrared. We find that the Fabry-Perot resonance effect periodically influences the sharpness of subwavelength focusing as the total thicknesses of the two structures increase, especially for the impedance-matched structure. On the basis of the improved multilayered structures, we design an optimized structure (i.e., the effective impedance is chosen between 0 and 1) for which a higher resolution less than lambda/12 (lambda is the wavelength in the air) can be obtained through weighing the advantages and disadvantages of the two different multilayered structures and choosing appropriate surface terminations.