Subwavelength focusing with a multilayered Fabry-Perot structure at optical frequencies

The Fabry-Perot resonance effect is studied in order to achieve subwavelength imaging at a far distance (e.g., about 10 wavelengths) from the source at optical frequencies. Two different structures (with matched and mismatched impedances) of alternative metal and air layers are considered first at a relatively short distance (e.g., about one wavelength) from the source. It is found that the impedance match is not necessary for subwavelength focusing since the Fabry-Perot resonance effect is utilized here. An appropriate period is chosen so that the Fabry-Perot resonance occurs in an evanescent regime, and consequently the evanescent waves near the Fabry-Perot resonance peak are amplified. With such a mechanism, a super lens with a resolution of about ${\ensuremath{\lambda}}_{0}∕30$ (${\ensuremath{\lambda}}_{0}$ is the wavelength in the air), acceptable sidelobes and a larger displacement range (when the thickness of the period is within such a displacement range, subwavelength focusing with acceptable sidelobes can be achieved) is designed. Subwavelength focusing (with a spotsize of ${\ensuremath{\lambda}}_{0}∕12$) at a distance far away from the source is also realized in the presence of some material loss.