Super-resolution imaging of a single metal layer: high loss but superior resolution

Abstract

changes of the conventional optical transfer function (OTF) and add a blurring effect to the index matching condition [7][8][9]. Actually, the phase correction could be achieved by either tuning the working wavelength [8,9] or adjusting the permittivity of the metal film [10]. However, no evidence shows that these phase-correction methods are related to the amplification of evanescent waves. On the other hand, subwavelength roughness on metal film provides imaging enhancement rather than distortion [11]. We can expect that the amplification of evanescent waves induced by SPP is suppressed. Hence, whether the amplification of evanescent waves benefits the super-resolution or not remains in doubt.The conventional OTF agrees very well with the imaging results [12]. Unfortunately, such a method does not bring much physical insight into the working principle. Note that, the ability of NFSL to realize super-resolution is the result of excitation of SPP waves on the metal film [3]. In this sense, a study of super-resolution imaging from the point of view of SPP theory will be beneficial.In this work, the super-resolution imaging of the typical NFSL is described and investigated in terms of the SPP mode theory. It is revealed that the modes with high loss will suppress the amplification of evanescent waves but bring us better imaging resolution. In addition, it is proposed and numerically demonstrated that surrounding medium with high refractive index benefits the super-resolution imaging. Meanwhile, we notice that index matching between metal and dielectric could not produce the best imaging result. Based on our study, a physical explanation is provided. Theory, simulation and discussionThe typical NFSL is a thin metal film, which is sandwiched by semi-infinite dielectric medium, as schematically shown Abstract In this work, we re-analyze the influence of the loss on the super-resolution imaging of a single metal layer superlens system and reveal its positive role of the imaging. The analysis is based on the surface plasmon polariton (SPP) theory. We show that SPP mode with high loss could suppress the amplification of evanescent waves and concentrate the energy, thus contribute to the imaging. We propose to surround the metal layer with high index medium to increase the loss of the SPP modes. The proposed structure shows better performance in super-resolution imaging than the low loss cases. Numerical simulations are performed to demonstrate the results by using two-dimensional finite element method.

Super-resolution imaging of Maxwell’s fish-eye lens based on surface polaritons

“…In recent decades, surface plasmonic polaritons (SPPs) have been widely studied [8,24,25] for their potential applications in sub-wavelength optics [26,27], biophotons [28] and imaging [29][30][31][32][33]. In addition, magnetic surface polaritons (MSPs) as another kind of surface polaritons have been proposed [34,35] and realized by ferromagnetic materials [36] and electromagnetic metamaterials [37].…”