Planar plasmonic lenses and their applications

The imaging resolution of conventional optical lenses is generally restricted to half the incident wavelength by the diffraction limit due to the decay of evanescent waves. Planar metallic lenses based on surface plasmons offer the possibility to overcome this limit by the enhancement of evanescent waves which carrying detailed feature information of object. In this paper, the structural design, physical mechanism and focusing performance of two types of typical planar metallic lenses are reviewed. Moreover, the existing problems in this imaging technology are discussed. Because there is a certain loss when the light propagates in the metal, how to more effectively enhance the high frequency evanescent wave signal and convert it to propagation wave which can participate in the imaging in order to better achieve the far-field super-resolution imaging, and how to further increase the ultra high resolution near-field focal depth of focusing spot and reduce size of the far-field focusing spot, are further research focuses of the surface plasmonic planar metallic lenses.