Wavefront engineering based on hybrid plasmonic mode

Plasmonic lens provided great optical performance through the interaction between light and metallic nanostructure in the past years. However, the wavefront control on the metallic lens was still limited by the fabrication and geometrical design. Here, an unconventional plasmonic lens with sufficient phase modulation was developed as a focusing device; it was constructed using both circular and annular apertures in a silver film. The circular and annular apertures induced localized and cylindrical surface plasmon modes with the incident light, respectively. The propagation phase in these apertures was related to their geometric parameters. These apertures with lower aspect ratios were designed to have the artificial phase from zero to Pi and arranged in concentric arrays to manipulate the wavefront of the lens. The focal length and spot size were determined by the phase distribution on the plasmonic lens. The focal spot with a subwavelength size was obtained by the appropriate manipulation of the phase. We also demonstrated the focusing properties of this plasmonic lens experimentally to validate our design. Owing to the circular symmetry of the circular and annular apertures, this type of plasmonic lens has considerable potential for use as a polarization-insensitive device.