Enhancement of focusing energy of ultra-thin planar lens through plasmonic resonance and coupling.

A metal-insulator-metal (MIM) structure which is used to enhance the focusing energy of planar lens is developed in this work. The top of the MIM structure is formed by circularly arranged V-shaped nanoantennas whose double resonance effect makes it possible for light to obtain great phase changes within an ultra-thin area. The middle and bottom of the structure is medium and gold film layer respectively. This structure produces plasmonic coupling between the antenna layer and gold film, thus reducing Ohmic loss and enhancing the effect of plasmonic excitation. When the distance between the antenna layer with a thickness of 30 nm and gold film is 88 nm, and the thickness of gold film is 20 nm, the enhancement of plasmonic coupling reaches to the strongest when the focusing intensity is 1.33 times higher than the lens only. With the advantages of small size, ultra-thin, great phase changes and high-efficient focusing ability, the enhanced plasmonic coupling lens structure can be widely applied in photoetching, and integrated optics.