We propose and experimentally demonstrate a broadband and high efficient circularly polarizing dichroism using a simple single-cycle and single-helical plasmonic surface array arranged in square lattice. Two types of helical surface structures (partially or completely covered with a gold film) are investigated. It is shown that the circular polarization dichroism in the mid-IR range (3µm - 5µm) can reach 80% (when the surface is partially covered with gold) or 65% (when the surface is completely covered with gold) with a single-cycle and single-helical surface. Experimental fabrications of the proposed helical plasmonic surface are implemented with direct 3D laser writing followed by electron beam evaporation deposition of gold. The experimental evaluations of the circular polarization dichroism are in excellent agreement with the simulation. The proposed helical surface structure is of advantages of easy-fabrication, high-dichroism and scalable to other frequencies as a high efficient broadband circular polarizer.

We propose and present a planar plasmonic lens formed by an array of spatially varying sub-wavelength rectangular annular patterned in the upper Au film of a metal-insulator-metal (MIM) structure. It is found that the reflected phase and amplitude can be well controlled by manipulating the width of the annular gaps and the length of the MIM cavity, in which localized surface plasmonic resonances occur. A reflective planar plasmonic lens that can generate a spherical wave-front in the reflected field has been realized through an optimized design at wavelength 1.55μm. Numerical results using the Finite Difference Time Domain (FDTD) method show that the focal length can be precisely controlled with a beam spot size at focal plane being close to the diffraction limits, and the focusing efficiency is up to 50%. It provides a great potential for applications in advanced nanophotonic devices and integrated photonic systems.