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A compact plasmonic structure is proposed to actualize the subwavelength beam focusing, through a metal slit array arranged along a triangular or trapezium surface profile. The incident light passes through the metal slits in the form of surface plasmon polaritons (SPPs) and then scattered into radiation fields. The constructive interference of radiation fields from individual slits with different depths and widths gives rise to beam focusing. The advantages of the proposed plasmonic lens are having a much smaller lateral dimension and broad working wavelength range. This is of importance for realizing densely integrated photonic circuits. The finite-difference time-domain (FDTD) method is employed to verify the proposed design. The simulation results indicate that the focal spot is beyond the diffraction limit. [ABSTRACT FROM AUTHOR]

Abstract: We design a novel plasmonic lens consisting of multiple nano-metal slits surrounded by dielectric air slot waveguides. The surface plasmon polaritons (SPPs) are excited from the metal slits. The slot waveguides provide desired phase retardations of light focusing. Numerical simulations with finite-difference time-domain (FDTD) method show that the transmitted fields through the design example can generate light focusing and deflection by altering the width or length of slot waveguides. The focal spot size is far narrower than the incident wavelength and the focal length can be controlled in several micrometers, which agree with our theoretical analysis. [Copyright &y& Elsevier]