A novel method is proposed to manipulate beam by modulating light phase through a metallic film with arrayed nano-slits, which have constant depth but variant widths. The slits transport electro-magnetic energy in the form of surface plasmon polaritons (SPPs) in nanometric waveguides and provide desired phase retardations of beam manipulating with variant phase propagation constant. Numerical simulation of an illustrative lens design example is performed through finite-difference time-domain (FDTD) method and shows agreement with theory analysis result. In addition, extraordinary optical transmission of SPPs through sub-wavelength metallic slits is observed in the simulation and helps to improve elements' energy using factor.

The propagation and combination of surface plasmon polaritons (SPPs) in Y-shaped metallic nanochannels are investigated numerically via finite difference time domain (FDTD). It is shown that the behavior of SPPs in nano-size channels resembles that of light guiding in conventional waveguides, and SPPs can also be combined effectively with appropriately designed structures. The loss associated with metal absorption and scattering with the multiple reflections between slit openings on the bend angle are analyzed numerically. The Fabry-Perot cavity effect displayed by SPPs traveling in channels with finite length is discussed as well.

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