Variable-focusing surface plasmon dielectric lens using air-gap modulation

We present a variable-focusing surface plasmon dielectric lens using the air-gap modulation. Based on the modal analysis of the planar slab waveguide consisting of the dielectric slab over the metal substrate, we examine the transmission characteristics of the single air-metal surface plasmon polariton (SPP) mode through the planar slab waveguide. Our simulation results reveal that the 2π modulation of the phase of the transmitted SPP mode can be realized. By using the lens with parabolic shape, the SPP mode converges and focuses to one point. It is shown that the dynamic modulation of the air-gap width gives rise to the dynamic change in the focal length.