Cascaded DBR plasmonic cavity lens for far-field subwavelength imaging at a visible wavelength

We experimentally demonstrate a novel cascaded plasmonic superlens, which can directly image subwavelength objects with magnification in the far field at a wavelength of 640nm. The lens consists of two plasmonic slabs. One is a plasmonic cavity lens used for near-field coupling, and the other one is a planar plasmonic lens for phase compensation and thus, image magnification. To tune the performance wavelength to visible and to enhance the near-field transmission, distributed Bragg reflectors are integrated to the plasmonic cavity lens around the lens center, forming additional lateral cavities for surface waves. In this article, we first show numerical results about the working principle and the performance of the lens. Then, we demonstrate the imaging performance of a fabricated superlens experimentally. The fabricated superlens exhibits a lateral resolution down to 200 nm at the wavelength of 640 nm observed in the far field. Compared to our earlier design, shift invariance is achieved with the current approach. Our results could open a way for designing and fabricating novel miniaturized plasmonic superlenses in the future.