A cascaded plasmonic superlens for far-field imaging with magnification at visible wavelength

We experimentally demonstrate a novel design of a cascaded plasmonic superlens for direct imaging subwavelength objects with magnification in the far field at visible wavelengths. The lens consists of two plasmonic slabs. Slab I is a plasmonic metasurface for near field coupling, and slab II is a planar plasmonic lens for magnification. First, we demonstrate the performance of the lens by numerical calculations, then describe the fabrication of both sub-structures. Finally, we demonstrate imaging performance of the lens with a subwavelength object. The fabricated superlens exhibits a lateral resolution down to 180 nm at a wavelength of 640 nm, as predicted by numerical calculations. Nevertheless, the experiment reveals that the imaging is sensitive to the relative position between the object and Slab I. In order to overcome the effect, Slab I is modified. The modified design is verified by numerical calculations and fabrications. A similar subwavelength resolution as the former lens is exhibited with a stable imaging performance against the lateral shift of the object. Our results could open a way for designing and fabricating novel miniaturized plasmonic superlenses in the future.