Net optical gain in a plasmonic waveguide embedded in a fluorescent polymer

Plasmonics - the study of the interaction between electromagnetic waves and electron plasmas on metal surfaces and in metallic nanostructures - has received much attention in recent years, with potential new applications ranging from subwavelength photonic circuits to photothermal cancer therapy. In many cases, however, the substantial attenuation of the electromagnetic wave due to absorption (ohmic loss) in the metal is of serious concern. Introduction of optical gain into the dielectric material adjacent to the metal surface has been identified as a means of compensating for the absorption loss, but the experimental realization of lossless propagation or optical gain in plasmonic waveguides has proven elusive. Here, we demonstrate direct proof of plasmonic propagation with net positive gain over macroscopic distances. The gain is provided by an optically pumped layer of fluorescent conjugated polymer adjacent to the metal surface in a dielectric-metal-dielectric plasmonic waveguide.