We report three recent studies of nanophotonic waveguides capable of greatly enhancing interactions between light and matter. Our approach is based on gap plasmonic waveguides that enable efficient photonic-to-plasmonic mode conversion, linking light constrained by the diffraction limit to modal areas (lambda)^2/100. While metals introduce loss, here low insertion loss is possible due to the capability to rapidly nano-focus and nano-defocus. We are thus capable of designing metallic components that efficiently focus light to a 10 nm scale where linear and nonlinear processes may be greatly enhanced. Unlike optical resonators, waveguides support a mode continuum that offers broad bandwidth enhancement; electronic and optical states do not require tuning and in principle, multiple electronic states may be simultaneously coupled to a single optical mode. We initially discuss how to achieve low-loss conversion from photonic-like states to plasmonic gap modes. We will then explore three applications of these waveguide for both nano-focusing and nano-defocusing. In the first case, nano-focusing allows intense optical fields to be achieved at relatively low input powers. This is highlighted in a our recent demonstration of four wave mixing (FWM) over micron-scale interaction lengths at telecommunications wavelengths [1]. In the case of nano-defocusing, we present new data on the collection of Erbium fluorescence from these waveguides [2]. Finally, we explore surface enhanced Raman scattering in confined nanophotonic waveguides, showing their ability to not only enhance Raman scattering, but also to direct it via a single mode with near unity efficiency. [3]<p>
