To put these numbers into perspective, it is instructive to look at the performance of currently available photonic devices that provide optical gain in the visible and near infrared range. For semiconductor lasers, a net modal gain of approximately is typical of state-of-the-art devices, operating around 1.5-μm wavelength and similar values have been realized only very recently in rare-earth doped devices at 980 nm.24 For organic gain media, net modal gains up to in slab waveguide geometries are reported in the visible range.25 Substantially higher material gain is often quoted for, e.g., quantum wells (QWs) or quantum dots (QDs). As an example, values up to have been reported for saturation material gain in 1.3-μm-emitting InGaAs QDs, measured at 77 K (26). However, due to inhomogeneous broadening and the low optical confinement factor (spectral and spatial overlap between the optical mode and the active gain material), this translates to a modal gain of only , even in state-of-the-art QD amplifiers.27 Using gain values from literature, Russev et al.28 found no materials that could provide sufficient effective gain to amplify SPPs on a single gold or aluminum surface, while simultaneously maintaining the surface-confinement of the SPP. On a silver-dielectric surface, however, they found that SPP net amplification should be possible using semiconductor QWs in the infrared region. Organic dyes providing effective gain at approximately 600-nm wavelength came close to the required gain values. Garcia et al.29 obtained a 33% loss reduction in a dielectric-loaded SPP waveguide [Fig. 2(a)], corresponding to of optical gain, using QD-doped PMMA ridges. Based on a survey of the current literature, they claimed that further loss reduction in similar plasmonic waveguides was unrealistic with currently available gain materials, due to photobleaching and thermal damage at strong pump intensities.