Supporting information: Functional plasmonic nano-circuits with low insertion and propagation losses

∗To whom correspondence should be addressed †University of Erlangen ‡Caltech uum light source is spectrally filtered by a programmed acousto-optic tunable filter (operated at λ = 1200− 1850nm) (NKT Koheras, SuperK Extreme) and is subsequently directed through a polarization filter (1) and a non-polarizing beam splitter (NPBS), that directs 50% of the power to a reference diode (InGaAs). The main beam is focused with a high NA objective (NA = 0.9 from air and NA = 1.3 immersion, from substrate) that was carefully characterized to preserve the polarization properties of the laser beam. The diameter of the collimated beam was carefully measured (FWHM = 1.6mm) with an InGaAs camera and the effective numeric aperture of the experimental focal spot was determined for all subsequent evaluation steps. The focus of the objective is adjusted on the investigated excitation nano-antenna. At the same time, the objective images the complete nano-circuit, including the emission from the other antennas. The collimated beam, carrying the image, is polarization filtered (polarizer 2) and passes imaging optics to form a real image on an InGaAs NIR CCD camera (Xenics XS, 320 x 256 pixels). The setup features a variable magnification factor (150x, 300x) and an additional, switchable focusing unit to allow for Fourier plane imaging. By adjusting the polarization filter (2) perpendicular to polarization filter (1), the reflection of