Figure 3. Excitation and detection of SPPs.

(a) Without waveguide light couples to free space and partially into the substrate. (b) An SPP can be excited on the gold surface, but is weakly bound to the interface. (c) The 200-nm-thick SiN_x layer on top of the gold surface leads to an increased confinement. Owing to the high confinement, this SPP can be coupled directly to a detector. (d) Coupling efficiency from the laser to detector facet over the distance between them, with the simulation as curves and the experiment as points. (e) Detector signal into 50 Ω compared with the laser power (front facet) over the laser current density for a distance of 50 μm. The inset shows the time-resolved detector signal. Opt., optical.