Figure 2. Simulations of DLSPP waveguides.

(a) Vertical confinement due to dielectric loading. A thicker dielectric layer leads to a better confinement of the SPP. The inset shows the modal intensity profile of the SPP for different SiN_x thickness, corresponding to the points at 0, 20, 50, 100, 200 and 500 nm, as well as the mode of the QCL/QCD ridge waveguide. (b) Simulated 2d mode profile of the DLSPP waveguide with a 200-nm-thick and 15-μm wide SiN_x stripe on top of a gold stripe, and (c) on an unpatterned gold surface. (d) Influence of the stripe width and the SiN_x layer thickness on the propagation length and (e) the effective modal index for the two waveguide configurations (gold stripe as solid lines and gold surface as dashed lines). For narrow waveguides, the additional loss because of the metal edges leads to a marked reduction of the propagation length. In this case, dielectric loading can improve not only the confinement, but also the propagation length significantly.