Figure 5.

Single-coax SPP dispersion. (a) Calculated SPP dispersion diagram of an infinitely long, single Si cylinder embedded in silver, with outer diameter 168 nm, and cylinder wall thickness 15 nm (as in sample 1). Both the real (solid line) and imaginary (dotted line) parts of the positive (red) and negative (blue) index mode are plotted. (b) Figure-of-merit (FOM) of the positive (red) and negative (blue) index mode. The FOM is defined as |n′/n″|, with n′ and n″ the real and imaginary part of the mode index shown in panel a, respectively. The black dots show the FOM calculated from the refractive index extracted from FDTD simulations (Table 2). (c) FDTD simulation of the transmission spectrum of the experimental metamaterial sample 1 (red), the 49 nm thick silicon membrane only (black), and the 91 nm thick metamaterial only (blue).