Localization and Waveguiding of Surface Plasmon Polaritons in Random Nanostructures

We propose to use channels in strongly scattering nonabsorbing random media for guiding electromagnetic waves, and demonstrate this concept using near-field microscopy of surface plasmon polaritons (SPP’s) propagating along the gold film surface covered with randomly located scatterers. In the wavelength range of 725–765 nm, we observe complete inhibition of the SPP propagation inside the random structures composed of $\sim 50\mathrm{\text{−}}\mathrm{n}\mathrm{m}\mathrm{\text{−}}\mathrm{\text{wide}}$ gold bumps and their clusters with the density of $50\mu {\mathrm{m}}^{-2}$, as well as well-defined SPP guiding along corrugation-free 2- and $4\mathrm{\text{−}}\mu \mathrm{m}\mathrm{\text{−}}\mathrm{\text{wide}}$ channels.

Figure 1

Scanning electron microscope pictures of random structures of individual $\sim 50\mathrm{\text{−}}\mathrm{n}\mathrm{m}\mathrm{\text{−}}\mathrm{\text{wide}}$ gold bumps and clusters with a nominal density of (a) 37.5 and (b) $50\mu {\mathrm{m}}^{-2}$.

Figure 2

Gray-scale (a) topographical and near-field optical images ($25\times 25\mu {\mathrm{m}}^2$) taken at $\lambda \cong (\mathrm{b})738$, (c) 785, and (d) 833 nm. Regions with random scatterers correspond to the structure shown in Fig. 1b. Depth of the topographical image is 120 nm.

Figure 3

Cross sections of the topographical [Fig. 2a] and near-field optical [Fig. 2b] images along the line marked $A$ on the optical image.

Figure 4

Cross sections of the near-field optical images [Figs. 2b, 2c] averaged along $1\mathrm{\text{−}}\mu \mathrm{m}\mathrm{\text{−}}\mathrm{\text{wide}}$ stripes positioned as the line marked $B$ on Fig. 2c.

Figure 5

Gray-scale (a) topographical and near-field optical images ($25\times 25\mu {\mathrm{m}}^2$) taken at $\lambda \cong (\mathrm{b})738$, (c) 763, and (d) 795 nm. Regions with random scatterers correspond to the structure shown in Fig. 1a. Depth of the topographical image is 110 nm.

Figure 6

Gray-scale (a) topographical optical images ($32\times 22\mu {\mathrm{m}}^2$) taken at $\lambda \cong (\mathrm{b})713$, (c) 750, and (d) 795 nm. Depth of the topographical image is 180 nm.