Coupling of Surface Plasmon Polaritons and Light in Metallic Nanoslits

We clarify the nature of coupling between surface plasmon polaritons (SPP) and transmitted light in metallic nanoslit structures. The coupling strength is found to be the product of the geometric opening ratio, the aperture momentum, and the Fabry-Perot factor. We determine the effective coupling, which includes corrections due to other SPPs, and show that this effective coupling causes enhanced transmission with redshifted or blueshifted transmission peaks. Without coupling, SPP is proven to suppress transmission due to the equipartition of diffraction orders. These results show good agreement with experiment.

Figure 1

(a) Schematic view of the nanoslit array on top of a substrate. (b) SEM image of slits used in experiment.

Figure 2

(a) Bare ($V_b$) and effective ($V_e$) coupling constants calculated along the resonance line of AM[1] (air-metal side SPP of order 1). (b) Shift of resonance wavelengths of AM[1] due to bare and effective coupling.

Figure 3

Transmission spectrum of (a) SPP of order 1 at the sapphire-metal side with $\theta =-3°$ and (b) SPP of order 1 at the air-metal side with $\theta =25°$. Thick lines are experimental results, whereas thin lines show theoretical results using DSPP.

Figure 4

Angle dependent transmission spectrum. (a) Result using rigorous diffraction theory. (b) Experimental measurement. (c) Labeling of SPP resonance lines. (d) Transmission curves at $\theta =25°$ [crosscut in (a)] showing blueshifted and redshifted SPPs obtained by theory (thin line) and experiment (thick line).