Role of Interference between Localized and Propagating Surface Waves on the Extraordinary Optical Transmission Through a Subwavelength-Aperture Array

We report in this Letter that when radiation is incident on a metal surface perforated with an array of ring-shaped subwavelength apertures, the phase difference between the propagating surface Bloch wave and the localized surface wave can be tailored by the geometrical parameters of the array so as to affect the shape of the transmission spectrum. Above the resonant frequency of the aperture, interference between the two kinds of surface waves leads to a minimum in the transmission spectrum, whereas below it, the interference leads to a maximum. We suggest that this feature provides flexibility in engineering surface-wave-based all-optical devices.

Figure 1

SEM micrographs of arrays of open square apertures (a) and ring-shaped apertures with a central solid square metal patch (b). The bar represents $2.0\mu \mathrm{m}$. (c) and (d) are the FDTD calculated spectra of an open aperture and a ring-shaped aperture, respectively. (e) and (f) show the phase shifts of an electromagnetic wave passing through an individual open square aperture and a ring-shaped aperture with respect to the free propagation wave, respectively.

Figure 2

The transmission spectra of arrays of open square apertures (a) and ring-shaped apertures (b). The solid lines are the calculated spectra and the open circles are the experimental data. The scale on the left side of the figure is for experimental data, and that on the right side is for the calculated spectra (the same in Figs. 3, 4).

Figure 3

The transmission spectra of ring-shaped aperture arrays with different lattice parameters: (a) $8.0\mu \mathrm{m}$, (b) $6.0\mu \mathrm{m}$, (c) $4.0\mu \mathrm{m}$. The bar in the inset represents $3.0\mu \mathrm{m}$. The solid lines are the calculated spectra and the open circles are the experimental data.

Figure 4

The transmission spectra of ring-shaped aperture arrays with different central patch sizes: (a) $0.6\mu \mathrm{m}$, (b) $0.8\mu \mathrm{m}$, (c) $1.0\mu \mathrm{m}$. The lattice parameter is kept at $3.0\mu \mathrm{m}$ and the outer rim of the aperture is fixed at $2.0\mu \mathrm{m}$ for all cases. The resonant feature of each individual aperture is illustrated by the dotted line, with the gray arrow indicating the resonant frequency. The solid lines are the calculated spectra, and open circles are the experimental data. The bar in the inset represents $2.0\mu \mathrm{m}$.