Windmill-Shaped Subwavelength Apertures Operating in the Mid-IR Regime

In this paper, windmill-shaped subwavelength apertures are proposed for the mid-IR regime. Spectral response of windmill-shaped subwavelength aperture with multiple sharp corners and small gap that gives rise to extreme EM field enhancements is investigated both numerically and experimentally. An equivalent circuit model for the resonant characteristic of the windmill-shaped subwavelength aperture is also presented. Electromagnetic field distributions and transmission characteristics of windmill-shaped subwavelength aperture arrays are obtained by finite difference time-domain (FDTD) method. The dependence of resonance characteristics on the polarization direction of the illumination source and the geometrical parameters of the windmill-shaped apertures are analyzed in detail. The windmill-shaped subwavelength aperture arrays exhibit extremely high near-field optical resolution and enhanced transmission compared to the bowtie-, cross, and x-shaped aperture arrays. Due to their electromagnetic properties, the proposed windmill-shaped subwavelength aperture array can be used in a wide range of applications, including biochemical sensors, optical filters, and modulators.