Asymmetric optical transmission through periodic arrays of cone air holes in a metal film.

Abstract

The metal film perforated with a micro-nano cone air hole (CAH) can serve as an optical device having asymmetric transmission. In this paper, we numerically investigate the metal film perforated with periodic arrays of cone air holes (PACAH) and find that the metal PACAH can also implement asymmetric optical transmission. In the short wave band of visible light, Al PACAH shows the most obvious effect of asymmetric optical transmission. And in the middle-long wave band, Ag PACAH shows the effect best. When R(L) (the radius of large end of hole) = 600 nm, R(S) (the radius of small end of hole) = 150 nm, t (the film thickness) = 1500 nm, and the substrate with a dielectric constant of 2.4 is placed on the side adjacent to the large end of hole, for Al PACAH (the CAHs arranged in a triangular array), the average forward transmittance and the average transmission ratio (the ratio of forward transmittance to backward one) in the region of 400 nm-600 nm are 28.4% and 7.6, respectively. Particularly, the forward transmittance and the transmission ratio at 448 nm are 43.0% and 12.4 respectively. And for Ag PACAH (the CAHs arranged in a square array), the average forward transmittance and the average transmission ratio in the region of 550 nm-800 nm are 25.4% and 5.7, respectively. Particularly, the forward transmittance and the transmission ratio at 611 nm are 36.5% and 8.5, respectively. This metal PACAH shows potential of application in secrecy equipment, such as a unidirectional optical transmission wall.