The effect of unit structural symmetry in periodic subwavelength metallic hole arrays on enhanced optical transmission

3D finite-difference time-domain method was employed to comparatively study the enhanced optical transmission of four kinds of periodic subwavelength hole arrays metallic films, such as circular-shaped, button-shaped, semicircular-shaped and Tai-Chi-shaped holes which had different symmetries and were deposited on a quartz substrate. The effect of the hole arrays periodicity and the hole size on the enhanced optical transmission of these four array structures were investigated. The results show that the enhanced optical transmission is strongly dependent on the symmetries of unit cells. Under the excitation of ultrashort Gauss light pulse, the normalized transmission increases gradually with the reduction of unit structural symmetries, the transmission peak in infrared wavelengths range undergoes a large spectral red-shift. The distance between the transmission peak in visible and infrared wavelengths range increases gradually. The largest distance of 1 300 nm is in symmetry breaking Tai-Chi-shaped arrays. The surface plasmon polaritons mode and the localized surface plasmon resonance mode play important roles in the process of the enhanced optical transmission. In visible wavelengths, the surface plasmonic polaritons mode is the dominant factor to the enhanced optical transmission of these four arrays structures. In infrared wavelengths, the localized surface plasmon resonance mode significantly affects the enhanced optical transmission of the hoel arrays in poor unit symmetries. © 2015, Chinese Optical Society. All right reserved.