The collective property of enhanced transmission through compound metal periodic arrays of subwavelength apertures Bo Ni, Lujun Huang, Jiayi Ding, Guanhai Li, Xiaoshuang Chen n , Wei Lu National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 200083 Shanghai, China article info Article history: Received 17 April 2012 Received in revised form 2 February 2013 Accepted 5 February 2013 Available online 13 March 2013 Keywords: Surface plasmon Compound hole Charge collective effect abstract The transmissions through a two-dimensional compound metal periodic hole arrays comprised of rectangle and cross-shaped holes are calculated by the finite-difference-time-domain (FDTD) method. The results show that the transmissions strongly depend on the collective effect of the compound hole cell. Moreover, the comparisons between transmission characteristics corresponding to the asymmetry of the cross-shaped hole in two different directions (vertical and parallel to the light polarization) are also studied. It is found that the 1168 nm peak is split into two peaks when the symmetry of the cross- shaped hole in y-axis direction is broken. However, it is shown that there is no obvious change of transmissions with changing the asymmetry in x-axis direction. Thus, it is concluded that the transmissions are more sensitive to the vertical direction asymmetry. The results may be utilized to tune the electromagnetic wave in subwavelength optics. & 2013 Elsevier B.V. All rights reserved. 1. Introduction The periodically patterned metal films have attracted consid- erable attention because of their interesting optical properties and potential applications in nanodevices since Ebbesen et al. reported the extraordinary optical transmission (EOT) through metallic films perforated by subwavelength hole arrays [1]. In attempts to understand the underlying physical mechanisms, many experimental [2–10] and theoretical [11–25] studies have been carried out. It is widely accepted that the surface plasmon resonance on the metal film is the main mechanism responsible for light enhancement, and the transmission spectra depend on the metal [6], hole size [4,7], hole depth [2], hole shape [8,9,19,21] and the polarization of incident light [5]. The influence of the hole shape is due to the effect of localized surface plasmon (LSP) around the aperture. In previous works, different hole shapes like circular [1], rectangular [5,19], cross-shaped [8], asymmetric cross-shaped [21] have been studied. On the other hand, the transmissions of light through various complicated structures [26–29], as an important research topic, have been investigated. Some compound structures are utilized to tune the enhanced transmissions of electromagnetic wave. In 2002, by combining thin copper wires and split ring resonators (SRRs) on the same board, Bayindir et al. reported that the transmission measure- ments exhibit a passband within the stop bands of SRRs and thin wire structures [26]. Later, Yuan et al. showed a dual-band measurement of planar metamaterial with two distinct electric resonances [27]. Li et al. obtained dual-band magnetic resonances by embedding the SRRs within the dielectric holes of the fishnet structure [28]. In addition, the structure of double sets of circular holes has been studied by Wang et al., a redshift of the transmis- sion peak can be seen clearly [29]. However, all the results mentioned above are exhibited in gigahertz or terahertz fre- quency ranges. It is significant to extend these particular proper- ties to infrared and optical frequency ranges. On the other hand, it is worthy to study the physical mechanism of tuning electro- magnetic wave by compound structures. These works have some potential applications for novel nanodevices. In this paper, the transmissions of light through two- dimensional compound metal periodic hole arrays, comprised of rectangle and cross-shaped holes, are studied by the finite- difference-time-domain (FDTD) method. It is found that the transmissions strongly depend on the collective effect of the compound cell by comparing to that of the individual rectangle or cross-shaped hole arrays, respectively. In addition, the trans- mission characteristics are obtained by changing symmetry of the cross-shaped hole in two different directions (vertical and parallel to the light polarization). It is shown that the transmissions are more sensitive to the asymmetry of vertical direction. 2. Numerical model and simulations We consider a freestanding gold film perforated by an array of two-dimensional compound rectangle and cross-shaped holes, as shown in Fig. 1. The cross-shaped hole are formed by two rectangle Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/optcom Optics Communications 0030-4018/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optcom.2013.02.002 n Corresponding author. E-mail address: xschen@mail.sitp.ac.cn (X. Chen). Optics Communications 298–299 (2013) 237–241