Using finite integration technique, the authors investigate the properties of a cross-nanoslot formed in silver film, from the perspective of a plasmonic antenna, and examine the transmission of light through its periodic array. The cross-slot nanoantenna (CSNA) can enhance the intensity of near field by orders of magnitude, independent of polarisation of incident light, and emit omnidirectionally when excited by two identical sources of orthogonal polarisation operating in phase quadrature. An array of CSNA exhibit extraordinary transmission, which can be enhanced further by placing complementary cross-nanostripe array at an optimum position. To the authors' best knowledge, this is the first exploration of a cross-nanoslot as an antenna.1. Introduction: An antenna acts as a progression device that converts guided electromagnetic (EM) waves into free space wave and vice versa. Recently, there has been a growing interest towards miniaturisation of RF antenna designs to optical frequency range for utilisation of their potential in the field of nanophotonics and plasmonics. It is believed that such nanoantennas could play a similar role in optical frequency range as played by conventional antennas in RFs [1-3]. Besides transmission and reception of optical signals these nanostructures may also find several other applications, such as biological imaging, efficient confinement and enhancement of light at nanoscale, efficient light coupling to nanoscale, guiding and redirecting light at nanoscale, near field and far field inter conversion, optical information processing at nanoscale, nanolight emitting devices/sources, nonlinear medium as an optical switch, solar cells, for realisation of metamaterials, etc. [4][5][6][7][8][9]. Thus, plasmonic nanoantennae may have much broader applications as compared with their RF counterparts and this urges for the exploration and design of novel antennas in optical frequencies. In this context, we can borrow ideas from highly developed RF antenna designs [10,11] to produce more sophisticated optical antennas.In this Letter, we investigate the EM properties of a crossnanoslot from the viewpoint of antenna and study optical transmission through its periodic array. The cross-slot nanoantenna (CSNA) is formed by extending the feedgap of the recently proposed slot nanoantenna (SNA) [12], so as to form another slot orthogonal to the former. The structures of SNA and CSNA formed in a silver film on a silica substrate are shown in Figs. 1a and b, respectively. Using CST Microwave Studio (MWS), which is a commercial 3D EM simulator based on finite integration technique [13], first we investigate the spectral response of CSNA and observe that it can enhance intensity of near field by orders of magnitude, independent of polarisation. Secondly, we calculate the far field emission for various angles of polarisation of incident light. It is found that the azimuthal pattern of CSNA maintains the shape but rotates with the polarisation angle. The emission from CSNA is omnidirectional when operated...
