The enhanced transmission of square arrays of nanoholes in thin and thick metal films has been studied. We show that normal incidence transmission spectra of an array of elliptical nanoholes in a 220 nm thick gold films have reduced symmetry with respect to the four-fold symmetry found in an equivalent array of circular nanoholes. Elliptical nanoholes milled in a 40 nm thick gold film show complex oscillatory behaviour of the transmission spectrum that has properties similar to those of a two-dimensional birefingent crystal. The transmission spectrum may also be controlled by polarisation selection due to the different degrees of the elliptical polarisation of the transmitted light. The enhanced transmission through 1D arrays of stripes is studied for a range of incident angles with a polarisation perpendicular to the stripe length. Increasing the incident angle increases the number of observed peaks, and changes their spectral positions. Changing the polarisation or the angle of incidence in a 1D array of stripes or a 2D array of reduced symmetry motifs allows control of the enhanced transmission spectrum and shows great potential for numerous applications in photonic and opto-electronic devices.
Polarization properties of the enhanced light transmission through a thin gold film perforated with an array of subwavelength elliptical holes have been studied. It is shown that broadband optical transmission can be achieved through such nanostructures due to the complex nature of the SPP Bloch modes related to a periodic lattice with a low symmetry primitive cell. The optical transmission is dependent on both the incident and transmitted light polarization states even at normal incidence. Using this feature it is therefore possible to tune the transmission spectrum by selecting the polarization of the incident and/or transmitted light. It is shown that such a nanostructure acts as a thin two-dimensional birefringent crystal with wavelength dependent principal optical axes: the property which is not encountered in natural crystals. A rotation of the polarization of the light transmitted through an array of subwavelength holes strongly depends on the thin layer of chiral material placed upon the nanostructured surface. The polarization rotation effect of the chiral molecules appeared to be coupled with the polarization properties of the metallic structure related to SPP excitations. Optical components based on nanostructured metallic systems can find numerous photonic applications space-based and terrestrial systems in extreme ambient conditions.