Enhanced optical transmission of composite subwavelength rectangular-hole array based on metal silver thin-film

Abstract

Metal nanostructures can effectively couple the optical radiation energy in free space to a highly confined surface mode due to the excitation of surface plasmons (SPs), resulting in a greatly enhanced local field in the nanoscale range of the metal surface, it’s great significance for the collection and excitation of broadband light. In order to achieve the broadband and high transmittance of metal nanostructures, a composite rectangular-hole array metal micro/nano structure was designed in this paper, and the transmission characteristics of the structure were studied by using the finite difference time domain (FDTD). The results showed that compared with the single hole array, the compound hole structure has many advantages, such as optical field enhancement, tenability and so on, and there are multiple transmission peaks in the transmission spectrum. In addition, we discussed the effects of the length and width of the rectangular holes on the light transmission characteristics of the structure array. For example, with the increase of the length b of the rectangular hole, the maximum transmittance of the structure increases from 79.7% to 88.3%, and corresponding to the central peak increases from 526 nm to 611 nm. Both the transmission bandwidth and transmittance are improved. While the change of the length a of the rectangular hole produces a peculiar multi-peak phenomenon, the analysis shows that when the length a of the rectangular hole is 250 nm, the maximum transmittance of the full symmetric composite rectangular hole array can reach up to 93% and the FWHM of the transmission peak is 354 nm, much larger than the 80 nm proposed in ref. [27] , so the frequency selectivity will be enhanced in the design of the filter. At the same time, the effect of the side length D of the center square hole on the transmission characteristics of the structure array is also discussed. The results of our research have certain guiding significance for the development of enhanced optical transmission theory and application value in the fields of novel optical sensors, t filter and optical transparent electrode.