Design, near-field characterization, and modeling of 45° surface-plasmon Bragg mirrors

Abstract

The development of surface plasmon polariton (SPP) optical elements is mandatory in order to achieve surface plasmon based photonics. A current approach to reach this goal is to take advantage of the interaction of SPP with defects and design elements obtained by the micro- or nano-structuration of the metal film. In this work, we have performed a detailed study of the performance and behavior of SPP-Bragg mirrors, designed for 45\ifmmode^\circ\else\textdegree\fi{} incidence, based on this approach. Mirrors consisting of gratings of both metal ridges on the metal surface and grooves engraved in the metal, fabricated by means of electron beam lithography and focused ion beam, have been considered. The performance of the mirrors has been characterized via near-field optical microscopy. An original procedure to obtain quantitative values of the mirrors' reflectivity and transmission coefficient from the near-field images is exposed. The mirrors composed of metal ridges are shown to act very efficiently, and a rather low number of elements (15 for the specific geometry studied) is able to deflect almost 100% of the incoming power. Conversely, the arrays of grooves produce a much lower reflectivity, which we attribute mostly to radiative scattering in the forward direction induced by the grooves. Besides, the considered systems have also been simulated by using the differential method. The results obtained from the numerical calculations present an excellent agreement with the experimental data, proving the reliability of this method to predict the behavior of this kind of systems while interacting with SPP. Based on the numerical modeling of the SPP-Bragg mirrors, the evolution of the mirrors' behavior with the ridges height is analyzed.