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Recently stacked metamaterial structures coupled to a conductive plane have been investigated and have been shown to exhibit the same properties as stacked structures with double the layers, due to dipole mirror coupling. Here we study a system of stacked subwavelength metallic grating layers coupled to a metal film and show that this system not only supports the localized modes of a doubly layered structure, but also, for non-normal incidence, supports modes that exhibit a clear propagation and in one case a simultaneous localization of the electromagnetic field in the region between the metal film and the first grating layer. Furthermore we show that this hybridized propagating mode, excited for any N number of periodic layers, is further influenced as it couples with the highest energy localized mode of the periodic layered stack. Additionally it is found that the localized modes of the structure can be spectrally positioned in a directly adjacent manner, resulting in wideband absorption that can effectively be tuned by varying the grating film spacing.

Due to their extreme sensitivity to refractive index changes, surface plasmon resonance (SPR) sensors have long been established as extremely valuable tools for biosensing. In the past few years researchers have begun investigating various other metallic nanostructures as candidates for localized SPR (LSPR) sensing. Although LSPR is not nearly as sensitive to bulk refractive index changes as standard SPR, is has the advantage of being extremely sensitive to local refractive index changes, thereby providing detection on the level of a single molecule. In practice such sensitivity criterion is of paramount importance since the analyte layer under investigation is often only a few nanometers thick and deposited directly on the surface of the metal. Most desirable, however, is a sensor that retains the total integrated sensitivity of a traditional SPR sensor and at the same time localizes this sensitivity right at the sensor surface. For this reason, we have investigated a hybrid structure composed of a 2D Au nanoparticle array coupled to a Au film. We show that this structure, when excited in the Kretschmann configuration, retains to a surprising degree the total integrated sensitivity of an ideal SPR sensor and is able to concentrate that sensitivity within a few nanometers of the sensor surface, thereby yielding a hybrid sensor with the advantages of both LSPR and SPR sensing, i.e. both a high local sensitivity and a high figure of merit (FOM).