Strong coupling between localized and propagating surface plasmon modes in a noncentrosymmetric metallic photonic slab

We have investigated the coupling behaviors between localized and propagating surface plasmon modes in a non-centrosymmetric structure consisting of an L-shaped metal nanoparticle array and a thick metal film, separated by a silica dielectric spacer layer. It is found that surface plasmon modes exhibit hybrid behaviors due to the non-centrosymmetry of the structure. The hybrid surface plasmon modes will interact with different-order localized plasmon modes in the nanoparticle in their spectrally overlapping regions. The strong coupling between the localized and propagating plasmon modes gives rise to the energy anticrossing behavior with large mode splitting. Furthermore, a narrow absorption branch is also observed between two anticrossing absorption branches, which is absent in the centrosymmetric system. The findings hold promise in applications such as photonic and energy conversion systems and the design of novel plasmonic nanodevices. (C) 2014 Optical Society of America