Influence of a gold nano-bumps surface lattice array on the propagation length of strongly coupled Tamm and surface plasmon polaritons

Abstract

The total internal reflection ellipsometry (TIRE) method was used for the excitation and study of the strong coupling between a Tamm plasmon polariton (TPP) and a surface plasmon polariton (SPP) in nanophotonic structures with 1D photonic crystals (PCs) and a gold nano-bumps lattice array on the top. Recent studies have shown that lattice of gold nano-bumps induced the generation of an additional Bragg mode, related with the lattice period which is not involved in the strong coupling of the hybrid TPP–SPP polaritonic mode. The detailed analysis has shown that the propagation length of the SPP increased, while the TPP decreased, due to the formation of an additional Bragg mode. The optical dispersion and propagation features of plasmons in 1D PCs with a uniform gold layer and the lattice of gold nano-bumps array were analysed by two coupled oscillator models and by wave vector vs. energy broadening. For the nanostructures with a uniform gold layer, the evaluated propagation length was δ_SPP ≈ 5.5–6.5 μm and δ_TPP ≈ 6.5–9.5 μm for SPP and TPP components in the hybrid polaritonic mode, respectively. Meanwhile, the changes induced by the periodic gold surface lattice resulted in a longer propagation length for the SPP component, where δ_SPPlattice ≈ 7–10.5 μm, and a decreasing length for TPP, where δ_TPPlattice ≈ 5.5–8.5 μm. The obtained results demonstrate a novel approach to control and change the propagation length under the strong coupling regime between TPP and SPP components in the hybrid plasmonic mode by using surface lattice arrays. The fabricated nanophotonic–plasmonic structures show the potential impact of direct laser writing (DLW) as a cost-effective, fast and large area coverage method for creating integrated photonic devices with designed properties, in this case changing the propagation length and coherence properties in the hybrid plasmonic mode. The application of surface lattice resonances together with the strong coupling regime leads to decreasing losses, resulting in the increasing propagation length and improved coherence properties of such plasmonic excitations, which, in turn, promises advanced properties for low electrical consumption or thresholdless plasmonic-based coherent emission nano-sources.