Tamm-surface plasmon hybrid mode for improving sensing figure of merit

The hybrid coupling of Tamm plasmon polariton (TPP) and surface plasmon polariton (SPP) on the surface of a gold film based on the prism coupling has attracted extensive attention and has been widely investigated. However, the traditional excitation configuration has bulky optical elements and requires accurate control of the angle of incident light, which limits its integration and practical application. In order to simplify the excitation condition of the TPP-SPP hybrid mode, a feasible grating-coupled multilayer stack structure is proposed in this paper. The structure mainly consists of three parts: a nanometric thin gold film on the top layer, a one-dimensional Bragg photonic crystal in the middle, and a gold nanograting on the bottom. In this structure, the SPR and TPP resonance excitations on the upper and lower surfaces of the top gold film are simultaneously achieved by utilizing the first-order transmitted light of the bottom nanograting. The hybrid coupling between the two modes greatly reduces the resonance bandwidth of the generated mode, thereby significantly improving the sensing figure of merit of the generated mode. Additionally, the hybrid coupling of both SPP and TPP modes can be realized in a wide spectral range by altering the period of the nanograting and the thickness of the one-dimensional Bragg photonic crystal. Compared with the traditional prism-coupled TPP and SPP dual-mode coupling structures, the designed grating-coupled multilayer nanostructure can realize the resonant coupling of the two modes at the normal incidence without prism and limitation of incident angle. This not only facilitates the further integration and miniaturization of the structure, but also has important significance for broadening the practical application of surface plasmon resonance sensors.