Polarization-Insensitive Ultra-Narrow Plasmon-Induced Transparency and Short-range Surface Plasmon Polariton Bloch Wave in Ultra-thin Metallic Film Nanostructures

We demonstrate that polarization-insensitive ultra-narrow double plasmon-induced transparency (PIT) can be achieved in the thin-metal-film nanostructures. Ultra-narrow PIT resonance with a bandwidth of 2.5nm at central wavelength of 768nm was obtained (similar to 1/307 of the peak wavelength). Multispectral PIT can be obtained, and its linewidth and the on-off state of the PIT peaks in the system can be adjusted by the metallic nanostructure thickness and particularly the waveguide layer thickness. The narrow transparency window is exhibited to be generated by the coupling and interference between a delocalized hybrid-waveguide photonics mode and the localized surface plasmon (LSP) mode. The angular-dependent dispersion of the system with double PITs is examined and investigated, where the high-order short-range surface plasmon polariton (SRSPP) Bloch waves excited for large incidence angles are indicated and revealed. The multispectral PITs with high quality in the large-area plasmonic system are promising for practical and compact nanophotonics applications such as optical buffers, ultra-sensitive sensor, plasmonic filters, and switches.