Plasmon-induced transparency and Fano resonances in metal-insulator-metal nanorod dimers: A numerical analysis

Three-dimensional plasmonic nanorods are theoretically investigated to achieve plasmon-induced transparency and Fano resonances in visible to near-infrared region. The plasmonic nanostructure consists of periodic array of a top in-plane side-by-side assembling nanorod dimer and a bottom nanorod separated by a dielectric spacer. With transverse excitation, which means that the E-component of the incident field is along the short axis of the nanorods, anti-parallel oscillations in the metal-insulator-metal (MIM) structure lead to magnetic resonances in the dielectric cavity, and magnetic surface plasmons (MSPs) can also be induced by the mode couplings in the in-plane nanorod dimer. Interferences of magnetic resonances and localized surface plasmons (LSPs) of nanorods lead to Fano resonances in MIM nanorod dimer. Furthermore, a significantly broad optical magnetism and transparency window is shown through the hybridization of the vertical and in-plane mode interactions. The extinction spectra can be tuned by the aspect ratio (AR), gap and periodicity of nanorods. This unique characteristic of MIM nanorod dimer can realize many potential applications of plasmon-induced transparency and Fano resonances, such as multi-wavelength biosensing and optical antenna. PMMA block is chosen to simulate non-uniform distributed analyte. It is localized on different zones upon the MIM dimer to theoretically determine the sensing effectiveness. Simulation shows that the in-plane small gap of the top MIM dimer largely increases the sensing sensitivity of the magnetic resonance of MIM structure.