We study biological sensing using the hybridization phase of localized surface plasmon resonances (LSPRs) with diffraction modes (photonic lattice modes) in arrays of gold nanoantennas. We map the degree of the hybridization process using an embedding dielectric material (Si), identifying the critical thicknesses wherein the optical responses of the arrays are mainly governed by pure LSPRs (insignificant hybridization), Fano-type coupling of LSPRs with diffraction orders (hybridization state), and their intermediate state (hybridization phase). The results show that hybridization phase can occur with slight change in the refractive index (RI), leading to sudden reduction of the linewidth of the main spectral feature of the arrays by about one order of magnitude while it is shifted nearly 140 nm. These processes, which offer significant improvement in RI sensitivity and figure of merit, are utilized to detect monolayers of biological molecules and streptavidin-conjugated semiconductor quantum dots with sensitivities far higher than pure LSPRs. We further explore how these sensors can be used based on the uncoupled LSPRs by changing the polarization of the incident light.

We study control of optical coupling of plasmon resonances in metallic nanoantenna arrays using ultrathin layers of silicon. This technique allows one to establish and tune plasmonic lattice modes of such arrays, demonstrating a controlled transformation from the localized surface plasmon resonances of individual nanoantennas to their optimized collective lattice modes. Depending on the polarization and incident angle of light, our results support two different types of the silicon-induced plasmonic lattice resonances. For $s$-polarization these resonances follow the Rayleigh anomaly, while for $p$-polarization an increase in the incident angle makes the lattice resonances significantly narrower and slightly blueshifted.

We show that under certain conditions the plasmonic field of a hybrid system consisting of a metallic nanoparticle and a semiconductor quantum dot can be converted into ultrashort stationary pulses with temporal widths as short as 300 ps. This happens as this system interacts with an infrared and visible laser fields, both with time-independent amplitudes. These fields generate quantum coherence via simultaneous interband and intersubband transitions of the quantum dot, forcing the polarization dephasing rate of the quantum dot to become negative during the plasmon pulses. This makes the amplitudes of such pulses time-independent (undamped), indicating total suppression of quantum decoherence of the quantum dot. These results suggest that hybrid quantum dot-metallic nanoparticle systems can act as undamped coherent-plasmonic oscillators.

We demonstrate tunable polarization-dependent infrared plasmonic lattice modes in the range of 1 to 1.7 μm in arrays of large gold nanodisks with a rectangle lattice structure. We show that when these arrays are exposed to air, their main mode appears around 1 μm. Under this condition, addition of chemicals leads to significant wavelength shifts in this mode, offering a refractive index sensitivity of about 795 nm/RIU (refractive index unit). Our results show that this process is accompanied by excitation of a sharp peak associated with an infrared lattice mode at about 1.62 μm, suggesting an abrupt refractive-index switching of the collective modes of the arrays. By depositing ultrathin layers of Si, we show that the wavelength of the 1 μm mode can be shifted, covering the whole telecom band ranges. We demonstrate that this can lead to tunable narrow- and wide-band polarization switching of the collective modes of the arrays within this range with a high extinction ratio.