Shan Wu

Enhanced optical transmission : Role of the localized surface plasmon

We report the observation of enhanced optical transmission through the metal subwavelength hole arrays with nanoparticle inside the hole, and demonstrate the transmission enhancement and the suppression due to the excitation of the localized surface plasmon (LSP). We interpret this phenomenon with the Fano theory considering the real and imaginary parts of the polarizability of the LSP.

Electric quadrupole excitation in surface plasmon resonance of metallic composite nanohole arrays

We present an experimental and theoretical study on the composite nanostructures composed of the LT-shaped metallic nanohole arrays. Multiple resonance transmission peaks are observed in the optical transmission spectra. By analyzing their electric field distributions on the interface, we infer the electric dipole and the electric quadrupole plasmonic resonances contribute to these transmission peaks. The electric quadrupole is a subradiant mode, which cannot be directly excited by the incident light. Here, we demonstrate that the surface plasmon polaritons can excite the electric quadrupole plasmonic resonance mode through the near-field interaction.

Enhanced optical transmission through metal-dielectric multilayer gratings

The optical transmission properties of metal-dielectric multilayer gratings have been investigated both experimentally and numerically. A remarkable transmission resonance, which makes a significant difference from that of traditional single/triple-layer analogs, has been reported. To understand its physical origin, a field-interference mechanism of dipole arrays induced by the lateral and vertical plasmon coupling has been suggested.

Photocurrent in Ag–Si photodiodes modulated by plasmonic nanopatterns

We demonstrate that Ag–Si photodiodes allow photocurrents to be modulated by changing periods of nanopatterns on Ag film. The maximum and minimum photocurrents occur in certain periods corresponding to the excitation of surface plasmon polariton and Wood’s anomaly, which can be predicted with the help of related theories. Therefore, it is feasible to design nanopatterns to satisfy special requirements.

Asymmetric transmission and optical rotation of a quasi-3D asymmetric metallic structure

Three-dimensional (3D) asymmetric plasmonic structures possessing asymmetric optical transmission properties have been widely studied. However, these structures have limitations for application due to fabrication techniques. Here, a quasi-3D asymmetric structure built up by a metallic rod-shaped particles layer and a metallic L-shaped holes layer was fabricated by the sputtering and the focused ion beam (FIB) milling. A broadband (1000-1600 nm) asymmetric transmission and optical rotation have been demonstrated experimentally. Numerical calculations show that the coupling between the cavity and particle plasmonic resonances contributes to this effect.

Hybridized effects of plasmonic quadrupolar and dipolar resonances on the perforated planar metallic film

We have designed a detuned double-L-shaped nanohole arrays in the metallic film, on which the hybridized plasmonic quadrupolar and dipolar resonance modes can be excited by the incident light, respectively. Compared with the conventional plasmonic resonance modes, the antibonding quadrupolar resonance mode has a higher quality factor due to its lower radiative loss. A quality factor of 38 (theoretical prediction exceeding 100) is obtained in the experiment.

Novel optical transmission property of metal–dielectric multilayered structure

A kind of planar metal–dielectric multilayered plasmonic structure has been proposed and its optical properties have been studied. Numerical calculations show that both the electric resonance (surface-plasmon polariton resonance) and the magnetic resonance (localized magnetic-plasmon resonance) can enhance the optical transmission. Moreover, by modulating the dimensions of the proposed structure, a large resonance quality factor and a continuum resonance can be achieved. These controllable optical properties might be useful for various practical implementations.

Giant circular dichroism and its reversal in solid and inverse plasmonic gammadion-shaped structures

Chiral plasmonic structures have been shown to possess large circular dichroism (CD) responses. Here, we investigate the CD responses in a solid and inverse metallic structure composed of a stacked right-twisted gammadion metallic nanoparticle and a left-twisted gammadion nanoaperture array, where a giant circular dichroism is achieved. In addition, the sign of the CD responses can be reversed through the changes of the geometric parameters. Further analysis reveals that the Fabry-Perot (F-P) resonance of cross-polarization conversion of electric field governs the change of the CD. It can be envisioned that our findings will allow further tuning and manipulation of the CD responses for tailored circular polarized light-matter interaction.

Phaselike resonance behavior in optical transmission of sandwich coaxial square ring arrays

We studied the optical transmission through sandwich coaxial square ring arrays experimentally and theoretically. The hybridized mode of the localized surface-plasmons and surface-plasmon polaritons has been observed. This hybridized mode resembles the phase resonance mode in a compound gratingstructure and can be named as phaselike resonance mode. For the 0-phase resonance mode, energy can tunnel through the sample due to coherent constructive interference, forming a peak in the transmission spectrum. For the π -phase resonance mode, a dip appears instead. When the incident angle is increased, the π -phase resonance mode is split into two branches, one is redshifted while the other blueshifted.

Multiple out-of-plane plasmonic resonances in thick metallic rod with a cavity

We propose a nanostructure composed of a thick metallic rod with a cavity, in which multiple out-of-plane plasmonic resonances can be excited. When the cavity is laterally shifted to form an asymmetric nanostructure, the coupling between the plasmonic resonances excited in an individual element of the rod produces high-order hybridized out-of-plane modes with narrow linewidth. A further analysis reveals that the hybridized modes have Fano-like spectral line-shapes, which can be accurately described by a coupled oscillator model.