Jia-Qi Li

Enhanced optical transmission through metal films with rotation-symmetrical hole arrays

The transmission of light through metal surface with subwavelength holes are influenced by many factors, and the rotational symmetry of hole arrays can be one of them. In this paper, we fabricated the hole lattices in metal films with different symmetry and measured the transmission spectra from the visible to near-infrared region. It is found that both the spectrum shape and the transmission efficiency are strongly dependent on the rotational symmetry. The spectrum shape is governed by the reciprocal vectors. And the higher is the symmetry order, the larger the peak efficiency. The results provide us with new insight into the unusual effect.

Exploring magnetic plasmon polaritons in optical transmission through hole arrays perforated in trilayer structures

Optical transmission properties through hole arrays in metal/dielectric/metal trilayer structures were demonstrated. Besides the surface plasmon induced strong transmission and well-recognized negative refraction band, a higher mode was observed and elaborately investigated. Detailed results showed that this mode belongs to a higher magnetic excitation related to the reciprocal vector G1,1 of the lattice, and a “magnetic plasmon polariton (MPP)” model was proposed to describe such magnetic excitations in periodically modulated structure. By adjusting the structural parameters, the authors can conveniently control the MPPs’ properties, which provide us another way to tailor the light propagation properties in subwavelength structures.

Optical toroidal dipolar response by an asymmetric double-bar metamaterial

We demonstrate that the toroidal dipolar response can be realized in the optical regime by designing a feasible nanostructured metamaterial, comprising asymmetric double-bar magnetic resonators assembled into a toroid-like configuration. It is confirmed numerically that an optical toroidal dipolar moment dominates over other moments. This response is characterized by a strong confinement of an E-field component at the toroid center, oriented perpendicular to the H-vortex plane. The resonance-enhanced optical toroidal response can provide an experimental avenue for various interesting optical phenomena associated with the elusive toroidal moment.

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.

All-optical Hall effect by the dynamic toroidal moment in a cavity-based metamaterial

Dynamic dipolar toroidal response is demonstrated by an optical plasmonic metamaterial composed of double disks. This response with a hotspot of localized E-field concentration is a well-behaved toroidal cavity mode that exhibits a large Purcell factor due to its deep-subwavelength mode volume. All-optical Hall effect (photovoltaic) due to this optical toroidal moment is demonstrated numerically, in mimicking the magnetoelectric effect in multiferroic systems. The result shows a promising avenue to explore various optical phenomena associated with this intriguing dynamic toroidal moment.

Dispersion of magnetic plasmon polaritons in perforated trilayer metamaterials

Multiple magnetic plasmon polariton (MPP) modes were recently explored in a well-known system—metal∕insulator∕metal layered structure perforated with periodic holes array [Appl. Phys. Lett. 90, 251112 (2007)]. Now, we consequently study the dispersions of the MPP modes in similar systems with rectangular hole arrays by analyzing the detailed optical transmittances at oblique incidences. Significantly, our results provide a definite polarization-dependent dispersion property of MPP modes: strong dispersive MPP(±1,±1) modes with the degeneration broken up and a remained degenerate MPP(0,±1) mode for s-polarization and almost flat dispersions of all MPP modes for p-polarization. Such a phenomenon is explained by the different coupling intensities among the artificial “magnetic atoms.” This finding helps us to make a deeper understanding on the artificial magnetic excitations in this trilayer metamaterial.

Excitation of plasmon toroidal mode at optical frequencies by angle-resolved reflection.

Plasmon toroidal mode is a unique electromagnetic resonance that cannot be expanded by general electronic or magnetic multipoles. Usually, this mode excitation needs complicated nanostructures, which is a challenge for sample fabrications, especially for nanodesigns with optical resonant frequencies. In this work, we designed a circular V-groove array and studied its toroidal-mode excitation by angle-resolved reflection experimentally and numerically. Our results show that a plasmon toroidal mode around wavelength 700 nm can be excited in this simple nanostructure for incident angles larger than 20°. Compared to reported papers, our design can realize the optical excitation of plasmon toroidal mode, which is useful in high-sensitivity plasmon sensors.

Suppression of transmission minima and maxima with structured metal surface

Extraordinary optical transmission through perforated metal films has received much attention recently. In this letter, the authors propose a method for studying the transmission properties, in which the Fourier coefficient of reciprocal lattice vectors is manipulated. Especially, due to a zero Fourier coefficient, the suppression of transmission minima and maxima has been experimentally observed. The results open a way to tailor the transmission properties of light.

Optical transmission through gold film with Archimedean-like subwavelength hole arrays

In this paper, two kinds of Archimedean-like hole arrays [Archimedean 4 (A4) and Archimedean 7 (A7)] that have been fabricated in gold films and the optical transmission spectra from the visible to near-infrared region have been measured. With A4 and A7 hole arrays, the Fourier coefficients of reciprocal lattice vectors are manipulated, with which the transmission suppression and enhancement have been experimentally observed. The results provide the possibility to manipulate the light transmission through the design of both reciprocal vectors and Fourier coefficients by engineering the metal surface.

Light reflection from a metal surface with subwavelength cavities

The interaction of light with the localized/delocalized system, i.e., a metal surface with rectangular cavities of finite depth, has been studied. Reflection spectrum has been measured in the optical frequencies, and resonant minima have been observed. We have developed an analytical model, which agrees well with the experiment. The localized waveguide resonance and delocalized surface resonance have been identified and discussed. The results may be useful for manipulating the coupling between light and matters.