Qian-jin Wang

Optical switching of a metamaterial by temperature controlling

We have fabricated a metamaterial of metal/semiconductor/metal sandwich nanostrips structure comprising a pair of gold strips and a vanadium dioxide (VO2) strip. The optical response of the metamaterial has been studied. The results indicate the nanostructure with VO2 strips can be used as a temperature-controlling optical switch and the mechanism of this switch can be explained by the magnetic resonance.

Extraordinary optical transmission induced by excitation of a magnetic plasmon propagation mode in a diatomic chain of slit-hole resonators

In this paper, we will propose that magnetic-resonance nanostructures in a metal surface could be used to realize extraordinary optical transmission EOT. Toward this goal, we designed and fabricated a onedimensional diatomic chain of slit-hole resonator SHR. Due to the strong exchange current interaction, a type of magnetic plasmon MP propagation mode with a broad frequency bandwidth was established in this system. Apparent EOT peaks induced by the MP mode were observed in our measured spectra at infrared frequencies. The strongest EOT peak was obtained at 1.07 eV with an incident angle of 20°. The measured dependence of EOT peaks on the incident angle coincided with the theoretical results quite well. This proposed MP propagation mode in SHR structure has good potential applications in multifrequency nonlinear optical processes.

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.

Dual effect of surface plasmons in light transmission through perforated metal films

The light transmission through square and rectangular holes in a metal film has been studied. By taking account of plasma response of real metal on hole walls as well as metal surface, an analytical result for the transmission has been deduced, which agrees well with the experiments. We show that the light transmission involves both the diffraction modes and the surface plasmons. Strong coupling of diffraction modes to surface-plasmon polariton results in the transmission minima, whereas the coupling to cavity surface plasmon leads to the transmission maxima. The results suggest a dual effect of the surface plasmons.

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.

Position-sensitive spectral splitting with a plasmonic nanowire on silicon chip

On-chip nanophotonics serves as the foundation for the new generation of information technology, but it is challenged by the diffraction limit of light. With the capabilities of confining light into (deep) subwavelength volumes, plasmonics makes it possible to dramatically miniaturize optical devices so as to integrate them into silicon chips. Here we demonstrate that by cascading nano-corrugation gratings with different periodicities on silver nanowires atop silicon, different colors can be spatially separated and chronologically released at different grating junctions. The released light frequency depends on the grating arrangement and corrugation periodicities. Hence the nanowire acts as a spectral splitter for sorting/demultiplexing photons at different nano-scale positions with a ten-femtosecond-level interval. Such nanowires can be constructed further into compact 2D networks or circuits. We believe that this study provides a new and promising approach for realizing spatiotemporal-sensitive spectral splitting and optical signal processing on nanoscales, and for general integration of nanophotonics with microelectronics.

Long-Wavelength Optical Properties of a Plasmonic Crystal

The optical properties of a plasmonic crystal composed of gold nanorod particles have been studied. Because of the strong coupling between the incident light and vibrations of free electrons, the long-wavelength optical properties such as the dielectric abnormality and polariton excitation etc., which were suggested originally in ionic crystals, can also be present in the plasmonic crystal. The results show that the plasmonic and ionic lattices may share a common physics.

Plasmonic antenna array at optical frequency made by nanoapertures

We show here that the plasmonic array based on nanoapertures in ultrathin silver film radiates at optical frequency and behaves as an optical antenna array (OAA). The far-field radiation originates from the coherent superposition of plasmonic emissions on each bank of the aperture. The radiation of OAA presents a strong directivity, which depends on the in-plane rotation of aperture array, and on the polarization and incidence angle of the excitation light as well. We suggest that these features have potential applications in photovoltaics, light-emitting devices, and optical sensors.

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.