Lingxi Wu

Modes and carrier density in dispersive and nonlinear gain planar photonic crystal cavity

The cavity mode and carrier density in dispersive and nonlinear gain planar photonic crystal cavities are studied with the three-dimensional finite-difference time-domain method. Planar photonic crystal cavity can enhance light mater interaction, which can be used to design a photonic crystal cavity laser. With the effect of both total internal reflection and photonic band gap confinement, the frequency responses of the planar photonic crystal cavity can be obtained by simulation. The effect of carrier diffusion is calculated through the laser rate equations. The electric field intensity distribution, temporal behavior of electric field energy, and carrier density characteristics are analyzed from the resonance cavity mode.

Second-order nonlinearity assisted by dual surface plasmon resonance modes in perforated gold film

We have studied analytically the reflection assisted with surface plasmon through the square lattice perforated gold film. Under the excitation of the external electromagnetic field with one or two different frequencies, the second-order nonlinearity exists in this noncentrosymmetric metal-based metamaterial. We employed the two surface plasmon resonances modes with different lattice periods. With the excitation of two different plasmon resonances modes, the strong local field induces an expected increase of the second-order nonlinearity including second harmonic generation as well as the sum (difference) frequency generation. The field distributions results also indicate that the enhancement of sum frequency signals and difference frequency signals strongly depends on surface plasmon resonance effect.

Fano resonances of a metal nanorod array with a symmetry breaking wedge and gain medium filling

Fano resonances of a metal nanorod array with a symmetry breaking wedge and gain medium filling have been explored using the finite-difference time-domain method. Results show that a periodic symmetry breaking nanorod array supports Fano resonance due to the interaction between a hybridized dipolar plasmon mode of the nanorod and a narrower quadrupolar mode of the slice. By a tiny increase of the imaginary part of the dielectric constant of the gain medium, the Ohmic loss can be counteracted, and Fano resonance dip gets deeper significantly. Additionally, the modulation depth can be improved by changing the real part of the gain medium dielectric constant. The results found are useful for further develop of the devices on the basis of the Fano resonance and its modulation.

Optical bistability effect in SPP-based metallic grating containing Kerr nonlinear medium

We theoretically investigate the characteristics of the resonant modes and the optical bistability (OB) effect in the proposed metal–insulator–metal plasmonic structure containing Kerr nonlinear medium. By using finite difference time domain (FDTD) method, it is found that the plasmon resonance modes can be modulated with the change of the height of metallic grating, the thickness of Kerr material layer and refractive index. We also study the characteristic of OB with the correspondingly detuning parameters. The designed plasmonic structure can be potentially applied to projecting SPP-based nonlinear optical devices in integrated optical circuits.

Second-order nonlinearity in triangular lattice perforated gold film due to surface plasmas resonance.

We have studied the excitation second-order nonlinearity through a triangular lattice perforated gold film instead of square lattice in many papers. Under the excitation of surface plasmas resonance effect, the second order nonlinearity exists in the noncentrosymmetric split-ring resonators arrays. Reflection of fundamental frequency wave through a triangular lattice perforated gold film is obtained. We also described the second harmonic conversion efficiencies in the second order nonlinear optical process with the spectra. Moreover, the electric field distributions of fundamental frequency above the gold film region are calculated. The light propagation through the holes results in the enhancement of the second order nonlinearity including second harmonic generation as well as the sum (difference) frequency generation.

Fano resonance of the symmetry-reduced metal bar grating structure

We demonstrate that Fano resonance and even multipole Fano resonance can be obtained in a symmetry-reduced structure composed of gold bars with different bar sizes or bar shapes on a layer of dielectric. There is a transparency window opened within the frequency region of the absorptive dipole resonance by metallic bars, as long as the narrow grating waveguide mode induced by reducing symmetry is coincided in spectrum with the dipole resonance such that a destructive interference happens between these two resonant modes. Line shape of the transmission spectra of the nanostructure can be modulated effectively by changing the size or shape of the series of metal bars. The results found can be useful in the design of novel optical device.

High absorption and second-harmonic generation in split ring resonator multilayer nanostructure

Second-harmonic generation in split ring resonator multilayer nanostructure is studied with the finite-difference time-domain (FDTD) method. The fundamental frequency wave and the second-harmonic generation at the resonant absorption wavelength are highly localized in the dielectric layer, and the absorption peak is sensitive to dielectric constant of the dielectric layer. Under the excitation of the plasmon resonances mode, the strong local field induces an expected increase of the second-harmonic generation with conversion efficiencies 10-6-10-7. The distributions of fundamental frequency electric field and second-harmonic electric field inside the central dielectric layer region are also shown.

Bloch harmonics and focusing properties in the photonic crystal planoconcave lens structure

Focusing properties of a plane wave by the photonic crystal (PC) concave lens placed in the air environment are studied through the finite-difference time-domain technique. The PC concave lens works in the frequency window located in the second transversal electric (TE)-polarized photonic band. A good-quality focus of a plane wave can form out of the planoconcave lens, while a plane wave is also formed for a point source placed at the focus point consistent with the analysis of the band structure and the equifrequency contours. Besides the plane-wave expansion method, we also analyze the Bloch harmonics inside the region of planoconcave lens with the Fourier analysis method. It is shown that the Bloch mode, which consists of more than one spatial frequency, contributes to the focus. The results show that the spatial frequencies in the second Brillouin zone are mainly generated due to the periodic potential arising from the PC or the existence of the interfaces.