Jiangrong Cao

Higher-order incidence transfer matrix method used in three-dimensional photonic crystal coupled-resonator array simulation

The plane-wave-based transfer matrix method with rational function interpolation and higher-order plane-wave incidence is proposed as an efficient calculation approach to simulate three-dimensional photonic crystal devices. As an example, the dispersion relations and quality factors are calculated for resonant cavity arrays embedded in a woodpile photonic crystal. An interesting ultraslow negative group velocity is observed in this structure.

Size-dependent permittivity and intrinsic optical anisotropy of nanometric gold thin films: a density functional theory study.

Physical properties of materials are known to be different from the bulk at the nanometer scale. In this context, the dependence of optical properties of nanometric gold thin films with respect to film thickness is studied using density functional theory (DFT). We find that the in-plane plasma frequency of the gold thin film decreases with decreasing thickness and that the optical permittivity tensor is highly anisotropic as well as thickness dependent. Quantitative knowledge of planar metal film permittivitys thickness dependence can improve the accuracy and reliability of the designs of plasmonic devices and electromagnetic metamaterials. The strong anisotropy observed may become an alternative method of realizing indefinite media.

High-efficiency calculations for three-dimensional photonic crystal cavities.

A numerical method was developed by combining a plane-wave-based transfer matrix method and a robust rational function interpolation algorithm. The optical properties of three-dimensional photonic crystal cavities were extracted in a short computation time with high numerical accuracy.

Anisotropic permittivity of ultra-thin crystalline Au films: Impacts on the plasmonic response of metasurfaces

It has been determined by density functional theory (DFT) simulations that the extracted permittivities of ultra-thin crystalline gold (Au) films exhibit large anisotropies which are not predicted by classical models or previous experimental determinations of the dielectric function. The optical scattering characteristics of a periodic array of Au discs are simulated with the DFT extracted permittivity and contrasted against those obtained with several commonly used Au permittivity models. It is demonstrated that the DFT-based transmittance spectra for these plasmonic metasurfaces lead to significantly redshifted results when compared to those predicted by standard Drude and Johnson-Christy permittivity models.

Perfectly matched layer absorption boundary condition in planewave based transfer-scattering matrix method for photonic crystal device simulation

The performance of the perfectly matched layer absorption boundary condition is fully exploited when it is applied to the planewave based transfer-scattering matrix method in photonic crystal device simulation. The mode profile of one dimensional dielectric waveguide and the optical properties of sub-wavelength aluminum grating with semi-infinite substrate are studied to illustrate the accuracy and power of this approach.

New plasmonic materials in visible spectrum through electrical charging

Due to their negative permittivity, plasmonic materials have found increasing number of applications in advanced photonic devices and metamaterials, ranging from visible wavelength through microwave spectrum. In terms of intrinsic loss and permittivity dispersion, however, limitations on available plasmonic materials remain a serious bottleneck preventing practical applications of a few novel nano-photonic device and metamaterial concepts in visible and nearinfrared spectra. To overcome this obstacle, efforts have been made and reported in literature to engineer new plasmonic materials exploring metal alloys, superconductors, graphene, and heavily doped oxide semiconductors. Though promising progress in heavily doped oxide semiconductors was shown in the near-infrared spectrum, there is still no clear path to engineer new plasmonic materials in the visible spectrum that can outperform existing choices noble metals, e.g. gold and silver, due to extremely high free electron density required for high frequency plasma response. This study demonstrates a path to engineer new plasmonic materials in the visible spectrum by significantly altering the electronic properties in existing noble metals through high density charging/discharging and its associated strong local bias effects. A density functional theory model revealed that the optical properties of thin gold films (up to 7 nm thick) can be altered significantly in the visible, in terms of both plasma frequency (up to 12%) and optical permittivity (more than 50%). These corresponding effects were observed in our experiments on surface plasmon resonance of a gold film electrically charged via a high density double layer capacitor induced by a chemically non-reacting electrolyte.

Gain-scattering-matrix method for photonic crystal laser simulations

We derive a light-intensity-dependent dielectric constant for gain medium based on the conventional rate equation model. A scattering-matrix method in conjunction with an efficient iteration procedure is proposed to simulate photonic crystal lasers (PCLs). The light output vs pumping (L-I) curve, lasing mode profile, and chirping effect of lasing wavelength can be calculated. We check our method in a 1D DBR laser and the L-I curve agrees well with results by the rate equation model. Our method can be extended to 3D systems. More complex 2D and 3D PCLs will be simulated in the future.

Improved transfer matrix method used in photonic crystal devices design

The planewave based transfer matrix method has been developed with rational function interpolation to efficiently simulate photonic crystal devices. Cavities embedded in three-dimensional layer-by-layer photonic crystal are systematically studied as an example to show the power of transfer matrix method with the relation between resonant frequencies and the cavity size obtained.