Eng Huat Khoo

Implementation of the FDTD Method Based on Lorentz-Drude Dispersive Model on GPU for Plasmonics Applications

We present a three-dimensional flnite difierence time domain (FDTD) method on graphics processing unit (GPU) for plasmonics applications. For the simulation of plasmonics devices, the Lorentz-Drude (LD) dispersive model is incorporated into Maxwell equations, while the auxiliary difierential equation (ADE) technique is applied to the LD model. Our numerical experiments based on typical domain sizes as well as plasmonics environment demonstrate that our implementation of the FDTD method on GPU ofiers signiflcant speed up as compared to the traditional CPU implementations.

Efficient Modeling and Simulation of Graphene Devices With the LOD-FDTD Method

The intraband term of the graphene electronic model is incorporated into Maxwell equations, and then the locally one-dimensional finite difference time domain (LOD-FDTD) method is applied to simulate graphene devices efficiently. Numerical results of the approach are compared with the explicit FDTD method. At Courant Friedrich Levy number (CFLN) equal to 100, the proposed approach is approximately 60% faster in terms of simulation time and with reasonable accuracy as compared to the FDTD method.

Modeling and simulation of active plasmonics with the FDTD method by using solid state and Lorentz–Drude dispersive model

An approach for the simulation of active plasmonics devices is presented in this paper. In the proposed approach, a multilevel multielectron quantum model is applied to the solid state part of a structure, where the electron dynamics are governed by the Pauli exclusion principle, state filling, and dynamical Fermi–Dirac thermalization, while for the metallic part, the Lorentz–Drude dispersive model is incorporated into Maxwell’s equations. The finite difference time domain method is applied to the resulting equations. For numerical results, the developed methodology is applied to a metal–semiconductor–metal plasmonic waveguide and a microcavity resonator.

A Hybrid Approach for Solving Coupled Maxwell and Schrödinger Equations Arising in the Simulation of Nano-Devices

A hybrid numerical technique for solving coupled Schrödinger and Maxwells equations for the simulation of nano-devices is presented. The finite-difference time-domain (FDTD) method is applied to Schrödingers equation, while the locally one-dimensional finite-difference time-domain (LOD-FDTD) method is applied to Maxwells equations for efficient simulation of the coupled equations. Results of the proposed approach are compared to those obtained via the conventional FDTD method.

Development of the CPML for Three-Dimensional Unconditionally Stable LOD-FDTD Method

A convolutional perfectly matched layer (CPML) is developed for three-dimensional unconditionally stable, locally one dimensional (LOD)-finite-difference time-domain (FDTD) method. The formulation of the LOD-FDTD CPML is derived and numerical results are demonstrated at different positions for different Courant Friedrich Levy numbers in the simulation domain. The method is validated numerically with FDTD-CPML.

Light Energy Extraction From the Minor Surface Arc of an Electrically Pumped Elliptical Microcavity Laser

In this paper, the efficiency of extracting light energy from the minor surface arc of the elliptical microcavity laser is investigated for the first time using the dynamic thermal electron quantum medium finite-difference time-domain model. Light energy is extracted from the minor surface arc of the elliptical microcavity to a perpendicular waveguide. It is deduced from the field distribution that extraction efficiency of the TM polarization is higher due to wider transverse field profile. Optimum light energy is extracted when the waveguide is 0.342 ¿m away from the edge of the elliptical minor arc. Higher extraction efficiency is also obtained when the waveguide index is lower than the microcavity index. It is believed that this method of extracting light energy allows for smaller device size with higher power output for building photonic integrated circuit.

π–π interactions mediated self-assembly of gold nanoparticles into single crystalline superlattices in solution

The first attempt of employing π–π interactions for the self-assembly of colloidal gold nanoparticles into 3D single crystalline superlattices in solution is presented. It is demonstrated that simple capping ligand exchange with aromatic thiols leads to self-assembly of gold nanoparticles into fcc packed superlattices with well-defined facets and long-range ordering. Stimuli that can break the π–π interactions lead to disassembly of gold nanoparticles, allowing the design of reversible assembly and reconfiguration. The crystallization of gold nanoparticles is shown to be kinetically controlled by the concentration of aromatic thiols in solution, enabling efficient tuning of the long- and short-range ordering in nanoparticle lattices, accompanied with corresponding changes of the effective optical properties.

Broadband Optical Response in Ternary Tree Fractal Plasmonic Nanoantenna

The ability to precisely tailor lineshapes, operational bandwidth, and localized electromagnetic field enhancements (“hot spots”) in nanostructures is currently of interest in advancing the performance of plasmonics-based chemical and biological sensing techniques. Fractal geometries are an intriguing alternative in the design of plasmonic nanostructures as they offer tunable multiband response spanning the visible and infrared spectral regions. A numerical study of the optical behavior of ternary tree fractal plasmonic nanoantenna is presented. Self-similar features are seen to emerge in the extinction spectra with the increase in fractal order N of the tree structure. Plasmon oscillations occurring at different length scales are shown to correspond to the multiple peaks and are compared with the spatial maps of electric field enhancement at the surface of the nanoantenna. The multiple peaks are shown to be independently tunable by structural variation. The robustness of the spectral response and polarization dependence arising due to various asymmetries is discussed.

Fabrication of suspended, three-dimensional chiral plasmonic nanostructures with single-step electron-beam lithography

Recent years have witnessed explosive development of chiral plasmonics due to the fact that chiral plasmonic nanostructures give rise to broadband and scalable chiroptical effects orders of magnitude larger than naturally occurring materials. Various chiral plasmonic nanostructures have been demonstrated based on top-down and bottom-up fabrication techniques. However, three-dimensional (3D) chiral plasmonic nanostructure fabrication still remains challenging in many aspects. Here, we demonstrate suspended 3D chiral plasmonic nanostructures fabricated with only one-step electron-beam lithography. Our approach is unique since no alignment is required in the fabrication processes and the top and the bottom structures are self-aligned. Our 3D chiral plasmonic nanostructure consists of a suspended ultrathin silicon nitride membrane with perfectly-aligned L-shape and disk-shape gold nanostructures on its two respective sides. Such suspended chiral plasmonic nanostructures possess strong chiroptical properties at optical frequencies, which can be engineered by simply changing the disk size on one side of the membrane. The origin of the chiroptical properties is also analyzed using the plasmon hybridization model. Experimental results are in good agreement with the finite-difference time-domain simulations. Such suspended chiral plasmonic nanostructures could be highly applicable for chirality analysis of biomolecules, drugs, and chemicals.

IMPLEMENTATION OF THE LORENTZ–DRUDE MODEL INCORPORATED FDTD METHOD ON MULTIPLE GPUs FOR PLASMONICS APPLICATIONS

The Lorentz–Drude model incorporated Maxwell equations are simulated by using the three-dimensional finite difference time domain (FDTD) method and the method is parallelized on multiple graphics processing units (GPUs) for plasmonics applications. The compute unified device architecture (CUDA) is used for GPU parallelization. The Lorentz–Drude (LD) model is used to simulate the dispersive nature of materials in plasmonics domain and the auxiliary differential equation (ADE) approach is used to make it consistent with time domain Maxwell equations. Different aspects of multiple GPUs for the FDTD method are presented such as comparison of different numbers of GPUs, transfer time in between them, synchronous, and asynchronous passing. It is shown that by using multiple GPUs in parallel fashion, significant reduction in the simulation time can be achieved as compared to the single GPU.