RESUMO
Due to the wide range of applications of plasmonic diffraction gratings, it has become essential to provide an analytical method for modeling performance of the devices designed based on these structures. An analytical technique, in addition to greatly reducing the simulation time, can become a useful tool for designing these devices and predicting their performance. However, one of the major challenges of the analytical techniques is to improve the accuracy of their results compared to those of the numerical methods. So, here, a modified transmission line model (TLM) has been presented for the one-dimensional grating solar cell considering diffracted reflections in order to improve the accuracy of TLM results. Formulation of this model has been developed for the normal incidence of both TE and TM polarizations taking into account diffraction efficiencies. The modified TLM results for a silicon solar cell consisting of silver gratings considering different grating widths and heights have shown that lower order diffractions have dominant effects on the accuracy improvement in the modified TLM, while the results have been converged considering higher order diffractions. In addition, our proposed model has been verified by comparing its results to those of the finite element method-based full-wave numerical simulations.
RESUMO
In this paper, a novel graphene-based dual-band perfect electromagnetic absorber operating in the mid-infrared regime has been proposed. The absorber has a periodic structure which its unit cell consists of a sliver substrate and two graphene nanoribbons (GNRs) of equal width separated with a dielectric spacer. Two distinct absorption peaks at 10 and 11.33 µm with absorption of 99.68% and 99.31%, respectively have been achieved due to a lateral displacement of the GNRs. Since graphene surface conductivity is tunable, the absorption performance can be tuned independently for each resonance by adjusting the chemical potential of GNRs. Also, it has been proved that performance of the proposed absorber is independent of the incident angle and its operation is satisfactory when the incident angle varies from normal to ±75°. To simulate and analyze the spectral behavior of the designed absorber, the semi-analytical method of lines (MoL) has been extended. Also, the finite element method (FEM) has been applied in order to validate and confirm the results.
RESUMO
This paper presents the design and comprehensive analysis of an ultra-fast fractional-order temporal differentiator (DIFF) based on a plasmonic inner-wall Bragg grating microring resonator (BG-MRR). Due to the ring radius of 1.1 µm and the strong confinement of the surface plasmon polaritons in the plasmonic waveguide with very small cross-section, the overall footprint of the DIFF circuit is significantly small (approximately 4 × 2.5 µm2). By changing the coupling regimes of the microring resonator, a broad range for the differentiation order α, i.e., 0.7-1.7 and a wide 3 dB bandwidth of 3.1 THz [24.8 nm] for α = 0.7 and 3.9 THz [31.2 nm] for α = 1.7 have been realized. Comparing the outputs of the BG-MRR-based DIFF with the corresponding mathematical DIFF indicates that deviations for α > 1 are significantly larger than those of α < 1. Therefore, a fractional-order temporal DIFF circuit based on plasmonic cascaded BG-MRR has been proposed for α > 1.
RESUMO
In this paper, a graphene plasmonic waveguide consisting of Si graded gratings and a SiO2 separator has been designed in order to rainbow trap and release in the mid-infrared frequencies. Tunability of the light trapping and releasing in this proposed structure has been realized thanks to the adjustable chemical potential of the graphene. Using this structure, the light velocity has been decreased by a slowdown factor above 1270 with a trapping bandwidth of 3.5 µm. Due to the high tunability of this miniaturized structure, it can be used in a variety of applications including optical switches, buffers, and storages.
RESUMO
On-chip optical tweezers based on evanescent fields overcome the diffraction limit of the free-space optical tweezers and can be a promising technique for developing lab-on-a-chip devices. While such trapping allows for low-cost and precise manipulation, it suffers from unavoidable contact with the device surface, which eliminates one of the major advantages of the optical trapping. Here, we use a 1D photonic crystal cavity to trap nanoparticles and propose a novel method to control and manipulate the particle distance from the cavity utilizing a self-induced back-action (SIBA) mechanism and electrical-double-layer (EDL) force. It is numerically shown that a 200 nm radius silica particle can be trapped near the cavity with a potential well deeper than 178kBT by 1 mW of input power without any contact with the surface and easily moved vertically with nanometer precision by wavelength detuning.
