Tunable power splitter based on MIM waveguide-rectangle cavity system with Kerr material

Analysis of the plasmonic power splitter and MUX/DEMUX suitable for photonic integrated circuits

Tunable dual-wavelength terahertz wave power splitter

Tunable lumped power splitter based on tunable parallel ferroelectric capacitor is proposed. The ferroelectric BST(barium strontium titanate) capacitor is fabricated on a sapphire substrate. The capacitance of this device has a tunability of 50% for an applied voltage of 5V. The performance of the power splitter is simulated with Agilent Technology ADS software tool. The lumped power splitter is fabricated on an FR-4 RF bread-board with discrete chip inductors and tunable capacitors. The maximum return loss frequency(notch frequency) of the power splitter can be tuned from 369 MHz to 626 MHz by applying a DC bias of 5V. Unlike p-n junction based power splitter, the tuning is independent of the polarity of the applied bias.

ABSTRACTWe have numerically investigated the tunable surface plasmon in graphene square-nanoring structure. Due to an enhancement of the local field, graphene surface plasmons (GSPs) can be strongly confined in the graphene grating region. The expressions of the lifetime for resonant modes have been investigated with the the finite difference time domain (FDTD) simulations and the coupled mode theory (CMT). Altering the Fermi energy and varying the carrier mobility have an important influence in optimizing the light absorption and the lifetime of GSPs. The CMT theoretical results agree well with FDTD simulations. Besides, by utilizing the different inner length and the different refractive index of substrate material, we find that the absorption peak of the GSPs structure can be tuned in a wide wavelength range. Our proposed graphene gratings structure shows good prospects in the mid-infrared region, such as ultracompact tunable integrated modulators and absorbers.

New version of FDTD with GFM program in Schwarzschild space–time

Ultrafast and low-power all-optical switch based on asymmetry electromagnetically induced transparency in MIM waveguide containing Kerr material

The Finite-Difference Time-Domain (FDTD) method is used to study the scattering effects of extreme ultraviolet (EUV) mask. It requires significant amounts of memory and computation time as the fine grid size is needed for simulation. Theoretically, the accuracy can be increased as the mesh size is decreased in FDTD simulation. However, it is not easy to get the accurate simulation results for the multilayer (ML) structures by FDTD method. The transmission line theory is used to calculate the equivalent refractive index for EUV mask ML to simulate the ML as one layer of bulk artificial material. The reflectivities for EUV light with the normal incidence and small-angle oblique incidence in the bulk artificial material and EUV mask ML are simulated by FDTD method. The Fresnel's equation is used to evaluate the numerical errors for these FDTD simulations, and the results show good agreement between them. Using the equivalent refractive index material for EUV multilayer mask can reduce the computation time and have the accuracy with tolerable numerical errors. The ML structure with periodic surface roughness is also studied by this method, and it shows that only half of computation time is needed to substitute ML to a bulk equivalent refractive index material in FDTD simulations. This proposed method can accelerate the simulations of EUV mask designs.

The numerical dispersion is one of the main factors to affect the accuracy of the finite-difference time-domain (FDTD) method. It can be easy to be taken for granted that a smaller time step leads to smaller simulation errors. This paper reveals that smaller time steps do not always make more accurate results in FDTD simulations. We analytically investigated how time steps affect the numerical dispersion of two FDTD methods: the leapfrog FDTD(2,2) method and the FDTD(2,4) method. The investigations in this paper show that in the FDTD(2,2) method, a larger time step limited by the Courant-Friedrichs-Lewy (CFL) condition is more helpful to reduce the numerical dispersion error. However, in the FDTD(2,4) method, as the time step grows, the numerical dispersion error decreases at the beginning and then increases. Several numerical examples are carried out to verify our analysis.

The perfect plasmon-induced absorption (PIA) effect is achieved in a simple plasmonic system, composed of two rectangle cavities side-coupled to the metal-insulator-metal (MIM) waveguide with a barrier. The transmission properties of the system are calculated by the finite-difference time-domain (FDTD) method and theoretically explained by the three-level plasmonic system. More interestingly, the broadband absorption window will be splitted into double windows by adding another rectangle cavity resonator, and the physical mechanism is presented. At the same time, multi-switching effect is also discovered. Undoubtedly, the proposed novel structures have potential application in highly integrated optical circuit and can be simply fabricated.

It is very useful to know the soil capabilities on different external impacts acting on it, especially for electromagnetic waves from Ground Penetrating Radar. In the underground detection domain actually, dealing with soil permittivity is one of the challenging research problems nowadays. In this paper, we study tropical soil constitution, taking in account the tropical climate region and we took Rwanda as a case study. Rwanda's elevation ranges from 1,000m (south and east) to 4,500m above sea level. The "thousand hills" terrain is dominated from north to south by a watershed (2.500m high) that separates the basin of the Congo River from that of the Nile and by the Ibirunga volcano chain. In spite of its proximity (2 degrees south) to the equator, the country enjoys a fine spring climate (due to its altitude), with two rainy seasons and two dry seasons. In fact, when considering the tropical climate region with his considerable rainfall period, it is better to collect information regarding the zone in consideration. Using Finite Difference Time Domain(FDTD) simulation with GPRMax simulator, and varying the permittivity, the aim of this paper is to have a benchmark of dry and rainfall season; this will help when doing measurements with the GPR instruments and others non destructive tools. In this paper, we analysed the clay soil (one of the component of Rwandan pedology) and from the variation of dry clay to wet clay associated with different fixed frequencies (300MHz, 600MHz, 900MHz, 1200MHz and 1500MHz). For each fixed frequency, we vary the clay permittivity from dry to wet clay and analysed data after simulation. From this benchmark, and in the near future work, we will use the GPR instrument and the Time Division Reflectometry(TDR) to verify the simulation results.

The importance of dielectric losses in planar microstrip structures is evaluated with the finite-difference time-domain (FDTD) method. This analysis was previously not possible in many FDTD simulators due to a lack of absorbing boundary conditions (ABCs), which appropriately terminate air/dielectric interfaces for which the dielectric is lossy. The newly proposed lossy two-time derivative Lorentzian material (L2TDLM) model ABC allows for these terminations and is presented and implemented here for three-dimensional FDTD simulations. The effect of dielectric losses on several well-known planar microstrip structures is evaluated. It is shown that the inclusion of these losses in FDTD simulations, which is facilitated by the L2TDLM ABC, is, in fact, important to predict the performance of resonant structure on lossy dielectric substrates.

Exploring a novel approach to manipulating plasmon-induced transparency

The Finite Difference Time Domain (FDTD) method for the numerical solution of Maxwell’s equations is widely used for simulation of microwave and high speed digital circuits. Frequently, large scale circuit simulations include features whose electromagnetic behavior is desired to be found, interconnected by networks whose behavior is known a priori, either through measurement, simulation, or analytical models. If the known, “circuit-like” parts of the problem can be separated from the pertinent electromagnetic features and replaced by behavioral macromodels, computational savings a can be realized. The technique presented allows for these “circuit-like” components to be described by macromodels based on the S-parameters at their connection points and integrated into an FDTD simulation. This technique is applicable to a class of problems composed of a mixture of circuit and electromagnetic features, where the known behavior of the circuit features can be separated from the other electromagnetic interests. 1 Macromodeling Macromodeling is a common practice in circuit simulation, where a complex system is represented by a simplified model at its connection points. Logic circuits or operational amplifiers are frequently encountered examples of macromodels. Methods for extracting low-order models of complex systems is an active area of research which is being investigated by a number of researchers [1]. The method presented here uses established extraction techniques to derive transfer functions, and then seeks to plug those derived macromodels back into the FDTD method to enable system level simulation of large circuits.

In this paper, we present finite difference time domain (FDTD) simulations of millimetre-wave propagation through the near-field plasma plume of low power Hall thrusters. The simulations are intended to address potential issues (collisions, magnetic fields) that may affect the validity of simple theory used for phase shift determination in the recent measurements of plasma density using microwave interferometry (Cappelli et al 2006 J. Phys. D: Appl. Phys. 39 4582). One-dimensional plane wave FDTD simulations indicate that plasma non-uniformities along the direction of wave propagation have only a minor effect on the phase shifts estimated from collisionless, non-magnetized wave propagation through a path-length averaged plasma slab. Three-dimensional FDTD simulations that also account for electron collisions and magnetic fields indicate that the departure from the use of usual simple models is no more than about 15%, well within the limits of uncertainty in the experimental measurements taken within the near field of these plasma sources.

Active microring based tunable optical power splitters