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In this Letter, the authors designed a photonic configurable logic block (pCLB) with 1×1 Mach–Zehnder modulator as a universal photonic gate (UPG) using electro‐optic mechanism. The UPG is capable of performing all the logical operations with the help of FPGA as a configuration controller. The functionality and its suitability is verified by forming a pCLB of ten UPGs, which finds applications in digital photonics. For the design of pCLB, traditional electronic design automation tools are used. The pCLB provides features namely scalability and modular approach, for the reconfigurable digital photonic integrated circuits. The photonic gate designed using a two‐dimensional finite difference time domain approach shows a crosstalk‐free operation with a negligible transmission loss of 0.18 dB and flexible switching control compared to the existing 2×2 MZI‐based photonic gate. [ABSTRACT FROM AUTHOR]

A fourth‐order finite‐difference time‐domain (FDTD) scheme is proposed for the solution of Maxwell's equations in cold plasma (Drude medium), based on the multistage method of Jameson, Schmidt and Turkel, which was originally introduced in the framework of fluid dynamics. First, the system of governing differential equations is formed as a general first‐order, operator‐based approach, and then a four‐stage algorithm is established. The accuracy of the method is verified in benchmark problems compared with analytical solutions and with the conventional second‐order FDTD algorithm. [ABSTRACT FROM AUTHOR]

The unconditionally stable alternating‐direction‐implicit finite‐difference time‐domain (ADI‐FDTD) method is extended for modelling anisotropic magnetised graphene sheets. In contrast to the conventional method for isotropic media, two additional sub‐stepping calculations are applied to incorporate anisotropic medium properties. The unconditional stability of the proposed extended method is examined numerically. The method is applied to study the transmission properties of graphene sheets. Numerical results show that the proposed method is more accurate than the recently developed locally one‐dimensional FDTD method. [ABSTRACT FROM AUTHOR]

A one‐step leapfrog weakly conditionally stable finite‐difference time‐domain method for modelling drude dispersive models is developed. Numerical results show that its stability condition remains invariant with respect to that in lossless media. The new algorithm is applied to efficiently investigate the transmission properties of a graphene sheet and a graphene‐based frequency selective surface. [ABSTRACT FROM AUTHOR]

A wavelength filter using a pair of one‐dimensional photonic crystal (1D‐PhC) waveguides incorporating cavity sections for one‐directional output is reported. The small number of holes for 1D‐PhC is used to attain distinct transmission peaks in the stop band. Two cavity sections are used to obtain peak with steep slope and widened top. The three‐dimensional finite difference time domain simulation results agree with the experimental result. [ABSTRACT FROM AUTHOR]

A semi‐implicit finite‐difference time‐domain thin‐wire (TW) scheme with a relaxed stability condition is proposed for modelling effective surface plasmons in waveguide metamaterials. Its formulation is based on introducing the Newmark‐Beta method into the TW formulation based on the contour‐path integral of Maxwell's equations around a wire. The resultant scheme is magnetically implicit. Its stability, accuracy and efficiency are assessed in the application to a wire‐added parallel‐plate waveguide perturbed with a small gap. [ABSTRACT FROM AUTHOR]

Via the auxiliary differential equation method, the authors propose a simple and efficient implementation of the stretched coordinate perfectly matched layer (SC‐PML) in this Letter. The proposal can successfully halve the number of auxiliary variables associated with the PML while maintaining the capacity of the original SC‐PML in terms of simple implementation. Thus, it can achieve a higher computational efficiency in the finite‐difference time‐domain simulations. The effectiveness of this new implementation is verified through an example carried out in a 3D Debye dispersive space. [ABSTRACT FROM AUTHOR]

An efficient 2D locally one‐dimensional finite‐difference time‐domain (LOD‐FDTD) method in lossy material is presented in this Letter. The weighted factor and scaling factors of the isotropic dispersion FDTD method are reformed for the LOD‐FDTD method in lossy media. Compared with the conventional LOD‐FDTD method, the relative attenuation and phase errors of the proposed method are significantly reduced. The numerical anisotropy is also greatly improved by using the proposed method. [ABSTRACT FROM AUTHOR]

In this Letter, the spectral technique that has been applied to the finite‐difference‐time‐domain (FDTD) method is applied to the alternating‐direction‐implicit higher‐order FDTD (ADI‐HO‐FDTD) method for solving periodic structures, resulting in the periodic spectral (PS) ADI‐HO‐FDTD. The algorithm for inversion of the block periodic tri‐diagonal matrices is presented. The effectiveness and computational efficiency of the proposed method are also shown. Numerical results indicate that the PS‐ADI‐HO‐FDTD algorithm can save computation time by more than 27% in comparison with the conventional HO‐FDTD method. [ABSTRACT FROM AUTHOR]

An antenna system composed of an activated patch backed by a ground plane and three square parasitic plates with inhomogeneous loops is analysed using the finite‐difference time‐domain method. Analysis of an antenna with an infinite ground plane reveals that a tilted beam of ∼60° from the broadside direction is obtained with a gain of ∼18 dBi. For confirmation, an antenna system with a finite‐sized ground plane that approximates the antenna characteristics for the infinite ground plane is fabricated and measured. The measured results are in good agreement with the analysis results. [ABSTRACT FROM AUTHOR]

A 3D alternating‐direction‐implicit finite‐difference time‐domain algorithm is presented for problems that involve material frequency dispersion described by generalised modified Lorentzian terms. The implementation exploits the auxiliary differential equations formulation and applies an order reduction technique in order to achieve synchronisation with the two‐step procedure. The efficiency of the proposed method is validated in a benchmark problem of a resonant metallic cavity filled with plasma. [ABSTRACT FROM AUTHOR]

A hybrid full‐wave and circuit model for spark gaps was constructed. The spark channel was modelled as a non‐linear time‐dependent resistor based on Rompe–Weizel's spark formula in SPICE. The linear full‐wave model of an air gap and other structures were simulated by the semi‐implicit finite‐difference time‐domain scheme based on the Newmark‐beta method. These two models were coupled and simultaneously solved in time domain. The coupled model was tested for different charged voltages and spark lengths, and also validated in comparison with measurements. [ABSTRACT FROM AUTHOR]

Application of direct radiation pattern estimation in finite difference time domain (FDTD) simulation environment as an alternative to cumbersome near‐to‐far field transformation is considered. With the proposed improvement, direct estimation of the radiation pattern from the field strength samples in FDTD method becomes significantly less sensitive to the antenna geometry and thus more applicable to practically relevant cases. The main idea is to use field samples taken at two different radii to account for antenna geometry. The samples are taken at radii that are as close as possible to the antenna but still not too close to spoil the correctness of the results. The introduced improvement, combined with multigrid simulation domain and higher order accuracy FDTD formulations, reduces the necessary size of the computational domain, which directly leads to reduced memory consumption and a smaller error due to numerical dispersion. [ABSTRACT FROM AUTHOR]

A novel 2D finite difference time domain (FDTD) subgridding method is proposed, only subject to the Courant limit of the coarse grid. By making μ or ε inside the subgrid dispersive, unconditional stability is induced at the cost of a sparse, implicit set of update equations. By only adding dispersion along preferential directions, it is possible to dramatically reduce the rank of the matrix equation that needs to be solved. [ABSTRACT FROM AUTHOR]

A nonlinear and partially implicit finite‐difference time‐domain scheme with a relaxed stability condition is presented for fast full‐wave simulation of electrostatic discharges occurred at a short gap. The nonlinear spark resistance model of Rompe and Weizel is directly incorporated in this scheme. Its stability, accuracy and computational efficiency are assessed in the application to a metallic structure system. [ABSTRACT FROM AUTHOR]

Radio wave propagation of three types of birdcage transmit/receive radio‐frequency (RF) coils (lowpass filter, highpass filter, and bandpass filter configurations) was analysed for mouse body magnetic resonance imaging at main magnetic fields of 1.5, 3.0, 4.7, 7.0, 9.4, and 11.7 T (Larmor frequencies of 63.87, 127.74, 200, 300, 400, and 500 MHz) in terms of magnetic (|B1|) field sensitivity and homogeneity. The observed radio wave propagation in the central axial |B1| field, as influenced by the biological subject, was calculated numerically in the finite‐difference time‐domain method and compared with assessment criteria using the mean value and standard deviation. The results for different Larmor frequencies RF shielding cage configurations, and biological subject loading versus unloading were compared and are discussed in detail. [ABSTRACT FROM AUTHOR]

An optimised low numerical dispersion unconditionally stable finite-difference time-domain (FDTD) method based on the isotropic dispersion (ID) scheme and weighted Laguerre polynomials (WLP) is presented. The proposed method adopts a scaling factor for permittivity and permeability in the ID-WLP-FDTD method, which can generate almost the exact phase velocity for a single frequency. In contrast with the traditional WLP-FDTD method and ID-WLP-FDTD method, the numerical dispersion of the new method is significantly reduced, and the proposed method can guarantee high accuracy and high efficiency simultaneously. [ABSTRACT FROM AUTHOR]

For analysing the scattering problem in conductive medium with the new unconditionally stable associated Hermite (AH) finite‐difference time‐domain (FDTD) method, the formulation of uniaxial anisotropic perfectly matched layer absorbing boundary condition (UPML‐ABC) and the total‐field/scattered‐field (TF/SF) implementation scheme are deduced. By virtue of AH differential transformation matrix and the eigenvalue transformation, frequency‐dependent parameters of the lossy medium can be well treated in AH‐UPML, without using any additional auxiliary variables. Numerical verification for the scattering of buried conductor in lossy half‐space is performed. Compared with Mur's ABC, UPML increases the absorbing performance by more than 80 dB in AH‐FDTD analysis. [ABSTRACT FROM AUTHOR]

A three‐dimensional implementation of the finite‐difference time‐domain method is used to estimate the down‐link outage probability of a direct‐sequence code division multiple access system operating in a multi‐storey office building in the presence of co‐channel interference. The numerical analysis is supported by experimental measurements and good agreement is found for the outage probability. Both simulation and measured results indicate that vertically aligned co‐channel base stations have lower outage than a vertically staggered configuration, which is explained by examining the correlation between the desired and interfering signals. [ABSTRACT FROM AUTHOR]

A novel and unsplit‐field implementation of the stretched coordinate perfectly matched layer (SC‐PML) is proposed for truncating the one‐dimensional (1D) frequency dispersive first‐order Debye medium. These formulations are based on the unconditional stable Crank‐Nicolson scheme and the Z‐transform method. Numerical results validate the effectiveness and performance of this new PML. [ABSTRACT FROM AUTHOR]

One order of magnitude detection enhancement of bow‐tie‐shaped InGaAs‐based terahertz detectors by on‐chip incorporation of the secondary diffractive optics is reported. Zone plates were produced directly on the bottom surface of 500 µm‐thick InP substrate using the direct laser write technique after an array of InGaAs detectors was formed on the front surface of the wafer. Measurements of detected signal dependence on the angle of the incident wave were performed at 0.76 THz and compared with finite‐difference time‐domain simulation results. Good correlation of the results shows that the observed enhancement is indeed caused by the focusing performance of the zone plate rather than by the exceptional sensitivity of the single detector. [ABSTRACT FROM AUTHOR]

To extend the Courant‐Friedrichs‐Lewy (CFL) limit, a discrete wavelet transform (DWT) is incorporated into the finite difference time domain (FDTD) scheme. With the Mallat algorithm for the decomposition and reconstruction of the electromagnetic components, the unstable spatial modes can be efficiently filtered out. Consequently, the original strict CFL limit of the FDTD can be significantly relaxed, and much execution time can be saved. The performance and versatility of the proposed method is demonstrated by the numerical examples. [ABSTRACT FROM AUTHOR]

A trapezoidal recursive convolution (TRC) technique is one of the simple ways to incorporate dispersive models into the finite‐difference time‐domain (FDTD) method. The authors newly develop the TRC–FDTD method for the analysis of arbitrary‐shaped dispersive materials using a dispersive contour‐path algorithm. The accuracy of the present method is found to be the same as that using the Z‐transform technique with reduced computational requirements. [ABSTRACT FROM AUTHOR]

Presented is a silicon solar cell model with fully passivated radial junction nanowire surface decoration and submerged nickel‐silicide contact. Numerical simulations using a finite‐difference time‐domain method have been done to investigate the spectral responses of the solar cell model. The experimental results indicate that, with proper nickel‐silicide thickness, the fill factor of the cell can be improved considerably without much degradation on short circuit current density. Under AM 1.5G illumination, the silicon nanowire solar cell device with 50 Å nickel‐silicide contact has short circuit current density of 26.3 mA/cm2, open circuit voltage of 586 mV and fill factor of 70.0%, contributing to power conversion efficiency of 10.8%, which is 19% higher than the control device without the nickel‐silicide contact. [ABSTRACT FROM AUTHOR]

Finite‐difference time‐domain (FDTD) schemes based on the bilinear z‐transform are introduced for modelling time‐domain wave propagation in dispersive Drude‐critical points media. The accuracy and efficiency of the proposed technique are verified by comparisons with other FDTD algorithms and analytical solutions. [ABSTRACT FROM AUTHOR]

Efficient wave equation perfectly matched layer (WE‐PML) formulations, based on the auxiliary differential equation (ADE) scheme, are presented for truncating scalar dispersive finite difference time domain (FDTD) grids. The formulations maintain the same accuracy as previous WE‐PML approaches but with fewer additional auxiliary variables. Moreover, the formulations can be coupled easily with the classical WE‐FDTD scheme. [ABSTRACT FROM AUTHOR]

A 3D optimised hybrid implicit–explicit finite‐difference time‐domain (HIE‐FDTD) method aimed at suppressing the numerical dispersion is proposed. Compared with the original HIE‐FDTD method, the optimised parameters are introduced without costing any additional computational resource. In addition, the proposed algorithm sacrifices Courant–Friedrichs–Lewy condition and just requires a modest amount of reprogramming. The update equations of the proposed HIE‐FDTD method are given and numerical results demonstrate that the proposed method performs better in the numerical dispersion. [ABSTRACT FROM AUTHOR]

A new correctional low‐dispersive finite‐difference time‐domain (FDTD) method based on hexagonal lattices (CH‐FDTD) is introduced. The proposed method adopts scaling factor for the permittivity and permeability, which can generate nearly the exact phase velocity for a single frequency. Compared to the conventional FDTD method based on hexagonal lattices (H‐FDTD) and rectangular lattices (Yee‐FDTD), the numerical dispersion of the new method is significantly reduced. [ABSTRACT FROM AUTHOR]

A novel chirped metal structure (CMS) is developed for polarimetric enhanced detection of both mid‐wave (MW) (3–5 µm) and long‐wave (LW) infrared (IR) wavelength bands (8–14 µm). The nano‐scale structure consists of parallel sub‐wavelength chirped‐width stripes together with graded‐width separating gaps. The CMS allows plasmonically enhanced polarisation‐sensitive absorption of dual‐bands simultaneously in underneath IR detection device. The finite‐difference‐time‐domain method is utilised to numerically evaluate gold CMS structure on an IR detector. Simulations show an excellent performance with high plasmonic absorption enhancement and polarisation extinction‐ratio over the continuous wavelength range 3–14 µm. The maximum recorded extinction‐ratios are 2900:1 and 400:1 in the LW and MW bands, respectively. The maximum estimated plasmonic absorption enhancements for TM‐polarisation in the LW and MW bands are 96 and 16%, respectively. The suppression of TE‐polarisation absorption is almost 100% over both bands. [ABSTRACT FROM AUTHOR]

A 3‐D non‐uniform time step locally one‐dimensional finite‐difference time‐domain (NUTS LOD‐FDTD) method is presented. Unlike conventional and the other LOD‐FDTD methods, NUTS LOD‐FDTD method employs NUTS for different periods during the simulation. The update equation of NUTS LOD‐FDTD method with arbitrary time step is given. Numerical results are provided to compare with conventional LOD‐FDTD method and trade‐off between efficiency and accuracy for different NUTSs. [ABSTRACT FROM AUTHOR]

A simple method for the computation of 3D scatterers remotely located from the source with layered media is presented. This domain decomposition method is based on the total‐field/scattered‐field formulation of the 3D finite‐difference in time‐domain method. The electromagnetic field along the propagation path is not directly involved; it focuses only on the electromagnetic field in the surroundings of the scatterer. The incident electromagnetic field radiated from the source is computed separately with an adaptive algorithm and then applied on the Huygens' surface, leading to the proposed hybridisation technique. [ABSTRACT FROM AUTHOR]

A two‐port microdisk laser connected to two radial waveguides is investigated using two‐dimensional finite‐difference time‐domain methods for realising single transverse mode lasing with a heptagonal mode field distribution. Based on the experimental results, it is found that two‐port microdisk lasers at the proper angles are easier to realise single transverse mode lasing compared with the one‐port microdisk laser. [ABSTRACT FROM AUTHOR]

A new implementation of a perfect matched layer with an auxiliary differential equation (ADE‐PML) is presented for the higher‐order finite‐difference time‐domain (FDTD) method. The implementation of the ADE‐PML is more straightforward and more memory saving than that of the traditional PML. A two‐dimensional (2D) case and two 3D cases with different microwave circuit components are designed to analyse the absorbing performance of the ADE‐PML and the simulation results show that the ADE‐PML can provide a quite satisfactory absorbing boundary condition. [ABSTRACT FROM AUTHOR]

A novel way to split terahertz (THz) surface waves is presented on the basis of propagation characteristics of spoof surface plasmon polaritons. Metal disc‐type splitters with a centre hole and radially placed gratings are proposed and analysed using the finite‐difference time‐domain (FDTD) method in cylindrical co‐ordinates. Numerical results demonstrate that the discs act as bi‐ and multi‐directional THz surface wave splitters with large coupling regions, the frequency of which is selected by grating structures. [ABSTRACT FROM AUTHOR]

Microwave tomography (MWT) is exploited for the detection of haemorrhagic stroke by using a nonlinear iterative imaging algorithm. An anatomically realistic two‐dimensional (2D) head model is simulated using a finite difference time‐domain numerical solver. By using an iterative optimisation algorithm based on the Gauss–Newton approach, the head model with an artificially embedded stroke region modelled as blood is successfully reconstructed through a blind reconstruction procedure (i.e. no a priori information about the shape or the dielectric properties of the model is assumed). It is observed that beginning from a homogeneous guess similar to the background material, right after the first iteration the shapes of the layers are clearly distinguished and the values of the dielectric properties converge to the actual values after only 10 iterations. [ABSTRACT FROM AUTHOR]

A discrete Green's function (DGF) approach to couple 3D FDTD subdomains is developed. The total‐field/scattered‐field subdomains are simulated using the explicit FDTD method whilst interaction between them is computed as a convolution of the DGF with equivalent current sources measured over Huygens surfaces. In the developed method, the DGF waveforms are truncated using the Hann's window. The error varies in the range − 65 to − 40 dB depending on the DGF length and positions of the subdomains. However, if the DGF length is equal to the number of iterations in a simulation, this approach returns the same results as the direct FDTD method. [ABSTRACT FROM AUTHOR]

ZnO nanostructures are proposed to enhance the performance of surface plasmon resonance (SPR). The ZnO nanostructures on a 50 nm‐thick Au thin‐film are composed of nano‐holes with a period of 300 nm. The ZnO nano‐holes coupled SPR was simulated using the three‐dimensionanl finite‐difference time‐domain method. The ZnO nano‐holes have been fabricated by a laser interference lithography and wet etching process. The measured resonance angle of 47.5° was obtained; this agreed well with the simulated result. In comparison with the author's previous report, the figure of merit of ZnO nano‐holes coupled SPR was two times higher than that of the ZnO grating structure. [ABSTRACT FROM AUTHOR]

Properties of zone plates with integrated bandpass filters were simulated numerically and demonstrated experimentally for 0.76 THz frequency. Finite‐difference time‐domain simulations were used to predict properties of a conventional zone plate and laser‐ablated zone plate with resonant filter areas. Zone plates were produced employing laser direct writing and characterised by Fourier spectroscopy and an optically pumped terahertz laser. [ABSTRACT FROM AUTHOR]