From Time-Collocated to Leapfrog Fundamental Schemes for ADI and CDI FDTD Methods

The leapfrog schemes have been developed for unconditionally stable alternating-direction implicit (ADI) finite-difference time-domain (FDTD) method, and recently the complying-divergence implicit (CDI) FDTD method. In this paper, the formulations from time-collocated to leapfrog fundamental schemes are presented for ADI and CDI FDTD methods. For the ADI FDTD method, the time-collocated fundamental schemes are implemented using implicit E-E and E-H update procedures, which comprise simple and concise right-hand sides (RHS) in their update equations. From the fundamental implicit E-H scheme, the leapfrog ADI FDTD method is formulated in conventional form, whose RHS are simplified into the leapfrog fundamental scheme with reduced operations and improved efficiency. For the CDI FDTD method, the time-collocated fundamental scheme is presented based on locally one-dimensional (LOD) FDTD method with complying divergence. The formulations from time-collocated to leapfrog schemes are provided, which result in the leapfrog fundamental scheme for CDI FDTD method. Based on their fundamental forms, further insights are given into the relations of leapfrog fundamental schemes for ADI and CDI FDTD methods. The time-collocated fundamental schemes require considerably fewer operations than all conventional ADI, LOD and leapfrog ADI FDTD methods, while the leapfrog fundamental schemes for ADI and CDI FDTD methods constitute the most efficient implicit FDTD schemes to date.

Extraordinary spin to orbital angular momentum conversion on guided zone plates

Focusing systems with high numerical aperture can be used to convert spin angular momentum into orbital angular momentum with efficiencies of 50%, while for low numerical apertures this conversion vanishes. In this paper, based on the properties of binary Fresnel zone plates, we propose a structure that is achieved by making an accurate selection of the width and the depth of the rings. This allows us to obtain a large increase in the spin to orbital angular momentum conversion of the resulting focusing fields, and it also has the special characteristic that the obtained conversion is higher for low numerical aperture structures, where standard focusing systems do not work. The ability of the system to perform this extraordinary conversion is demonstrated by FDTD methods and an analytical model developed using a combination of guided mode theory for the structure and Stratton–Chu diffraction theory.

Compact and ultrafast all optical 1-bit comparator based on wave interference and threshold switching methods

In this study, we are going to design all optical 1-bit comparator by combining wave interference and threshold switching methods. The final structure composed of two nonlinear ring resonators and seven waveguides. The functionality of the suggested logical structure is analyzed and simulated by using plane wave expansion (PWE) and finite difference time domain (FDTD) methods. According to results, the proposed all optical 1-bit comparator has faster response and smaller footprint than all previous works. The maximum ON-OFF contrast ratio, delay time and area of the suggested optical comparator are about 16.67 dB, 1.8 ps, and 513 µm2, respectively.

Extraordinary Spin to Orbital Angular Momentum Conversion on Guided Zone Plates

Focusing systems with high numerical aperture can be used to convert spin angular momentum into orbital angular momentum with efficiencies of 50%, while for low numerical apertures this conversion vanishes. In this paper, based on the properties of binary Fresnel zone plates, we propose a structure that is achieved by making an accurate selection of the width and the depth of the rings. This allows us to obtain a large increase in the spin to orbital angular momentum conversion of the resulting focusing fields, and it also has the special characteristic that the obtained conversion is higher for low numerical aperture structures, where standard focusing systems do not work. The ability of the system to perform this extraordinary conversion is demonstrated by FDTD methods and an analytical model developed using a combination of guided mode theory for the structure and Stratton-Chu diffraction theory.

Dual-Band Plasmonic Perfect Absorber Based on the Hybrid Halide Perovskite in the Communication Regime

Due to the weak absorption of (CH3NH3)PbI3 in the communication regime, which restricts its optoelectronic applications, we design a adjustable dual-band perfect absorber based on the (CH3NH3)PbI3 to significantly enhance its absorption capability. Since the localized plasmon (LP) mode and surface plasmon (SP) mode are excited in the structure, which can both greatly enhance light absorption of the (CH3NH3)PbI3 layer, dual-band perfect absorption peaks are formed in the communication regime, and the absorption of (CH3NH3)PbI3 layer is increased to 43.1% and 64.2% at the dual-band absorption peaks by using finite-difference time-domain (FDTD) methods, respectively. By varying some key structural parameters, the dual-band absorption peaks of (CH3NH3)PbI3 can be separately shifted in a wide wavelength region. Moreover, the designed absorber can keep good performance under wide angles of incidence and manifested polarization correlation. Furthermore, not just for (CH3NH3)PbI3, the physical mechanism in this absorber can also be utilized to strengthen the absorption of other halide perovskites.