Stacked annular ring dielectric resonator antenna excited byaxi-symmetric coaxial probe

A stacked annular ring dielectric resonator (DR) antenna composed of commercially available dielectric resonators and exited by axi-symmetric coaxial probe is studied computationally using the finite-difference time-domain (FDTD) method. The numerical results are checked against experimental measurements, and good agreement is observed. It is demonstrated that the introduction of air-gaps between the two DR's and also between the driven DR and the ground plane can improve the impedance bandwidth of the antenna significantly. The effects of the air-gaps thickness on the return loss and the bandwidth are discussed. The far-fields are also calculated by applying the electromagnetic field equivalence principle. The antenna produces an end-fire radiation field similar to that of an electric monopole     

Electrically tunable dispersion compensator with fixed center wavelength using fiber Bragg grating

We present the design and development of a novel tunable dispersion compensator with fixed center wavelength that is based on the electrical adjustment of the chirp of a fiber Bragg grating (FBG). Both temperature gradient and strain gradient are employed to adjust the chirp of the FBG jointly. The electrical current flowing through the taper on-fiber thin-film heater will introduce a temperature gradient on the FBG. The shrinkage of a negative thermal expansion coefficient (NTEC) ceramic due to the temperature rise will compress the tapered FBG mounted inside it, and this will introduce a strain gradient on the FBG. The center wavelength of the FBG will be kept fixed because the effect of temperature rise on the FBG and the effect of compression of the FBG will offset each other. Applying an electrical power of less than 0.68 W, we demonstrate a linearly chirped FBG whose dispersion can be continuously adjusted from -178 ps/nm to -302 ps/nm with a central wavelength shift of as small as 0.16 nm.     

Analytical Solution for SOA-Based All-Optical Wavelength Conversion Using Transient Cross-Phase Modulation

All-optical wavelength conversion (WC) based on transient cross-phase modulation (T-XPM) of semiconductor optical amplifier (SOAs) is a promising approach to accelerate the gain recovery of SOAs. An analytical solution is deduced to explain the polarity variation of WC based on T-XPM of SOAs from the viewpoint of the impulse response functions. We conclude that both inverted and noninverted WCs can be realized when the central wavelength of the optical bandpass filter is either blue-shifted or red-shifted with respect to the wavelength of the probe signal. We are able to validate the formula against our experimental results recently published     

Electrocontrolled Liquid Marbles for Rapid Miniaturized Organic Reactions

Miniaturized droplet reactors hold great promise for the development of green and sustainable chemistry. However, handling liquids with small volumes, especially viscous ones, in a convenient and loss‐free manner remains a challenge. Here, by electrically controlling the coalescence and mixing of particle‐coated droplets, also known as liquid marbles, an effective microreactor is demonstrated for miniaturized chemical reactions involving viscous reagents. By applying an electric voltage to marbles, the induced electromixing of marble microreactors promotes the reaction rate and the product yield. The advantages of electromixed marble reactors are manifested by a series of chemical reactions between aldehydes and 2‐methylindole in viscous glycerol solution. The electrically‐controlled coalescence and mixing establish liquid marbles as microreactors for rapid, efficient, and miniaturized chemical reactions.     

Generalized Finite-Difference Time-Domain Method Utilizing Auxiliary Differential Equations for the Full-Vectorial Analysis of Photonic Crystal Fibers

We present the generalized finite-difference time-domain full-vectorial method by reformulating the time-dependent Maxwell's curl equations with electric flux density and magnetic field intensity, with auxiliary differential equations using complex-conjugate pole-residue pairs. The model is generic and robust to treat general frequency-dependent material and nonlinear material. The Sellmeier equation is implicitly incorporated as a special case of the general formulation to account for material dispersion of fused silica. The results are in good agreement with the results from the multipole method. Kerr nonlinearity is also incorporated in the model and demonstrated. Nonlinear solutions are provided for a one ring photonic crystal fiber as an example.     

Switching dynamics of short optical pulses in a nonlineardirectional coupler

It has been shown recently that the propagation of short optical pulses in a nonlinear directional coupler consisting of two parallel waveguides or fibers should be described more generally by a pair of coupled nonlinear equations that take into account the dispersion properties of the coupling coefficient. In this paper, we use the Fourier series analysis method to solve these equations, and study the effects of a dispersive coupling coefficient on the switching dynamics of short optical pulses in a nonlinear directional coupler. We demonstrate, with numerical examples, that a dispersive coupling coefficient could cause significant pulse distortion and affect the threshold switching intensity. The effects of introducing frequency chirps in the input pulses are also discussed     

On‐Demand Droplet Collection for Capturing Single Cells

Droplet‐based microfluidic techniques are extensively used in efficient manipulation and genome‐wide analysis of individual cells, probing the heterogeneity among populations of individuals. However, the extraction and isolation of single cells from individual droplets remains difficult due to the inevitable sample loss during processing. Herein, an automated system for accurate collection of defined numbers of droplets containing single cells is presented. Based on alternate sorting and dispensing in three branch channels, the droplet number can be precisely controlled down to single‐droplet resolution. While encapsulating single cells and reserving one branch as a waste channel, sorting can be seamlessly integrated to enable on‐demand collection of single cells. Combined with a lossless recovery strategy, this technique achieves capture and culture of individual cells with a harvest rate of over 95%. The on‐demand droplet collection technique has great potential to realize quantitative processing and analysis of single cells for elucidating the role of cell‐to‐cell variations.     

Fuzzy layer selection method in hierarchical cellular systems

Hierarchical cellular systems are proposed to accommodate mobile users of different speeds. While the microlayer serves the slow users, the macrolayer serves the fast users. After a handoff request is initiated, we must make a decision determining whether it should go to the micro or macrocell. In this paper, this problem is tackled by making use of the past cell dwell times and occupancies in the target micro and macrocell. We want those mobile users with high velocity to join the macrolayer. It is also desirable to select the target cell which has lower occupancy in order to prevent call blocking. These heuristics are incorporated in a fuzzy layer selection (FLS) algorithm, which is devised in terms of fuzzy set and fuzzy logic. The performance is compared to the popular threshold method in the literature by simulation