Narrow Results

The application of the subwavelength planar structure to control the propagation direction of surface plasmon polaritons (SPPs) has attracted many interests in recent years. However, the traditional unidirectional transmission devices of SPPs are limited by the low extinction ratio, narrow working band and the incapability of controlling the transmission directions. In this study, a novel SPPs unidirectional transmission device based on metallic aperture arrays of the right triangle (RT) is proposed and demonstrated by numerical simulations (finite-difference time-domain method). The maximum extinction ratio of the unidirectional transmission device can reach upto 33 dB under the irradiation of linearly polarized light, and the device possesses a wide operating band ($\sim 300$ nm) while the extinction ratio is greater than 10 dB. Moreover, the transmission direction of SPPs can be flexibly controlled by tuning the polarization of the incident beam. This broadband, polarization-mediated and high extinction ratio unidirectional transmission device shows great potential in the compact plasmonic devices.

The high efficiency and the wideband properties are not easy to be obtained by the conventional binary grating-based polarizer. Although the grating polarizer was demonstrated in experiments, the performance should be improved further to meet the practical applications. A novel sandwiched two-layer grating polarizer is presented to improve the efficiency and the bandwidth. Such a polarizer can have advantages of high efficiency of the sandwiched grating and wide bandwidth of the two-layer grating. The grating depths of two layers are optimized for the special duty cycle of 0.3 and the given period. The diffraction efficiency and the incident bandwidth of the novel grating polarizer are improved greatly compared with the conventional simple grating and the sandwiched single-layer grating. Moreover, high extinction ratio can be shown in both two orders and the moderate fabrication tolerance should be good guideline for practical applications.

Two photonic crystal fiber (PCF) polarization beam splitters (PBSs) featuring ultra-short length and ultra-high extinction ratios at wavelengths of 1.31 $\mu$m and 1.55 $\mu$m are designed and investigated. Non-silicon materials, such as gallium arsenide (GaAs) and nematic liquid crystal (NLC), are incorporated into the structure to ensure operation of the splitters in the communication bandwidth. Based on the full-vector finite element method (FEM), numerical simulation is carried out to optimize the structural parameters systematically. Specifically, for the splitter operating at 1.31 $\mu$m, the optimal optical fiber length, extinction ratio, and bandwidth are 27.87234 $\mu$m, $-152.40$ dB, and 152 nm, respectively. In comparison, the optimal fiber length, extinction ratio, and bandwidth of the splitter at the wavelength of 1.55 $\mu$m are 15.59356 $\mu$m, $-137.21$ dB, and 200 nm, respectively. The results reveal that the splitters have great potential in environmental monitoring, biochemical detection, and optical communication.

A multi-functional dual-core photonic crystal fiber (PCF) polarization beam splitter with a central oval hole filled with gold is designed and described. The first layer on the circular holes around the core is filled with the nematic liquid crystal (NLC) to enhance birefringence. The full-vector finite element method is employed to study the characteristics of the polarization beam splitter and derive the optimal parameters. When the fiber length is 14.55 $\mu$m, the polarized light in the $x$- and $y$-directions can be separated at a wavelength of 1.31 $\mu$m and the bandwidths are 257 and 238 nm, respectively, for extinction ratios bigger than 10 dB. When the fiber length is 10.86 $\mu$m, the polarized light in the $x$- and $y$-directions can be separated at a wavelength of 1.55 $\mu$m and the bandwidths are 239 and 174 nm, respectively for extinction ratios larger than 10 dB. The multifunctional polarization beam splitter with an ultra-short fiber length and broad bandwidth improves the sensing performance in comparison with single-function devices and our results provide insights into the design of beam splitters with multiple functions.

Push-pull electro-optic polymeric Mach-Zehnder modulators with photo-bleaching induced waveguides and dual-driving electrodes operating at 1.55 μm wavelength have been demonstrated. The nonlinear electro-optic polymer used in this work was based on a phenyltetraene bridged chromophore in polycarbonate, APC-CLD1. It has been shown that the predominant photo-bleaching mechanism was a photochemical decomposition of the chromophore. The half-wave voltage of the integrated polymeric modulator was 4.5 V in a push-pull configuration with a 1.5 cm interaction length. The extinction ratio was greater than 20 dB, and the fiber-to-fiber insertion loss was 8 dB for the TM polarization at 1.55 μm wavelength.

In the presented structure, the performance of the all-optical XOR logic gate (AO-XOR-LG) is investigated. The XOR-LG is designed and simulated using a photonic crystal semiconductor optical amplifier (PC-SOA) based on Mach–Zehnder interferometer (MZI) and cross-phase modulation (XPM) nonlinear mechanism. The input optical pulse train used in this simulation is the type of RZ (Return-to-Zero). The finite difference method (FDM) has been used to solve the rate and propagation equations. The effect of input signal energy, bias current, and group refractive index on the output signal and gain of the XOR-LG is studied. The optimal mode is obtained for the XOR-LG with a bit rate of 80 Gbps. Furthermore, for the first time, the effects of quality factor (QF), conversion efficiency (CE), extinction ratio (ER), pattern effect (PE), and gain recovery are simultaneously analyzed in the simulation to increase PC-SOA performance. According to the results, PC-SOA has a more reasonable logic performance than conventional SOA, and due to its much shorter length than SOA, it can be a much better choice for integrated optical circuits.