Amplitude-phase modulated composite waves in coupled nonlocal system with self-induced PT symmetric potential.

We consider a coupled nonlocal nonlinear Schrödinger equation (nNLSE) with self-induced parity-time (PT) symmetric potential and investigate abundant amplitude-phase modulated composite waves manifesting diverse evolution patterns. It is found that the coupled nonlocal model can be decoupled into nNLSEs with self-induced PT symmetric potential under certain constraints through a general linear transformation with amplitude and phase modulation. Based on the exact solutions of the nNLSEs with self-induced PT potential, we study various composite waves superposed by bright and/or dark soliton solutions, rogue waves, bright/dark soliton and periodic soliton, and present the abundant evolution patterns under amplitude-phase modulation. The results here only demonstrate the characteristics of limited superposed composite waves. In fact, there exist infinite possible evolution patterns of composite waves due to the arbitrary amplitude-phase modulation in coupled nonlocal nonlinear system with self-induced PT symmetric potential.

VO2-assisted multifunctional metamaterial for polarization conversion and asymmetric transmission.

A VO2-assisted temperature-controlled multifunctional metamaterial polarization converter with large asymmetric transmission (AT) is proposed by introducing a gold-VO2 grating. The converter can be switched between reflection mode and transmission mode by controlling the phase transition. When VO2 is in the metallic state, the converter works in reflection mode, converting the incident forward/backward linearly/circularly polarized waves into the cross-polarized waves, and the broadband polarization conversion rates (PCRs) can reach 90% with relative bandwidth of up to 91.1% and 87.5%, respectively; when VO2 is in the insulating state, the converter shows giant AT effect for circularly polarized waves at 0.64 THz and 1.28 THz. The multifunctional polarization converter holds great potential in the fields of communication and imaging, which provides a new way to design optical devices such as polarizers, isolators.

Frequency-reconfigurable metamaterial absorber/reflector with eight operating modes.

Reconfigurable design is an effective way to achieve multifunctional devices for system integration. Limited by the feeding network for multi-resonators, multimode absorbers with more than four modes are rarely reported. In this paper, a frequency-reconfigurable metamaterial absorber/reflector resonating at 3.05, 4.45 and 5.54 GHz is proposed. Based on a stereoscopic feeding network and a strategic arranged structure with loaded switching diodes, the proposed structure can realize the reconfigurable eight operating modes, including triple-band (111)/dual-band (110, 101, 011)/single-band (100, 010, 001) absorption and reflection (000) without re-optimizing and re-engineering the structure. The simulated results are confirmed by measuring a fabricated prototype. Our design provides a strategy to realize multifunction devices in microwave or even higher frequencies.

High-power pulse, pulse pair, and pulse train generated by breathers in dispersion exponentially decreasing fiber.

Based on the derived rational solutions of the nonautonomous nonlinear Schrödinger equation with varying coefficients, we present a simple scheme to generate a high-power pulse, pulse pair, and pulse train with non-oscillating amplitudes in dispersion exponentially decreasing fiber. Without requiring elimination of the background, the stable pulse train can be generated from the first-order Akhmediev breather, and the high-power pulse and pulse pair can be generated from the second-order Kuznetsov-Ma breather. Moreover, it is found that the characteristics of these pulses can be controlled by adjusting the eigenvalue parameter and fiber parameters. The results presented here are expected to be useful in large-capacity and high-power optical communication systems.

Polarization-Controlled and Flexible Single-/Penta-Band Metamaterial Absorber.

In this paper, a polarization-controlled and flexible metamaterial absorber made of a set of wires etched on ultrathin teflon dielectric substrate is proposed. The simulation results showed that the proposed absorber achieved single-band absorptivity of 99.8% at 6.64 GHz for the TM (transverse magnetic) polarization wave and penta-band absorptivity of more than 99% at 11.68 GHz, 13.58 GHz, 15.48 GHz, 17.38 GHz, and 19.28 GHz for the TE (transverse electric) polarization waves. Moreover, each absorption peak had very narrow relative bandwidth and the position of penta-band absorption peaks could be adjusted by changing the length of the corresponding wire or selecting suitable substrate material according to actual requirements, because each wire can independently respond to electromagnetic (EM) waves. Furthermore, the surface current distributions corresponding to each absorption peak were studied to demonstrate the absorption mechanism. The absorption properties of the proposed structure with different bending radii and under different incident angles of the EM waves were investigated, showing good flexibility and incident angle-insensitive properties. In addition, the simulation results were confirmed by measuring a fabricated prototype. The proposed absorber may have useful applications in polarizers, sensors, bolometers, polarization detectors, etc.

Grating-type mid-infrared light absorber based on silicon carbide material.

A kind of grating-type mid-infrared light absorber based on silicon carbide (SiC) material is designed and its absorption properties are studied using the finite-difference frequency-domain (FDFD) method. The results show that, its absorption mechanism is the excitation of surface plasmon and magnetic polariton as well as the loss of materials. Due to the optical characteristics of the SiC material in the mid-infrared band and the truncated pyramid structure in the grating, in the range of 10.5-12.5µm and 0-80°, absorptivity of higher than 80% can be obtained with optimized structural parameters. Among six structural parameters, the layer number of the composite layers has a relatively great influence on the absorption properties, while the thickness of the dielectric layer has less influence on the absorption properties.

Gray solitary-wave solutions in nonlinear negative-index materials.

We predict the existence of gray (dark) solitary waves in negative-index materials on the basis of a derived higher-order nonlinear Schrödinger equation. The conditions for the formation of three cases of gray solitary waves and exact analytical expressions are presented. Furthermore, we investigate the properties of these gray solitary waves in negative-index materials. The results show that the higher-order linear and nonlinear effects play a crucial role for the formation and properties of the second and third cases of gray solitary waves.

Numerical simulations of a surface plasmonic waveguide with three circular air cores.

In this paper, a kind of surface plasmonic waveguide (SPW) with three circular air cores is presented. Based on the finite-difference frequency-domain (FDFD) method, dependence of the distribution of energy flux density, effective index, propagation length and mode area of the fundamental mode on the geometrical parameters and the working wavelengths is analyzed firstly. Then, comparison with the SPW which was proposed in our previous work has been carried out. Results show that this kind of three cores structure has better propagation properties than the double cores structure. To investigate the relative advantages of this kind of SPW over other previous reported SPWs, comparison with the SPW with a single wedge has been carried out. Results show that this kind of SPW has shorter propagation length and larger mode area. Finally, the possibility to overcome the large propagation loss by using a gain medium as core material is investigated. Since the propagation properties can be adjusted by the geometrical and electromagnetic parameters, this kind of surface plasmonic waveguide can be applied to the field of photonic components in the integrated optical circuits and sensors.

Spatial soliton tunneling, compression and splitting.

We numerically investigate the tunneling of spatial solitons through a focusing Kerr nonlinear optical lattice with longitudinal potential barrier, and find that the position of input beams apparently affects the tunneling behaviors of spatial solitons, which exhibit compression or splitting when passing through the barrier, and that the transverse modulation frequency of lattice and the intensity of input beams strongly affect the ability of tunneling. Based on these properties, we present a scheme for compressing soliton and splitting soliton into stable twin beams. The obtained results may have promising applications in all-optical devices based on spatial solitons.

Combined solitary wave solutions for the inhomogeneous higher-order nonlinear Schrodinger equation.

We consider the inhomogeneous higher-order nonlinear Schrodinger equation and explicitly present exact combined solitary wave solutions that can describe the simultaneous propagation of bright and dark solitary waves in a combined form in inhomogeneous fiber media or in optical communication links with distributed parameters. Furthermore, we analyze the features of the solutions, and numerically discuss the stabilities of these solitary waves under slight violations of the parameter conditions and finite initial perturbations. The results show that there exist combined solitary wave solutions in an inhomogeneous fiber system, and the combined solitary wave solutions are stable under slight violations of the parameter conditions and finite initial perturbations. Finally, the interaction between two neighboring combined solitary waves is numerically discussed.