Hongping Zhou

Orbital Angular Momentum Shift Keying Based Optical Communication System

In the free space optical communication, the information can be encoded as the orbital angular momentum (OAM) state of light, which is called OAM shift keying (OAM-SK). This paper has proposed a communication system with OAM-SK, in which an image has been delivered from the transmitter to the receiver successfully in the simulation environment. Specifically, we have carefully designed and implemented the phase holograms used at the transmitter and the receiver for multiplexing and de-multiplexing the OAM states, respectively. At the transmitter, the multiplexing phase hologram designed by the modified Lins algorithm is loaded on the spatial light modulator 1 (SLM1) to generate the multiplexing vortex beam, which is a superposition of multiple vortex beams with different OAM states. Correspondingly, at the receiver, a novel phase hologram is designed and loaded on the SLM2 to effectively de-multiplex the multiplexing vortex beam in different directions. In our phase hologram used at the receiver, the detected power of each OAM state can be controlled by adjusting the weight coefficient by the modified Lins algorithm. This way, the incident power can be concentrated to the target OAM states, from which the target OAM states can be detected more effectively than conventional fork grating.

High-Efficiency Visible Transmitting Polarizations Devices Based on the GaN Metasurface

Metasurfaces are capable of tailoring the amplitude, phase, and polarization of incident light to design various polarization devices. Here, we propose a metasurface based on the novel dielectric material gallium nitride (GaN) to realize high-efficiency modulation for both of the orthogonal linear polarizations simultaneously in the visible range. Both modulated transmitted phases of the orthogonal linear polarizations can almost span the whole 2π range by tailoring geometric sizes of the GaN nanobricks, while maintaining high values of transmission (almost all over 90%). At the wavelength of 530 nm, we designed and realized the beam splitter and the focusing lenses successfully. To further prove that our proposed method is suitable for arbitrary orthogonal linear polarization, we also designed a three-dimensional (3D) metalens that can simultaneously focus the X-, Y-, 45°, and 135° linear polarizations on spatially symmetric positions, which can be applied to the linear polarization measurement. Our work provides a possible method to achieve high-efficiency multifunctional optical devices in visible light by extending the modulating dimensions.

Enhanced Forward Scattering of Ellipsoidal Dielectric Nanoparticles

Dielectric nanoparticles can demonstrate a strong forward scattering at visible and near-infrared wavelengths due to the interaction of optically induced electric and magnetic dipolar resonances. For a spherical nanoparticle, the first Kerker’s condition within dipole approximation can be realized, where backward scattering can reach zero. However, for this type of dielectric sphere, maximum forward scattering without backward scattering cannot be realized by modulating the refractive index and particle size of this nanoparticle. In this paper, we have demonstrated that a larger directional forward scattering than the traditional spherical nanoparticle can be obtained by using the ellipsoidal nanoparticle, due to the overlapping electric and magnetic dipolar modes. For the oblate ellipsoid with a determined refractive index, there is an optimum shape for generating the suppressed backward scattering along with the enhanced forward scattering at the resonant wavelength, where the electric and magnetic dipolar modes overlap with each other. For the prolate ellipsoid, there also exist the overlapping electric and magnetic dipolar modes at the resonant wavelength of total scattering, which have much higher forward scattering than those for both oblate ellipsoid and sphere, due to the existence of the higher multipolar modes. Furthermore, we have also demonstrated the realization of the dimensional tailoring in order to make the strong forward scattering shift to the desired wavelength.

Review of the Functions of Archimedes’ Spiral Metallic Nanostructures

Here, we have reviewed some typical plasmonic structures based on Archimedes’ spiral (AS) architectures, which can produce polarization-sensitive focusing phenomenon and generate plasmonic vortices (PVs) carrying controllable orbital angular momentum (OAM) because of the relation between the incident polarized states and the chiralities of the spiral structures. These features can be used to analyze different circular polarization states, which has been one of the rapidly developing researching topics in nanophotonics in recent years. Many investigations demonstrate that the multifunctional spiral-based plasmonic structures are excellent choices for chiral selection and generating the transmitted field with well-defined OAM. The circular polarization extinction ratio, as an evaluation criterion for the polarization selectivity of a designed structure, could be effectively improved by properly modulating the parameters of spiral structures. Such functional spiral plasmonic nanostructures are promising for applications in analyzing circular polarization light, full Stokes vector polarimetric sensors, near-field imaging, and so on.

Actively Tunable Terahertz Switches Based on Subwavelength Graphene Waveguide

As a new field of optical communication technology, on-chip graphene devices are of great interest due to their active tunability and subwavelength scale. In this paper, we systematically investigate optical switches at frequency of 30 THz, including Y-branch (1 × 2), X-branch (2 × 2), single-input three-output (1 × 3), two-input three-output (2 × 3), and two-input four-output (2 × 4) switches. In these devices, a graphene monolayer is stacked on the top of a PMMA (poly methyl methacrylate methacrylic acid) dielectric layer. The optical response of graphene can be electrically manipulated; therefore, the state of each channel can be switched ON and OFF. Numerical simulations demonstrate that the transmission direction can be well manipulated in these devices. In addition, the proposed devices possess advantages of appropriate ON/OFF ratios, indicating the good performance of graphene in terahertz switching. These devices provide a new route toward terahertz optical switching.

Anomalous forward scattering of gain-assisted dielectric shell-coated metallic core spherical particles

Abstract We have investigated the scattering properties of an individual core-shell nanoparticle using the Mie theory, which can be tuned to support both electric and magnetic modes simultaneously. In general, the suppression of forward scattering can be realized by the second Kerker condition. Here, a novel mechanism has to be adopted to explain zero-forward scattering, which originates from the complex interactions between dipolar and quadrupolar modes. However, for lossy and lossless core-shell spherical nanoparticles, zero-forward scattering can never be achieved because the real parts of Mie expansion coefficients are always positive. By adding proper gain in dielectric shell, zero-forward scattering can be found at certain incident wavelengths, which means that all electric and magnetic responses in Mie scattering can be counteracted totally in the forward direction. In addition, if the absolute values of dipolar and quadrupolar terms are in the same order of magnitude, the local scattering minimum and maximum can be produced away from the forward and backward directions due to the interacting effect between the dipolar and quadrupolar terms. Furthermore, by adding suitable gain in shell, super-forward scattering can also be realized at certain incident wavelengths. We also demonstrated that anomalously weak scattering or superscattering could be obtained for the core-shell nanoparticles with suitable gain in shell. In particular, for such a choice of suitable gain in shell, we can obtain zero-forward scattering and anomalously weak scattering at the same wavelength as well as super-forward scattering at another wavelength. These features may provide new opportunities for cloaking, plasmonic lasers, optical antennas, and so on.

Current statistic model and adaptive tracking algorithm based on Kalman and Smooth Variable Structure Filters

Target tracking is an essential part in automotive driver assistance systems. Most maneuvering target tracking algorithms are based on model, and an accurate model can enhance the tracking performance. Compared with constant velocity (CV) model, constant acceleration (CA) model and Singer model, the current statistical (CS) model matches well with the actual motion of target vehicle. But when a target maneuvers in the acceleration with a larger changing range or in the form of sudden change of state, the performance of CS model will become worse. To improve the accuracy of CS model responding to strong maneuvering of target and modeling uncertainties, we propose a novel strategy named KF-SVSF with the combination of the Kalman filter (KF) and Smooth Variable Structure filter (SVSF). A simulated result of target vehicle running in variable acceleration movement demonstrates that the KF-SVSF is a good solution to the fault of CS model.

Gain-enhanced plasmon metal nanoslit sensor

We have designed and investigated a double-band gain-assisted nanoslit array for the sensor applications. We find that the height, width and period of nanoslit array are the main factors for determining (he sensors performances. Due to the intrinsic Ohmic loss of system, the sensing efficiency has been hindered seriously. By implanting the gain medium into the designed structure, the sensing performance can be enhanced greatly due to a dramatic amplification of the EOT resonance by the energy transfer from the gain medium. Serving as gain-assisted refractive index senor, the corresponding FOM can reach to 440 with a gain value of corresponding threshold. It has a big potential in biomedical and sensing applications.

Parameter estimation and multi-pulse target detection of MIMO radar

Multiple-input and multiple-output (MIMO) radar is a new radar system which is proposed in recent years. Taking advantages of waveform diversity, MIMO radar can improve the identifiability of the parameter and the adaptive technology for receiving data on radar, and enhance the parameter estimation and target detection performance. In this paper, several traditional nonparametric adaptive technologies are introduced in parameter estimation method. In the case of a known number of targets, a multi-target parameter estimation method that combines Capon, Generalized-Likelihood Ratio (GLR) and approximate maximum likelihood (AML) estimation is proposed, which is called CGAML. It can estimate the target position and the corresponding complex amplitude accurately. And then a target detection model is established under multi-pulse accumulation conditions of MIMO radar, which analyses the performance of MIMO radar on target detection. Compared with the conventional phased array radar, MIMO radar system shows better advantages.