Polariton assisted tunable directionality provides an intrinsic ingredient to various micro/nano integrated optical systems. Their capabilities of light manipulation in mesoscopic structures allow numerous beneficial properties in information processing. The realization of active near-field directionality by tuning the input signal of system bias is more preferable than that by reconfiguring the nanostructures. Recent progresses on the multiple hybrid dipole radiations ensure another methodology in realizing tunable directionality. Here we investigate some exotic near-field phenomena in a 5-layer waveguide consisted of graphene and hexagonal boron nitride (hBN) illuminated by hybrid dipole sources such as a Circular dipole, a Huygens dipole or a Janus dipole. We demonstrate divergent behaviors of hybrid polariton excitations subject to various source types and the tunability of switching between phonon-like polaritons and plasmon-like polaritons. We also show that the flipping of the group velocity of excited hybrid polaritons can be used to flexibly tune the transportation direction away from the dipolar sources. To be specific, when the group velocity of supported polariton flips its sign, the energy flow will shift to the opposite side accordingly. Such phenomena are promising in the design of reconfigurable and multifunctional nanophotonic devices.
Recently, the number of electric vehicles (EVs) is increasing due to the declining of oil resources and rising of greenhouse gas emission. However, EVs have not received wide acceptance by consumers due to the limitations of the stored energy and charging problems in batteries. The dynamic or in motion charging solution becomes a suitable choice to solve the battery related issues. Many researchers and vehicle manufacturers are working to develop an efficient charging system for EVs which is based on magnetic emissions to transfer power. These emissions must be evaluated and compared to limits specified by standards (in and outside the vehicle) in order to not cause harmful effects on their environment (humans, pets, electronic devices...). This paper presents an efficient method for modeling electromagnetic emission in near field and sizing a magnetic shield for a wireless power transfer (WPT) system for EVs. A model based on elementary magnetic dipoles is developed in order to obtain the same radiation as the real WPT coil. This model is used to size a magnetic shield which will be placed under the vehicle to protect human body from magnetic emissions. The obtained shielding plate allows to respect the standards of magnetic emission by bringing a decrease of 43 dB to the levels of magnetic fields. This approach is experimentally validated.
Wheat, canola, and pasture are three of the major vegetation types studied during the Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12) conducted to support NASA's Soil Moisture Active Passive (SMAP) mission. The utilized model structure is integrated in the SMAP baseline active retrieval algorithm. Forward lookup tables (data-cubes) for VV and HH backscatters at L-band are developed for wheat and canola fields. The data-cubes have three axes: vegetation water content (VWC), root mean square (RMS) height of rough soil surface and soil permittivity. The volume scattering and doublebounce scattering of the fields are calculated using the distorted Born approximation and the coherent reflectivity in the double-bounce scattering. The surface scattering is determined by the numerical solutions of Maxwell equations (NMM3D). The results of the data-cubes are validated with airborne radar measurements collected during SMAPVEX12 for ten wheat fields, five canola fields, and three pasture fields. The results show good agreement between the data-cube simulation and the airborne data. The root mean squared errors (RMSE) were 0.82 dB, 0.78 dB, and 1.62 dB for HH, and 0.97 dB, 1.30 dB, and 1.82 dB for VV of wheat, canola, and pasture fields, respectively. The data-cubes are next used to perform the time-series retrieval of the soil moisture. The RMSEs of the soil moisture retrieval are 0.043 cm3/cm3, 0.082 cm3/cm3, and 0.082 cm3/cm3 for wheat, canola, and pasture fields, respectively. The results of this paper expand the scope of the SMAP baseline radar algorithm for wheat, canola, and pastures formed and provide a quantitative validation of its performance. It will also have applications for the upcoming NISAR (NASA-ISRO SAR Mission).
In this paper, we propose a fine scale partially coherent patch model (FPCP) for GNSS-R land applications for soil moisture retrieval. The land surface is divided into coherent planar patches on which microwave roughness is superimposed. The scattered waves of the coherent patch are decomposed into the coherent specular reflection and diffuse incoherent scattering. A fine scale of 2 meter patch size is chosen for the coherent patch to be applicable to complex terrain with large varieties of topographical elevations and with small to large topographical slopes. The summation of scattered fields over patches is carried out using physical optics. The phase term of the scattered wave of each patch is kept so that correlation scattering effects among patches are accounted for. Results are illustrated for power ratio for areas near the specular point and areas far away from the specular point. Comparisons are made with the radiative transfer geometric optics model. DDM simulations are performed with good agreement with CYGNSS data.
In this paper, high efficiency multi-functional all-optical logic gates based on a metal-insulator-metal (MIM) plasmonic waveguide structure with Kerr-type nonlinear nano-ring resonators are proposed. The proposed structure consists of three straight input ports, eight nano-ring resonators filled with the Kerr-type nonlinear medium, and one straight output port. By fixing the input signal power and properly changing the control power, it can be used to design high efficiency multi-functional all-optical logic gates. The numerical results show that the proposed Kerr-type nonlinear plasmonic waveguide structures could really function as all-optical XOR/NXOR, AND/NAND, and OR/NOR logic gates in the optical communication spectral region. The transmission efficiency of the high logic state is higher than 95%, and that of the low logic state is about 0% at the wavelength 1310nm. The performance of the proposed logic gates was analyzed and simulated by the finite element method (FEM).
In the simulation of high frequency nanoscale semiconductor devices in which electromagnetic (EM) fields and carrier transport are coupled, and optoelectronic devices in which strong interactions between EM fields and charged particles exist, both the Maxwell's equations and the time-dependent Schrödinger equation (TDSE) need to be solved to capture the interactions between EM and quantum mechanics (QM). One of the numerical simulation methods for solving these equations is the finite difference time domain (FDTD) method. In this review paper, the development of FDTD method applied in EM and QM simulation is discussed. Several widely used FDTD techniques, i.e., explicit, implicit, explicit staggered-time, and Chebyshev methods, for solving the TDSE are introduced and compared. The hybrid approaches based on FDTD method, which are used to solve the Poisson-TDSE and Maxwell-TDSE coupled equations for EM-QM simulation, are also discussed. Furthermore, the applications of these simulation methods for nanoscale semiconductor devices and optoelectronic devices are introduced. Finally, a conclusion is given.
χ(3) nonlinearity enables ultrafast femtosecond scale light-to-light coupling and manipulation of intensity, phase, and frequency. χ(3) nonlinear functionality in micro- and nano-scale photonic waveguides can potentially replace bulky fiber platforms for many applications. In this review, we summarize and comment on the progress on χ(3) nonlinearity in chip-scale photonic platforms, including several focused hot topics such as broadband and coherent sources in the new bands, nonlinear pulse shaping, and all-optical signal processing. An outlook of challenges and prospects on this hot research field is given at the end.
Quantum interactions between a single particle and nanoinclusions of spherical or cylindrical shape are optimized to produce scattering lineshapes of high selectivity with respect to impinging energies, excitation directions and cavity sizes. The optimization uses a rigorous solution derived via electromagnetic scattering formalism while the adopted scheme rejects boundary extrema corresponding to resonances that occur outside of the permissible parametric domains. The reported effects may inspire experimental efforts towards designing quantum sensing systems employed in applications spanning from quantum switching and filtering to single-photon detection and quantum memory.