An electro-optic modulator based on hybrid plasmonic micro-ring-disks with submicron radii is designed and rigorously investigated via the finite-element method. The device is based on the ...conductor-gap-silicon hybrid plasmonic platform and utilizes an embedded electro-optical polymer to control the resonant wavelengths of micro-ring-disk resonators. Such elements combine the easier fabrication of microdisks with the lower capacitance of microring resonators and provide high modulation depths, low insertion losses, and energy consumption around 1 fJ/bit. Finally, an add-drop filter configured in a
2
×
2
switching matrix is presented and its performance is preliminary assessed.
Locally one-dimensional finite-difference time-domain formulations implemented with the auxiliary differential equation technique are presented for the study of plasmonic devices that comprise ...dispersive materials described by the generalized modified Lorentz and partial fraction models. The convolutional perfectly matched layer is employed for the termination of the computational domain. The performance of the proposed algorithms is evaluated in benchmark problems on guided-wave plasmonic structures, which demonstrate satisfactory numerical accuracy with significantly reduced computational times.
The tunable properties of nematic liquid crystals (NLC) are here exploited in a peculiar leaky waveguide with artificial magnetic conductors as the lateral walls, a bottom metal ground plane, and a ...homogenized metasurface on top to obtain dynamic beamsteering at a fixed terahertz frequency. The waveguide consists of an NLC cell sandwiched between two dielectric layers. The proposed antenna system works on its transverse-magnetic leaky mode and is capable of radiating a beam that scans either by frequency or by changing the bias voltage applied across the NLC cell. The design parameters are optimized through a rigorous modal analysis of the structure, and the radiation performance is validated through full-wave simulations. The results are promising for the realization of next-generation tunable terahertz leaky-wave antennas.
The two main problems of dielectric metasurfaces for sensing and spectroscopy based on electromagnetic field enhancement are that resonances are mainly localized inside the resonator volume and that ...experimental Q-factors are very limited. To address these issues, a novel dielectric metasurface supporting delocalized modes based on quasi-bound states in the continuum (quasi-BICs) is proposed and theoretically demonstrated. The metasurface comprises a periodic array of silicon hollow nanocuboids patterned on a glass substrate. The resonances stem from the excitation of symmetry-protected quasi-BIC modes, which are accessed by perturbing the arrangement of the nanocuboid holes. Thanks to the variation of the unit cell with a cluster of four hollow nanocuboids, polarization-insensitive, delocalized modes with ultra-high Q-factor are produced. In addition, the demonstrated electric field enhancements are very high (103–104). This work opens new research avenues in optical sensing and advanced spectroscopy, e.g., surface-enhanced Raman spectroscopy.
This letter addresses the stability problem of two auxiliary differential equation (ADE) finite-difference time-domain (FDTD) methods for the case of modified Lorentz media, using the combination of ...the von Neumann method and the Routh-Hurwitz criterion. A rigorous investigation supported by FDTD simulations designates that the stability criterion of the conventional FDTD method can be preserved via the proper selection of the difference and averaging operators. A set of conditions for the dispersive medium parameters is derived, providing the stability limit for both FDTD schemes with practical guidelines for evaluating the fitting of experimentally studied materials.
A novel terahertz (THz) Fabry-Perot cavity (FPC) antenna is proposed, based on a multistack of alternating layers of highly birefringent nematic liquid crystal (NLC) and high-permittivity dielectric, ...which comprehensively acts as a Bragg reflector. This layout is able to provide enhanced reconfigurability and improved directivity with respect to standard FPC leaky-wave antenna (LWA) designs. The application of a low driving voltage to the NLC layers allows for the dynamic control of the radiating properties of the LWA, at a fixed frequency in the low-THz range. The attractive features and performance of two different configurations are rigorously discussed in a theoretical context, taking into account the realistic implementation of the proposed device.
A conductive meta-atom of toroidal topology is studied both theoretically and experimentally, demonstrating a sharp and highly controllable resonant response. Simulations are performed both for a ...free-space periodic metasurface and a pair of meta-atoms inserted within a rectangular metallic waveguide. A quasi-dark state with controllable radiative coupling is supported, allowing to tune the linewidth (quality factor) and lineshape of the supported resonance via the appropriate geometric parameters. By conducting a rigorous multipole analysis, we find that despite the strong toroidal dipole moment, it is the residual electric dipole moment that dictates the electromagnetic response. Subsequently, the structure is fabricated with 3D printing and coated with silver paste. Importantly, the structure is planar, consists of a single metallization layer and does not require a substrate when neighboring meta-atoms are touching, resulting in a practical, thin and potentially low-loss system. Measurements are performed in the 5 GHz regime with a vector network analyzer and a good agreement with simulations is demonstrated.
A comprehensive framework for the theoretical and experimental investigation of thin conducting films for terahertz applications is presented. The electromagnetic properties of conducting polymers ...spin-coated on low-loss dielectric substrates are characterized by means of terahertz time-domain spectroscopy and interpreted through the Drude-Smith model. The analysis is complemented by an advanced finite-difference time-domain algorithm, which rigorously deals with both the dispersive nature of the involved materials and the extremely subwavelength thickness of the conducting films. Significant agreement is observed among experimental measurements, numerical simulations, and theoretical results. The proposed approach provides a complete toolbox for the engineering of terahertz optoelectronic devices.
Mussels (Mytilus galloprovincialis) collected at three locations in Boka Kotorska Bay, on the Montenegrin Adriatic coast, were analyzed for the first time by optical and Raman microscopy to detect ...microplastics (MPs) and other emerging contaminants in their soft tissues. Concentrations of six trace metals (Cu, Zn, Mn, Fe, Cd, and Hg) were also measured in the same samples by atomic absorption spectroscopy. Mussels from a location near the urban area of Kotor were found to exhibit the highest content of MPs and other pollutants originating from anthropogenic sources, while farmed mussels showed higher carotenoid as well as nylon content. The hypothesis of MPs acting as a possible secondary route of trace metals ingress in mussels, a thus far scarcely studied topic, was evaluated based on a comparative analysis of the obtained results. In this context, it was noticed that nylon filaments originating from mussel farming equipment might contribute to higher trace metal content. The results showed that the simultaneous analysis of different contaminants in mussels can be a significant step forward in marine environment pollution monitoring and the assessment of human health risks associated with the consumption of contaminated seafood.
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