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.
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 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.
An all‐dielectric metasurface exhibiting a strong toroidal resonance is theoretically designed and experimentally demonstrated as an angular‐dependent resonant polarization beam‐splitter in the ...microwave K‐band. The metasurface is fabricated by embedding a square periodic array of high‐permittivity ceramic cuboid resonators in a 3D‐printed substrate of polylactic acid. It is demonstrated that by properly selecting the resonator geometry and by tuning the angle of incidence through mechanical rotation, the metasurface can switch between a polarization beam splitting and bandpass or bandstop operation. Such performance is achieved by exploiting the highly asymmetric Fano spectral profile of the toroidal resonance and the very low (high) dispersion of the associated p‐(s‐) polarized mode resulting from the resonant toroidal dipole mode's field profile, as evidenced by both full‐wave and band structure simulations. Theoretically infinite extinction ratios are achievable for polarization beam splitting operation with very low insertion losses and adjustable bandwidth. The experimental demonstration of such a compact, all‐dielectric metasurface expands the research portfolio of resonant metasurfaces toward not only the investigation of the intriguing physics of toroidal modes but also to the engineering of functional millimeter‐wave components for polarization control, for instance, in the context of 5G wireless communication networks.
Toroidal resonances are an elusive class of electromagnetic excitations, rarely found in natural materials. Here, strong toroidal dipole resonances in all‐dielectric metasurfaces composed of high‐permittivity, low‐loss ceramic resonators are demonstrated. By harnessing their particular polarization‐dependent properties, toroidal metasurfaces for angular‐dependent resonant polarization beam splitting in the microwave K‐band are engineered and experimentally demonstrated.
A rectangular metallic leaky waveguide loaded with liquid crystals (LC) and operating in its fundamental TE mode at 1 THz is proposed to mitigate the well-known trade-off between directivity and ...tunable angular range of dynamic beamscanning antennas. The radiating aperture consists of a partially reflecting surface (PRS) realized through a one-dimensional array of longitudinal slots etched on one of the metallic walls of the waveguide to efficiently couple with the propagating TE leaky mode. The antenna performance is evaluated by defining suitable figures of merit that take into account the beamscanning feature and the gain peak. These figures of merit are evaluated for different combinations of the antenna design parameters. After optimization, a tunable angular range of about 28° is reached, while maintaining a gain of around 7 dBi. A leaky-wave analysis of a simplified model of the structure allows to design the antenna without resorting to computationally expensive optimization processes. More rigorous models are then considered to accurately analyze the LC dynamics and the radiating properties of PRS. The three-dimensional structure is finally validated through full-wave simulations, showing a remarkable agreement with the theoretical predictions obtained with the simplified model.
By structuring a luminescent dielectric interface as a relief diffraction grating with nanoscale features, it is possible to control the intensity and direction of the emitted light. The composite ...structure of the grating is based on a fluorescent dye (Lumogen F RED 305) dispersed in a polymeric matrix (poly(methyl methacrylate)). Measurements demonstrate a significant enhancement of the emitted light for specific directions and wavelengths when the grating interface is compared to nonstructured thin films made of the same material. In particular, the maximum enhancement of photoluminescence for a given pump wavelength is obtained at an angle of incidence that is close to the Rayleigh anomaly condition for the first-order diffracted waves. In this condition, the maximum extinction of incident light is observed. Upon excitation with coherent and monochromatic sources, photoluminescence plots show that the Rayleigh anomalies confine the angular interval of the emitted light. Being the anomalies directly related to the pitch of the diffraction grating, the system can be thus implemented as an optical device whose directional emission can be designed for specific applications. The exploitation of nanoimprinting techniques for the fabrication of the luminescent grating enables production of the device on large areas, paving the way for low-cost lighting and solar applications.
Microwave fabrication and design techniques are commonly employed in the terahertz (THz) domain. However, a characterization of commercially available microwave dielectric materials is usually ...lacking at sub-THz and THz frequencies. In this work, we characterized four substrates by Rogers and an Ordyl dry resist between 0.2 and 2 THz, in terms of relative permittivity and loss tangent. The reflectance spectra of the investigated materials were retrieved by means of THz time-domain spectroscopy in reflection mode and post-processed according to a transmission-line model in which the materials’ parameters are fit by means of the Havriliak–Negami variation of the Debye model. The relative permittivity of the investigated materials showed negligible frequency dispersion in the sub-THz and in the THz range. In terms of the loss tangent, the Rogers substrates revealed a more pronounced frequency-dispersive behavior among different materials, as dictated by the Havriliak–Negami model. The Ordyl resist was dispersive in the 0.2–1.2 THz range and presented a nearly constant loss tangent value between 1.2 and 2 THz. These results may represent a reference for the development of innovative components for THz and sub-THz emerging applications.
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