Polymeric zone plates for THz focusing Tofani, Silvia; Zografopoulos, Dimitrios C.; Missori, Mauro ...
2016 41st International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz),
2016-Sept.
Conference Proceeding
A conventional binary zone plate for terahertz focusing is compared with a proposed new configuration in which two zone plates are stacked, showing an increased focusing efficiency. The field ...intensity in the focal spot is enhanced by employing a low-loss cyclo-olefin polymer instead of more conventional materials.
In this work, a design flow for leaky-wave antennas based on metasurfaces is proposed. In particular, the possibility to extract the surface impedance of partially reflecting surfaces (PRS) for which ...homogenization formulas are not yet available in the literature has been exploited by means of numerical tools. The knowledge of the surface impedance in a PRS-based Fabry-Perot cavity leaky-wave antenna (FPC-LWA) allows for accurately evaluating the radiating performance by means of simple analytical formulas. A fishnet-like metasurface is designed to validate the proposed approach and its implementation as a partially reflective sheet for a highly-directive FPC-LWA working at terahertz frequencies is discussed.
This paper demonstrates the application of the Finite-Difference Time-Domain method for dispersive media to indoor ultra-wideband channel modeling. A new description of the frequency dispersion of ...building materials, based on a partial-fraction approach, is proposed, utilizing experimentally measured data on complex permittivity values reported in the literature. The analytical dispersion model for a series of building materials is estimated through the Vector Fitting technique and the through-the-wall penetration is calculated for indicative cases. Finally, a small two-dimensional office environment is studied and several channel characteristics are calculated demonstrating the flexibility and robustness of the proposed formulation in communication modeling. The proposed FDTD implementation covers all the bandwidth in a single run instead of running simulations for every frequency or subband.
Mechanically tunable Bragg filters for terahertz applications Ferraro, Antonio; Zografopoulos, Dimitrios C.; Caputo, Roberto ...
2016 41st International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz),
2016-Sept.
Conference Proceeding
Mechanically tunable Bragg filters at terahertz frequencies are designed, fabricated by a simple procedure, and characterized via THz time-domain spectroscopy. The Bragg reflectors are composed by ...stacking thin cyclo-olefin Zeonor polymer layers, which are separated by spacers made of a bi-adhesive tape. The defect cavity is void and its thickness is mechanically tuned by means of a translation stage. The filters show high transmittance and quality factors, owing to the selected very low-loss polymer.
We discuss arrays of metal-semiconductor-metal cavities as electrically tunable terahertz metasurfaces. The operation of the considered device is based on reverse biasing the Schottky junction formed ...between top metal strips and the n-type semiconductor buried beneath. The effective Drude permittivity of the cavity array is tuned by changing the depletion layer thickness via a gate bias applied between the strips and a back metal reflector. Combining Maxwell equations for terahertz waves with a drift-diffusion model for the semiconductor carriers into a multiphysics framework, we show that the proposed modulation concept is promising for a large part of the terahertz spectrum.
In this work, the spatially dispersive behavior of three different metasurface geometries has been investigated. A patch-like, a strip-like, and a fishnet-like unit cell have been compared in terms ...of their surface impedance for different angle of incidence at terahertz frequencies. The fishnet-like metasurface shows a TE-TM polarization independent behavior and a remarkable non-dispersive behavior, opening to very interesting possibilities in the design of Fabry-Perot cavity leaky-wave antennas with a reconfigurable pointing angle and equalized patterns at terahertz frequencies.
In this work, the tunable properties of nematic liquid crystals are exploited in order to design a Fabry-Perot cavity (FPC) leaky-wave antenna (LWA) with beam steering capability at fixed frequency ...in the THz range. The considered design is a grounded dielectric slab covered with a multistack of alternating layers of low- and high-permittivity dielectric materials, consisting of nematic liquid crystals and alumina thin films, respectively. The former allows for achieving the beam-steering capability at a fixed frequency. Full-wave simulations confirmed the pattern reconfigurability of the device, thus opening very interesting possibilities for the realization of reconfigurable THz antennas.
An optical switch based on liquid-crystal tunable long-range metal stripe waveguides is proposed and theoretically investigated. A nematic liquid crystal layer placed between a vertical configuration ...consisting of two gold stripes is shown to allow for the extensive electro-optic tuning of the coupler's waveguiding characteristics. Rigorous liquid-crystal switching studies are coupled with the investigation of the optical properties of the proposed plasmonic structure, taking into account different excitation conditions and the impact of LC-scattering losses. A directional coupler optical switch is demonstrated, which combines low power consumption, low cross-talk, short coupling lengths, along with sufficiently reduced insertion losses.
Soliton-like propagation in dispersion-managed silicon nanowaveguides Tsilipakos, Odysseas; Zografopoulos, Dimitrios C.; Kriezis, Emmanouil E.
2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC
Conference Proceeding
Over the last few years, significant research effort has been devoted to the study of nonlinear phenomena in silicon nanowaveguides (SNWs) 1. In particular, the capability for extensively engineering ...the dispersion characteristics of SNWs 1, has directed considerable interest to the dynamics of femtosecond solitonic pulses 2. However, the formation of pure solitons in SNWs is hindered (besides linear propagation losses) by the presence of nonlinear losses, namely, two-photon (TPA) and free-carrier absorption (FCA). Despite these extra loss mechanisms, we demonstrate in this work the possibility for quasi-soliton propagation in dispersion-managed SNWs. Both single-pulse and, more importantly, pulse-train cases are thoroughly examined, by employing a vectorial nonlinear Schrödinger equation (NLSE) formulation 4, rigorously taking into account all relevant phenomena, including free-carrier and higher-order nonlinear effects such as self-steepening.
The polarization properties of photonic crystal fibers infiltrated by nematic liquid crystals are investigated for various structural and material parameters. It is demonstrated that by proper design ...single-polarization or controllable highly-birefringent light guidance can be achieved. In addition, such favourable polarization properties may also be dynamically tuned via the application of an external field or the variation of the operating temperature.
PDF
