Showing papers by "Odysseas Tsilipakos published in 2023"
TL;DR: In this paper , a conductive meta-atom of toroidal topology is studied both theoretically and experimentally, demonstrating a sharp and highly controllable resonant response for a free-space periodic metasurface and a pair of meta-atoms inserted within a rectangular metallic waveguide.
Abstract: 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.
1 citations
TL;DR: In this article , a photonic laser cavity consisting of a silicon-rich-nitride-on-insulator disk resonator overlaid with a transition-metal dichalcogenide (TMD) bilayer heterostructure acting as the gain medium is evaluated.
Abstract: We assess the continuous-wave and dynamic performance of a photonic laser cavity consisting of a silicon-rich-nitride-on-insulator disk resonator overlaid with a transition-metal dichalcogenide (TMD) bilayer heterostructure (${\mathrm{WSe}}_{2}/{\mathrm{Mo}\mathrm{S}}_{2}$) acting as the gain medium. The optically pumped TMD heterostructure fosters an interlayer exciton with long radiative recombination lifetime, providing light emission in the near-infrared ($\ensuremath{\sim}1130$ nm). Following a meticulous design process, we propose a silicon-on-insulator-compatible, monolithically integrated optical source capable of emitting milliwatt power inside an integrated waveguide, featuring a low pump-power threshold of $\ensuremath{\sim}16\phantom{\rule{0.2em}{0ex}}{\mathrm{kW}/\mathrm{cm}}^{2}$, and exhibiting an estimated total quantum efficiency of approximately 1.7%. The proposed laser cavity is analyzed and designed using a rigorous theoretical framework based on perturbation theory and temporal coupled-mode theory, capable of treating nanophotonic cavities of any geometry and material composition comprising both bulk and/or sheet gain media. The framework is built upon fundamental electromagnetic and semiclassical gain equations, rendering it general and adaptable to different cavity configurations and gain-media descriptions. It constitutes a powerful tool for the efficient analysis of contemporary micro- and nanophotonic semiconductor lasers, since it is capable of predicting fundamental laser characteristics, providing design directives, deriving continuous-wave design metrics, and evaluating the dynamic response of realistic laser cavities.
TL;DR: In this paper , the authors show that ultrathin metasurfaces with a specific multiresonant response can enable simultaneously arbitrarily-strong and arbitrarily-broadband dispersion compensation, pulse (de-)chirping and compression or broadening.
Abstract: We show that ultrathin metasurfaces with a specific multiresonant response can enable simultaneously arbitrarily-strong and arbitrarily-broadband dispersion compensation, pulse (de-)chirping and compression or broadening. This breakthrough overcomes the fundamental limitations of both conventional non-resonant approaches (bulky) and modern singly-resonant metasurfaces (narrowband) for quadratic phase manipulations of electromagnetic signals. The required non-uniform trains of resonances in the electric and magnetic sheet conductivities that completely control phase delay, group delay, and chirp, are rigorously derived and the limitations imposed by fundamental physical constraints are thoroughly discussed. Subsequently, a practical, truncated approximation by finite sequences of physically-realizable linear resonances is constructed and the associated error is quantified. By appropriate spectral ordering of the resonances, operation can be achieved either in transmission or reflection mode, enabling full space coverage. The proposed concept is not limited to dispersion compensation, but introduces a generic and powerful ultrathin platform for the spatio-temporal control of broadband real-world signals with a myriad of applications in modern optics, microwave photonics, radar and communication systems.
22 Mar 2023
TL;DR: In this paper , the photo-elasticity of Silk fibroin was investigated using optical whispering gallery mode resonation of light at the wavelength of 1550 nm, and the strain optical coefficient K' was found to be 0.059 ± 0.004.
Abstract: Silk fibroin is an important biomaterial for photonic devices in wearable systems. The functionality of such devices is inherently influenced by the stimulation from elastic deformations, which are mutually coupled through photo-elasticity. Here, we investigate the photo-elasticity of silk fibroin employing optical whispering gallery mode resonation of light at the wavelength of 1550 nm. The fabricated amorphous (Silk I) and thermally-annealed semi-crystalline structure (Silk II) silk fibroin thin film cavities display typical Q-factors of about 1.6 × 104. Photo-elastic experiments are performed tracing the TE and TM shifts of the whispering gallery mode resonances upon application of an axial strain. The strain optical coefficient K' for Silk I fibroin is found to be 0.059 ± 0.004, with the corresponding value for Silk II being 0.129 ± 0.004. Remarkably, the elastic Young's modulus, measured by Brillouin light spectroscopy, is only about 4% higher in the Silk II phase. However, differences between the two structures are pronounced regarding the photo-elastic properties due to the onset of β-sheets that dominates the Silk II structure.