All-optical tuning of EIT-like dielectric metasurfaces by means of chalcogenide phase change materials

Electromagnetically induced transparency (EIT) is a pump-induced narrowband transparency window within an absorption lin e of the probe beam sp ectrum in an atomic system. In this paper we propose a way to bring together the all-dielectric metamaterials to have EIT-like effects and to optically tune the response by hybridizing them with a layer of a phase change material. We propose a design of the metamaterial based on Si nanoresonators that can support an EIT-like resonant response. On the top of the resonators we consider a thin layer of a chalcogenide phase change material, which we will use to tune the optical response. Our choice is Ge 2 Sb 2 Te 5 (GST), since it has two stable phases at room temperature, namely amorphous and crystalline, between which it can be switched quickly, nonvolatively and reversibly, sustaining a large number of switching cycles. They differ in optical properties, while still having moderately low losses in telecom range. Since such dielectric resonators do not have non-radiative losses of metals around 1550nm, they can lead to a high- Q factor of the EIT-like response in this range . Firstly, we optimize the starting structure so that it gives an EIT-like response at 1550 nm wh en the GST layer is in the amorphous state. Our starting design uses glass as a substrate, but we also consider implementation in SOI technology. If we then switch the thin layer of GST to its crystalline phase, which has higher losses, the EIT-like response is red shifted, pr oviding around 10:1 contrast at 1550nm. This reversible tuning can be done with an ns visible pulsed laser. We discuss the results of the simulation of the dielectric metasurface for differe nt configurations and the tuning possibilit

Random nonlinear layered structures as sources of photon pairs for quantum-information processing

Random nonlinear layered structures have been found to be a useful source of photon pairs with perfectly indistinguishable un-entangled photons emitted into a very narrow spectral range. Localization of the interacting optical fields typical for random structures gives relatively high photon-pair fluxes. Superposing photon-pair emission quantum paths at different emission angles, several kinds of two-photon states (including states with coincident frequencies) useful in quantum-information processing can easily be generated.Comment: 4 pages, 5 figure

Management of the orbital angular momentum of vortex beams in a quadratic nonlinear interaction

Light intensity control of the orbital angular momentum of the fundamental beam in a quadratic nonlinear process is theoretically and numerically presented. In particular we analyzed a seeded second harmonic generation process in presence of orbital angular momentum of the interacting beams due both to on axis and off axis optical vortices. Examples are proposed and discussed

Coherence effects in propagation through photonic crystals

We have analytically studied how a partially coherent quasi plane wave is affected by a photonic crystal structure including a grating. The analysis is presented for spatial and temporal cases showing the possibility to determine the coherence characteristics of the pulse.

Influence of pump-field scattering to nonclassical-light generation in a photonic band-gap nonlinear planar waveguide

Optical parametric process occurring in a nonlinear planar waveguide can serve as a source of light with nonclassical properties. Properties of the generated fields are substantially modified by scattering of the nonlinearly interacting fields in a photonic band-gap structure inside the waveguide. A quantum model of linear operator amplitude corrections to amplitude mean-values provides conditions for an efficient squeezed-light generation as well as generation of light with sub-Poissonian photon-number statistics. Destructive influence of phase mismatch of the nonlinear interaction can fully be compensated using a suitable photonic-band gap structure inside the waveguide. Also an increase of signal-to-noise ratio of an incident optical field can be reached in the waveguide.Comment: 10 pages, 12 figure

The Cognition of Hunger and Eating Behaviours

Hunger is a poorly defined cognition, assumed to motivate overeating, but there is no firm evidence that the intensity of a sense of hunger is related to overweight. Recent research has suggested instead that irregular eating habits, as deriving from dieting, emotional stressors or other causes may have a role in the weight gain of obese people. These "borderline eating behaviours" (or BEB), targeted in cognitive behavioural therapy of obesity, were found associated to the body mass index both in normal and in overweight subjects in previous studies, using a specific scale called SENICAL. This study aimed at exploring the role of the sense of "unbearable hunger" on these eating irregularities, as measured with SENICAL, which provides an overall measure of BEB. SENICAL has been administered to a sample of 365 university students, together with other self-report measures; one item of SENICAL has been used to measure the frequency of the feeling of "unbearable hunger". An ANCOVA performed on the total SENICAL scores showed a linear increase of BEB along with the frequency of perceived "unbearable hunger", independently form age and gender. An item analysis of the SENICAL scale, performed with Chi square, showed that 15 out of 27 of these behavioural and emotional responses comprising the scale were associated with the sense of hunger, such as to diet or try to fast, to eat at irregular times, to eat more than usual when in emotional state, to eat quickly and not to taste the food, and to worry about weight increase. The "sense of hunger" may contribute to disrupt the eating habits, and maintain many of the eating irregularities associated to weight gain called "borderline eating behaviours". These results suggest that the cognition of hunger is worth to be targeted in the treatment of obese people

Photoacoustic technique for the characterization of plasmonic properties of 2D periodic arrays of gold nanoholes

We apply photo-acoustic (PA) technique to examine plasmonic properties of 2D periodic arrays of nanoholes etched in gold/chromium layer upon a glass substrate