Graphene-based absorber exploiting guided mode resonances in one-dimensional gratings

A one-dimensional dielectric grating, based on a simple geometry, is proposed and investigated to enhance light absorption in a monolayer graphene exploiting guided mode resonances. Numerical findings reveal that the optimized configuration is able to absorb up to 60% of the impinging light at normal incidence for both TE and TM polarizations resulting in a theoretical enhancement factor of about 26 with respect to the monolayer graphene absorption (about 2.3%). Experimental results confirm this behaviour showing CVD graphene absorbance peaks up to about 40% over narrow bands of few nanometers. The simple and flexible design paves the way for the realization of innovative, scalable and easy-to-fabricate graphene-based optical absorbers

Graphene-based perfect optical absorbers harnessing guided mode resonances

We numerically and experimentally investigate graphene-based optical absorbers that exploit guided mode resonances (GMRs) achieving perfect absorption over a bandwidth of few nanometers (over the visible and near-infrared ranges) with a 40-fold increase of the monolayer graphene absorption. We analyze the influence of the geometrical parameters on the absorption rate and the angular response for oblique incidence. Finally, we experimentally verify the theoretical predictions in a one-dimensional, dielectric grating and placing it near either a metallic or a dielectric mirror

High sensitivity photonic crystal pressure sensor

A two-dimensional photonic crystal microcavity coupled with a waveguide is proposed to realise a high sensitive force sensor, designed on a GaAs membrane. A theoretical model is developed to evaluate the change of the refractive index induced by the application of the force onto a sensing surface. A linear calibration curve is obtained relating the resonant drop position to the applied force

Optical filter based on a coupled bilayer photonic crystal

We report on the fabrication of an ultra-compact optical filter based on photonic crystal free-standing membranes in bi-layer configuration. The basic heterostructure consists of two 376nm-thick GaAs-membranes sandwiched between air on a GaAs substrate. The air gap between the two membranes is 520nm thick. The normal-incidence reflectance measurements and the numerical simulation of reflection spectra show a high sensitivity to the holes diameter

Label-free biomechanical nanosensor based on LSPR for biological applications

A label-free localized surface plasmon resonance (LSPR)-based biosensor exploiting gold nanorods (ONRs) is proposed and demonstrated. For this aim, 35 +/- 5 nm long and 20 +/- 4 thick GNRs spaced by a few nanometers thick polyelectrolytes (PE) from a gold thin film was analyzed and synthesized. The morphology of the GNRs, the plasmon properties of GNRs, swelling of PE layers and the wettability of the surfaces were characterized by transmission and scanning electron microscopy, spectroscopic reflectivity and contact angle measurements, respectively. Indeed, when immersed in a phosphate buffer saline solution, the GNRs-PE-gold system shows an optical shift of the LSPR wavelength. This shift was found to correspond to a vertical swelling of about 2 nm, demonstrating the extreme sensitivity of the biosensor. Finally, we show that LSPR measurements can be used to detect dynamic resonance changes in response to both thickness and buffer solution, while the hydrophobic behavior of the surface can be exploited for reducing the number of liquid analytes in clinical biosensing application. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Acquired nasopharyngeal stenosis correction using a modified palatal flaps technique in obstructive sleep apnea (OSA) patients

Background: Acquired nasopharyngeal stenosis is a rare and heterogeneous pathological condition that has different causes, generally resulting as a complication of a pharyngeal surgery, especially in patients affected by obstructive sleep apnea (OSA). Different approaches have been proposed for the treatment of nasopharyngeal stenosis but a unique and standardized management has not yet been presented. The aim of our paper is to evaluate the efficacy of our surgical technique, describing its steps and results with the aim to consider it as a possible solution for the treatment of this condition. Methods: This is a retrospective cohort study. Eight patients (mean age 27.25 years old (yo), range 8–67 yo; Male/Female ratio 4/4; mean body mass index (BMI) 26.1) affected by OSA (mean apnea hypopnea index (AHI) before OSA surgery was 22.1) and acquired nasopharyngeal stenosis as a consequence of different pharyngeal surgeries were treated with our modified approach in the Department of Otolaryngology, Morgagni Pierantoni Hospital, Forlì, Italy. Resolution of stenosis and complication rate were the main outcome measures. Results: Complete resolution of the stenosis was achieved in all cases and no complications were recorded at three weeks, six months, and 2 years follow-up. Conclusions: Our technique appears to be a promising method for the management of nasopharyngeal stenosis in OSA patients. However, further studies comparing different techniques and reporting on larger series and longer follow up time are needed to prove the efficacy of the proposed technique

Optical Properties of Ordered Plasmonic Nanostructures in Linear and Nonlinear Regimes

ABSTRACT In this paper we review our recent advances in subwavelength plasmonic structures in linear and nonlinear regimes. We show several examples of subwavelength plasmonic devices in different configurations and schemes. We emphasize how these devices can be exploited for many applications, such as sensing, spectroscopy, photovoltaics and optical communications. Finally we will illustrate some challenges that are still open and need to be fulfilled. Keywords: plasmonics, plasmonic resonance, scattering, field enhancement, thin film, nonlinear harmonic generation. INTRODUCTION The propagation of Surface Plasmon Polaritons (SPPs) has gained great interest in the last decades since it has been demonstrated that their excitation on metal gratings or metal nanostructures can be usefully exploited to solve several problems relative to many applications, such as Raman spectroscopy, sensing, data storage, light emission and amplification as well as absorption enhancement for energy harvesting purpose