V. Petruzzelli

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 (≈2.3%). Experimental results confirm this behavior showing CVD graphene absorbance peaks up to about 40% over narrow bands of a few nanometers. The simple and flexible design points to a way to realize innovative, scalable and easy-to-fabricate graphene-based optical absorbers.

Photonic Crystal Sensors

The paper deals with the possibility of using photonic crystals for sensing purpose. The optical properties of photonic crystals allow to realize sensing devices characterized by a high degree of compactness and a good resolution of the quantity to detect. A particular attention is devoted to force/pressure sensors and the design of a PhC microcavity pressure sensor is reported

Photonic band gap filter for wavelength division multiplexer

An optical multiplexer-demultiplexer based on an index-confined photonic band gap waveguide is proposed. The dropping of electromagnetic waves having a given frequency or a certain frequency band is obtained via a phase-shifted grating obtained by breaking the uniform period sequence to include a defect layer. The selective filtering properties of the proposed structure are simulated by means of a computer code relying on a bi-directional beam propagation method based on the method of lines.

Graphene-based perfect optical absorbers harnessing guided mode resonances

We investigate graphene-based optical absorbers that exploit guided mode resonances (GMRs) attaining theoretically 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 by placing it near either a metallic or a dielectric mirror, thus achieving very good agreement between numerical predictions and experimental results.

Experimental demonstration of a novel bio‑sensing platform via plasmonic band gap formation in gold nano‑patch arrays

In this paper we discuss the possibility of implementing a novel bio-sensing platform based on the observation of the shift of the leaky surface plasmon mode that occurs at the edge of the plasmonic band gap of metal gratings, when an analyte is deposited on top of the metallic structure. We report numerical calculations, fabrication and experimental measurements to prove the sensing capability of a two-dimensional array of gold nano-patches in the detection of a small quantity of Isopropyl Alcohol (IPA) deposited on top of sensor surface. The calculated sensitivity of our device approaches a value of 1000 nm/RIU with a corresponding Figure of Merit (FOM) of 222 RIU(-1). The presence of IPA can also be visually estimated by observing a color variation in the diffracted field. We show that color brightness and intensity variations can be ascribed to a change in the aperture size, keeping the periodicity constant, and to different types of analyte deposited on the sample, respectively. Moreover, we demonstrate that unavoidable fabrication imperfections revealed by the presence of rounded corners and surface roughness do not significantly affect device performance.

Tunability of Photonic Band Gap Notch Filters

A notch filter based on an index confined photonic band gap waveguide is proposed. The dropping of an electromagnetic wave having a specific wavelength is obtained by opportunely designing a periodically corrugated overlay. The selective filtering properties of the proposed structure are identified by using a computer code based on the bidirectional beam propagation method with the aid of the method of lines. The optimized design of a notch filter, characterized by a full-width half-maximum (FWHM) bandwidth of 2 nm, is given. The tunability is reached by exploiting the electroclinic effect of smectic-A * liquid crystals.

Optimization and Characterization of Rare-Earth-Doped Photonic-Crystal-Fiber Amplifier Using Genetic Algorithm

A genetic-algorithm (GA) procedure has been ad hoc implemented to obtain a tool for both design and characterization of rare-earth-doped optical amplifiers and lasers. In particular, the routines performing the selection, crossover, mutation, and elitism operations have been written with the aim to investigate the optimal erbium-doped amplifier or laser configuration. Conversely, the GA can be employed in device characterization to identify those parameters of the erbium-energy-level transitions, which are not directly measurable, e.g., the cross-relaxation and up-conversion coefficients. The GA appears intriguing because of its efficiency and versatility. Its operation strategy is noticeably for the capability to identify solutions in complex multidimensional spaces. In this paper, the GA application for modeling and characterizing erbium-doped photonic-crystal-fiber amplifiers is described in detail.

Broadband Mach–Zehnder Switch for Photonic Networks on Chip

In this paper, we propose a broadband silicon Mach-Zehnder switch (MZS) for wavelength division multiplexing applications on photonic networks on chip. The proposed reconfigurable switch is based on a single-stage three-waveguide interferometric configuration in which the phase shift is achieved via a p-i-n diode. The device is analyzed by the coupled-mode theory and by the finite-difference beam propagation method. The proposed configuration leads to a considerable increase in the bandwidth with respect to the conventional MZS. For example, the two-waveguide MZS with a gap g=0.30 μm between the two coupled waveguides exhibits bandwidth Δλ = 60 nm, crosstalk CT = - 15 dB, and insertion loss IL = 1.1 dB. Conversely, a bandwidth Δλ = 115 nm is achieved for the three-waveguide configuration to parity of the other parameters.

Color control through plasmonic metal gratings

We experimentally demonstrate the color tuning abilities of two-dimensional periodic arrays of gold nano-patches on silicon substrate. We observe that changes in the geometrical parameters of the array can shift significantly the plasmonic resonance that occurs at the edge of the plasmonic band gap. Experimental proof of this shift is provided by the observation of an important change in the color of the diffracted field. Calculations of the diffracted spectra match the observed color changes very well and provide an efficient means for the design of sensing platforms based on color observation.

Second harmonic generation from nanoslits in metal substrates: applications to palladium-based H2 sensor

We conducted a theoretical investigation of second harmonic generation and other nonlinear features that result from the magnetic Lorentz force, when a single aperture is cut on a thick, opaque palladium substrate. We studied the dependences of linear pump transmission and second harmonic generation near resonance conditions, and explored the different physical mechanisms and their dependences, for example, geometrical features. We found that it is possible to exploit field localization and surface plasmon generation to enhance second harmonic generation in the regime of extraordinary transmittance of the pump field. Both transmitted and backward second harmonic generation conversion efficiencies were investigated. The results reveal that it may be possible to access several potential new applications. In particular, we demonstrated that the exploitation of a combination of nonlinear effects and enhanced transmission makes possible a palladium-based device suitable for H 2 -leak-detection.