Papers by Author: Simone Berneschi

Abstract: The possibility to confine the light in optical planar structures represented the milestone for the development of integrated optical devices in different application areas, such as communications and sensing. In particular, rare-earth (RE) doped planar waveguides demonstrated to be an interesting solution in the realization of integrated optical lasers and amplifiers suitable for the generation/regeneration of the signal in metropolitan and local area networks. Nowadays, although these devices are commercially available, the major contribution of the research consists in discovering and developing better combinations of materials and fabrication processes, in order to reduce the costs and increase the performance of the aforesaid devices. In this context glass-ceramic waveguides, activated by RE ions, seem to fully respond to these requests. The aim of this paper is to offer a comprehensive review on the main results obtained in our Labs in the field of glassceramics. Fabrication and characterization of different silicate glass-ceramic thin films, doped with different percentages of RE ions, will be presented and discussed. The interesting results obtained make these systems quite promising for development of high performance integrated optical amplifiers and lasers.

Abstract: We report on fabrication and characterization of two different opal-like structures: (i) crystal exhibiting mechanochromism, i.e. change of colour when subjected to mechanical stress, composed of closely packed colloidal polystyrene particles (CPCP) embedded in a poly-dimethylsiloxane (PDMS) elastomeric matrix; (ii) metallo-dielectric systems (MDCS), based on the realization of inverse silica opal and following attachment of gold nanoparticles on the silica network of the inverse colloidal structure. Optical measurements, performed on the two structures, have demonstrated that: (i) when an horizontal strain is applied on the CPCP embedded in PDMS, a blue shift of the diffraction peak occurs as a function of the applied strain and (ii) MDCS have unique optical properties that combine the localized surface plasmon resonance (LSPR) of gold nanoparticles (Au NPs) with the photonic band gap features of colloidal crystal structures. Finally, preliminary results on MDCS used as SERS substrate evidence a higher increase of the Raman signal in respect to that observed for others metallic structures.

Abstract: We report experimental results obtained in our laboratories in the development of Er3+- doped glass microspherical cavities for the fabrication of compact and low threshold laser sources at 1.55 μm. We investigate three different approaches in order to fabricate the microspheres including direct melting of Er3+-doped glass powders, coating of silica microspheres with an Er3+- doped sol-gel layer, and synthesis of Er3+-doped monolithic microspheres using the sol-gel route in acid catalysis. Details of the different fabrication processes are presented together with the photoluminescence characterization in free space configuration of the microspheres and of the glass precursor. We analyse the photoluminescence spectra of the whispering gallery modes of the microspheres exited using evanescent coupling and we demonstrate laser action in a wide range of wavelengths around 1.55 μm.

Abstract: We present the details of the sol-gel processing used to realize inverse silica opal, where the silica was activated with 0.3 mol% of Er3+ ions. The template (direct opal) was obtained assembling polystyrene spheres of the dimensions of 260 nm by means of a vertical deposition technique. The Er3+-activated silica inverse opal was obtained infiltrating, into the void of the template, the silica sol doped with Er3+ ions and subsequently removing the polystyrene spheres by means of calcinations. Scanning electron microscope showed that the inverse opals possess an fcc structure with a air hollow of about 210 nm. A photonic band gap in the visible range was observed from reflectance measurements. Spectroscopic properties of Er3+activated silica inverse opal were investigated by photoluminescence spectroscopy. A bandwidth of 21 nm was measured for the 4I13/2 → 4I15/2 transition of Er3+ ions upon excitation at 514.5 nm. The luminescence decay curve of the 4I13/2 metastable state of the Er3+ ions presents a lifetime τ = 16.8 ± 0.1 ms giving a very high quantum efficiency of the fabricated system. Core-shell Er3+-activated silica spheres, where the core is the silica sphere and the shell is an Er2O3-SiO2 coating is proposed as a possible route for opal fabrication. For core-shell system a quantum efficiency of about 70% was estimated.

Abstract: Erbium-doped tellurite glasses show great potential for the fabrication of high-performance integrated optical amplifiers and lasers, thanks to their unique properties in terms of bandwidth and rare earth solubility. As a first step towards the development of smart multi-functional integrated optical circuits, the fabrication of multimode channel waveguides in a sodium-tungsten-tellurite glass, by using nitrogen ions implantation, has been recently demonstrated [1]. The effects of the ion implantation process, however, have not been fully clarified, and a deeper investigation would be necessary in order to optimize the process and to truly exploit the glass useful characteristics. We therefore report here the results of a broad optical, topographic, and structural characterization of tellurite samples irradiated with various doses of nitrogen ions, while keeping constant the beam energy at 1.5 MeV. Characterization techniques have included absorption and luminescence spectroscopy, modal (dark-line) spectroscopy, surface profilometry, scanning electron microscopy, cathodoluminescence spectroscopy and EDX analysis.