Search

Whispering Gallery Mode (WGM) hollow microcavities turn out to be the site of an extremely rich and complex phenomenological scenario when pumped with a continuous-wave laser source. The coexistence of numerous non-linear and optomechanical effects have been reviewed in this paper. In our previous works we have investigated and described non-linear emissions as the stimulated Brillouin and Raman scattering, the degenerated and non-degenerated Kerr effects, such as four wave mixing (FWM). These effects happened concomitantly to parametric optomechanical oscillations which are the consequence of the radiation pressure. We have confirmed the regenerative oscillation of acoustic eigenmodes of the cavity leading to parametric instabilities and the activation of optomechanical chaotic oscillations. Finally, we have demonstrated that the blue-side excitation of WGM resonances lead to the chaos transition with a spectral evolution depending on the cavity size.

We report the activation of optomechanical chaotic oscillations and chaos transfer from a strong pump to a very weak probe in microbubble resonators, both signals follow the same route to chaos.

We present a proof-of-concept experiment where the absorbance spectra of suspensions of plasmonic nanoparticles are accurately reconstructed through the photothermal conversion that they mediate in a microbubble resonator. This thermal detection produces spectra that are insensitive towards light scattering in the sample, as proved experimentally by comparing the spectra of acqueos gold nanorods suspensions in the presence or absence of milk powder. In addition, the microbubble system allows for the interrogation of small samples (below 40 nl) while using a low-intensity beam (around 20 µW) for their excitation. In perspective, this system could be implemented for the characterization of turbid biological fluids through their optical absorption, especially when considering that the microbubble resonator naturally interfaces to a microfluidic circuit and may easily fit within portable or on-chip devices.

We report on the experimental and theoretical analysis of parametrical optomechanical oscillations in hollow spherical phoxonic whispering gallery mode resonators due to radiation pressure. The optically excited acoustic eigenmodes of the phoxonic cavity oscillate regeneratively leading to parametric oscillation instabilities.

In integrated optics, optical waveguides are fundamental elements for the development of integrated devices, including light sources, modulators, detectors, optical pathways, receivers and switches. For the fabrication of optical integrated waveguide components, grating couplers or other complex integrated structures realized on planar optical waveguides, materials with high photorefractivity are surely of great interest since they allow applying photorefractive direct-laser-writing techniques which are of lower cost and less time-consuming than conventional photolithography and etching processes. This chapter provides an overview of classes of photorefractive materials such as photorefractive glasses, glass-ceramics, crystals and polymers, which are promising candidates for integrated optics. Different aspects, including material preparation, photorefractivity investigation and the fabrication of photorefractive direct-laser-written micro/nano-optical structures such as channel waveguides and gratings in each type of photorefractive materials, are also discussed.

We report on the experimental analysis of parametrical optomechanical oscillations and photo-acoustical applications such as flow cytometers in hollow phoxonic whispering gallery mode resonators. Both phenomena can be enchanced or suppressed and showed chaotic behavior.

This work presents state of the art rare-earth activated SnO2 nanocrystals - based transparent glass-ceramics. With combined enhancements in both photorefractivity and rare-earth photoluminescence, the glass-ceramic has unique benefits as a lasing material. It exhibits high photorefractivity with UV induced refractive index modifications in the order of 10-3. Exploiting its high photorefractivity, optical gratings are fabricated on the glass-ceramic under an energy-efficient direct UV writing process. Furthermore, SnO2 semiconductor nanocrystals are also employed as efficient rare-earth sensitizers enhancing drastically the rare-earth photoluminescence.

We developed an all-optical photoacoustic (PA) sensing platform based on whispering gallery mode (WGM) hollow resonators able to detect plasmonic nanoparticles in microfluidics. A silica microbubble resonator (MBR) made on a capillary and exhibiting high optical and mechanical Q factors acts as a unique ultrasound transducer for photoacoustic characterization of metallic nanoparticles. The system was tested with gold nanorods (GNR) placed inside the MBR and acoustic detection was achieved by monitoring the enhanced modulation of the optical resonances at the microbubble mechanical eigenfrequencies.

Some materials present difficulties for the fabrication of channel waveguides with standard technologies. They may suffer incompatibilities with the physical or chemical processes required in one or more steps involved in the fabrication technology itself or in the standard patterning techniques. An experimental Er3+ doped tungsten-tellurite glass, which gets damaged by standard lithographic techniques is one of such cases. However, this glass is of great interest thanks to its excellent optical and spectroscopic properties, high refractive index (nbulk < 2.0 at 635 nm), low cut-off phonon energy and broad emission bandwidth for the erbium (< 60 nm) within the C band of optical telecommunications. We have therefore successfully demonstrated a novel method of fabrication, namely by focussed C4+ ion beam implantation (FIB). Relatively heavy and swift ions like the ones used in this experiment allow to change the material properties with fluencies even 10 times lower than those required when using light ions. The use of a focussed beam has also allowed us to directly write the channel waveguides on the sample, without the use of any lithographic procedure, which renders the whole process flexible and simpler. The Er3+ doped tellurite glass with 60TeO2–25WO3–15Na2O-0.5Er2O3 (mol. %) composition was prepared by melt-quenching technique. The FIB irradiations were carried out at the 3 MV Tandetron 4130 MC (High Voltage Engineering Europa B.V.) of the Nuclear Physics Institute AV CR, Řež, with 4–6 nA beam current, 1·1014-5·1016 ions/cm2 fluence and the size of the scanning beam was 8 μm × 12 μm. The as-implanted waveguides showed very high propagation losses, about 14-20 dB/cm at 1400 nm, outside the absorption band of Er3+. A stepwise (each step 30 minutes long) thermal annealing allowed to reduce losses. At 150 °C, propagation losses decreased to 1.5 dB/cm. At higher temperatures propagation losses rose again, but at 200 °C coupling losses decreased, so that the best insertion loss, about 5 dB, was measured at this stage. The near-field images showed that the waveguide was monomode up to 1540 nm and that the mode width does not vary significantly with increasing temperature, whereas the estimated depth of the waveguides shows a slight increase. In order to obtain more information about the structural changes caused by the ion beam irradiation, profilometry and Raman characterisation has been carried out on the channel waveguides and also these results will be presented at the conference.

This paper discusses ongoing research at Lawrence Livermore National Laboratory (LLNL) that investigates the effectiveness of spherical micro-resonators, coupled to a symmetrically tapered optical fiber, as a gas sensor. We will discuss silica-based microspheres and optimized tapered fiber coupling systems to detect greenhouse gases, i.e. CO2 in this context. The coupling setup is designed to be portable and amenable to different controlled environments, from constrained and controlled geometries to open and flexible enclosures. 3D-printed spherical resonator and tapered-fiber holders were made to satisfy different requirements. We produced microspheres for absorption spectroscopy of targeted gas and fabricated tapers by HF etching, using an HF-resistant fixture for safer handling and reduced waste. Detection within loose enclosures was performed as a preliminary study, where we observed spectral shift and broadening in the cavity resonances induced by the gaseous environments. Optically coupled vacuum-tight vessels have been designed and built to understand environmental effects.

In this paper, we implement a Whispering Gallery mode microbubble resonator (MBR) as an optical transducer to detect the photoacoustic (PA) signal generated by plasmonic nanoparticles. We simulate a flow cytometry experiment by letting the nanoparticles run through the MBR during measurements and we estimate PA intensity by a Fourier analysis of the read-out signal. This method exploits the peaks associated with the MBR mechanical eigenmodes, allowing the PA response of the nanoparticles to be decoupled from the noise associated with the particle flow whilst also increasing the signal-to-noise ratio. The photostability curve of a known contrast agent is correctly reconstructed, validating the proposed analysis and proving quantitative PA detection. The experiment was run to demonstrate the feasible implementation of the MBR system in a flow cytometry application (e.g., the detection of venous thrombi or circulating tumor cells), particularly regarding wearable appliances. Indeed, these devices could also benefit from other MBR features, such as the extreme compactness, the direct implementation in a microfluidic circuit, and the absence of impedance-matching material.

Trabajo presentado al XVII Optical Components and Materials, celewbrado en San Francisco, California (USA) del 1 al 6 de febrero de 2020., SnO2-based glass-ceramics activated by rare earth ions have been extensively investigated because of the need to develop reliable fabrication protocols and clarify some interesting optical, structural, and spectroscopic features of the system. There is one important weakness in glass photonics when the rare earth ions are employed as luminescent sources. This is the low absorption cross section of the electronic states of the rare earth ions. A sensitizer is therefore requested. In the last years, we demonstrated that SiO2-SnO2 glass ceramics, presenting a strong absorption cross section in the UV range due to the SnO2 nanocrystal, are effective rare earth ions sensitizers. Another interesting property of the SiO2-SnO2 system is its photorefractivity. The high photorefractivity of sol-gel-derived SnO2-SiO2 glass-ceramic waveguides has been demonstrated in several papers published by our consortium. It has been shown that the UV irradiation induces refractive index change allowing the direct writing of both channel waveguides and Bragg gratings. The results presented in this communication not only demonstrate the viability and outstanding properties of the SiO2- SnO2 glass-ceramics for photonic applications but also put the basis for the fabrication of solid state and integrated lasers. The next steps of the research are the fabrication of the channels and mirrors exploiting the photorefractivity as well as to draw glass ceramic fiber, checking the lasing action and corresponding functional characteristics. Finally, it is worth noting that the dynamic of the energy transfer from the nanocrystals to the rare earth ions is still an exciting open question., This research is performed in the framework of the projects ERANet-LAC “RECOLA” (2017-2019), Centro Fermi MiFo (2017–2020) and NaWaGui (ANR-18-MRS1-0014). WB and MF acknowledge the support of CNR-STM - Short Term Mobility program 2019-2020.

We report on the experimental analysis of parametrical optomechanical oscillations and nonlinear frequency generation in hollow phoxonic whispering gallery mode resonators. Both phenomena can be enchanced or suppressed and showed chaotic behavior.

Water pollution is a severe worldwide problem that urgently requires development of novel sensing concepts allowing for monitoring in situ a variety of contaminants at very low concentrations in a costeffective and multiplexed format. Whispering Gallery Mode (WGM) resonators represent novel and promising tools for the development of high-performance sensing platforms for environmental monitoring. Here we report an overview of WGM platforms for monitoring different classes of water contaminants. The theoretical basis of these novel sensing platforms are presented. Several chemical/biochemical strategies for binding specific chemo/bio-receptors on the surface of the optical resonators are discussed. Finally, the main issues that currently hinder these devices from leaving research laboratories towards the development of high compact and sensitive tools to be launched on the market are reviewed and discussed together with future perspectives. (C) 2020 Elsevier B.V. All rights reserved.

Channel waveguides were directly written in Er: TeO2W2O3 glass using 11 MeV C4+ ion microbeam with fluences in the range of 1·1014–5·1016 ion/cm2. The channel waveguides supported a single guided mode at λ = 1540 nm. Propagation losses of the as-irradiated channel waveguides were around 14 dB/cm. A 30-min thermal annealing at 150 °C in air reduced propagation losses at λ = 1400 nm to 1.5 dB/cm. This method produced channel waveguides with confinement and propagation losses comparable to or better than other current methods, such as MeV energy focused proton or helium ion beam writing. Keywords: Integrated optics, Rare earth doped materials, Channel waveguides, Optical design and fabrication, Microstructure fabrication

We present and discuss an analytical model for the propagation of light in a glass microsphere resonator based on wave optics and Maxwell's equations in the formulation of vector and scalar Debye's potential. References and connections with geometrical optics and quantum mechanics theory are given in order to better understand the electromagnetic phenomenon of whispering-gallery modes (WGMs). The problem of light coupling into a glass microsphere and the various strategies usually adopted for this purpose are also detailed.