Vertical coupling of laser glass microspheres to buried silicon nitride ellipses and waveguides

We demonstrate the integration of Nd3+ doped Barium-Titanium-Silicate microsphere lasers with a Silicon Nitride photonic platform. Devices with two different geometrical configurations for extracting the laser light to buried waveguides have been fabricated and characterized. The first configuration relies on a standard coupling scheme, where the microspheres are placed over strip waveguides. The second is based on a buried elliptical geometry whose working principle is that of an elliptical mirror. In the latter case, the input of a strip waveguide is placed on one focus of the ellipse, while a lasing microsphere is placed on top of the other focus. The fabricated elliptical geometry (ellipticity=0.9) presents a light collecting capacity that is 50% greater than that of the standard waveguide coupling configuration and could be further improved by increasing the ellipticity. Moreover, since the dimensions of the spheres are much smaller than those of the ellipses, surface planarization is not required. On the contrary, we show that the absence of a planarization step strongly damages the microsphere lasing performance in the standard configuration.Comment: 10 pages, 4 figure

Optical and mechanical mode tuning in an optomechanical crystal with light-induced thermal effects

Under the terms of the Creative Commons Attribution (CC BY) license to their work.We report on the modification of the optical and mechanical properties of a silicon 1D optomechanical crystal cavity due to thermo-optic effects in a high phonon/photon population regime. The cavity heats up due to light absorption in a way that shifts the optical modes towards longer wavelengths and the mechanical modes to lower frequencies. By combining the experimental optical results with finite-difference time-domain simulations, we establish a direct relation between the observed wavelength drift and the actual effective temperature increase of the cavity. By assuming that the Young's modulus decreases accordingly to the temperature increase, we find a good agreement between the mechanical mode drift predicted using a finite element method and the experimental one.This work was supported by the EU through the project TAILPHOX (ICT-FP7-233883) and the ERC Advanced Grant SOULMAN (ERC-FP7-321122) and the Spanish projects TAPHOR (MAT2012-31392).Peer Reviewe

Spectroscopy of silica layers containing Si nanocrystals: Experimental evidence of optical birefringence

We report an unusual case of spectral filtering by a silica waveguide containing Si nanocrystals (Si-nc's) deposited on a silica plate. For a number of Si-rich silica (Si Ox) slab waveguides annealed at 1100 °C, the TE and TM waveguide mode cutoff positions are found in the inversed order with respect to the classical waveguide theory for an isotropic material. Using the cutoff and m -line spectra, this unusual behavior was explained assuming an optical birefringence of the material. For the highest Si content (x∼1.5), we estimated a maximal positive birefringence of ∼8%. The cutoff spectrum simulated with the optical parameters extracted from the m -line measurements corresponds well to the cutoff spectrum directly obtained by measuring waveguided luminescence. This agreement shows that the spectral filtering effect of silica layers containing Si-nc can be described within the quantitative model of delocalized waveguide modes. The possible origin for the observed birefringence is discussed. © 2007 American Institute of Physics

Laser emission in Nd3+ doped barium-titanium-silicate microspheres under continuous and chopped wave pumping in a non-coupled pumping scheme

Laser action using non-coupled excitation and detection of microspheres made of Nd3+ doped barium-titanium-silicate glass has been demonstrated and measured. The microspheres have also been successfully deposited over Si3N4 strip waveguides with a SiO2 separation layer, thus enabling the laser emission extraction onto a CMOS compatible photonic circuit. The dynamics of the lasing wavelength and intensity has been studied as a function of the pump power and interpreted in terms of thermal effects generated through non-radiative recombination of the excited ions. © 2013 Astro Ltd.The authors thank the Ministerio de Economía y Competitividad of Spain (MINECO) within the National Program of Materials (MAT2010-21270-C04-02/-03/-04), the Consolider-Ingenio 2010 Program (MALTA CSD2007-0045, www.malta-consolider.com), the EU-FEDER, the GICSERV NGG-268 for their financial support and ACIISI of Gobierno de Canarias for the project ID20100152 and FPI. DN-U acknowledges the financial support of Generalitat de Catalunya through the Beatriu de Pinòs program.Peer Reviewe

Dataset related to the publication "Mechanical oscillations in lasing microspheres", DOI: 10.1063/1.4997182

This folder contains the raw data from which the graphs in paper "Mechanical oscillations in lasing microsphere", DOI: 10.1063/1.4997182, have been obtained.European Commission: PHENOMEN - All-Phononic circuits Enabled by Opto-mechanics (713450)Peer reviewe

Dataset related to the publication "Optical modulation of coherent phonon emission in optomechanical cavities", DOI: 10.1063/1.5040061

This folder contains the raw data from which the graphs in paper "Optical modulation of coherent phonon emission in optomechanical cavities", DOI: 10.1063/1.5040061, have been obtained.European Commission: PHENOMEN - All-Phononic circuits Enabled by Opto-mechanics (713450)Peer reviewe

Contactless characterization of the elastic properties of glass microspheres

Glass microspheres are of great interest for numerous industrial, biomedical, or standalone applications, but it remains challenging to evaluate their elastic and optical properties in a non-destructive way. In this work, we address this issue by using two complementary contactless techniques to obtain elastic and optical constants of glass microspheres with diameters ranging from 10 to 60 µm. The first technique we employ is Brillouin Light Scattering, which yields scattering with longitudinal acoustic phonons, the frequency of which is found to be 5% lower than that measured in the bulk material. The second technique involves exciting the optical whispering gallery modes of the microspheres, which allows us to transduce some of their vibrational modes. The combined data allow for extracting the refractive index and the elastic constants of the material. Our findings indicate that the values of those properties are reduced with respect to their bulk material counterpart due to an effective decrease of the density, resulting from the fabrication process. We propose the use of this combined method to extract elastic and optical parameters of glass materials in microsphere geometries and compare them with the values of the pristine material from which they are formed

Self-sustained coherent phonon generation in optomechanical cavities

Optical forces can set tiny objects in states of mechanical self-sustained oscillation, spontaneously generating periodic signals by extracting power from steady sources. Miniaturized self-sustained coherent phonon sources are interesting for applications such as mass-force sensing, intra-chip metrology and intra-chip time-keeping among others. In this paper, we review several mechanisms and techniques that can drive a mechanical mode into the lasing regime by exploiting the radiation pressure force in optomechanical cavities, namely stimulated emission, dynamical back-action, forward stimulated Brillouin scattering and self-pulsing.This work was supported by the European Comission project TAILPHOX (ICT-FP7-233883), the Spanish Severo Ochoa Excellence program and the MINECO project PHENTOM (FIS2015-70862-P). DNU and MFC gratefully acknowledge the support of a Ramón y Cajal postdoctoral fellowship and a Severo Ochoa studentship, respectivelyn.Peer Reviewe

Dataset related to the publication "Nonlinear dynamics and chaos in an optomechanical beam", DOI: 10.1038/ncomms14965

This folder contains the raw data from which the graphs in paper "Nonlinear dynamics and chaos in an optomechanical beam", DOI: 10.1038/ncomms14965, have been obtainedPHENOMEN - H2020 Fet Open projectPeer reviewe

Thermal Properties of Nanocrystalline Silicon Nanobeams

Altres ajuts: this work was supported by the CERCA Programme / Generalitat de Catalunya.Controlling thermal energy transfer at the nanoscale and thermal properties has become critically important in many applications since it often limits device performance. In this study, the effects on thermal conductivity arising from the nanoscale structure of free-standing nanocrystalline silicon films and the increasing surface-to-volume ratio when fabricated into suspended optomechanical nanobeams are studied. Thermal transport and elucidate the relative impact of different grain size distributions and geometrical dimensions on thermal conductivity are characterized. A micro time-domain thermoreflectance method to study free-standing nanocrystalline silicon films and find a drastic reduction in the thermal conductivity, down to values below 10 W m K is used, with a stronger decrease for smaller grains. In optomechanical nanostructures, this effect is smaller than in membranes due to the competition of surface scattering in decreasing thermal conductivity. Finally, a novel versatile contactless characterization technique that can be adapted to any structure supporting a thermally shifted optical resonance is introduced. The thermal conductivity data agrees quantitatively with the thermoreflectance measurements. This study opens the way to a more generalized thermal characterization of optomechanical cavities and to create hot-spots with engineered shapes at the desired position in the structures as a means to study thermal transport in coupled photon-phonon structures