Rapid Fabrication of Silica Microlens Arrays via Glass 3D Printing.

Rapid manufacturing of high purity fused silica glass micro-optics using a filament-based glass 3D printer has been demonstrated. A multilayer 5 × 5 microlens array was printed and subsequently characterized, showing fully dense lenses with uniform focal lengths and good imaging performance. A surface roughness on the order of Ra = 0.12 nm was achieved. Printing time for each lens was <10 s. Creating arrays with multifocal imaging capabilities was possible by individually varying the number of printed layers and radius for each lens, effectively changing the lens height and curvature. Glass 3D printing is shown in this study to be a versatile approach for fabricating silica micro-optics suitable for rapid prototyping or manufacturing.

Structured-light-sheet imaging in an integrated optofluidic platform.

Heterogeneity investigation at the single-cell level reveals morphological and phenotypic characteristics in cell populations. In clinical research, heterogeneity has important implications in the correct detection and interpretation of prognostic markers and in the analysis of patient-derived material. Among single-cell analysis, imaging flow cytometry allows combining information retrieved by single cell images with the throughput of fluidic platforms. Nevertheless, these techniques might fail in a comprehensive heterogeneity evaluation because of limited image resolution and bidimensional analysis. Light sheet fluorescence microscopy opened new ways to study in 3D the complexity of cellular functionality in samples ranging from single-cells to micro-tissues, with remarkably fast acquisition and low photo-toxicity. In addition, structured illumination microscopy has been applied to single-cell studies enhancing the resolution of imaging beyond the conventional diffraction limit. The combination of these techniques in a microfluidic environment, which permits automatic sample delivery and translation, would allow exhaustive investigation of cellular heterogeneity with high throughput image acquisition at high resolution. Here we propose an integrated optofluidic platform capable of performing structured light sheet imaging flow cytometry (SLS-IFC). The system encompasses a multicolor directional coupler equipped with a thermo-optic phase shifter, cylindrical lenses and a microfluidic network to generate and shift a patterned light sheet within a microchannel. The absence of moving parts allows a stable alignment and an automated fluorescence signal acquisition during the sample flow. The platform enables 3D imaging of an entire cell in about 1 s with a resolution enhancement capable of revealing sub-cellular features and sub-diffraction limit details.

All-silica optical fiber bonding.

In this work, we demonstrate a spot-welding method for fabrication of all-silica fiber components. A CO2 laser was used to locally sinter sub-micron silica powders, enabling rigid bonding of optical fiber to glass substrates. The bonding was achieved without inducing any fiber transmission losses. The components showed no sign of deterioration or structural change when heated up to 1100 °C. These single material assemblies are therefore well suited for use in harsh environments where high stability and robustness is required.

UV-written grating couplers on thin-film lithium niobate ridge waveguides.

Grating couplers on thin-film lithium niobate ridge waveguides were designed and fabricated using UV-laser ablation. The calculated coupling efficiency with a sinusoidal grating can be as large as 53% in a 0.5 µm thin film. The maximum grating depth we fabricated was 130nm, limiting the coupling efficiency to a theoretical value of 18%. We fabricated grating couplers on adhered ridge waveguides of 20 µm thickness. Coupling light to waveguides on thin-film lithium niobate is still challenging, and here we present a fast, cheap and reliable fabrication alternative. It will benefit the on-chip testing of integrated components developed on this novel and promising material platform.

Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres.

Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core.

Influence of pre-annealing on the thermal regeneration of fiber Bragg gratings in standard optical fibers.

A detailed study of the dynamics during thermal regeneration of fiber Bragg gratings, written in hydrogen-loaded standard single-mode fibers using a ns pulsed 213 nm UV laser, is reported. Isothermal pre-annealing performed in the range 85 °C to 1100 °C, with subsequent grating regeneration at 1100 °C, resulted in a maximum refractive index modulation, Δn(m) ~1.4⋅10(-4), for gratings pre-annealed near 900 °C while a minimum value of Δn(m) ~2⋅10(-5) was achieved irrespective of pre-annealing temperature. This optimum denote an inflection point between opposing thermally triggered processes, which we ascribe to the reaction-diffusion mechanism of molecular water and hydroxyl species in silica. The results shed new light on the mechanisms underlying thermal grating regeneration in optical fibers.

Fabrication and optical characterization of silica optical fibers containing gold nanoparticles.

Gold nanoparticles have been used since antiquity for the production of red-colored glasses. More recently, it was determined that this color is caused by plasmon resonance, which additionally increases the material's nonlinear optical response, allowing for the improvement of numerous optical devices. Interest in silica fibers containing gold nanoparticles has increased recently, aiming at the integration of nonlinear devices with conventional optical fibers. However, fabrication is challenging due to the high temperatures required for silica processing and fibers with gold nanoparticles were solely demonstrated using sol-gel techniques. We show a new fabrication technique based on standard preform/fiber fabrication methods, where nanoparticles are nucleated by heat in a furnace or by laser exposure with unprecedented control over particle size, concentration, and distribution. Plasmon absorption peaks exceeding 800 dB m(-1) at 514-536 nm wavelengths were observed, indicating higher achievable nanoparticle concentrations than previously reported. The measured resonant nonlinear refractive index, (6.75 ± 0.55) × 10(-15) m(2) W(-1), represents an improvement of >50×.

Gold nanoparticles on the surface of soda-lime glass: morphological, linear and nonlinear optical characterization.

Materials presenting high optical nonlinearity, such as materials containing metal nanoparticles (NPs), can be used in various applications in photonics. This motivated the research presented in this paper, where morphological, linear and nonlinear optical characteristics of gold NPs on the surface of bulk soda-lime glass substrates were investigated as a function of nanoparticle height. The NPs were obtained by annealing gold (Au) thin films previously deposited on the substrates. Pixel intensity histogram fitting on Atomic Force Microscopy (AFM) images was performed to obtain the thickness of the deposited film. Image analysis was employed to obtain the statistical distribution of the average height of the NPs. In addition, absorbance spectra of the samples before and after annealing were measured. Finally, the nonlinear refractive index (n2) and the nonlinear absorption index (α2) at 800 nm were obtained before and after annealing by using the thermally managed eclipse Z-scan (TM-EZ) technique with a Ti:Sapphire laser (150 fs pulses). Results show that both n2 and α2 at this wavelength change signs after the annealing and that the samples presented a high nonlinear refractive index.

All-fiber devices based on photonic crystal fibers with integrated electrodes.

A special kind of microstructured optical fiber is proposed and fabricated in which, in addition to the holey region (solid core and silica-air cladding), two large holes exist for electrode insertion. Either Bi-Sn or Au- Sn alloys were selectively inserted into the large holes forming two parallel, continuous and homogeneous internal electrodes. We demonstrate the production of a monolithic device and its use to externally control some of the guidance properties (e.g. polarization) of the fiber.

Thermal stability of oxygen-modulated chemical-composition gratings in standard telecommunication fiber.

Experimental results and a discussion on the formation and decay of oxygen-modulated chemical-composition gratings in a standard telecommunication fiber are presented. Comparison between the decay experiment and the model provides a diffusion coefficient with an activation energy of 490 kJ/mol, which is in close agreement with reported values of oxygen self-diffusion in silica. The gratings have a diffusion-controlled decay behavior, with more than 50% of the reflectivity remaining after 7.5 h at a temperature of 1230 degrees C. The gratings show higher thermal stability when heated in air than in an inert argon atmosphere.

Grating formation in pure silica-core fibers.

Strong grating formation in pure silica-core fibers by use of 193-nm ArF-laser radiation is reported. Unsaturated refractive-index changes of Dn~0.3x10(-3) were observed in nontreated fiber, and changes of Dn~0.5x10(-3) were observed in fibers with a high hydroxyl concentration. Possible mechanisms of photosensitivity in pure silica-core fibers are discussed.

Thermal stability of chemical composition gratings in fluorine-germanium-doped silica fibers.

A model based on diffusion of dopants in a periodic structure has been applied to describe thermal decay of chemical composition gratings in fluorine-germanium-doped silica fibers. The good agreement between previously reported values and the diffusion coefficients derived here from experiments and models in the 1000-1200 degrees C temperature range indicate that fluorine diffusion is the main mechanism of grating decay. Experimental results also indicate that the presence of phosphorous significantly increases the decay rate of chemical composition gratings.

Growth dynamics of chemical composition gratings in fluorine-doped silica optical fibers.

The refractive-index modulation of chemical composition gratings in fluorine-germanium-doped silica fibers as a function of thermal treatment during manufacturing has been studied. The final grating strength was found to depend strongly on an intermediate annealing step, with an optimum temperature near 600-700 degrees C, before development at a fixed temperature of 1000 degrees C. Low-temperature treatment, aimed at removing any remaining hydrogen from the fiber, performed at 100 degrees C for 20 h before the annealing step, also significantly increased the final refractive-index modulation.