Macrobending SMS fiber-optic anemometer and flow sensor

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORWe report a simple, high sensitivity, good resolution and low-cost fiber-optic anemometer and flow sensor based on reflective single mode-multimode-single mode structure bent by air flow. The dragging force on the multi-mode section causes it to bend resulting in multimodal interference (MMI) effects which are related to the fluid velocity and flow rate. Bending effects on the output power profile are investigated and numerical simulation combined with experimental data demonstrate that the output power intensity may increase or decrease with the rise of curvature, depending on MMI conditions and field deformation. The sensor behavior with air flow velocity is evaluated by spectral analysis using a variety of methods as wavelength shifting of a selected peak and output power intensity of selected wavelength and output power intensity of selected points. Experimental tests using air stream inside a wind tunnel provided a reliable dynamic range from 4 to 10 m/s. Peak sensitivities of 435.13 pm/(m/s) with resolution of 17.4x10(-3) m/s for wavelength shifting and 2.62 dB/(m/s) for output power intensity are obtained. These results assure that the sensor can be effectively used in a wide variety of applications, such as anemometer and flow rate meter.5219CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORSem informaçãoSem informaçã

Second harmonic generation and enhancement in microfibers and loop resonators

We model and experimentally investigate second harmonic generation in silica microfibers and loop resonators, in which the second order nonlinearity arises from the glass-air surface dipole and bulk multipole contributions. In the loop resonator, the recirculation of the pump light on resonance is used to increase the conversion. The effect of the loop parameters, such as coupling and loss, is theoretically studied to determine their influence on the resonance enhancement. Experimentally, microfibers were fabricated with diameters around 0.7µm to generate the intermodally phase matched second harmonic with an efficiency up to 4.2×10-8 when pumped with 5ns 1.55µm pulses with a peak power of 90W. After reconfiguring the microfiber into a 1 mm diameter loop, the efficiency was resonantly enhanced by 5.7 times

Biomechanical behaviour of bulk-fill resin composites in class II restorations

The aim of this study was to evaluate the biomechanical properties expressed by shrinkage stress, cuspal strain, fracture strength and failure mode in molars with large class II mesio-occlusal-distal restorations. Sixty-four human caries-free third molars were selected and distributed randomly into four groups: Z100 restorative material (Z100), Tetric N-Ceram Bulk-Fill (TNC), Filtek Bulk-Fill (FBF) and Aura Ultra Universal (ABF). The bulk-fill materials were inserted in one singular bulk increment and the conventional composite resin in three ones. Polymerisation shrinkage stress was evaluated by optical Fibre Bragg Gratings (FBG) sensors (n = 6). The cuspal deformation was measured using an extensometer during three moments: restorative procedure, axial compressive loading and at fracture (n = 10). The fracture strength was evaluated on a universal machine. The failure mode was analysed by Scanning Electron Microscopy (SEM). Data were analysed using one-way ANOVA tests with Tukey's posthoc test (α = 5%). Data of the failure mode were submitted to a likelihood ratio chi-square test. Z100 presented the highest mean value for the shrinkage stress (p  0.05). Bulk-fill composites promoted less polymerisation shrinkage stress than conventional microhybrid composite during and after the light curing process in class II posterior resin composite restorations98255261This study was supported by the Institute of Physics Gleb Wataghin (University of Campinas) and Dental Research Center Biomechanics, Biomaterials and Cell Biology (Dental School of Federal University of Uberlândia

Mid-IR Hollow-core microstructured fiber drawn from a 3D printed PETG preform

Mid-infrared (mid-IR) optical fibers have long attracted great interest due to their wide range of applications in security, biology and chemical sensing. Traditionally, research was directed towards materials with low absorption in the mid-IR region, such as chalcogenides, which are difficult to manipulate and often contain highly toxic elements. In this paper, we demonstrate a Polyethylene Terephthalate Glycol (PETG) hollow-core fiber (HCF) with guiding properties in the mid-IR. Guiding is provided by the fiber geometry, as PETG exhibits a material attenuation 2 orders of magnitude larger than the HCF propagation loss. The structured plastic fiber preforms were fabricated using commercial 3D printing technology and then drawn using a conventional fiber drawing tower. The final PETG fiber outer diameter was 466 µm with a hollow-core diameter of 225 µm. Thermal imaging at the fiber facet performed within the wavelength range 3.5 – 5 µm clearly indicates air guidance in the fiber hollow core