Abstract This work shows the experimental validation of a method developed for determining the strain profile applied to a fiber Bragg grating by solving the inverse scattering problem. The non-uniform strain profile is recovered by formulating an optimization problem, solved with an algorithm based on differential evolution. The method has proved to be able of recovering the shape and approximate amplitude of the actual strain profile applied to the FBG, opening new perspectives for optical sensing with fiber Bragg gratings.

Abstract Analysis of the state of polarization of light guided by structures recorded in lithium niobate and lithium fluoride crystals indicates that the recording method is determinant in the formation of birefringent structures. Each structure was written with a single and continuous translation of the crystal transversally to the laser beam. Birefringence was observed in the structures recorded in both crystals, despite the lack of intrinsic birefringence in lithium fluoride. The recorded structures are anisotropic showing regions with different birefringence. The structure generated with femtosecond laser is directly linked to the recording method and the crystalline lattice. This characteristic can be advantageous for application in photonic devices.

AbstractIn this work, a refractometric fiber sensor for the liquid fuels sector is described. The use of etched FBGs produced in multimode fibers is proposed to overcome the drawbacks associated with sensing high refractive index samples employing fiber transducers. The transducer sensitivity can be tailored by adjusting the final diameter of the etched Bragg grating. Due to a trade-off between the signal-to-noise ratio and the sensitivity, operational parameters of the sensor must be designed to match the expected refractive index dynamic range for specific applications. Metrological properties of the sensor are determined, resulting in resolution from 5.6 % v/v to 0.4 % v/v for refractive indexes ranging from 1.4562 to 1.4729. Specific applications regarding the quality assessment of biodiesel and conformity analysis of diesel-biodiesel blends are discussed.

We report the use of an optical fiber sensor to measure the soybean oil concentration in samples obtained from the mixture of pure biodiesel and commercial soybean oil. The operation of the device is based on the long-period grating sensitivity to the surrounding medium refractive index, which leads to measurable modifications in the grating transmission spectrum. The proposed analysis method results in errors in the oil concentration of 0.4% and 2.6% for pure biodiesel and commercial soybean oil, respectively. Techniques of total glycerol, dynamic viscosity, density, and hydrogen nuclear magnetic resonance spectroscopy were also employed to validate the proposed method.

Neste trabalho propomos um experimento simples que tem por finalidade auxiliar no aprendizado dos fenômenos de interferência e difração da luz. Após uma análise pertinente da teoria de Fresnel da difração, os conhecimentos são aplicados na compreensão do funcionamento das placas de zonas de Fresnel. Apresentamos uma descrição detalhada dos processos usados para a fabricação e caracterização destas placas zonais, o que possibilita a produção de lentes difrativas com a distância focal desejada para um dado comprimento de onda de operação. As placas zonais produzidas e caracterizadas no trabalho atuam como lentes positivas com distâncias focais variando entre 8 e 50 cm para luz visível com comprimentos de onda compreendidos entre 630 e 680 nm de um apontador laser.

In this work we present a simple experiment that may be used to help in the learning of interference and diffraction of light. After an analysis of the Fresnel diffraction theory, the concepts are applied in the understanding of the working principle of the Fresnel zone plates. We present a detailed description of the process used in the production and characterization of the devices, allowing making diffractive lenses with the required focal length for a specific wavelength of operation. The zonal plates produced in this work behave like positive lenses with focal lengths in the range from 8 to 50 cm for light with wavelengths from 630 to 680 nm of a laser pointer.