Luiz C. G. Valente

Hydrostatic Pressure Sensing with High Birefringence Photonic Crystal Fibers

The effect of hydrostatic pressure on the waveguiding properties of high birefringence photonic crystal fibers (HiBi PCF) is evaluated both numerically and experimentally. A fiber design presenting form birefringence induced by two enlarged holes in the innermost ring defining the fiber core is investigated. Numerical results show that modal sensitivity to the applied pressure depends on the diameters of the holes, and can be tailored by independently varying the sizes of the large or small holes. Numerical and experimental results are compared showing excellent agreement. A hydrostatic pressure sensor is proposed and demonstrated using an in-fiber modal interferometer where the two orthogonally polarized modes of a HiBi PCF generate fringes over the optical spectrum of a broad band source. From the analysis of experimental results, it is concluded that, in principle, an operating limit of 92 MPa in pressure could be achieved with 0.0003% of full scale resolution.

Photonic crystal fiber sensor for magnetic field detection

A magnetic field sensor comprised of a high birefringence photonic crystal fiber coated by a Terfenol-D/Epoxy composite layer is proposed. Magnetic fields induce strains in the magnetostrictive composite that are transferred to the fiber interfering with light propagation. The sensitivity of the developed sensor with magnetic fields is measured to be 6 pm mT-1.

Mechanical Characterization Using Optical Fiber Sensors of Polyester Polymer Concrete Made with Recycled Aggregates

The sustainable management of solid wastes encourages metallurgic and metal-mechanic industries to look for safety applications for their wastes, thereby attenuating the environmental impact or lowering the costs. The study herein proposes strain monitoring the recycling of foundry sand with organic pollutants, as inert, in the manufacturing process of polymer concrete using optical fiber sensors. This work also analyzes the compressive strength of polyester polymer concrete made with foundry waste, i.e., recycled foundry sand and polyester polymer concrete made with fresh sand. The foundry sands are contaminated with Sodium Silicate from the mould-making process. Polymer Concrete (PC) is a composite material in which the binder consists entirely of a synthetic organic polymer. Optical fiber sensors present a great deal of potential in monitoring the structural health condition of materials. Experimental results show that the use of the embedded FBG sensor can accurately measure strain, providing information to the operator that the structure is subjected to failure. Multiplexed FBG strain sensors enable measuring strain in different locations by occupying only one tiny optical fiber.

Thermal treatment of fiber Bragg gratings for sensing and telecommunication applications

In this work, we evaluated the performance, at elevate temperatures, of fiber Bragg gratings recorded using high power UV lasers. The evolution of grating wavelengths and reflectivities when fibers were submitted to several thermal cycles was determined. The range of thermal stability of the gratings was found to be suitable for telecommunication and sensing applications.

Bragg grating fabrication by the external method with 266-nm light

Two experimental setups, using the fourth harmonic of a Nd:YAG laser (266 nm), for producing Bragg gratings by the external method are described and their results presented and discussed. The two different setups allow the fabrication of gratings of controlled spectral bandwidth (0.3 to 5 nm) with peak position between 1.3 and 1.6 micrometers . The stability of the system and the possibility of writing type IIA gratings are also discussed.

Analysis of mechanical and thermal response of rock due to laser drilling using optical fiber Bragg grating sensors

Optical fiber Bragg grating sensors (FBGs) were used to measure strain and the temperature field that develop during laser drilling of carbonate rock samples. The shear deformation and high temperature gradient measured are clearly correlated with traces of fractures observed. Beyond the volume directly evaporated by laser exposure, a greater volume around the drilling area was fractured. From the perforation process point of view, it results in an increase of efficiency.

Investigation on Hydrogen-induced Attenuation in Optical Fibers for DTS Application

We analyze hydrogen-induced attenuation of the pure silica core and conventional fibers subjected to high temperature and hydrogen pressure. Hydrogen-induced attenuation in optical fibers is directly influenced by partial pressure of hydrogen surrounding the fiber

Bragg wavelength deviation for TDM/WDM multiplexing systems

An analysis of the Bragg wavelength deviation generated by TDM/WDM multiplexing of large number of fiber Bragg grating (FBG) sensors has been proposed. Demodulation technique based on Fixed Spectrum Filters is compared with peak position of full wavelength spectrum. Results indicate that the fixed filter approach is less sensitive to wavelength distortion due to shadow of other sensors operating at the same nominal wavelength, allowing much larger number of FBG sensors. A simulated result show less than 1 pm deviation with up to 100 sensors at same wavelength, with 1% peak reflectivity for each sensor.