Antonio Quintela

A quasi-distributed level sensor based on a bent side-polished plastic optical fibre cable

A flexible quasi-distributed liquid level sensor based on the changes in the light transmittance in a plastic optical fibre (POF) cable is proposed. The measurement points are constituted by small areas created by side-polishing on a curved fibre and the removal of a portion of the core. These points are distributed on each full turn of a coil of fibre built on a cylindrical tube vertically positioned in a tank. The changes between the refractive indices of air and liquid generate a signal power proportional to the position and level of the liquid. The sensor system has been successfully demonstrated in the laboratory, and experimental results of two prototypes with 15 and 18 measurement points in a range of 33 mm and 39 mm respectively and a resolution of 0.08 mm with bend radii of 5 mm and 8 mm are presented.

Uniform fiber Bragg grating first- and second-order diffraction wavelength experimental characterization for strain-temperature discrimination

A full experimental characterization of the first- and second-order diffraction wavelengths of fiber Bragg gratings (FBGs) fabricated in a single optimized UV-writing process is presented in this letter. These devices are useful for the simultaneous measurement of strain and temperature.

Stability Comparison of Two Ring Resonator Structures for Multiwavelength Fiber Lasers Using Highly Doped Er-Fibers

An experimental comparison of stability between two different fiber laser topologies is carried out. The lasers are based on ring resonators that include highly doped Er-fibers. Both topologies use fiber Bragg grating reflectors in order to select the emission wavelengths. The experimental results confirms that the novel topology based on fiber optic circulators arranged in a hybrid serial-parallel configuration offers better stability and a higher optical signal-to-noise ratio (OSNR) than the simpler one based on a parallel configuration.

Interrogation unit for fiber Bragg grating sensors that uses a slanted fiber grating

A novel interrogation technique for fiber Bragg gratings is presented. It is based on measuring the characteristics of the outgoing near-field radiation from a tilted fiber grating. This scheme was experimentally checked and was found to offer a wide wavelength interrogation range as well as a good linearity, stability, and wavelength resolution.

Embedded temperature–strain fibre Bragg grating sensor system validation for concrete structures

The transducer manufacture and calibration, the in-laboratory sensor system characterization and their in-field validation are described and discussed in this paper. This sensor system was installed in key zones of a bridge and was used to determine the characteristics of the structure during the load test. The results were successfully checked with those obtained by traditional means.

Embedded spectroscopic fiber sensor for on-line arc-welding analysis.

A new fiber sensor system designed for spectroscopic analysis and on-line quality assurance of arc-welding processes is presented here. Although several different approaches have been considered for the optical capture of plasma emission in arc-welding processes, they tend to be invasive and make use of optical devices such as collimators or photodiodes. The solution proposed here is based on the arrangement of an optical fiber, which is used at the same time as the optical capturing device and also to deliver the optical information to a spectrometer, embedded within an arc-welding torch. It will be demonstrated that, by using the shielding gas as a protection for the fiber end, the plasma light emission is efficiently collected, forming a sensor system completely transparent and noninvasive for the welding operator. The feasibility of the proposed sensor designed to be used as the input optics of a welding quality-assurance system based on plasma spectroscopy will be demonstrated by means of several welding tests.

Torsion-induced effects on UV long-period fiber gratings

The spectral properties of long period fiber gratings (LPFG) are modified when twisting is applied. Herein, results of applying torsion to UV-induced LPFGs are presented for comparing with others which have already been presented in literature and where the LPFGs are fabricated using different techniques. Both, the resonant wavelength and the peak attenuation of the resonance, have similar behaviors to those obtained by other authors. However, in spite of the fact that the values of sensitivity to twist rate are sensibly lower in the case of UV-LPFGs, its bigger mechanical strength lets them be subjected to higher twist rates, which could be useful in determinate applications.

Fabrication of FBGs With an Arbitrary Spectrum

A fiber Bragg grating (FBG) with an arbitrary spectrum can be obtained as the addition of the contribution of some concatenated subFBGs written without phase jumps using the same phase mask. An adaptive filter is used to obtain the parameters of the different subFBGs required to reproduce the desired response.

Bragg Gratings Written in Tapered Solid-Core Photonic Crystal Fibers

Fiber Bragg gratings are very useful in many applications. This is why a higher control of their properties is desirable. Therefore, a grating preprocessing technique, based on the dependence of the index guided photonic crystal fiber (IG-PCF) properties on their structural parameters, is proposed allowing a higher control of the Bragg wavelength. Using the proper combination of thermo-mechanical IG-PCFs tapering and ultraviolet photoinscription methods, it is possible to develop new optical fiber devices. Their effectiveness is demonstrated by comparison with the results on single-mode fiber. Finally, to demonstrate the feasibility of the technique, a wideband chirped Bragg grating is fabricated.

Optically Tunable Long-Period Fiber Grating on an Er

An optically tunable long-period grating (LPG) on an erbium-doped fiber (EDF) is experimentally demonstrated. It is based on the core refractive index changes induced by the pump power on an LPG written in the EDF core. With an optimized design of the LPG, a shift of 5.5 nm of the attenuation band wavelength is obtained with a pump power of 100 mW at 1480 nm