30cm of spatial resolution using pre-excitation pulse BOTDA technique

A pre-excitation pulse technique in Brillouin optical time domain analysis (PP-BOTDA) for enhancement of the spatial resolution is shown. The technique here exposed is based on the pre-excitation of the stimulated Brillouin scattering and the subtraction of the Brillouin scattering due to the intensity dc level present in the optical pulse. A main optical pulse with 3ns of duration followed by a pulse of 40ns and half the intensity of the main one are used for obtaining 30cm of spatial resolution. The spatial range is 3600m on a standard single mode optical fiber

Quasi-distributed liquid level measurement with adaptable optical fiber transducers

A level and flexible quasi-distributed liquid sensor based on the changes in the light transmittance in a plastic optical fiber cable is proposed. The measurement points are constituted by small areas created by side-polishing on a curved fiber and the removal of a portion of the core. These points are distributed and adapted on each full-turn of a spire of fiber built on a cylindrical tube vertically positioned in a tank. The changes between the refractive indexes of air and liquid generate a signal power proportional to the position and level of the liquid. The sensor system was successfully demonstrated in the laboratory and experimental results of three prototypes with 10, 8, and 5 measurement points and with bend radius of 5mm are presented in this paper

Tunable fiber laser using concatenated non-adiabatic single-mode fiber tapers

An erbium doped fiber ring laser (EDFRL) that incorporates four non-adiabatic concatenated single-mode fiber tapers (acting as tunable filter in the laser cavity) is presented. These concatenated fiber tapers integrates a filter with a narrower band-pass and a higher modulation depth than a single taper. The tuning of this filter was implemented applying a controlled perturbation in the fiber taper. The proposed laser architecture was successfully demonstrated in the laboratory in which a tuning range of 20.8nm (1544.5nm-1565.3nm) were measured

Welfare and sectoral productivity shifts in a small open economy with imported agricultural inputs : the case of Sub‑Saharan Africa

This paper studies the impact of sectoral productivity growth on welfare in Sub- Saharan Africa. Using the analytical framework of a DSGE model, the main finding is that, for the estimated values of structural parameters, the allocation of scarce resources to the tradable agricultural sector for boosting productivity leads to a greater increase in overall welfare than would be the case if they were allocated to the non-traded goods sector.info:eu-repo/semantics/publishedVersio

Spectral evolution of long-period fiber grating during written process and their influence in the sensitivity

The peak loss wavelength shift, attenuation and bandwidth values on a LPG during the UV multi-pass writing process can be used to estimate the LPG sensitivities in real-time during the fabrication task

Optimal design and implementation of a temperature and strain optical transducer using FBGs and fiber taper hybrid structure

A temperature and strain optical fiber transducer and its optimal design are presented. The hybrid structure is composed of two Fiber Bragg Gratings (FBG) in a fused taper. Using the same phase mask one of the FBG is written outside of the taper, and the other one in the middle of the taper, in the area with constant diameter. The taper diameter and the structure length play a key role on the transducer behaviour. Useful results to optimize the transducer structure design, from a theoretical and experimental investigation, are reported in this paper

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 resolutio

In-fiber Mach-Zehnder interferometer inscribed with femtosecond laser for high temperature sensing

In this work, an In-fiber Mach-Zehnder Interferometer has been manufactured within a standard optical fiber using direct inscription with a femtosecond laser. Different geometries have been tested in order to enhance the sensitivity of manufactured devices to high temperature sensing, reducing the total device up to 300µm. The achieved results exhibit a remarkably good response for temperature sensing up to 650°C.This work has been supported by the projects TEC2013-47264-C2-1-R, TEC2016-76021-C2-2-R and grant BES-2014-069736 of the Spanish government and by the Parliament of Cantabria postdoc grant

New method for previsional design of fabrication process of LPG’s with a given sensitivity

A theoretical-experimental based method able to design in advance the fabrication process for a given sensitivity (temperature, strain, surround index, ...) is proposed. Previous and proper characterization of the LPG specific fabrication technique is required