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RESUMEN: En este trabajo se compara el funcionamiento de dos técnicas de demultiplexación de sensores basados en redes de difracción Bragg e interrogados interferométricamente: la Transformada Rápida de Fourier (FFT) y el método de Clasificación de Múltiples Señales (MUSIC). Los experimentos demuestran que el método MUSIC se comporta mejor que la FFT. ABSTRACT: We present a performance comparison between two techniques for demultiplexing of interferometrically interrogated Fibre Bragg Grating sensors: the Fast Fourier Transform (FFT) and the Multiple Signal Classification method (MUSIC). Experiments prove that the latter behaves better than the first one.

A non-intrusive, non-contact, real-time system for the detection of non desirable material in raw material chains on industry environments is presented. Through a spatial optical spectroscopic technique, scene line spectrographs based on the Visible-Near Infrared (Vis-NIR) reflectance of the material under study, are obtained. To reach a representative spectral fingerprint, the large amount of data is compressed using Principal Component Analysis (PCA) fast algorithm prior to the classification made by a Neural Network. The technique has been successfully checked on the tobacco industry. However, instead of tobacco leaves, other materials can be discriminated or classified using this technique.

RESUMEN: Se presenta un nuevo sensor de nivel de líquido multipunto basado en las pérdidas por curvatura y pulido de una parte del núcleo de fibras ópticas plásticas. El pulido de la fibra en la zona curvada pone al descubierto el núcleo de la fibra, aumentando para el haz de luz que se propaga, la sensibilidad con el medio exterior. Sobre un mismo trozo de fibra se han practicado 8 puntos de zonas curvadas de 180º, cada una de las cuales presenta una atenuación característica, que es detectada. Los resultados experimentales en presencia de agua y la unidad electrónica son igualmente presentados. ABSTRACT: In this paper we present a novel multipoint liquid level sensor based on radiation losses in bends of partially polished plastic optical fibers (POF). When a POF is partially polished at a bend, light propagation along the fiber core is more sensitive to outer media changes. 8 turns of 180º located along a POF piece yield a well defined attenuation that is detected by the sensor. Experimental results of the sensor for water as an outer media are given.

RESUMEN: En este trabajo se presenta la aplicación de la amplificación Raman a la multiplexación en longitud de onda de sensores de fibra óptica. Para ello se ha desarrollado experimentalmente una red en forma de bus utilizando fibra convencional monomodo en la que se direccionan los sensores utilizando multiplexación en longitud de onda. Cada sensor viene identificado únicamente por la reflexión desde una red de difracción Bragg (FBG) y la ganancia distribuida tiene por objeto aumentar el número de sensores sin utilizar costosos amplificadores discretos. Mostramos que esta topología permite ecualizar la potencia recibida de los sensores, utilizando sólo una longitud de onda de bombeo e investigamos la dependencia con la potencia de bombeo utilizada. El filtrado espectral de las FBGs, junto con la ganancia distribuida, permiten reducir el ruido. Mostramos las relaciones señal a ruido medidas. ABSTRACT: We experimentally demonstrate a novel application of distributed fiber Raman amplification to a bus network for the wavelength multiplexing of optical sensors. Each sensor is uniquely identified by reflection from a fiber Bragg grating (FBG) and the distributed gain allows the number of sensors to be increased without using costly lumped amplifiers. We show how the topology allows the received powers from the sensors to be equalized, even though only one Raman pump wavelength is used and we investigate how the performance depends on the launched pump power. The spectral filtering of the FBGs, combined with the distributed gain, jointly reduce the noise and we report measured signal to noise ratios.

RESUMEN: En el presente artículo se presentan y discuten los resultados preliminares obtenidos al aplicar el algoritmo multilínea de calibración por regresión múltiple inversa (ILS) a la detección del gas metano usando espectroscopia de absorción por modulación en longitud de onda (WMS). Se han usado tres longitudes de onda en la banda de 1.66 μm para dicha calibración y los resultados obtenidos se han contrastado con los ofrecidos por el método de calibración más usual basado en regresión lineal para una única línea. ABSTRACT: In the present article, the preliminary results obtained with the multiline calibration algorithm Inverse Least Squares (ILS) applied to the detection of methane are presented and discussed. In order to achieve this goal, this algorithm is combined with wavelength modulation absorption spectroscopy (WMS). Three different wavelengths in the 1.66 μm band of methane have been used and the results obtained have been compared to the most usual single-line calibration method based on linear regression.

RESUMEN: La respuesta de los sistemas caóticos presenta una fuerte dependencia de sus condiciones iniciales. Es por ello que este tipo de sistemas pueden emplearse para hacer sensores. Así, en este trabajo se presenta un estudio sobre la viabilidad de emplear un resonador caótico en fibra óptica como sensor fotónico. Para ello se ha desarrollado un modelo matemático del resonador caótico cuya descripción se incluye en el artículo. Asimismo se presentan y discuten resultados de simulación del resonador caótico cuando éste se emplea como sensor para medir elongación y atenuación. ABSTRACT: The response of chaotic systems is highly dependent on their initial conditions. That’s why this kind of systems is naturally well fitted for making sensors. Thus, in this work the feasibility of using a fiber-ring chaotic resonator for sensing is analyzed. In order to do so, a theoretical model of the chaotic resonator has been developed. Its description is included in this paper. Besides, several simulation results are presented and discussed. These correspond to the use of the resonator as a sensor of both strain and attenuation.

Sistema optoelectrónico para el aforo y clasificación del tráfico rodado en vías monocarril y multicarril. El sistema de aforo y clasificación de tráfico rodado comprende al menos: - dos emisores de luz colimada situados a un lado de la calzada. - dos receptores de luz situados a un lado de la calzada (pueden estar situados en el mismo lado de los emisores, necesitando por tanto la presencia de unos reflectores situados enfrente, o al otro lado de la calzada). - una unidad de procesado y registro del tráfico detectado. El sistema puede ser completado con uno o más conjuntos adicionales de emisor/receptor y reflector para mejorar las características de las medidas. Entre otras se reivindica el uso de este sistema para el aforo y la clasificación del tráfico rodado en viales multicarril. Solicitud: 200402519 (18.10.2004) Nº Pub. de Solicitud: ES2257185A1 (16.07.2006) Nº de Patente: ES2257185B1 (01.07.2007)

Experimental measurements of the evolution of the optical signal polarisation state with shifts in pump power in Erbium doped fibers has been carried out. The results show that these fibers should be used in Michelson interferometer, for small pump power and wavelengths in which the absorption spectrum of the Erbium doped fiber is maximum.

Structural health and behavior monitoring have always been both a common concern and need in civil engineering. Several classical approaches have been given to this problem including the widley used strain gauges as well as the topographic measurements. These two techniques are almost always used to monitor the behavior of the structures whereas the health monitoring is accomplished by a simple periodic visual inspection. These approaches present serious problems that limit their practical use in real structures such as: lack of fiability, long-term drift, impossibility of full-time measurements, or lack of thoroughness. Centering the discussion in the strain gauges, for being the most representative of the classical civil engineering monitoring methods, it must be said that due to their electric nature they are exposed to both electromagnetic interference and corrosion. The latter greatly reduces their operating life time pushing it typically to less than one year after installation. That is whey new ways of monitoring civil structures were looked for, and that is how photonic fiber sensing came up. Characteristics shared by all fiber senors are their electromagnetic immunity for being manufactured using a dielectric material, low weight, small size, and compatibility with construction materials. As can be seen these inherent characteristics make them very suitable for their use in civil engineering structures. An example of a quasi-distributed transducer is presented in this communication. First the theoretical fundamentals of the transducer and its behavior is explained, and an in-field experiment consisting on monitoring a bridge is described and its results reported.

The photonic sensing technology is an area of very rapid growth and increasing interest nowadays. This is due in part to devices such as Fiber Bragg Gratings (FBG), whose inherent characteristics make them very suitable for different sensing fields such as civil engineering, aeronautics or medicine just to mention a few. Among the characteristics that make these devices so versatile, one can find their electromagnetic immunity due to the fact that they are made of dielectric material, both their low size and weight, and their ability to be multiplexed in the same fiber. Even more important is the fact that the information is wavelength encoded and so it is not altered by the attenuations of the transmission channel. This last characteristic transforms these devices into very reliable ones. A new FBG-based transducer for monitoring civil engineering structures is presented in this paper. It is able to monitor both strain and temperature at the same time, giving them very useful information about the actual behavior of their host structure. These transducers were fully characterized and tested in laboratory in order to evaluate their performance. The paper is organized as follows: first of all a brief theoretical introduced to FBG is given, and after that the design of the trasnducer is discussed. Then the characterization process, as well as its results, are presented. At the end, the final laboratory test in a well-known structure is described.