BUSCADOR RECOLECTA

In this study, a new method for increasing simultaneously the sensitivity and interrogation stability of fiber-optic intensity sensors is presented. The configuration is based on a double-coupler ring resonator. On one side, the attenuation sensitivity of the sensor is enhanced by placing it inside a ring resonator. On the other side, the stability of the interrogation method is widely improved by creating an external lasing ring resonator with matched spectral response. The combination of the wavelength selective response of the ring resonator and optical amplification from Er-doped fiber amplifier is used to create different fiber lasers. The resulting lasers present an impressive sensitivity enhancement and a dynamic range increment up to 15 dB. Simultaneously, the instability of the system is reduced to ±0.05 dB. In comparison with systems based on tunable laser interrogation, our method is >100 times more stable and also simpler, as no wavelength tunable elements are required., Ministerio de Economía y Competitividad, European Commission

We present theoretical and experimental results on a slow-light assisted all-fiber configuration that can be used for
efficient sensing of a variety of parameters (pressure, displacement...). In particular, we report here a structure that can be
transformed into a slow-light assisted displacement sensor capable of sub-micrometric resolution values with a
potentially simple intensiometric measurement scheme. The basic element in the structure is a lossy ring resonator tuned
close to the critical coupling regime. In this working regime, the resonator transfer function displays extremely high
group delay values close to the resonances, and, accordingly, a large sensitivity to additional losses. A mechanic
transducer transforms displacement into small additional losses in the ring. This leads to strong variations in the log
transmission of the resonances, which are shown to scale with the group index. This scheme shows orders of magnitude
sensitivity enhancements over a conventional bending-loss configuration. We believe that this structure can be further
developed to provide large sensitivity enhancements to conventional intensiometric fiber sensors., European Commission, Ministerio de Economía y Competitividad, Comunidad de Madrid, Ministerio de Ciencia e Innovación

In this work, we present a new method for increasing simultaneously the sensitivity and interrogation stability of fiberoptic intensity sensors. The configuration is based on a double-coupler ring resonator. On one side, the attenuation sensitivity of the sensor is enhanced by placing it inside a ring resonator. On the other side, the stability of the interrogation method is rendered close to perfect by creating an external lasing ring resonator with matched spectral response. The resulting lasers allow the stable interrogation of the sensors with an impressive sensitivity enhancement. In our experiments, the dynamic range of the intensity sensor (and consequently its sensitivity) is increased 15 dB by using this laser-based interrogation system. Simultaneously, the instability of the system is reduced to ±0.05 dB. In comparison with systems based on external interrogation, our method is <100 times more stable and also simpler, as no wavelength tunable elements are required., Ministerio de Ciencia e Innovación, Ministerio de Economía y Competitividad, European Commission

Along the last years, much debate has been done on the efficiency of slow-light phenomena in order to enhance light-matter interactions, especially for sensing purposes. This improvement could be key to develop more compact and sensitive devices. In this work we develop an all-fiber sub-micrometric displacement sensor using slow-light sensitivity enhancement in a lossy ring resonator. In the proposed structure the losses produced by the displacement of a mechanic transducer can be translated into strong variations of group index and therefore strong transmittance variations. We show that this effect is strictly related to slow light, and not related to confinement effects or any other., European Commission, Ministerio de Economía y Competitividad, Comunidad de Madrid, Ministerio de Ciencia e Innovación

High-Q resonators have been widely used for sensing purposes. High Q factors normally lead to sharp spectral peaks which accordingly provide a strong sensitivity in spectral interrogation methods. In this work we employ a low-Q ring resonator to develop a high sensitivity sub-micrometric resolution displacement sensor. We use the slow-light effects occurring close to the critical coupling regime to achieve high sensitivity in the device. By tuning the losses in the cavity close to the critical coupling, extremely high group delay variations can be achieved, which in turn introduce strong enhancements of the absorption of the structure. We first validate the concept using an Optical Vector Analyzer (OVA) and then we propose a simple functional scheme for achieving a low-cost interrogation of this kind of sensors., European Commission, Ministerio de Ciencia e Innovación, Comunidad de Madrid, Ministerio de Economía y Competitividad

22nd International Conference on Optical Fiber Sensors, OFS 2012, Beijing, China, 15-19 Oct. 2012, We demonstrate theoretically and experimentally that a wide-range tuning of group delay values can be achieved in a
lossy fiber ring resonator. The tuning mechanism relies simply on varying the loss/coupling ratio in the resonator. This
simple structure may be used advantageously in different regimes for many sensing configurations, both for achieving
extremely high sensitivity enhancements (by working close to critical coupling, where the group index becomes
extremely large) or suppression of undesired refractive index effects (e.g. Kerr effect), by working in the under-coupled
regime., Ministerio de Ciencia e Innovación, Comunidad de Madrid

We demonstrate a novel dynamic BOTDA sensor based, for the first time to our knowledge, on the use of the Brillouin phase-shift instead of the conventional Brillouin gain. This provides the advantage of measurements that are largely immune to variations in fiber attenuation or changes in pump pulse power. Furthermore, the optical detection deployed can lead to an enhanced precision or measurement time and to the broadening of the measurement range. Proof of concept experiments demonstrate 1.66 kHz measurement rate with 1 m resolution over a 160 m sensing fiber length., The authors wish to acknowledge financial support from the Spanish Ministerio de Educación y Ciencia through the
project TEC2010-20224-C02-01 and from the Universidad Pública de Navarra.

We introduce a novel phasorial differential pulse width pair (PDPP) method for Brillouin optical time domain analysis (BOTDA) sensors that combines spatial resolution enhancement with increased tolerance to non local effects. It is based on the subtraction of the complex time domain traces supplied by a sensor configuration that uses a phase modulated probe wave and RF demodulation. The fundamentals of the technique are first described theoretically and using numerical simulation of the propagating waves. Then, proof of concept experiments demonstrate the measurement of the Brillouin frequency shift distribution over 50 km. The system is shown to withstand large variations of the pump power generated by its interaction with a powerful probe wave along the fiber; hence, highlighting the potential of the PDPP technique to increase the detected signal to noise ratio in long range BOTDA. Moreover, the PDPP is also shown to increase the measurement contrast by allowing the use of relatively long duration pulses while retaining 1 m spatial resolution., The authors wish to acknowledge the financial support from the Spanish Ministerio de
Ciencia e Innovación through the project TEC2010-20224-C02-01 and from the Universidad
Pública de Navarra.

We propose and demonstrate the use of spatial multiplexing as a means to reduce the costs of distributed sensing networks. We propose a new scheme in which remote power-by-light switching is deployed to scan multiple branches of a distributed sensing network based on Brillouin Optical Time Domain Analysis (BOTDA) sensors. A proof-of-concept system is assembled with two 5-km sensor fiber branches that are alternatively monitored using a fast remotely controlled and optically powered optical switch. The multiplexed distributed sensor fibers were located 10 km away from the interrogation unit and a Raman pump is used to remotely power the switch. Furthermore, the deployed BOTDA unit uses an alternative configuration that can lead to simplified setups., This work was supported by the Spanish Government projects TEC2010-20224-C01 and TEC2010-20224-C02.

A sensing head based on a hollow-core photonic crystal fiber for in-reflection measurement of micro-displacements is presented. The sensing structure takes advantage of the multimodal behavior of a short segment of hollow-core photonic crystal fiber in-reflection, being spliced to a single mode fiber at its other end. A modal interferometer is obtained when the sensing head is close to a mirror, through which displacement is measured., The authors are grateful to the Spanish Government project TEC2010-20224-C02-01 and the
European COST Action TD1001.

We demonstrate a Brillouin optical time domain analysis sensor based on a phase modulated probe wave and RF demodulation that provides measurements tolerant to frequency dependent variations of the pump pulse power induced by non local effects. The tolerance to non local effects is based on the special characteristics of the detection process, which provides an RF phase shift signal that is largely independent of the Brillouin gain magnitude. Proof of concept experiments performed over a 20 km long fiber demonstrate that the measured RF phase shift spectrum remains unaltered for large frequency dependent deformations of the pump pulse power. Therefore, it allows the use of a higher optical power of the probe wave, which leads to an enhancement of the detected signal to noise ratio. This can be used to extend the sensing distance, to improve the accuracy of the Brillouin frequency shift measurements, and to reduce the measurement time., The authors wish to acknowledge the financial support from the Spanish Ministerio de
Educación y Ciencia through the project TEC2010-20224-C02-01, from the Spanish
Ministerio de Economía y Competitividad through the project IPT-2011-12-920000 and from
the Universidad Pública de Navarra.

We demonstrate a novel Brillouin optical time domain analysis sensor deploying a polarization diversity technique which eliminates the need for polarization scrambling, providing measurements that are largely immune to the state of polarization of the probe wave and the pump pulses throughout the sensing fiber. This can be exploited to reduce the measurement time or can lead to an enhanced precision. Proof of concept experiments demonstrate a 651 Hz sampling rate with 1m resolution over a 930m sensing fiber., The authors wish to acknowledge the financial support from the Spanish Ministerio de Ciencia e Innovación through the
project TEC2010-20224-C02-01 and from the Universidad Pública de Navarra.

This paper presents an overview of optical fiber sensor networks for remote sensing. Firstly, the state of the art of remote fiber sensor systems has been considered. We have summarized the great evolution of these systems in recent years; this progress confirms that fiber-optic remote sensing is a promising technology with a wide field of practical applications. Afterwards, the most representative remote fiber-optic sensor systems are briefly explained, discussing their schemes, challenges, pros and cons. Finally, a synopsis of the main factors to take into consideration in the design of a remote sensor system is gathered., This work was supported by the Spanish Government project TEC2010-20224-C02-01.

Brillouin hedatuko denbora eremu optikoaren analisian (BOTDA) oinarritutako sentsoreak,
estruktura handien (100 km luzerako estrukturak) deformazioa eta tenperatura neurtzeko gaitasuna
dute. Lan honetan, BOTDA konfigurazio sinplifikatua aurkezten dugu. Erabilitako konfigurazioaren
helburua sentsorearen prezioa murriztea da, detekzio prozesuan parte hartzen duten seinale optikoen
sortze prozesua sinplifikatuz. Proposatutako teknika hau, iturri optiko bati irrati-maiztasun (IM) pultsu
modulatu bat aplikatuz sortutako osagai espektralen iragazketa optiko pasiboan oinarritzen da.
Laborategiko esperimentuek frogatzen dute tenperatura hedatuko neurriak 1,1 metroko
erresoluzioarekin 5 km zuntz optikoan zehar, Distributed Brillouin optical time domain analysis (BOTDA) sensors can provide high precision
distributed measurements of the strain and temperature profile over extremely large structures
(structures of 100 km). In this work, we present a simplified configuration for BOTDA sensors. The
aim of this configuration is to reduce the cost of the sensor by simplifying the generation of the optical
waves involved in the sensing process. The proposed technique is based on passive optical filtering of
the spectral components generated in an RF-pulse-modulated optical source. Proof of concept
experiments demonstrate distributed temperature measurement with 1.1 m resolution over a 5 km
sensing fiber, Los autores agradecen al Ministerio de Ciencia e Innovación (a través del proyecto TEC2010-20224-C02-01) y a la Universidad Pública de Navarra la financiación recibida.

The ability to operate despite failure will become increasingly important as the use of optical sensor networks grows, and the amount of sensing information to be handled by a sensor network is increasing, especially for safety and security applications. In this review, the four categories of protection to allow service to be reestablished after a failure (dedicated/shared and line/path) are thoroughly discussed. This paper also presents an overview of the most representative robust fiber-optic sensor systems, discussing their schemes, pros and cons., The authors are grateful to the Spanish
Government project TEC2010-20224-C02-01.

Desde la irrupción de la fibra óptica en las telecomunicaciones, han surgido multitud de desarrollos basados en sus propiedades. Así, en las últimas décadas, la rápida evolución de los sistemas basados en fibra óptica, así como la aparición en el mercado de dispositivos como los amplificadores ópticos, los láseres de semiconductor de alta potencia, y otros elementos, ha hecho avanzar considerablemente la investigación en este campo. Además de la utilización de la fibra óptica en telecomunicaciones, han surgido nuevas aplicaciones, generando nuevas familias de dispositivos. Dos de ellas particularmente interesantes, son los láseres de fibra óptica y los sensores de fibra óptica. Ambas familias pueden combinarse de manera que sensores y redes de sensores de fibra óptica pueden interrogarse por medio de láseres de fibra óptica. En este marco de investigación se centra esta tesis, donde se han desarrollado estructuras avanzadas de fibra óptica para láseres y sensores. El objetivo ha sido mejorar las propiedades de los láseres de fibra, sensores y sus sistemas de monitorización, así como abordar los diferentes problemas que éstos presentan actualmente. Los retos encontrados, así como los objetivos de cada sistema, varían en función del tipo de sistema desarrollado. De esta forma, la primera parte de este trabajo ha sido dedicada al desarrollo de láseres de fibra óptica, buscando mejorar sus propiedades en términos de estabilidad, relación señal ruido, modos longitudinales, múltiples líneas de emisión y anchura de las mismas. Se han abordado diferentes tipos de configuraciones clásicas de láseres en anillo y de cavidad lineal. También se han realizado estudios de láseres de cavidad distribuida mediante dispersión Rayleigh (random). Estos láseres han suscitado gran interés en los últimos años dado que no presentan modos longitudinales. Por otro lado en el ámbito de la monitorización de sensores, se han desarrollado transductores ópticos basados en fibras micro-estructuradas, aprovechando las ventajas que éstas presentan en comparación con las fibras ópticas estándar. Finalmente se han desarrollado diferentes configuraciones de sistemas sensores con el objetivo de contribuir a la mejora de alguno de sus parámetros, como su alcance, capacidad de multiplexación, sensibilidad, rango dinámico y estabilidad de los sistemas sensores., Optical fiber technology as well as its rapidly evolution, has attracted the scientific community attention to develop lasers, fiber optic transducers and sensor networks. In this regard, the appearance in the last decades of commercial devices such as optical amplifiers, semiconductor high power lasers and others, has contributed to the rise of this technology. In this framework, a contribution to the improvement of the performance of fiber lasers and fiber optic sensors is presented in this PhD. work, taking into account their main merits and addressing their principal challenges. The challenges as well as the objectives addressed in each design vary depending on the application. In this way, the first part of the thesis has been dedicated to the development of optical fiber lasers. And it is focused on improving their properties in terms of stability, signal noise ratio, longitudinal modes, multiwavelength emission and bandwidth of the emission lines. Different classical configurations based on ring and linear cavity lasers have been addressed. Also, random cavity lasers, which have attracted great interest in recent years due to their longitudinal modeless behavior, have been studied. On the other hand, in the field of sensor monitoring, optical transducers based on micro-structured fibers have been developed, exploiting their advantages in comparison with standard optical fibers. Finally different optical sensor networks have been developed, whose main goal have been the improvement of features such as monitoring distance, multiplexing skill, sensitivity, dynamic range and stability., Este trabajo se ha llevado a cabo gracias a las aportaciones económicas recibidas
de los siguientes organismos y proyectos:
- Universidad Pública de Navarra mediante la ayuda de investigación
predoctoral, la ayuda para movilidad y las ayudas complementarias a
tesis doctorales.
- Secretaria de Estado de Investigación, Desarrollo e Innovación, Ministerio
de Economía y Competitividad de España a través del programa de
Formación del Personal Investigador y asociado al proyecto de investigación
TEC2010-20224-C02-01.
- Proyecto de investigación TEC2013-47264-C2-2-R a través del Fondo
Europeo de Desarrollo Regional (FEDER).
- Acción Europea COST- TD1001: Novel and Reliable Optical Fibre Sensor
Systems for Future Security and Safety Applications (OFSeSa)
- Proyecto INTERREG SUDOE Project “ECOAL-MGT - Ecological Management
of Coal Waste Piles, SOE3/P2/P714”.
- Ministerio de Economía y Competitividad de España a través del Proyecto
campus de excelencia-Iberus (Innocampus).
- Grupo de investigación Comunicaciones Ópticas y Aplicaciones Electrónicas
de la Universidad Pública de Navarra mediante la financiación
de material y participación en congresos., Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007), Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007)

We present a novel technique for Brillouin optical time domain analysis (BOTDA) sensors that simultaneously compensates non local effects and reduces Brillouin noise. The technique relies on the wavelength modulation of the optical source to modify the Brillouin interaction between probe and pump waves during their propagation. The resulting Brillouin distribution mimics the wavelength modulation, creating a virtual Brillouin frequency shift profile along the sensing fiber. The fundamentals of the technique are first described theoretically and using numerical simulations. Then, proof of concept experiments demonstrate the capabilities of the system to reduce large variations of the pump power resulting from the interaction with high probe powers and to decrease the Brillouin induced noise enhancing the signal to noise ratio (SNR) of the system. Furthermore, we show, for the first time to our knowledge, measurements of the Brillouin distribution using an injected optical power higher than the Brillouin threshold of the fiber., The authors wish to acknowledge the financial support from the Spanish Ministerio de
Ciencia e Innovación through the project TEC2010-20224-C02-01 and from the Universidad
Pública de Navarra.

We demonstrate a novel dynamic BOTDA sensor based, for the first time to our knowledge, on the use of the Brillouin phase shift in addition to the conventional Brillouin gain. This provides the advantage of measurements that are largely immune to variations in fiber attenuation or changes in pump pulse power. Furthermore, the optical detection deployed leads to an enhanced precision or measurement time and to the broadening of the measurement range. Proof of concept experiments demonstrate 1.66 kHz measurement rate with 1 m resolution over a 160 m sensing fiber length. Moreover, a measurement range of 2560 µε with a precision of 20 µε is successfully proved., The authors wish to acknowledge the financial support from the Spanish Ministerio de
Educación y Ciencia through the project TEC2010-20224-C02-01 and from the Universidad
Pública de Navarra.

We report the experimental demonstration of an Ytterbium doped fiber laser (YDFL) composed by two stages in cascade. Two sorts of Ytterbium doped fiber (YDF) with different concentration have been used. A proper characterization of the YDFs has been performed in order to find the optimum YDF length. To this end, the output power and the slope-efficiency have been calculated and the signal amplification and the amplified spontaneous emission (ASE) spectra have been analyzed, which are strictly related to the absorption and emission cross-section of the YDF. The first stage has been studied for both continuous wave (CW) and pulsed regime. The results show that by using an YDF with a high slope-efficiency, up to 66%, it is possible to reach an emitted peak power of 30 W in a pulsed regime., This work was supported by the Spanish Government
projects TEC2007-67987-C02 and TEC2010-20224-C02-01,
the European COST action-299 and the Spain-Italy
Cooperation Project “Development of new all-fiber lasers for
telecom, sensors and industrial applications”.

This work experimentally demonstrates a remote sensing network which interrogates bending sensors using time-division multiplexing techniques and a broadband light source. The bending sensors are located 50 km away from the monitoring station. They are based on a simple tie displacement sensor and offer high-resolution measurements of displacement., The authors are grateful to the Spanish Government Project
TEC2010-20224-C02-01.

We introduce a modification of the differential pulse width pair technique in a BOTDA sensor based on a phase modulated probe wave and RF demodulation. This provides a differential Brillouin phasorial signal with high spatial and spectral resolution in both components (magnitude and phase shift). Moreover, the use of a phase modulated probe wave provides RF phase shift measurements tolerant to the emergence of non local effects. The combination of both techniques can lead to the development of long range BOTDA sensors. Proof of concept experiments demonstrate RF phase shift measurements with 1m spatial resolution over 50km and an uncertainty of 1.3ºC at the worst contrast position., The authors wish to acknowledge the financial support from the Spanish Ministerio de Ciencia e Innovación through the
project TEC2010-20224-C02-01 and from the Universidad Pública de Navarra.

We demonstrate a BOTDA sensor based on the use of the Brillouin phase shift that performs measurements tolerant to non local effects. This technique raises opportunities to increase the distance covered by these sensors and the maximum optical power of the probe wave injected to the fiber. As a result, the system has the potential to increase the SNR achieved at the last meters of the fiber. Proof-of-concept experiments demonstrate unaltered measurements of the phase shift spectrum in a 20Km long fiber for large frequency-dependent distortions of the pump pulse., The authors wish to acknowledge financial support from the Spanish Ministerio de Educación y Ciencia through the
project TEC2010-20224-C02-01 and from the Universidad Pública de Navarra.

A photonic crystal fiber-based sensing head is proposed for strain measurements. The sensor comprises a Hi-Bi PCF sensing head to measure interferometric signals in-reflection. An experimental background study of the sensing head is conducted through an optical backscatter reflectometer confirming the theoretical predictions, also included. A cost effective setup is proposed where a laser is used as illumination source, which allows accurate high precision strain measurements. Thus, a sensitivity of ~7.96 dB/me was achieved in a linear region of 1,200 μe., The authors are grateful to the Spanish government projects TEC2010-20224-C02-01 and Innocampus.

Trabajo presentado a IEEE Sensors 2014, celebrado en Valencia (España) del 2 al 5 de noviembre de 2014., We demonstrate, for the first time to our knowledge, the extension of the measurement range of Brillouin distributed sensors (BDS) by using a distributed Brillouin amplifier (DBA) to compensate the attenuation of the sensor's pump pulses. The technique is based on injecting an extra DBA pump wave in the fiber to generate an additional Brillouin interaction to that used for sensing. Moreover, the bandwidth of the DBA is tailored to fit that of the pump pulses by deploying a wavelength modulation of the DBA pump that is synchronized to the pump. Experimental proof of concept results demonstrate a fivefold enhancement of the measurement range of a BDS, from 10.36 km to more than 50 km in this particular case. Moreover, it is found that the use of the DBA does not introduce any significant penalty in the detection signal to noise ratio, highlighting the potential of the technique to provide much larger sensing lengths., The authors wish to acknowledge the financial support from
the Universidad Pública de Navarra and Spanish Ministerio de
Ciencia e Innovación through the projects TEC2010-20224-
C02-01 and TEC2013-47264-C2-2-R.

En este trabajo de doctorado se presentan nuevos sistemas y subsistemas de sensores de fibra óptica. Así, se proponen y desarrollan nuevas técnicas, componentes y tecnologías basadas en láseres de fibra con espejos distribuidos (random), fibras de cristal fotónico, estructuras de luz lenta, multiplexores de inserción y extracción (add and drop), conmutadores tele-alimentados por luz, reflectometría óptica tanto en el dominio del tiempo como de la frecuencia o filtros ópticos reconfigurables. También se han demostrado nuevas aplicaciones para estructuras de sensores tradicionales y técnicas de medida ya conocidas. Todas ellas dirigidas a la mejora del funcionamiento de los actuales transductores, redes de sensores y aplicaciones de monitorización de salud estructural.
De este modo, y en primer lugar, se han desarrollado nuevos transductores puntuales. En concreto, dos sensores interferométricos basados en fibras de cristal fotónico y otro basado en una estructura resonante en anillo.
También se han realizado diferentes redes de sensores utilizando OTDRs comerciales. Por un lado, se han multiplexado diferentes sensores utilizando una red en forma de bus y, por el otro, se ha interrogado de manera remota un sensor FLM/LPG a una distancia de 253 km sin necesidad de amplificación.
Se han estudiado láseres basados en efecto de realimentación distribuida random (RDFB) para su uso en interrogación de sensores. Para ello, se han demostrado dos nuevos láseres multi-longitud de onda y también, por primera vez, se ha modulado un laser random.
Después, se han demostrado experimentalmente varias redes de sensores de fibra óptica teniendo en cuenta los principales desafíos que estas presentan: multiplexar varios sensores en una misma red y permitir su monitorización de manera remota. En primer lugar, se han multiplexado sensores basados en la modulación de la intensidad óptica utilizando técnicas de multiplexación en dominio del tiempo. En segundo lugar, se han multiplexado sensores basados en fibras de cristal fotónico. En tercer lugar, se presentan tres nuevos métodos para la medida remota de sensores. Por último, se incluye la demostración de un conmutador de fibra óptica tele-alimentado a través de luz. Éste se utiliza en tres redes diferentes para añadir robustez e incrementar la versatilidad en la multiplexación.
Finalmente, se han realizado tres pruebas de campo para aplicaciones de monitorización de salud estructural., In this PhD work, different new photonic systems and subsystems for fiber optic sensing are presented. The aim of this thesis has been to contribute to the fiber optic sensors field using modern techniques, components and technologies such as random fiber lasers, photonic crystal fibers, slow light structures, add and drop multiplexers, powered by light switches, optical frequency and time domain reflectometry or reconfigurable optical filters, among others. New applications of traditional sensing structures or techniques have been also demonstrated. All of them focused on improving the performance of current sensors transducers, multiplexing networks and structural health monitoring applications.
Thus, new point transducers have been developed: two of them are interferometric sensors based on photonic crystal fibers; and another one is based on a fiber ring resonator structure.
Fiber optic sensor networks using commercial OTDRs have been also explored. On the one hand, different sensors have been successfully multiplexed in the same bus network. And, on the other hand, a FLM/LPG sensor was remotely interrogated at a distance of 253 km without using amplification.
Random distributed feedback (RDFB) lasers have been explored for sensors interrogation. Two multi-wavelength Raman fiber lasers suitable for sensors interrogation have been demonstrated. Also, a random fiber laser has been internally modulated for the first time.
Then, some experimental demonstrations of fiber optic sensors networks have been carried out taking into account the principal challenges they pose: multiplexing a number of optical sensors in a single networks, and enabling the possibility of remote sensing. Firstly, intensity sensors using TDM technology have been multiplexed. Secondly, PCF sensors have been successfully multiplexed. Thirdly, three new approaches to enable remote sensing are presented. Finally, a remote powered by light fiber optic switch have been included in three networks in order to add robustness and multiplexing versatility., Este trabajo se ha llevado a cabo gracias a las aportaciones económicas recibidas de los siguientes organismos, entre otros:
- Secretaría de Estado de Investigación, Desarrollo e Innovación, Ministerio de Economía y Competitividad de España a través del programa de Formación del Personal Investigador y asociado al proyecto de investigación TEC2010-20224-C02-01.
- Universidad Pública de Navarra mediante las ayudas a tesis doctorares.
- Acción Europea COST- TD1001: Novel and Reliable Optical Fibre Sensor Systems for Future Security and Safety Applications (OFSeSa)
- También se ha recibido financiación del Proyecto de Investigación de la Secretaría de Estado de Investigación, Desarrollo e Innovación, Ministerio de Economía y Competitividad de España TEC2013-47264-C2-2-R, de Innocampus, del Proyecto Europeo SUDOE-ECOAL-Intereg Project ECOAL-MGT y de los Fondos FEDER., Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007), Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007)

We demonstrate a novel concept for Brillouin optical time domain analysis sensors that is based on synthesizing a virtual Brillouin frequency shift profile along the sensing fiber. The technique is based on modulating the wavelength of the optical source with a periodic waveform that is synchronized to the pump pulse. Application of this new tool to the compensation of non local effects and Brillouin induced noise in distributed sensors is experimentally demonstrated., The authors wish to acknowledge the financial support from the Spanish Ministerio de Ciencia e Innovación through the
project TEC2010-20224-C02-01 and from the Universidad Pública de Navarra.

Photonic crystal fibers are a kind of fiber optics that present a diversity of new and improved features beyond what conventional optical fibers can offer. Due to their unique geometric structure, photonic crystal fibers present special properties and capabilities that lead to an outstanding potential forsensing applications. A review of photonic crystal fiber sensors is presented. Two different groups of sensors are detailed separately: physical and biochemical sensors, based on the sensor measured parameter. Several sensors have been reported until the date, and more are expected to be developed due to the remarkable characteristics such fibers can offer., The authors are grateful to the Spanish Government project
TEC2010-20224-C02-01.