Esta tesis investiga la aplicación de conceptos de codificación al diseño de sensores ópticos basados en redes de difracción de Bragg de Bragg (FBG). Específicamente, se presenta el diseño, la caracterización y la validación experimental de dispositivos de detección codificados personalizados que se pueden diseñar y fabricar como dispositivos FBG súper estructurados (SSFBG). El objetivo de esta tesis es mejorar la capacidad y el rendimiento general de los sistemas de detección óptica basados en sensores FBG convencionales. Para ello, se han propuesto tres metodologías de codificación de dispositivos de detección SSFBG, con el objetivo de dotar a cada sensor con información adicional útil para la identificación de cada sensor incluso en condiciones de superposición. Un sensor codificado basado en FBGs es una estructura FBG cuya forma se ha adaptado a una palabra-código ortogonal, de tal manera que su longitud de onda central se puede distinguir inequívocamente de otras señales en el espectro. El diseño de los sensores SSFBG codificados se realiza modificando el espectro de reflexión de dispositivos FBG multibanda, esto se logra traduciendo las palabras-código ortogonales en los términos de amplitud y fase de los sensores FBG. La codificación en amplitud de los sensores SSFBG consiste en traducir las palabras-código \textit{"Optical Orthogonal Codewords"} (OOC), desarrolladas para sistemas de comunicaciones de acceso múltiple por división de código óptico (OCDMA), en el patrón de reflexión de los dispositivos. La codificación en amplitud y fase se ha propuesto mediante dos enfoques diferentes: en el primero, palabras-código de amplitud y fase personalizadas ($ a_ {k} $, $ f_ {k} $) fueron diseñadas específicamente para exhibir un comportamiento ortogonal obtenido por la combinación de dos palabras-código. La técnica de interrogación basada en una fuente dual sintonizable fue específicamente diseñada para recuperar la medición diferencial de los sensores y decodificar efectivamente su información. El segundo enfoque utiliza las secuencias \textit{"Discrete Prolate Spheroidal Sequences"} (DPSS), que son secuencias mutuamente ortogonales desarrolladas para sistemas de comunicaciones. Se demostró el uso de estas estructuras como elementos de detección ortogonales con patrones específicos de fase y amplitud. La fabricación y validación experimental de los dispositivos SSFBG propuestos se realizaron para demostrar el rendimiento de los sensores inclusive en condiciones de superposición espectral. La longitud de onda central de los sensores se recupera con éxito en las tres metodologías, además, el error del sistema de detección se caracterizó en términos de los parámetros de diseño. / Esta tesi investiga l'aplicació de conceptes de codificació al disseny de sensors òptics basats en xarxes de difracció de Bragg de Bragg (FBG) . Específicament, es presenta el disseny, la caracterització i la validació experimental de dispositius de detecció codificats personalitzats que es poden dissenyar i fabricar com a dispositius FBG súper estructurats (SSFBG) . L'objectiu d'esta tesi és millorar la capacitat i el rendiment general dels sistemes de detecció òptica basats en sensors FBG convencionals. Per a això, s'han proposat tres metodologies de codificació de dispositius de detecció SSFBG, amb l'objectiu de dotar a cada sensor amb informació addicional útil per a la identificació de cada sensor inclús en condicions de superposició. Un sensor codificat basat en FBGs és una estructura FBG la forma de la qual s'ha adaptat a una paraula-codi ortogonal, de tal manera que la seua longitud d'ona central es pot distingir inequívocament d'altres senyals en l'espectre. El disseny dels sensors SSFBG codificats es realitza modificant l'espectre de reflexió de dispositius FBG multibanda, açò s'aconseguix traduint les paraules-codi ortogonals en els termes d'amplitud i fase dels sensors FBG. La codificació en amplitud dels sensors SSFBG consistix a traduir les paraules-codi extit \textit{"Optical Orthogonal Codewords"} (OOC) , desenrotllades per a sistemes de comunicacions d'accés múltiple per divisió de codi òptic (OCDMA) , en el patró de reflexió dels dispositius. La codificació en amplitud i phase s'ha proposat per mitjà de dos enfocaments diferents: en el primer, paraules-codi d'amplitud i fase personalitzades ($ a_ {k} $, $ f_ {k} $) van ser dissenyades específicament per a exhibir un comportament ortogonal obtingut per la combinació de dos paraules-codi. La tècnica d'interrogació basada en una font dual sintonizable va ser específicament dissenyada per a recuperar el mesurament diferencial dels sensors i descodificar efectivament la seua informació. El segon enfocament utilitza les seqüències \textit{"Discrete Prolate Spheroidal Sequences"} (DPSS), que són seqüències mútuament ortogonals desenrotllades per a sistemes de comunicacions. Es va demostrar l'ús d'estes estructures com a elements de detecció ortogonals amb patrons específics de fase i amplitud. La fabricació i la validació experimental dels dispositius SSFBG proposats es van realitzar per a demostrar el rendiment dels sensors inclusivament en condicions de superposició espectral. La longitud d'ona central dels sensors es recupera amb èxit en les tres metodologies, a més, l'error del sistema de detecció es va caracteritzar en termes dels paràmetres de disseny. / This thesis investigates the application of encoding concepts to the design of optical sensors based on fiber Bragg grating (FBG) devices. Specifically, we present the design, characterization and experimental validation of custom encoded sensing devices that can be designed and manufactured as super-structured FBG (SSFBG) devices. The aim of this thesis is to enhance the capacity and the overall performance of the optical sensing systems based on conventional FBG sensors. To do so, three encoding methodologies of SSFBG sensing devices have been proposed, aiming to endow each sensor with additional information useful to identify each sensor even under overlapping conditions. An encoded FBG-based sensor is a FBG structure whose shape has been tailored after an orthogonal codeword in such a way that their central wavelength can be distinguished unequivocally from other signals in the spectrum. The design of encoded SSFBG sensors is performed by modifying the reflection spectrum of multi-band FBG devices, this is achieved by translating orthogonal codewords into the amplitude and phase terms of the FBG sensors. Amplitude encoding of SSFBG sensors consists in translating the binary optical orthogonal codewords (OOCs), developed for optical-code division multiple-access (OCDMA) communications systems, into the reflection pattern of the devices. Amplitude $\&$ phase encoding has been proposed in two different approaches: in the first one, custom amplitude and phase codewords ($a_{k}$, $f_{k}$) were specifically devised to exhibit orthogonal behavior by combining the two codewords. The dual-wavelength tunable interrogation technique was also specifically designed to retrieve the differential measurement of the sensors and effectively decode their information. The second approach uses the discrete prolate spheroidal sequences (DPSS), which are mutually orthogonal sequences developed for communications systems. We demonstrated the use of this structures as orthogonal sensing elements with definite phase and amplitude patterns. The manufacturing and experimental validation of the proposed SSFBG devices were carried out to prove the overlap-proof performance of the devices. The central wavelength of the sensors is successfully retrieved in the three methodologies, additionally, the error of the sensing system was characterized in terms of the design parameters. / Triana Infante, CA. (2018). Enoding optial FBG sensors to enhance the capacity of optial sensing systems [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/114824

The duty-cycle randomness (DCR) lying the Bragg grating of the distributed feedback (DFB) lasers introduced by the fabrication process is inevitable even with the state-of-the-art technologies such as the electron beam lithography and dry or wet etching. This thesis investigates the impact of grating DCR on DFB laser performance through numerical simulations. The result reveals that such a randomness causes a reduction on the side mode suppression ratio (SMSR), and deteriorates the noise characteristics, i.e., broadens the linewidth and increases the relative intensity noise (RIN). With the grating DCR, the effective grating coupling coefficient decreases as evidenced by the reduced Bragg stopband width. However, the longitudinal spatial hole burning (LSHB) effect in the DFB lasers can somewhat be diminished by the grating DCR. The seriousness of these effects depends on different grating structures and their coupling strengths. Our simulation shows that a degradation of 17dB can be brought to the SMSR of the uniform grating DFB lasers with their duty-cycles taking a deviation of ±25% in a uniformly distributed random fashion. It also broadens the linewidth of the quarter-wavelength phase-shifted DFB lasers by more than 2.5 folds. The impact of this effect on the RIN is moderate – less than 2%. All the performance deteriorations can partially be attributed to the effective reduction of the grating coupling coefficient around 20% by such a DCR. / Thesis / Master of Applied Science (MASc)

Tesis por compendio / [ES] Con el continuo desarrollo de materiales y tecnologías de fabricación durante las últimas tres décadas, la atenuación de la transmisión de las fibras ópticas de polímero (POF) se ha reducido considerablemente. Las POF son ventajosas para las redes domésticas, así como para las interconexiones de almacenamiento, y tienen ventajas significativas para muchas aplicaciones de detección, que incluye el límite alto de tensión elástica, alta resistencia a la fractura, alta flexibilidad en la flexión, alta sensibilidad a la tensión y coeficientes termoópticos negativos. Esta tesis consigue mejorar la tecnología de irradiación con láser para POF e investiga dispositivos especiales basados en redes de difracción en POF para comunicaciones ópticas, microondas, fotónica y detección. En particular, desarrollamos la tecnología de fabricación rápida de FBGs en POF con un estudio detallado y la optimización de los parámetros de fabricación de redes de difracción de Bragg en fibra (FBG). Los resultados más destacados incluyen un FBG uniforme de 8 dB con un solo pulso láser Nd: YAG (26 nsm) (8 ns) basado en fibra dopada con BDK, que es el tiempo más corto presentado hasta ahora para la fabricación de FBGs en POF. La irradiación de fibras ópticas de polímero utilizando diferentes materiales basado en el láser KrF a 248 nm permitió demostrar un mejor rendimiento en comparación con el sistema que emplea el láser He-Cd a 325 nm. Además, se fabricaron FBGs uniformes en POFs de índice escalón dopadas con TS en menos de 1 segundo mediante la repetición de pulsos con baja energía. Finalmente, el estudio de la irradiación UV con pulsos de baja energía para la fabricación de redes de difracción estables permitió ahorrar energía en el proceso de fabricación de FBGs en POF, como uno de los principales requisitos para la producción en masa. Basándonos en la tecnología de fabricación mejorada, nos centramos en la fabricación de redes de difracción con diferentes estructuras: se fabricó un FBG con desplazamiento de fase utilizando dos pulsos de 15 ns a 248 nm KrF superpuestos por el método de Moiré; el primer FBG con chirp sintonizable se logró utilizando un solo pulso corto del láser, que abrió nuevas perspectivas a las aplicaciones basadas en redes de difracción con chirp en POF; también se propuso un nuevo método basado en gradientes térmicos para obtener FBG con chirp en POF basadas en FBG uniformes, y se demostró como la forma más conveniente publicada hasta la fecha para lograr este tipo de FBGs no uniformes en POF; y, finalmente, también se han fabricado redes de difracción de largo período utilizando un proceso de fabricación de corto tiempo, especialmente en comparación con investigaciones anteriores. En la última parte de la tesis, y en base a los dispositivos basados en redes de difracción obtenidos a lo largo de este trabajo, se han propuesto varias aplicaciones . De manera similar a los FBG en fibra de sílice, los FBGs con chirp en POF tienen muchas aplicaciones futuras en las áreas de comunicaciones ópticas y de los sensores. Este documento describe la aplicación de detección de tensión basada en una FBG con chirp sintonizable en POF, su aplicación para detección térmica en sistemas biomédicos; e ilustra el potencial de los dispositivos de dispersión sintonizables en el campo de las comunicaciones ópticas, bien como compensación de dispersión o en fotónica de microondas. / [CA] Amb el continu desenvolupament de materials i tecnologies de fabricació durant les últimes tres dècades, l'atenuació de la transmissió de les fibres òptiques de polímer (POF) s'ha reduït considerablement. Els POF són avantatjosos per a les xarxes domèstiques, així com per a les interconnexions d'emmagatzematge, i tenen avantatges significatius per a moltes aplicacions de detecció, inclosos els límits de tensió elàstica alta, alta resistència a la fractura, alta flexibilitat en la flexió, alta sensibilitat a la tensió i potencials coeficients termoópticos negatius. Aquesta tesi va millorar la tecnologia d'irradiació amb làser per a POF i va investigar dispositius basats en xarxes difracció de Bragg (FBG) especials en POF per a comunicació òptica, microones, fotònica i detecció. En particular, desenvolupem la tecnologia de fabricació ràpida de FBG en POF amb un estudi detallat i l'optimització dels paràmetres per a la seua fabricació. Els punts destacats dels resultats inclouen un FBG uniforme de 8 dB amb un sol pols del làser Nd: YAG (266 nm) (8 ns) basat en fibra dopada amb BDK, que és el temps més curt reportat per a la fabricació de POF FBG. La irradiació de fibres òptiques de polímer utilitzant diferents materials sota el sistema de làser KrF a 248 nm va permetre demostrar un millor rendiment en comparació amb el sistema de làser Kimmon de 325 nm. A més, els FBG uniformes en el POF dopat amb TS d'índex escalonat es van aconseguir amb menys d'1 segon mitjançant la repetició de polsos de control i l'energia baixa de pols. Finalment, l'estudi de la irradiació d'energia de pols per a la fabricació de FBGs estables va permetre estalviar energia en el procés de fabricació de FBGs en POF, com un dels principals objectius de la producció en massa. Basant-nos en la tecnologia de fabricació millorada, ens centrem en la fabricació de diferents estructures de xarxes de difracció: es va fabricar un FBG amb desplaçament de fase utilitzant dos polsos de 15 ns a 248 nm KrF superposats pel mètode de Moiré; el primer FBG amb chirp sintonitzable es va aconseguir utilitzant un sol pols curt de làser, que va obrir les aplicacions basades en FBG amb chirp en POF; també es va proposar un nou mètode amb gradients tèrmics per a obtindre FBG en POF basat en FBG uniformes, i es va demostrar com la forma més convenient publicada fins hui per a aconseguir FBG POF estimulada; i, finalment, també s'han aconseguit xarxes de llarg període utilitzant un procés de fabricació de curt temps, especialment en comparació amb investigacions anteriors. Finalment, sobre la base dels dispositius de xarxes de difracció obtinguts al llarg d'aquest treball, s'han proposat diverses aplicacions potencials en aquesta tesi. De manera similar que per als FBG amb silici, el FBG amb chirp en POF té moltes aplicacions potencials en comunicacions òptiques i a l¿àrea de sensors. Aquest document descriu l'aplicació de detecció de tensió basada en FBG amb chirp sintonitzable en POF; a més, l'aplicació de detecció tèrmica en sistemes biomèdics; i el potencial dels dispositius de dispersió sintonitzables en les comunicacions òptiques, com per eixample a la compensació de dispersió o a la fotònica de microones. / [EN] With the continuing development of material and fabrication technologies over the last three decades, the transmission attenuation of polymer optical fibers (POF) has been greatly decreased. POFs are advantageous for home networks as well as storage interconnections and have significant advantages for many sensing applications, including high elastic strain limits, high fracture toughness, high flexibility in bending, high sensitivity to strain and potential negative thermo-optic coefficients. This thesis improved the laser irradiation technology for POF and investigated special grating devices in POF for optical communication, microware photonics and sensing. In particular, we developed fast POF grating fabrication technology with a detailed study and optimization of the polymer optical fiber Bragg grating (POFBG) fabrication parameters. Highlights of the results include an 8 dB uniform POFBG with one single Nd:YAG (266nm) laser pulse (8 ns) based on BDK doped fiber, which is the shortest time ever reported for POFBG fabrication. The irradiation of polymer optical fibers using different materials under 248 nm KrF laser system allowed to demonstrate a better performance compared with 325 nm Kimmon laser system. Furthermore, uniform FBGs in step-index TS doped POF were achieved with less than 1 second by means of controlling pulse repetition and low pulse energy. Finally, the study of low UV pulse power irradiation for fabricating stable gratings allowed to save energy in the POF grating fabrication process, as one of the main goals for mass production. Based on the improved fabrication technology, we focused on the fabrication of different grating structures: a phase-shifted FBG was fabricated by using two 15 ns 248 nm KrF pulses overlapped by Moiré method; the first tunable chirped FBG was achieved by using a single laser short pulse, which opened the applications based on chirped POF BGs; also a novel thermal annealing method was proposed to obtain chirped POFBGs based on uniform FBGs, and proved as the ever published most convenient way to achieve chirped POFBG; and finally, long period gratings have been also achieved by using a short time fabrication process, specially when compared with previous research. Finally, based on the grating devices obtained throughout this work, several potential applications have been proposed in this thesis. Similarly, to silica chirped FBG, chirped FBG in POF have many potential applications in optical communications and sensing area. This document described the potential strain sensing application based on tunable chirped POFBG; also, the thermal detection application in bio-medical systems; and the potential of tunable dispersion devices in optical communications, i.e., dispersion compensation or microwave photonics. / Min, R. (2019). Polymer optical fiber gratings for microwave photonics and communications application [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/125473 / Compendio

Optical resonators such as silica micro-spheres and micro-toroids can support whispering gallery modes (WGMs), where light circulates near the resonator surface and is confined by the total internal reflection at the dielectric boundary. Such resonators can exhibit very high quality (Q) factors, since the resonator surface can maintain atomic level smoothness. The combination of high Q factors and small resonator volumes has led to a wide range of applications in sensing, optomechanics, nonlinear optics, and quantum optics. In this dissertation, we introduce a new type of whispering gallery resonators (WGRs) based on micro-droplets in an immiscible liquid-liquid system. Within such an all-liquid platform, it is possible to achieve highly nonlinear coupling between light and liquid that can potentially lead to single-photon level optical nonlinearity. Specifically, we experimentally characterize a droplet (D~500um) of index matching fluid submerged in the water as a high-Q optical resonator, where we use an optical fiber taper to couple light into the droplet through non-contact evanescent coupling. The highest Q-factor observed in the experiment is 2x10^7 which closely matches the upper limit of intrinsic Q-factor set by the material absorption. Given with such a high Q factor, the WGM can exert strong radiation pressure on the droplet interface, push it outward, increase the length of optical path, and produce a red-shift in WGM resonance. Our experimental results have found that the ratio of those resonance shifts and the optical power coupled into the resonator is approximately 60 fm/μW. The result closely matches to our steady-state estimation based on solving the coupled Maxwell-Navier-Stokes equation. To investigate the dynamic interplay of light and liquid, we develop a harmonic oscillator (HO) model to describe the time-domain behaviors of the coupled optofluidic system. We find a good agreement between theoretical predictions and our experimental data. The shift of WGM resonance can potentially be induced by thermal effects. To estimate the magnitude of thermal effects, we also investigate the thermally induced nonlinear behaviors of WGMs in a cylindrical fiber resonator (D~125um), where we change the mechanism of heat dissipation by changing the cladding material (e.g. air and water). For direct temperature measurements, we use a fiber optical resonator with a fiber Bragg grating (FBG) inscribed in the fiber core to observe temperature shifts induced by the high-Q WGMs. Our result shows that the temperature increase in the fiber resonator in the water is 0.13 C, whereas the fiber resonator in air shows ~4.5 C increase in temperature. Our results suggest that the relatively high thermal conductivity of water suppresses thermal nonlinearity by ~50 times, and that the red-shifts of WGMs can largely be attributed to radiation pressure effect. / Ph. D. / Optical resonators are used to confine incoming light and store its energy in a small volume. The quality of such resonators’ optical confinement is represented by quality factor (<i>Q</i>). Among different types of optical resonators, whispering gallery resonator (WGR) is well known for its high-<i>Q</i>, where strong optical confinement is achieved by the total internal reflection at the curved internal surface of spherical / cylindrical dielectric volume. The combination of high <i>Q</i> factors and small resonator volumes has led to a wide range of applications in sensing, optomechanics, nonlinear optics, and quantum optics. In this dissertation, we introduce a new type of WGR based on oil micro-droplet in water. Such an all-liquid platform enables highly nonlinear coupling between optical power and liquid matter that can potentially lead to optical nonlinearity at single-photon energy level. Specifically, we experimentally characterize an oil droplet (<i>D</i> ≈ 500 <i>um</i>) submerged in the water as a high-<i>Q</i> optical resonator, where we use a tapered optical fiber to inject optical power into the droplet. The highest <i>Q</i> of whispering gallery mode (WGM) observed in our experiment is 2×10⁷ and given with the high amplification of optical power in droplet, the WGM can exert strong radiation pressure on the droplet interface, push it outward, increase the length of optical path, and produce a red-shift in WGM resonance. Our experimental results have found that the ratio of those resonance shifts and the optical power coupled into the resonator is approximately 60 fm/<i>μ</i>W. The result closely matches to our steady-state estimation based on solving the coupled Maxwell-Navier-Stokes equation. To investigate the dynamic interplay of light and liquid, we develop a harmonic oscillator (HO) model to describe the time-domain behaviors of the coupled optofluidic system. We find a good agreement between theoretical predictions and our experimental data. The shift of WGM resonance can potentially be induced by thermal effects. To estimate the magnitude of thermal effects, we also investigate the thermally induced nonlinear behaviors of WGMs in a cylindrical fiber resonator (D ≈ 125 <i>um</i>), where we change the mechanism of heat dissipation by changing the media (e.g. air and water) surrounding the resonator. For direct temperature measurements, we use a fiber optical resonator with a temperature sensor equipped inside to observe temperature shifts induced by the high-<i>Q</i> WGMs. Our result shows that the temperature increase in the fiber resonator in the water is 0.13 °C, whereas the fiber resonator in air shows ~4.5 °C increase in temperature. Our results suggest that the relatively high thermal conductivity of water suppresses thermal nonlinearity by ~50 times, and that the red-shifts of WGMs can largely be attributed to radiation pressure effect.

In this thesis, we explore the four aspects of fiber Bragg grating sensors: mathematical modeling of Fiber Bragg Grating response/spectral characteristics, fabrication using phase mask, application and interrogation. Applications of fiber Bragg gratings, also known as in-fiber gratings, with emphasis on their sensing capabilities, interrogation of an array of sensors and their performance in structural health monitoring scenario are documented. First, we study the process of photosensitivity phenomenon in glasses, in particular GeO2:SiO2 glasses. For mathematical modeling we consider the 1-D refractive index profile along the propagation axis of an optical fiber drawn from the preform of such glasses. These 1-D index structures exhibit a bandgap for propagation along the fiber axis. We show how the bandgap is dependent on the two structural parameters: index periodicity and effective refractive index. The mathematical model provides the characteristics of three sensor parameters -resonance wavelength also known as the Bragg wavelength (λB ), filter bandwidth (ΔλB ), and reflectivity (R). We show that the evolution of the index structure in germanosilicate glasses is dependent on the inscription parameters such as exposure time, intensity of the laser used for inscribing, the interference pattern, and coherence of the laser system. In particular, a phase mask is used as the diffffacting element to generate the required interference pattern, that is exposed on the photosensitive fiber. We present a mathematical model of the electromagnetic diffraction pattern behind the phase mask and study the effect of the limited coherence of the writing laser on the interference pattern produced by the diffracting beams from the mask. Next, we demostrate the sensing capabilities of the fiber Bragg gratings for measuring strain, temperature and magnetic fields. We report linearity of 99.7% and sensitivity of 10.35pm/◦C for the grating temperature sensor. An array of gratings assigned with non-overlapping spectral windows is inscribed in a single fiber and applied for distributed sensing of structural health monitoring of an aircraft’s composite air-brake panel. The performance of these sensors is compared with the industry standard resistance foil gauges. We report good agreement between the two gauges (FBG and RSG). In some applications it is more desirable to know the spectral content, rather than the magnitude of perturbation. Fiber Bragg gratings sensors can be used to track events that occur in a very small span of time and contain high frequencies. Such applications demand very high speed wavelength demodulation methods. We present two interrogation techniques: wavelength-shift time-stamping (WSTS) and reflectivity division multiplexing (RDM). WSTS interrogation method employs the multiple threshold-crossing technique to quantize the sensor grating fluctuations and in the process produces the time stamps at every level-cross. The time-stamps are assembled and with the a priori knowledge of the threshold levels, the strain signal is reconstructed. The RDM methodology is an extension of the WSTS model to address multiple sensors. We show that by assigning unique reflectivities to each of the sensors in an array, the time-stamps from each of the sensors can be tagged. The time-stamps are collected by virtue of their corresponding pulse heights, and assembled to reconstruct the strain signal of each of the array sensor. We demonstrate that the two interrogation techniques are self-referencing systems, i.e., the speed at which the signals are reconstructed is instantaneous or as fast as the signal itself.

[pt] A magnetostricção é a propriedade dos materiais ferromagnéticos de se deformarem pela presença de um campo magnético externo. Trata-se de uma propriedade inerente ao material, que não muda com o tempo. Materiais que apresentam deformações da ordem de 10-3 são conhecidos como materiais de magnetostricção gigante (GMM). Esta dissertação de mestrado estuda a aplicação destes materiais em sensores de deslocamento onde não há contacto entre o elemento cursor (um ímã) e o elemento sensor (GMM). O princípio de funcionamento consiste em aplicar um gradiente de campo magnético ao GMM que está fixo. O gradiente de campo magnético é gerado por um ímã preso ao componente ou estrutura na qual se quer medir o deslocamento. As variações no campo magnético no material GMM originados pelo deslocamento do ímã (estrutura), provocam uma deformação no GMM, que é detectada com extensômetros do tipo Strain Gauge ou Redes de Bragg. Neste trabalho apresenta-se a caracterização da deformação de GMM em relação a um campo constante aplicado, e análises do seu comportamento para diferentes geometrias. Efeitos de pressão, polarização com um segundo ímã, e diferentes gradientes de campo magnético são também estudados. É observado um comportamento local para a deformação quando a medida é realizada em diferentes regiões do GMM. Os resultados obtidos permitiram a medição de deslocamentos de alguns micra estando o elemento sensor a até 10 mm de distância do elemento cursor. / [en] Magnetostriction is a property of ferromagnetic materials to deform in the presence of a magnetic field. Magnetostriction is an inherent property of magnetic materials, which is unchangeable with time. Materials exhibiting strains in the order of 10-3 are known as giant magnetostrictive materials (GMM).In this dissertation we study the application of these materials in displacement sensors where there is not contact between the cursor element (magnet) and sensor element (GMM). Its principle of operation consists of applying a magnetic field gradient to a GMM located at a fixed position. The magnetic field gradient is produced by a magnet attached to the component or structure in which the displacement will be measured.The variation on the magnetic field in the GMM position originated from the displacement of the magnet, results in a strain in the GMM that can be detected with a Strain Gauge or Bragg Grating extensometers. In this work is presented the characterization of the strain on GMM cuboids against a constant magnetic field and the analysis of its behavior for different geometries. Effects of pressure, polarization with a second magnet, and different gradients of magnetic field are also studied. It is observed a local behavior for strains when it is measured in different regions of GMM cuboid. The results obtained allow us to measure displacements of about few micra when the sensor is at a distance of 10 mm from the cursor element.

Fibre Bragg gratings (FBGs) are key components for a vast number of applications in optical communication systems, microwave photonics systems, and optical sensors, etc. The main topic of this thesis is fibre Bragg grating fabrication and applications in direct microwave optical filtering, high speed switching and switchable dual-wavelength fibre lasers. First, a brief overview is given about the photosensitivity in optical fibre, basic FBG fabrication techniques, the popular coupled-mode theory for describing fundamental characteristics of FBGs and the Transfer Matrix method for the numerical simulations of complex-structured FBGs. An advanced FBG fabrication system based on the technique of multiple printing in fibre (with a continuous-wave source) has been used to write complex FBGs incorporating phase shifts, apodization and chirp.      A single double-peaked superimposed grating working in reflection can be employed as a direct optical filter for millimetre-wave signals. Bit error rate measurements confirmed that the filter exhibited nearly on-off behaviour in the passband with a 3-dB bandwidth of 2 GHz for a central frequency of 20 GHz, as expected from the optical spectrum reflection. The presented technique can be used in radio-over-fibre systems or simultaneous up-conversion of ultra-wide band signals and filtering. This thesis focused mostly on the research of two 4-cm long Hamming-apodized gratings written in side-hole fibres with internal electrodes. The temperature dependence measurements showed that the birefringence of the component increased with the temperature. Dynamic measurement has shown nanosecond full off-on and on-off switching. During the electrical pulse action, the grating wavelength was blue-shifted for the x-polarization and red-shifted for the y-polarization due to the mechanical stress. Both peaks subsequently experienced a red-shift due to the relaxation of mechanical stress and the increasing core temperature transferred from the metal in many microseconds. All the wavelength shifts of the two polarizations depend quadratically on the electrical pulse voltage and linearly on the pulse duration. Numerical simulations gave accurate description of the experimental results and were useful to understand the physics behind the birefringence switching. Finally, two switchable dual-wavelength erbium-doped fibre lasers based on FBG feedback were proposed. In one method, an overlapping cavity for the two lasing wavelengths and hybrid gain medium in the fibre laser were introduced. Dual-wavelength switching was achieved by controlling the Raman pump power. The other method employed an injection technique and the dual-wavelength switching was controlled by the power of the injection laser. The switching time was measured to be ~50 ms. Detailed characteristics of the dual-wavelength switching in the two fibre lasers were experimentally studied and corresponding principles were physically explained. / QC 20100922

The nuclear industry shows an increasing interest in the fiber optic technology for both data communication and sensing applications in nuclear plants. The optical fibers offer several advantages and the sensors based on this technology do not need any electrical power at the sensing point, they have a quick response and they can be easily multiplexed: in the case of a temperature sensor, several thermocouples can be substituted by a single fiber, resulting in a decrease of the waste material. The fission reactors are a very harsh environment: it is characterized by the highest dose of gamma-rays, of the order of magnitude of GGy, besides a high flux of neutrons and high operating temperature (300°C for the current reactors, known as generation III). This work has been carried out in collaboration with AREVA, a French industrial conglomerate active in the energy domain, with the aim of realizing a temperature sensor resistant to the environment of nuclear reactor of generation IV, in particular a Sodium-cooled Fast Reactor. The currently used technology, the thermocouples, presents a drift of the measurement due to irradiation, that needs a calibration, and a long response time on the order of seconds. In order to remove the drift, to reduce the response time and to increase the precision, a Fiber Bragg Grating temperature sensor was chosen, in regard to all the advantages of the optical fibers. To understand the behavior of such system in a harsh environment, as the nuclear reactor core, we used an experimental approach based on complementary techniques such as radiation-induced attenuation, photoluminescence, electron paramagnetic resonance and Raman spectroscopies

Multimode devices play an increasingly important role in both communication and sensing systems. Mode division multiplexing (MDM) in multimode fiber (MMF) is becoming a promising method to further increase the capacity of optical transmission link with a controllable mode coupler. Similarly, optic sensors based on core-cladding-mode interference can be widely used in measurement of refractive index (RI), temperature and strain. Fiber Bragg gratings (FBGs) in single mode operation have been extensively studied as in-line optical components for both communication and sensing applications. In recent years, research has been extended to FBGs in few-mode operation as mode couplers in MDM applications. Experimentally, mode conversion from fundamental linear polarization (LP) mode LP01 to higher order LP11 mode in two-mode FBG (TMFBG) has been observed. Index asymmetry and electric field distortion induced by ultraviolet (UV) side illumination in fabrication of FBG make the two modes no longer orthogonal. However, its spectrum analysis mainly depends on experimental data and software simulation using the complex finite element method (FEM). Here a simpler theoretical model based on coupled mode theory (CMT) and Runge-Kutta method (RKM) is proposed. An analytical expression of the mode coupling coefficient is derived and the modeling results match very well with experimental data. Abrupt fiber tapers allow power transfer between core and cladding modes and show promise as RI sensing components when two abrupt tapers are cascaded into an in-line Mach-Zehnder interferometer (MZI). The main advantage of the MZI taper sensor is its low manufacturing cost. However, the optical spectrum analyzer (OSA) used as the receiver and demodulation device in the conventional setup is still expensive. Three simplified schemes of fiber taper MZI RI sensor systems are designed and demonstrated experimentally. The transmitter and the demodulation devices for the three schemes are a single wavelength laser and a photodetector (PD), two modulated lasers and a PD together with data acquisition and processing module, and a broadband source (BBS) and a PD together with matched MZI, respectively. In all those implementations OSA is not required, which significantly lowers the cost and leads to easy integration. Although extra modulation/demodulation devices are required, the second implementation has the best performance. Automatic operation is realized by LabVIEW programming. High sensitivity (2371 mV/RI unit (RIU)) and high stability are achieved experimentally. Those new schemes have great potential to be applied to other interferometric optic sensor systems. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2014-05-09 11:44:44.837

In this thesis, miniaturized wavelength interrogators based on planar lightwave circuits (PLCs) are investigated and developed for the optical fiber sensing applications in the aircraft structural health monitoring (SHM) and optofluidic analysis. Two interrogation systems based on an arrayed waveguide grating (AWG) and an Echelle diffractive grating (EDG) are developed and used to convert the optical sensing signals into strain, temperature, vibration, damage, and humidity information for the aircraft SHM. A fiber Bragg grating (FBG) sensing system using developed interrogators is then demonstrated in a field test for aircraft SHM applications. For optofluidic analysis, a PLCs based optofluidic device consisting of two on-chip lens sets is built to enhance the optical manipulation capability of particles. Then, a solution to a multi-functional Lab-on-a-Chip platform for optofluidic analysis is proposed, which integrates the developed particle maneuvering device, grating-structured sensors, and miniaturized interrogators.