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.

<p>Photonic crystals (PhCs) are structures periodic in thedielectric constant. They exhibit a photonic bandgap, i.e., arange of wavelengths for which light propagation is forbidden.Engineering of defects in the PhC lattice offers new ways toconfine and guide light. PhCs have been manufactured usingsemiconductors and other material technologies. This thesisfocuses on two-dimensional PhCs etched in InP-based materials.Only recently, such structures were identified as promisingcandidates for the realization of novel and advanced functionsfor optical communication applications.</p><p>The primary focus was on fabrication and characterization ofPhC structures in the InP/GaInAsP/InP material system. Thedemands on fabrication are very high: holes as small as100-300nm in diameter have to be etched at least as deep as 2µm. Thus, different etch processes had to be explored andspecifically developed for InP. We have implemented an etchingprocess based on Ar/Cl₂chemically assisted ion beam etching (CAIBE), thatrepresents the state of the art PhC etching in InP.</p><p>Different building blocks were manufactured using thisprocess. A transmission loss of 10dB/mm for a PhC waveguide, areflection of 96.5% for a 4-row mirror and a record qualityfactor of 310 for a 1D cavity were achieved for this materialsystem. With an etch depth of 4.5 µm, optical loss wasfound to be close to the intrinsic limit. PhC-based opticalfilters were demonstrated using (a) a Fabry-Pérot cavityinserted in a PhC waveguide and (b) a contra-directionalcoupler. Lag effect in CAIBE was utilized positively to realizehigh quality PhC taper sections. Using a PhC taper, a couplingefficiency of 70% was demonstrated from a standard ridgewaveguide to a single line defect PhC waveguide.</p><p>During the course of this work, InP membrane technology wasdeveloped and a Fabry-Pérot cavity with a quality factorof 3200 was demonstrated.</p><p><b>Keywords:</b>photonic crystals, photonic bandgap materials,indium phosphide, dry etching, chemically assisted ion beametching, reactive ion etching, electron beam lithography,photonic integrated circuits, optical waveguides, resonantcavities, optical filtering, finite difference time domain,plane wave expansion.</p>

Light can exert optical forces on matter. In the macroscopic world these forces are minuscule, but on the microscopic or atomic scale, these forces are large enough to trap and manipulate particles. They may even be used to cool atoms to a fraction of a degree above absolute zero. This thesis details a number of experiments concerned with the optical manipulation of atoms and micron-size particles using free space light beams and photonic crystal fibres. Two atom guiding experiments are described. In the first experiment, a spatial light modulator is used to generate higher blue-detuned azimuthal Laguerre-Gaussian LG) beams, which are annular beams with a hollow core. These LG beams are then used to guide laser cooled rubidium-85 atoms within the dark core over a distance of 30 mm. The second atom guiding experiment involves attempting to guide laser cooled and thermal rubidium atoms through a hollow-core photonic crystal fibre using red-detuned light. Hollow-core photonic crystal fibres are fibres that are able to guide light with low attenuation within a hollow core. For this experiment a hot wire detection system was designed, along with a number of complex vacuum systems. The first dual-beam fibre trap for micron-size particles constructed using endlessly single-mode photonic crystal fibre (ESM-PCF) is described. The characteristics of dual-beam fibre traps are governed by the fibres used. As ESM-PCF has considerably different properties in comparison to conventional single- or multimode fibres, this dual beam ESM-PCF trap exhibits some novel characteristics. I show that the dual beam ESM-PCF trap can form trapping, repulsive and line potentials; an interference-free ‘white light’ trap; and a dual-wavelength optical conveyor belt.

[ES] El cuidado de la salud es un campo en el que la detección precoz de enfermedades está cobrando cada vez más importancia. Hoy en día, profesionales y ciudadanos demandan que las técnicas de diagnóstico sean de alta calidad, tanto para el sistema de sanidad privado como para el público. Cuando se utilizan técnicas de diagnóstico de manera inadecuada, eso puede acarrear bastantes consecuencias, tales como un serio peligro sobre la salud y la sobrecarga técnica y económica de los servicios de salud. Eso es debido a que las técnicas de diagnóstico disponibles hoy en día son demasiado costosas, centralizadas en laboratorios y necesitan profesionales altamente cualificados para poder llevar a cabo dichas tareas, lo que conllevaría una demora en el tiempo, siendo este muchas veces vital para los enfermos. Es muy necesario, por lo tanto, reflexionar sobre la necesidad y emergencia de tales prácticas preventivas, especialmente para enfermedades de alto riesgo como el cáncer, el Alzheimer o la primera causa de muerte en el mundo, las enfermedades cardiovasculares. En este contexto, el objetivo principal del trabajo realizado durante esta Tesis Doctoral es ayudar a superar estos problemas mediante la exploración de la posibilidad de utilizar tecnología fotónica para el desarrollo de sistemas de análisis que puedan ser utilizados para el diagnóstico y pronóstico de las enfermedades cardiovasculares. Este objetivo se ha abordado mediante la combinación de la tecnología nanofotónica, consistiendo en la nanofabricación de las estructuras PBG de sensado que ofrece varios beneficios, como una alta sensibilidad, una extrema reducción de tamaño y un proceso de fabricación compatible con el de la industria microelectrónica, con un método de biofuncionalización obteniendo una capa de bioreconocimiento estable y selectiva mediante el uso de la reacción TEC asistida por luz capaz de proporcionar unas capas de bio-reconocimiento extremadamente finas con una inmovilización espacialmente selectiva. / [CAT] L'atenció a la salut és un camp en què la detecció precoç de malalties està cobrant cada vegada més importància. Hui en dia, professionals i ciutadans demanen que les tècniques de diagnòstic siguin d'alta qualitat, tant per al sistema de sanitat privat com per al públic. Quan s'utilitzen tècniques de diagnòstic de manera inadequada, això pot comportar bastants conseqüències, com ara, un seriós perill sobre la salut i la sobrecàrrega tècnica i econòmica dels serveis de salut. Això és degut al fet que les tècniques de diagnòstic disponibles hui en dia són molt costoses, centralitzades en laboratoris i necessiten professionals altament qualificats per poder realitzar aquestes tasques, lo que comportaria a una demora en el temps que moltes vegades es vital pels malalts. És molt necessari, per tant, reflexionar sobre la necessitat i emergència de tals practiques preventives, especialment per a malalties d'alt risc com el càncer, l'Alzheimer o la primera causa de mort al món, les malalties cardiovasculars. En aquest context, l'objectiu principal del treball realitzat durant aquesta Tesi Doctoral és ajudar a superar aquests problemes mitjançant l'exploració de la possibilitat d'utilitzar tecnologia fotònica per al desenvolupament de sistemes d'anàlisis que puguin ser utilitzats per al diagnòstic i pronòstic de les malalties cardiovasculars. Aquest objectiu s'ha abordat mitjançant la combinació de la tecnologia nanofotònica, consistint en la nanofabricació de les estructures de detecció de PBG fotòniques que ofereix diversos beneficis, com una alta sensibilitat, una extrema reducció de mida i un procés de fabricació compatible amb el de la indústria microelectrònica, amb un mètode de biofuncionalització obtenint una capa de bio-reconeixement estable i selectiva mitjançant l'ús de la reacció TEC assistida per llum capaç de proporcionar unes capes de bioreconeixement extremadament fines amb una immobilització espacialment selectiva. preventives, especialment per a malalties d'alt risc com el càncer, l'Alzheimer o la primera causa de mort al món, les malalties cardiovasculars. En aquest context, l'objectiu principal del treball realitzat durant aquesta Tesi Doctoral és ajudar a superar aquests problemes mitjançant l'exploració de la possibilitat d'utilitzar tecnologia fotònica per al desenvolupament de sistemes d'anàlisis que puguin ser utilitzats per al diagnòstic i pronòstic de les malalties cardiovasculars. Aquest objectiu s'ha abordat mitjançant la combinació de la tecnologia nanofotònica, consistint en la nanofabricació de les estructures de detecció de PBG fotòniques que ofereix diversos beneficis, com una alta sensibilitat, una extrema reducció de mida i un procés de fabricació compatible amb el de la indústria microelectrònica, amb un mètode de biofuncionalització obtenint una capa de bio-reconeixement estable i selectiva mitjançant l'ús de la reacció TEC assistida per llum capaç de proporcionar unes capes de bioreconeixement extremadament fines amb una immobilització espacialment selectiva. / [EN] Healthcare is a field where the early detection of diseases is becoming more and more important. Nowadays, professionals and citizens demand high quality diagnosis techniques offered by both private and public health systems. When the application of diagnostic tests is not adequate, different consequences can be observed such as health hazard and technical and economic overload of health services. This is due to the fact that the diagnostic techniques available are expensive, centralized in laboratories and with the need for highly qualified professionals to carry out these tasks, what can fundamentally lead to delays in time, being critical for the patient's health. It is very necessary, therefore, to reflect on the need and emergency of such preventive practices, especially for high-risk diseases such as cancer, Alzheimer or the first cause of death in the world, the cardiovascular diseases. Within this context, the main objective of the work done during this PhD Thesis is to help on overcoming these problems by exploring the possibility of using photonic technology for the development of analysis devices which might be used for the early diagnosis and prognosis of cardiovascular diseases. This objective has been addressed by combining nanophotonic technology, by the nanofabrication of the photonic PBG sensing structures, which provides several benefits such as a high sensitivity, an extreme size reduction and a fabrication process being compatible with that from the microelectronics industry, with a light-assisted biofunctionalization method forming a stable and selective biorecognition layer using TEC reaction able to provide extremely thin biorecognition layers with a spatially-selective immobilization. / Sabek, J. (2019). Combination of nanophotonic biosensors and light-assisted immobilization procedures for the detection of cardiac biomarkers [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/124821 / TESIS