M.Ing. (Electrical and Electronic Engineering) / An experimental study of a multi-point optic fibre sensor for monitoring temperature changes is presented. The multi-point optic fibre sensor is made of a serial array of weak-reflectivity identical gratings. The weak-reflectivity identical gratings form the interferometric cavities UV printed on the single mode fibre. The ability to measure temperatures changes at different cavities along the serial array is particularly interesting for the monitoring of power transformers, high temperature furnaces and jet engines. Changes in temperature in each respective cavity is measured based on the spectral shift in the phase of the light from each respective cavity. The performance of the multi-point fibre sensor system is evaluated. Further, a theoretical and experimental investigation of a serial array composed of two cavities of different lengths is conducted. This investigation is aimed at measuring the impact of the overlap of the two distinct cavities in their respective frequency domain and determining the accuracy of the measurement. The result found shows that the sensor phase response is no more linear to temperature changes. It is also found that the nonlinear response of the sensor to temperature changes increases with the magnitude of the overlap.

[ES] La fibra óptica ha supuesto una gran revolución en el mundo de las telecomunicaciones debido a su alta capacidad de transmisión y sus bajas pérdidas. Hoy en día no sería posible transportar la cantidad de tráfico que se genera en internet si no fuera por sis- temas de comunicaciones basados en fibras ópticas. Sin embargo, el número de dispo- sitivos conectados a internet es cada vez mayor, por lo que la capacidad de la fibra óptica estándar de un solo núcleo se puede ver limitada en un futuro no muy lejano. Una forma de aumentar dicha capacidad es utilizar fibras ópticas con varios núcleos. Actualmente existe un gran interés sobre la investigación en este tipo de fibras para aplicaciones de telecomunicaciones, por lo que no es difícil encontrar fibras multinú- cleo comerciales. Aunque el uso más común de la fibra óptica es para telecomunicaciones, también se puede utilizar como sensor. Uno de los métodos más comunes para la implementa- ción de sensores es la inscripción de redes de difracción en fibras ópticas de un solo núcleo. Sin embargo, la inscripción de redes de dirección en fibras de múltiples núcleos abre nuevas líneas de investigación para el desarrollo de sensores avanzados. En esta tesis se ha estudiado distintos tipos de redes de difracción inscritas en una fibra de siete núcleos para su aplicación en la implementación de sensores. En primer lugar, se describe el sistema de fabricación que permite inscribir distintos tipos de redes de difracción en la fibra multinúcleo de forma selectiva, es decir, permite seleccionar en que núcleos se va a inscribir la red. Mediante este sistema se han inscrito redes de periodo largo y posteriormente se han caracterizado como sensor de deformación, tor- sión y curvatura. Después, se han inscrito redes de Bragg inclinadas para aumentar de forma intencionada la diafonía entre los núcleos de la fibra mediante el acoplo de luz entre ellos. Además, se ha demostrado experimentalmente que esta diafonía es sensible a la deformación de la fibra, a la curvatura, a la temperatura y al índice de refracción que rodea la fibra. Por otro lado, se ha demostrado que las redes de Bragg inscritas en fibras multinúcleo se pueden utilizar para implementar sensores de curvatura capaces de operar en entornos radioactivos. Finalmente se han fabricado redes de Bragg rege- neradas capaces de operar a altas temperaturas, estas redes se han caracterizado como sensor de temperatura, deformación y curvatura. / [CAT] La fibra òptica ha suposat una gran revolució en el món de les telecomunicacions a causa de la seua alta capacitat de transmissió i les seues baixes pèrdues. Hui en dia no seria possible transportar la quantitat d'informació que es genera en internet si no fos pels sistemes de comunicacions basats en fibres òptiques. No obstant això, el nombre de dispositius connectats a internet es cada vegada més gran, per la qual cosa la capacitat de la fibra òptica estàndard d'un sol nucli es pot veure limitada en un futur no gaire llunyà. Una manera d'augmentar aquesta capacitat es utilitzar fibres òptiques amb diversos nuclis. Actualment existeix un gran interès sobre la investigació en aquesta mena de fibres per a aplicacions de telecomunicacions, per la qual cosa no es difícil trobar fibres de múltiples nuclis comercials. Encara que l'ús mes comú de la fibra òptica es per a telecomunicacions, també es pot utilitzar com a sensor. Un dels mètodes més comuns per a la implementació de sensors es la inscripció de xarxes de difracció en fibres òptiques d'un sol nucli. No obstant això, la inscripció de xarxes de difracció en fibres de múltiples nuclis obri noves línies d'investigació per al desenvolupament de sensors més complexos. En aquesta tesi s'ha estudiat diferents tipus de xarxes de difracció inscrites en una fibra de set nuclis per a la seua aplicació en la implementació de sensors en fibra òptica. En primer lloc, es descriu el sistema de fabricació de xarxes de difracció que permet inscriure diferents tipus de xarxes de difracció en la fibra de múltiples nuclis de manera selectiva, es a dir, permet seleccionar en que nuclis s'inscriurà la xarxa. Mitjançant aquest sistema s'han inscrit xarxes de període llarg i posteriorment s'han caracteritzat com a sensor de deformació, torsió i curvatura. Després, s'han inscrit xarxes de Bragg inclinades per a augmentar de manera intencionada la diafonia entre els nuclis de la fibra mitjançant l'acoblament de llum entre ells. A més d'això, s'ha demostrat experimentalment que aquesta diafonia es sensible a la deformació de la fibra, a la curvatura, a la temperatura i a l'índex de refracció que envolta la fibra. D'altra banda, s'ha demostrat que les xarxes de Bragg inscrites en fibres múltiples nuclis es poden utilitzar per a implementar sensors de curvatura que poden operar en entorns radioactius. Finalment s'han fabricat xarxes de Bragg regenerades que suporten altes temperatures, aquestes xarxes s'han caracteritzat com a sensor de temperatura, deformació i curvatura. / [EN] Optical fiber has been a great revolution in the world of telecommunications due to its high transmission capacity and low attenuation. Today it would not be possible to transport the amount of traffic that is generated on the Internet without communication systems based on optical fibers. However, the number of devices connected to the Internet is increasing, so the capacity of standard single-core fiber optics may be limited so far in the future. One way to increase this capacity is to use multi-core optical fibers. Nowadays is a great interest in research in this type of fibers for telecommunications applications, so it is not difficult to find commercial multicore fibers. Although the most common use of fiber optics is for telecommunications, it can also be used as a sensor. One of the most common methods for sensor implementation is the inscription of diffraction gratings on single-core optical fibers. However, the enrollment of steering networks in multi-core fibers opens new lines of research for the development of advanced sensors. In this thesis, different types of diffraction gratings inscribed in a seven-core fiber have been studied for their application in the implementation of sensors. In the first place, the diffraction grating manufacturing system is described that allows to inscribe different types of diffraction gratings in the multicore fiber selectively, that is, it allows to select in which cores the grating is going to be inscribed. By means of this system, long-period networks have been inscribed and subsequently they have been characterized as a deformation, torsion, and curvature sensor. Then, slanted Bragg gratings have been inscribed to intentionally increase the crosstalk between the fiber cores by coupling light between them. Furthermore, this crosstalk has been experimentally shown to be sensitive to fiber deformation, curvature, temperature, and the index of refraction surrounding the fiber. On the other hand, it has been shown that Bragg networks inscribed in multicore fibers can be used to implement curvature sensors capable of operating in radioactive environments. Finally, regenerated Bragg nets capable of operating at high temperatures have been manufactured. These nets have been characterized as a temperature, deformation, and curvature sensor. / Agradezco a la Universitat Politècnica de València la beca FPI (PAID-01-18) que me fue concedida para realizar está tesis. / Madrigal Madrigal, J. (2022). Diseño, fabricación y caracterización de sensores basados en fibras ópticas de múltiples núcleos [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/180806 / TESIS

Optical waves propagation in various types of volume gratings, materials with constant impendence and optical fibers are studied. Instability of cross–phase modulation and of Energy transfer via GRON-type (Grating-type Orientational Nonlinearity in Liquid Crystal) Stimulated Scattering is numerically observed. Two diffractive optical elements made of volume gratings are suggested and analyzed. A transmission hologram based on the analogy with Stimulated Raman Adiabatic Passage (STIRAP) in nonlinear optics is proposed. This transmission hologram demonstrates high diffraction efficiency and low sensitivity to polarization and hologram strength. The other is a reflection hologram with two crossed-gratings. It features good angular selectivity in comparison with the poor angular selectivity of conventional Bragg grating mirror. This defense also contains the approximation of Maxwell equations for the description of depolarized light sources and polarization-insensitive detectors. A scalar wave equation, Z-Helmholtz equation, is proposed and discussed in the approximation of constant impedance media. As examples, this equation successfully describes a) Fresnel transmission coefficient, and b) Goose-Hanschen shift in total internal reflection, for depolarized incident light and, at the same time, polarization-insensitive detectors. Evolution of polarization during light propagation in an inhomogeneous locally isotropic medium, and also in a single-mode fiber is described by Rytov's non-rotation equation. With arbitrary chosen real unit vector, the complete description of polarization change can be described in a single rotation angle obtained from the integral of rotation rate. Based on introduction of this reference frame, a device is suggested as rigid body's rotation sensor due to polarization change in a twisted fiber.

High power lasers with diffraction limited beam quality are desired for many applications in defense and manufacturing. A lot of applications require laser beams at the 100 kW power level along with divergence close to the diffraction limit. The figure of merit for a beam used in such applications should be radiance which determines the laser power delivered to a remote target. One of the primary limiting factors is thermal distortion of a laser beam caused by excessive heat generated in the laser media. Combination of multiple laser beams is usually considered as a method to mitigate these limitations. Spectral beam combining (SBC) by volume Bragg gratings (VBGs) is a very promising method for the future of high radiance lasers that needs to achieve 100 kW-level power. This work is dedicated to development of methods to increase spectral density of combined beams keeping their divergence at an acceptably low level. A new figure of merit for a beam combining system is proposed, the Beam Combining Factor (BCF), which makes it possible to distinguish the quality of the individual beams from the quality of beam combining. Also presented is a method of including the effect of beam divergence and spectral bandwidth on the performance of VBGs, as well as a method to optimize VBG parameters in terms of thickness and refractive index modulation for an arbitrary number of beams. A novel thermal tuning technique and apparatus is presented with which the SBC system can be tuned for peak efficiency from low to high power without the need for mechanical re- iv alignment. Finally, a thermally tuned SBC system with five beams, with a spectral separation between beams of 0.25 nm at a total power of 685 W is presented. The results show the highest power spectral density and highest spectral radiance of any SBC system to date. Recent demonstrations in SBC by multiplexed VBGs and the use of super Gaussian beams for beam quality improvement are also discussed.

The realization of wavelength scale and sub-wavelength scale fabrication of integrated optical devices has led to a concurrent need for computational design tools that can accurately model electromagnetic phenomena on these length scales. This dissertation describes the physical, analytical, numerical, and software developments utilized for practical implementation of two particular frequency domain design tools: the modal method for multilayer waveguides and one-dimensional lamellar gratings and the Rigorous Coupled Wave Analysis (RCWA) for 1D, 2D, and 3D periodic optical structures and integrated optical devices. These design tools, including some novel numerical and programming extensions developed during the course of this work, were then applied to investigate the design of a few unique integrated waveguide and grating structures and the associated physical phenomena exploited by those structures. The properties and design of a multilayer, multimode waveguide-grating, guided mode resonance (GMR) filter are investigated. The multilayer, multimode GMR filters studied consist of alternating high and low refractive index layers of various thicknesses with a binary grating etched into the top layer. The separation of spectral wavelength resonances supported by a multimode GMR structure with fixed grating parameters is shown to be controllable from coarse to fine through the use of tightly controlled, but realizable, choices for multiple layer thicknesses in a two material waveguide; effectively performing the simultaneous engineering of the wavelength dispersion for multiple waveguide grating modes. This idea of simultaneous dispersion band tailoring is then used to design a multilayer, multimode GMR filter that possesses broadened angular acceptance for multiple wavelengths incident at a single angle of incidence. The effect of a steady-state linear loss or gain on the wavelength response of a GMR filter is studied. A linear loss added to the primary guiding layer of a GMR filter is shown to produce enhanced resonant absorption of light by the GMR structure. Similarly, linear gain added to the guiding layer is shown to produce enhanced resonant reflection and transmission from a GMR structure with decreased spectral line width. A combination of 2D and 3D modeling is utilized to investigate the properties of an embedded waveguide grating structure used in filtering/reflecting an incident guided mode. For the embedded waveguide grating, 2D modeling suggests the possibility of using low index periodic inclusions to create an embedded grating resonant filter, but the results of 3D RCWA modeling suggest that transverse low index periodic inclusions produce a resonant lossy cavity as opposed to a resonant reflecting mirror. A novel concept for an all-dielectric unidirectional dual grating output coupler is proposed and rigorously analyzed. A multilayer, single-mode, high and graded-index, slab waveguide is placed atop a slightly lower index substrate. The properties of the individual gratings etched into the waveguide's cover/air and substrate/air interfaces are then chosen such that no propagating diffracted orders are present in the device superstrate and only a single order is present outside the structure in the substrate. The concept produces a robust output coupler that requires neither phase-matching of the two gratings nor any resonances in the structure, and is very tolerant to potential errors in fabrication. Up to 96% coupling efficiency from the substrate-side grating is obtained over a wide range of grating properties.

No description available.

<p> Ion implanted Bragg gratings integrated in rib waveguide structures were simulated, fabricated and characterized for the silicon-on-insulator (SOI) photonics platform. After selective silicon self-implantation, to an amorphizing dose of 2x10^15 ions/cm^2, the approximately 0.3 damage-induced increase in the refractive index provided the modulation mechanism necessary for the formation of a Bragg grating. The benefits of implanted Bragg gratings compared to the more widely utilized surface relief type gratings include planar surface retention, desirable for subsequent processing and wafer bonding, and a smaller depth of the index modulation, important for minimizing filtering bandwidths. To our knowledge, this is the first time ion implantation has been utilized to produce Bragg gratings integrated in an SOI rib waveguide. The benefits of using SOI for an optoelectronics platform include: cost minimization, reduced device size, and compatibility with silicon based microelectronics.</p> <p> Device performance was simulated using coupled mode theory (CMT) in conjunction with beam propagation methods (BPM), to determine transverse modal profiles for computing coupling coefficients and to determine geometric dimensions suitable to achieve adequate grating strength and single-mode operation. The Monte Carlo ion implantation simulator SUSPREM4, implementing the binary collision approximation (BCA), was used to determine the amorphous silicon grating profiles. Implanted grating devices were then fabricated into SOI having a 2.5 μm device layer and were optically characterized. For a grating length of 2100 μm and an implant energy of 60 keV, the extinction ratio of the resonant wavelength was found to be -18.11 dB and -0.87 dB for TE and TM polarizations respectively. The excess loss per unit length was measured to be 1.2 dB/mm for TE polarization and 0.6 dB/mm for TM polarization. After annealing the gratings at temperatures of up to 300 °C, used to annihilate low energy point defects responsible for absorption, it was found that the excess loss per unit length was reduced to 0.3 dB/mm for TE polarization. Compared to etched gratings with similar dimensions, it was determined that the strength of the implanted gratings was approximately 2.5 times stronger for grating lengths one third the length as result of mode-shifting due to the higher index of refraction. This is of great consequence to the miniaturization and densification of Bragg grating based devices in silicon photonics.</p> / Thesis / Master of Applied Science (MASc)

This research presents a novel biosensor which utilizes the refractive index sensitivity of a fiber optic long-period grating. The long period grating couples light from the forward propagating guided core mode of a single-mode fiber into discrete circularly symmetric cladding modes. Due to imperfections in the cladding surface, loss bands are seen in the transmission spectrum corresponding to the coupled wavelengths. Based on the phase-matching condition between the coupling and coupled modes, the loss bands shift with changes in the refractive index of the surrounding medium. The grating surface is chemically treated to covalently bond antibody to the cladding of the sensor. Treatment with the proper antigen increases the effective index seen by the cladding modes and affects the placement of the loss bands. This sensor demonstrates specific antigen binding capacity with loss band shifts of 10 nm or more. The device offers several advantages over the widely used Enzyme-Linked Immuno-Sorbent Assays. Diagnostic applications can be expanded beyond the tests presented here. / Master of Science

Les éléments de diffraction sont largement utilisés aujourd'hui dans un nombre grandissant d'applications grâce à la progression des technologies de microstructuration dans le sillage de la micro-électronique. Pour un design optimal de ces éléments, des méthodes de modélisation précises sont nécessaires. Plusieurs méthodes ont été développées et sont utilisées avec succès pour des réseaux de diffraction unidimensionnel de différents types. Cependant, les méthodes existantes pour les réseaux deux dimensionnel ne couvrent pas tous types de structures possibles. En particulier, le calcul de l'efficacité de diffraction sur les réseaux métalliques à deux dimensionnel avec parois verticales représente encore une grosse difficulté pour les méthodes existantes. Le présent travail a pour objectif le développement d'une méthode exacte de calcul de l'efficacité de diffraction de tels réseaux qui puisse servir de référence. La méthode modale développée ici - dénommée ,,true-mode" en anglais - exprime le champ électromagnétique sur la base des vrais modes électromagnétiques satisfaisant les conditions limites de la structure 2D à la différence d'une méthode modale où les modes sont ceux d'une structure approchée obtenue, par exemple, par développement de Fourier. L'identification et la représentation de ces vrais modes à deux dimensions restait à faire et ce n'est pas le moindre des résultats du présent travail que d'y avoir conduit. Les expressions pour la construction du champ sont données avec des exemples de résultats concrets. Sont aussi fournies les équations pour le calcul des intégrales de recouvrement et des éléments de la matrice de diffusion / Diffractive elements are widely used in many applications now as the microstructuring technologies are making fast progresses in the wake of microelectronics. For the optimization of these elements accurate modeling methods are needed. There exists well-developed and widely used methods for one-dimensional diffraction gratings of different types. However, the methods available for solving two-dimensional periodic structures do not cover all possible grating types. The development of a method to calculate the diffraction efficiency of two dimensional metallic gratings represents the objective of this work. The one-dimensional true-mode method is based on the representation of the field inside the periodic element as a superposition of particular solutions, each one of them satisfying exactly the boundary conditions. In the developed method for the two-dimensional gratings the representation of the field within the grating in such way is used. In the present work, the existing modal methods for one-dimensional gratings can be used as the basis for the construction of the modal field distribution functions within two-dimensional gratings. The modal function distributions allow to calculate the overlap integrals of the fields outside the grating with those within the structure. The transition matrix coefficients are formed on the basis of these integrals. The final stage is the calculation of the scattering matrix based on two transition matrices. The equations for the field reconstruction are provided and accompanied by examples of results. Further equations used to calculate the overlap integrals and scattering matrix coefficients are provided

Orientador: Jose Antonio Siqueira Dias / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-24T00:41:09Z (GMT). No. of bitstreams: 1 Pfrimer_FelipeWalterDafico_D.pdf: 3374919 bytes, checksum: aa34af0e6bc2013297d4bd53c2901a20 (MD5) Previous issue date: 2013 / Resumo: O crescente interesse na utilização de Grades de Bragg (FBG) em sistemas sensores pode ser explicado por algumas de suas características, que são: imunidade à interferência eletromagnética (EMI), isolamento elétrico, baixo peso, flexibilidade, e transmissão de informações a longa distância. Este trabalho apresenta uma nova técnica de interrogação capaz de medir a temperatura de uma rede de sensores de grades de Bragg em fibras ópticas, onde um circuito eletrônico realiza rotinas de controle possibilitando a implementação de uma realimentação óptica. O esquema optoeletrônico empregado é capaz de realizar a interrogação de todos os sensores da rede de maneira quase instantânea, além de permitir que novos sensores possam ser facilmente acrescentados. Um protótipo contendo dois sensores foi construído e testado para validar a técnica obtendo-se uma alta resolução de ± 1 mºC na medida de temperatura em uma faixa de 72ºC / Abstract: The increasing interest in the use of fiber Bragg gratings (FBG) in sensing systems can be explained by some of its features, which are immunity to electromagnetic interference (EMI), electrical insulation, low weight, flexibility, and long distance data transmission capability. This work presents a new interrogation technique capable of measuring temperature of Bragg gratings sensor networks in optical fibers, where an electronic circuit, capable to perform control routines, allows the implementation of an optical feedback. The optoelectronic scheme used is capable of performing the interrogation of all the sensors of the network almost instantly, and allows new sensors to be easily added. A prototype containing two channels was built and tested to validate the technique achieving a high resolution of ± 1 mºC in temperature measurements in a range of 72º C. / Doutorado / Eletrônica, Microeletrônica e Optoeletrônica / Doutor em Engenharia Elétrica