Dissertations / Theses on the topic 'Grating'
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Dadiotis, Konstantinos. "Improving phase grating and absorption grating diffusers." Thesis, University of Salford, 2010. http://usir.salford.ac.uk/26633/.
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This thesis investigates room acoustic diffusers based on number sequences, exploring their shortcomings and presents improvements. Standard Phase Grating Diffusers display frequencies where they act like flat plates and fail to diffuse. To overcome this, two new sequences (Luke and power residue) are introduced. The diffusers based on these sequences display extended frequency range compared to standard ones such as Quadratic Residue and Primitive Root Diffusers. Their performance is studied using Boundary Element Modelling which shows that they can avoid flat plate phenomena in the audible frequency range. Furthermore, it is shown that by taking advantage of their inner symmetries Quadratic Residue and Primitive Root Diffusers can be created from smaller components thus allowing for the flat plat effect to be mitigated. Next, Absorption Grating Diffusers are investigated. They consist of ideally absorbing and reflecting elements. For their implementation heavily damped Helmholtz Resonators are investigated showing that they give an approximation of the required distribution of admittance on the surface. Then the performance of ideal Absorption Grating Diffusers is investigated using Boundary Element Modelling. Even with idealised completely absorbing elements, the performance of the diffuser is shown not to achieve substantial diffusion. This arises because edge diffraction from the reflecting elements weakens at high frequencies. At frequencies where smaller elements are creating substantial scattering, larger elements are producing specular reflections. Furthermore, due to the lack of cancellation, the specular reflected lobe is insufficiently attenuated, because it can only be changed through absorption. Improvements to the original design are suggested. By changing reflective elements to reactive ones, scattering can be extended to higher frequencies. This allows for a range of frequencies were more reflecting elements display substantial dispersion. Also, implementing the absorbing elements using porous material in a shallow well allows some reflection, resulting in cancellation in the specular reflection lobe due to interference. Measurements of the scattered pressure distribution of absorption grating surfaces are carried out and then compared to Boundary Element Modelling simulations using surface admittance data measured in an impedance tube. The agreement between measurement and simulation is excellent proving the accuracy of this simulation method for these applications. The results show that the samples tested perform as two level Phase Grating Diffusers, with some energy loss, while their diffusion characteristics are shifted to lower frequencies. This arises because of the lower speed of sound in the porous medium. This implementation is shown to absorb 50% of the incident sound while the rest is scattered uniformly but only over a limited bandwidth.
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Greenwell, Andrew. "RIGOROUS ANALYSIS OF WAVE GUIDING AND DIFFRACTIVE INTEGRATED OPTICAL STRUCTURES." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4346.
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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.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
3
Hajibaratali, Babak. "Dynamics of Bragg Grating Solitons In Coupled Bragg Gratings With Dispersive Reflectivity." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/12080.
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We study dynamics of Bragg grating solitons in a system of linearly coupled Bragg gratings with Kerr nonlinearity. The effects of dispersive reflectivity on the behaviour of solitons in the system are investigated by solving the coupled mode equations numerically. Gap solitons, are found to exist throughout the bandgap of the structure. The system supports two types of symmetric and asymmetric solitons that can have any velocities from zero to the speed of light in the medium. At given soliton parameters a critical coupling coefficient is found above which only symmetric solitons exist. Below the critical point however, both types of gap solitons may exist at the same time. Linear forms of coupled mode equations are solved analytically. The results are in excellent agreement with the gap soliton tails. Also, using the linear analysis a condition is found for the solitons to have sidelobes in their tails. Stability of solitons are investigated using systematic simulations. Generally, when dispersive reflectivity is zero, asymmetric solitons are stable for ω≥0. While with increase of dispersive reflectivity the stable region expands into the negative frequencies. Symmetric solitons on the other hand are found to be stable where they exist on their own. Interactions of quiescent gap solitons in the model are studied numerically. The outcomes generally depend on the initial separation (Δx) and phase difference. However, when the dispersive reflectivity is small, Δx-dependence is very weak. Interactions are found to result in a number of outcomes including merger into a single quiescent soliton, destruction, formation of a bound state that eventually breaks up into two separating solitons, formation of two moving and one quiescent solitons, and repulsion. The most interesting outcomes of the collisions of counter-propagating in-phase moving solitons are merger and 2→3 transformation. On the contrary, out-of-phase collisions generally result in the repulsion of the pulses.
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Li, Lifeng. "Application of diffraction grating theory to analysis and fabrication of waveguide gratings." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184388.
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This dissertation includes three separate studies of related waveguide grating phenomena. These studies deal with a numerical improvement of the integral method of diffraction grating theory, the theoretical analysis of waveguide gratings, and fabrication techniques for photoresist grating masks. The first topic addresses the acceleration of the convergence of the integral kernels. To improve the performance of the integral method for calculating diffraction grating efficiencies, the convergence of the integral kernels is studied. A nonlinear sequence transformation, Levin's u-transformation, is successfully applied to accelerate the convergence of the integral kernels. The computer execution time saving is significant. The application details and many numerical examples are given. The second subject is the ray optics theory of waveguide grating analysis. To establish a linkage between the analysis of diffraction gratings and the analysis of waveguide gratings, a new rigorous ray optics theory is developed. It takes into account phase changes on diffraction, multiple diffraction processes, depletion of the incident guided wave, and lateral shifts. A general characteristic equation that determines the waveguide grating attenuation (coupling) coefficient is derived. The symmetry properties of grating diffraction are applied to waveguide grating analysis for the first time. Lateral shifts of optical rays at a periodically corrugated interface similar to the Goos-Haenchen shift at a planar interface are suggested. The third subject is the in situ control of the development of photoresist grating masks. The existing method for monitoring and modeling photoresist grating development are modified and extended to monitoring and modeling photoresist grating mask development. Experimental examples, detailed theoretical considerations, and computer simulations are presented.
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Barnier, Fabien. "Fibre Bragg grating techniques." Thesis, University of Hull, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322570.
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MORIKAWA, SERGIO RICARDO KOKAY. "TRIAXIAL BRAGG GRATING ACCELEROMETER." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=5413@1.
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AGÊNCIA NACIONAL DE PETRÓLEOTRANSMISSÃO DE ENERGIA ELÉTRICA S.A
Desde o final da década de 80 a indústria de fibras óticas têm passado por avanços consideráveis. Através de técnicas controladas, as fibras ópticas podem gerar sinais associados a uma vasta gama de grandezas físicas funcionando como sensores denominados de Sensores a Fibra Óptica (SFO s). Diversas técnicas podem ser empregadas para tal, e entre as existentes a baseada em redes de Bragg é a que mais tem se destacado. O interesse por transdutores empregando esta técnica se justifica pelas vantagens proporcionadas pelo uso da luz, tais como sua capacidade de multiplexação, boa relação sinal/ruído, medições a longas distâncias, imunidade a campos eletromagnéticos, ausência de faísca, entre outras. Neste trabalho buscou-se desenvolver um transdutor e uma técnica de medição baseada em sensores a rede de Bragg para medição de vibrações mecânicas. Um acelerômetro óptico triaxial é projetado e construído. Diferentes modelos foram testados em busca das características de desempenho desejadas. Simulações numéricas empregando o método dos elementos finitos auxiliaram na decisão por melhores desenhos para o transdutor. Resultados de testes experimentais e calibrações empregando um sistema de aquisição de sinais desenvolvido são mostrados. Medições de longa duração para avaliação de estabilidade do sistema e efeitos de temperatura também são apresentados.
Since the end of the 1980s, the fiber optics industry has experienced considerable advances. Through a number of controlled techniques, fiber optics can generate signals associated with a vast array of physical measures, working as sensors denominated Optical Fiber Sensors (OFS s). Many different techniques can be employed to achieve this objective. Among these, the one based on Bragg networks has received the greatest amount of attention. The interest in transducers employing this technique is justified by the advantages of using light, such as its multiplexing capability, good signal-to-noise ratio, possibility of long distance measurements, immunity to electromagnetic fields, and absence of sparks. In the present work, a transducer and measurement technique based on Bragg network sensors vibration are developed, in order to measure mechanical vibrations. A triaxial optical accelerometer is designed and built. Different models are tested in the search for the desired performance characteristics. Numerical simulations employing the finite element method help the decision making process for better transducer designs. Results from experimental and calibration tests using a newly developed signal acquisition system are presented. Long duration measurements to evaluate system stability and temperature effects are also shown.
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Anderson, Brian Benjamin. "Grating light reflection spectroscopy /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/8600.
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Aslund, Mattas L. "Bragg grating interference devices." Thesis, The University of Sydney, 2004. https://hdl.handle.net/2123/28157.
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This thesis is about novel components designed to enable low-cost optical
fiber networks. These networks constitute the global backbone of the in—
ternet and all other telecommunication. However, the available technologies
are much to expensive to be considered for home-users, so the optical fiber
networks only reach as far as the substations half—way to the home—user. Op—
tical fiber networks all the way to the home—users is potentially an immense
market, and there is a large interest from the industry in novel enabling
technologies.
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Gibson, Steven Ross. "KiwiSpec: The Design and Performance of a High Resolution Echelle Spectrograph for Astronomy." Thesis, University of Canterbury. Physics and Astronomy, 2013. http://hdl.handle.net/10092/8811.
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This document describes the design, analysis, construction and testing of KiwiSpec, a fibre-fed, high resolution astronomical spectrograph of an asymmetric white pupil design. The instrument employs an R4, 31.6 groove mm⁻¹ échelle grating for primary dispersion and a 725 lines mm⁻¹ volume phase holographic (VPH) based grism for cross-dispersion. Two versions of the prototype were designed and constructed: an 'in-air' prototype, and a prototype featuring a vacuum chamber (to increase the stability of the instrument).
The KiwiSpec optical design is introduced, as well as a description of the theory behind a cross-dispersed échelle spectrograph. The results of tolerancing the optical design are reported for alignment, optical fabrication, and optical surface quality groups of parameters. The optical windows of an iodine cell are also toleranced.
The opto-mechanical mounts of both prototypes are described in detail, as is the design of the vacuum chamber system. Given the goal of 1 m/s radial velocity stability, analyses were undertaken to determine the allowable amount of movement of the vacuum windows, and to determine the allowable changes in temperature and pressure within and outside of the vacuum chamber.
The spectral efficiency of the instrument was estimated through a predictive model; this was calculated for the as-built instrument and also for an instrument with ideal, high-efficiency coatings. Measurements of the spectral efficiency of various components of the instrument are reported, as well as a description of the measurement system developed to test the efficiency of VPH gratings. On-sky efficiency measurements from use of KiwiSpec on the 1-m McLellan telescope at Mt John University Observatory are reported.
Two possible exposure meter locations are explored via an efficiency model, and also through the measurement of the zero-order reflectivity of the échelle grating.
Various stability aspects of the design are investigated. These include the stability of the optical mounts with temperature changes, and also the effect of the expansion and contraction of the supporting optical tables. As well, the stability of the in-air prototype was determined through measurement of the movement of thorium-argon emission lines within spectra as the temperature, atmospheric pressure and relative humidity (naturally) varied. Current and planned testing for determining the stability of the vacuum chamber prototype is discussed.
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Roberts, Karl Anton. "Opponent processes in human motion perception : shear and compression sensitivity, induced motion and motion capture." Thesis, Brunel University, 1994. http://bura.brunel.ac.uk/handle/2438/5444.
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Sensitivity to differential motion components, shearing and compressive (opposed) motion, was examined. The hypothesis that the visual system contains local mechanisms specifically sensitive to these types of motion was tested. Stimuli consisted of two moving sinusoidal gratings. Sensitivity to shear and compression was compared with sensitivity for linear motion. Lower thresholds of motion and contrast sensitivities were obtained. Subjects were more sensitive to opposed than to non-opposed motion for a range of grating orientations and different grating spatial frequencies. However sensitivity for opposed motion decreased in the presence of a second added linear motion. The hypothesis of local shear and compression mechanisms was rejected in favour of antagonistic (opponent) interactions between local motion mechanisms. Motion capture was examined. Stimuli were made up of a circular test grating surrounded by another grating. Subjects were required to judge the direction of motion of the test grating. Experiments examined the effects on motion capture of: centre grating size; orientation of surround; relative contrast of centre and surround; plaids in the surround. Conditions favouring motion capture were: with the smallest centre grating; with surround and centre orientations within thirty degrees; with surround had higher contrast than the centre; and only when a plaid surround contained a component of similar orientation as the centre. For conditions of motion capture relative to those of no-capture, increased velocity thresholds for judging the centre direction were found. This was associated with a shift in the bias point between opposed directions with no change in overall sensitivity to motion. It is suggested that a cooperative network of local motion mechanisms featuring centre-surround opponency can account for all the results of this study.
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Harper, Kevin Randolph. "Theory, Design, and Fabrication of Diffractive Grating Coupler for Slab Waveguide." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd281.pdf.
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Hnatiuk, Heather Joanne. "Integrated linear diffraction grating spectrometer." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0021/NQ45000.pdf.
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Schultz, Stephen M. "High efficiency volume grating coupler." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/16899.
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Jafari, Amir. "Distributed etched diffraction grating demultiplexer." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107746.
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This doctoral thesis studies the concept of a distributed etched diffraction grating (DEDG) and presents a methodology to engineer the spectral response of the device. The design which incorporates a distributed Bragg reflector (DBR) at the facets of a conventional etched diffraction grating demultiplexer promises for a superior performance in multiple aspects. Where in a conventional etched diffraction grating, smooth vertical deep etched walls are required in order to realize a low insertion loss device; in the DEDG such requirement is significantly mitigated. Deep etched walls are replaced with shallowly etched diffraction grating facets followed by a DBR structure and as a result devices with significantly lower insertion loss are achievable. The feasibility of the application of DEDG as a wavelength demultiplexer was demonstrated through fabrication and characterization of a prototype device. The proof of concept device was fabricated using the state of the art deep UV optical lithography and reactive ion etching in a nano-photonic silicon-on-insulator (SOI) material platform. The fabricated device was then characterized in the lab. Furthermore, incorporation of the DBR structure at the facets of the conventional etched diffraction grating decouples the reflection and diffraction functionalities, rendering the DEDG suitable for spectral response engineering. According to the application, the output spectral response of the device can be tailored through careful design and optimization of the incorporated DBR. In this thesis, through numerical simulations we have shown that functionalities such as polarization independent performance and at top insertion loss envelop are viable. A methodology to engineer the spectral response of the DEDG is discussed in details.Cette thèse de doctorat examine le concept d'un réseau de diffraction gravé et distribué (DEDG) et présente une méthodologie pour concevoir la réponse spectrale de l'appareil. Cette conception qui incorpore un réflecteur de Bragg distribué (DBR)aux facettes d'un démultiplexeur conventionnel basé sur un réseau de diffraction gravé (RDG), promet une performance supérieure sur plusieurs aspects. Alors que dans un RDG conventionel, il faut des murs gravés qui soient verticals et profonds afin d'obtenir une faible perte d'insertion; dans le DEDG, une telle exigence est considérablement atténuée. Les murs profondément gravés sont remplacés par des facettes peu profonde, suivis par un DBR; par conséquent des appareils avec une perte d'insertion nettement inférieure sont réalisables. La faisabilité de l'application de DEDG comme un démultiplexeur de longueur d'onde a été démontré grace à la fabrication et la caractérisation d'un prototype. Un exemple de l'appareil a été fabriquéen utilisant la lithographie optique et la gravure ionique réactive sur une plateformede silicium sur isolant(SOI). L'appareil a été ensuite caractérisé dans le laboratoire. Par ailleurs, l'incorporation de la structure de DBR aux facettes du RDG conventionel découple la réflexion et la diffraction, rendant le DEDG approprié pour l'adaptationde la réponse spectrale. Selon l'application, la réponse spectrale de l'appareil peut etre adapté grace à une conception et une optimisation méticuleuses de la DBR incorporé. Dans cette thése nous avons démontré par des simulations numériques que des fonctionnalités telles que la performance indépendante de la polarisation et la performance uniforme en ce qui concerne la perte d'insertion sont réalisable. Une méthodologie pour adapter la réponse spectrale de la DEDG est discutée en détails.
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Veerasubramanian, Venkatakrishnan. "Applications of sidewalled grating resonators." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114418.
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Recent developments in cutting edge fabrication techniques have led to research focused oncombining multiple optical and electronic functionalities, and to the integration of variousactive and passive components onto a single die. Integrated optical devices using waveguidesare being developed to replace traditional free space propagating devices utilizinglenses and mirrors. Silicon based photonic integrated circuits (PIC) are being investigatedfor intra-board and board-to-board optical interconnection in high speed computing, andas transceivers in high speed optical communications. One of the major aspects in PICresearch is the miniaturization of passive devices performing various functions such as opticalfiltering, multiplexing, demultiplexing, wavelength routing, and optical isolation. Inthis thesis, we study and demonstrate the feasibility of using sidewalled gratings for opticalfiltering, wherein optical feedback is obtained by the interaction of the guided mode withperiodic index modulations realized vertically on the waveguide walls.A novel design based on a horizontal evanescent coupling scheme in sidewalled gratingresonators for realizing low reflection filters that reduces the need for isolators or circulatorsis presented and demonstrated. We utilize the narrowband filter response of aquarter wave shifted cavity to obtain transmission filters with 110 GHz bandwidth. A coupledcavity scheme wherein multiple identical cavities are coupled back-to-back to obtaintop-hat like filter response (with 50 dB/nm roll-off) is also demonstrated. Multichannelwavelength filters designed using sampled grating distributed Bragg reflectors (SG-DBR)is introduced, and a novel dual apodization method for realizing comb resonances withhigh side mode suppression ratio (SMSR) is discussed in detail. The apodized comb filtersare shown to exhibit channel spacing, bandwidth, and SMSRs within prescribed standardlimits. We also present through numerical simulations, the feasibility of employing sidewalledgratings as wavelength selective cavities in hybrid III–V silicon lasers, and in tunableevanescent lasers. Results on dimensional engineering of the cavity to obtain the requiredlasing wavelength and confinement factors are presented. All the devices being presentedin this thesis were fabricated using an inductively coupled plasma based dry etch processon a silicon-on-insulator (SOI) wafer, where the pattern transfer was done using e-beamlithography (EBL).Les développements récents dans les techniques de fabrication de pointe ont conduit à des recherches axées sur la combinaison de multiples fonctionnalités optiques et électroniques et à l'intégration de différents composants actifs et passifs sur une matrice unique. Des dispositifs optiques intégrés à l'aide de guides d'ondes sont en cours de développement pour remplacer les traditionnels dispositifs de propagation en espace libre qui utilisent des lentilles et des miroirs. Des circuits photoniques intégrés (PIC) à base de silicium sont à l'étude pour les connexions optiques à l'intérieur d'un circuit ou entre des circuits pour le traitement de donnée à haute vitesse et comme émetteurs-récepteurs dans les communications optiques à haut débit. L'un des aspects majeurs de la recherche sur les PIC est la miniaturisation des dispositifs passifs qui exercent des fonctions diverses telles que le filtrage optique, le multiplexage, le démultiplexage, le routage des longueurs d'onde et l'isolement optique. Dans cette thèse, nous étudions et démontrons la faisabilité d'utiliser des réseaux sur les parois d'un guide d'ondes pour le filtrage optique. Dans ces dispositifs, la rétroaction optique est obtenue par l'interaction du mode de propagation avec des modulations périodiques de l'index de réfraction réalisées à la verticale sur les parois du guide d'ondes.Une conception originale reposant sur un système de couplage évanescent horizontaldans les résonateurs à réseaux est présentée et démontrée pour la réalisation de filtres à faible réflexion qui réduit la nécessité d'utiliser des isolateurs ou des circulateurs. Nous utilisons la réponse à bande étroite d'une cavité quart d'onde décalée afin d'obtenir des filtres de transmission de 110 GHz de bande passante. Un système dans lequel plusieurs cavités identiques sont couplées en série pour obtenir un filtre avec une réponse chapeau haut de forme (avec 50 dB/nm d'affaiblissement) est également démontré. Des filtres de longueurs d'onde à multiple canaux conçus à l'aide de réflecteurs de Bragg à multiples réseaux (SGDBR) sont présentés et une nouvelle méthode d'apodisation double pour la réalisation de filtre en peigne avec une grande suppression des modes secondaires (SMSR) est discutée en détails. Les filtres en peigne apodisés présentés démontrent des espacements de canaux, des bandes passantes et des SMSRs dans les limites standard. Nous présentons également, pardes simulations numériques, la possibilité d'employer des réseaux sur les parois d'un guide d'ondes comme cavités sélectives de longueurs d'onde pour les lasers hybrides III–V sur silicium et les lasers évanescents accordables. Les résultats sur la détermination des dimensions de la cavité pour obtenir la longueur d'onde d'émission et les facteurs de confinement requis sont présentés. Tous les dispositifs présentés dans cette thèse ont été fabriqués en utilisant un procédé de gravure sèche à plasma couplé par induction sur un substrat de silicium sur isolant (SOI), où le transfert de motif a été fait en utilisant la lithographie par faisceau d'électrons (EBL).
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Nyairo, Kennedy Obare. "The multichannel grating cavity laser." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240058.
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Smith, Mark Anthony. "Grating interactions in photorefractive polymers." Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314312.
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Hallam, Benjamin Thomas. "Grating alignment of liquid crystals." Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312444.
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Fallon, Richard W. "Fibre Bragg grating strain sensors." Thesis, Aston University, 2000. http://publications.aston.ac.uk/15304/.
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The fabrication of in-fibre Bragg gratings (FBGs) and their application as sensors is reported. The strain and temperature characteristic results for a number of chirped and uniform gratings written into three different host fibres are presented. The static and dynamic temperature response of a commercially available temperature compensated grating is reported. A five sensor wavelength division multiplexed fibre Bragg grating strain measurement system with an interrogation rate of 25 Hz and resolution of 10 was constructed. The results from this system are presented. A novel chirped FBG interrogation method was implemented in both the 1.3 and 1.5 m telecommunication windows. Several single and dual strain sensor systems, employing this method, were constructed and the results obtained from each are reported and discussed. These systems are particularly suitable for the measurement of large strain. The results from a system measuring up to 12 m and with a potential measurement range of 30 m are reported. This technique is also shown to give an obtainable resolution of 20 over a measurement range of 5 000 for a dual sensor system. These systems are simple, robust, passive and easy to implement. They offer low cost, high speed and, in the case of multiple sensors, truly simultaneous interrogation. These advantages make this technique ideal for strain sensing in SMART structures. Systems based on this method have been installed in the masts of four superyachts. A system, based on this technique, is currently being developed for the measurement of acoustic waves in carbon composite panels. The results from an alternative method for interrogating uniform FBG sensors are also discussed. Interrogation of the gratings was facilitated by a specifically written asymmetric grating which had a 15 nm long linearly sloped spectral edge. This technique was employed to interrogate a single sensor over a measurement range of 6 m and two sensors over a range of 4.5 me. The results obtained indicated achievable resolutions of 47 and 38 respectively.
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Triggs, Graham J. "Resonant grating surfaces for biosensing." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/13210/.
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Optical biosensors make up a valuable toolkit for label-free biosensing. This thesis presents a detailed study on resonant grating surfaces for biosensing. The focus is on silicon nitride gratings, which exhibit a guided-mode resonance that is highly sensitive to refractive index variations in the vicinity of the grating. A sensitivity of 143 nm/RIU (refractive index units) is measured, leading to a detection limit of 2.4×10−4 RIU. This performance is shown to be sufficient for the detection of biomolecular binding down to ng/mL concentrations. With out-of-plane excitation, these gratings can be used as a sensing surface, enabling a spatially-resolved measurement of variations in refractive index; resonance imaging. The minimum detection distance (sensing depth) is measured to be 183 nm away from the grat- ing, while the spatial resolution of resonance imaging is found to be asymmetric: 2 μm parallel to, or 6 μm perpendicular to the gratings. Using a novel approach of fabricating a resolution test pattern on top of the grating, the relationship between resolution and index contrast is studied - an important question in the context of biosensing - where it is found to decrease with index contrast. All experimental results are supplemented with theoretical and computational models. The resonant gratings are then extensively applied to the study of biofilm development, cellular imaging, and the imaging of cellular secretion. Finally, a miniaturised biosensor is demonstrated, based on a chirped resonant grating. By tuning the resonance wavelength spatially on the chip, the resonance information is directly translated into spatial informa- tion. Instrument read-out requires just a monochromatic light source and a simple CCD camera, resulting in a final device that is inexpensive, compact, robust and can be remotely operated. Performance is proven with successful detection of biomolecular binding.
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DeRoo, Casey T. "Fabrication and testing of off-plane gratings for future X-ray spectroscopy missions." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2067.
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Soft X-ray spectroscopy is a useful observational tool, offering information about high-temperature (10⁶ -- 10⁷ K) astrophysical plasmas and providing useful characterizations of a number of energetic systems, including accreting young stars, cosmic filaments between galaxies, and supermassive black holes. In order to yield high resolution spectra with good signal-to-noise, however, soft X-ray spectrometers must realize improvements in resolving power and effective area through the development of high performance gratings. Off-plane reflection gratings offer the capability to work at high dispersions with excellent throughput, and are a viable candidate technology for future X-ray spectroscopy missions. The off-plane geometry requires a customizable grating meeting distinct fabrication requirements, and a process for producing gratings meeting these requirements has been developed. These fabricated gratings have been evaluated for performance in terms of resolution and diffraction efficiency. Furthermore, these gratings have been conceptually implemented in a soft X-ray spectrometer, the Off-Plane Grating Rocket Experiment (OGRE), whose optical design provides a template for future missions to achieve high performance within a small payload envelope.
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Rabady, Rabi Ibrahim. "Waveguide grating mirror for laser resonators." Connect to online resource - WSU on-site and authorized users, 2003.
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Xu, Yanping. "Fiber Random Grating and Its Applications." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36597.
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Femtosecond (fs) laser micromachining has been a useful technique either to modify and remove materials or to change the properties of a material, and can be applied to transparent and absorptive substances. Recently high-power fs laser radiation has drawn intensive attention for the induction of refractive index change to fabricate micro-structures in dielectric materials. This thesis studies the optical properties of a novel fiber random grating fabricated by fs laser micromachining technique and extends its applications from optical sensing to random fiber lasers and optical random bit generations.
The thesis mainly consists of three parts. In the first part, the physical mechanism behind the fs laser micromachining technique and the fabrication of the fiber random grating are introduced. By employing a wavelength-division spectral cross-correlation algorithm, a novel multi-parameter fiber-optic sensor based on the fiber random grating is proposed and demonstrated to realize simultaneous measurements of temperature, axial strain, and surrounding refractive index.
In the second part, Brillouin random fiber laser (BRFL) and Erbium-doped fiber random laser (EDFRL) are introduced, respectively. Firstly, we propose a novel Brillouin random fiber laser with a narrow linewidth of ~860 Hz based on the bi-directionally pumped stimulated Brillouin scattering (SBS) in a 10-km-long optical fiber. A random fiber Fabry-Perot (FP) resonator is built up through the pump depletion effects of SBS at both ends of the fiber. The novel laser is successfully applied for linewidth characterization beyond 860 Hz of light source under test. Secondly, the random grating-based FP resonator is introduced to build up a novel BRFL with narrow-linewidth of ~45.8Hz and reduced lasing threshold. The intensity and frequency noises of the proposed random laser are effectively suppressed due to the reduced resonating modes and mode competition. Finally, the fiber random grating is used as random distributed feedback in an EDFRL to achieve both static (temperature, strain) and dynamic (ultrasound) parameter sensing. Multiple lasing lines with high signal-to-noise ratio (SNR) up to 40dB are achieved, which gives an access for a high-fidelity multiple-static-parameter sensing application. By monitoring the wavelength shifts of each peak, temperature and strain have been simultaneously measured with small errors. The fiber random grating in the EDFRL is also able to sense the ultrasound waves. By achieving single mode lasing with the EDFRL, ultrasound waves with frequencies from 20kHz to 0.8MHz could be detected with higher sensitivity and SNR improvement up to 20dB compared with conventional piezoelectric acoustic sensors.
In the third part, we demonstrate that a semiconductor laser perturbed by the distributed feedback from a fiber random grating can emit light chaotically without the time delay signature (TDS). A theoretical model is developed by modifying the Lang-Kobayashi model to numerically explore the chaotic dynamics of the laser diode subjected to the random distributed feedback. It is predicted that the random distributed feedback is superior to the single reflection feedback in suppressing the TDS. In experiments, The TDS with the maximum suppression is achieved with a value of 0.0088, which is the smallest to date.
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Sun, Zhijian. "Demultiplexer based on integrated concave grating." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq32024.pdf.
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Watts, Duncan Joseph Michael. "Circular, grating-coupled, surface-emitting lasers." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342904.
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Chuang, Chin-Jung. "Proximity projection grating structured illumination microscopy." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12262/.
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Structured illumination has been employed in fluorescence microscopy to extend its lateral resolution. It has been demonstrated that a factor of 2 improvement can be achieved. In this thesis, we introduce a novel optical arrangement, which we call Proximity Projection Grating Structure Illumination Microscopy (PGSIM). Although the method is based on the original structured illumination, the present technique can further improve the lateral resolution of the microscope. The technique makes use of a fine grating held in close proximity to the sample, with a layer of high refractive index optical thin film sandwiched between the two. The fringe pattern thus projected onto the sample contains grating vectors substantially higher than those that are possible with the original structured illumination setup. The presence of these very high grating orders is the basis for the significant improvement in the system resolution. In this thesis, the principle behind the PGSIM will be explained. The optical system used to demonstrate the technique will be described, with particular attention paid towards the construction and alignment of the unit containing the fine grating. Experimental results will be presented to demonstrate the characteristics of the grating unit and the operation of the system. Further results obtained with the system applied to fine particles will be given, showing the resolution improvement of greater than a factor of 2 compared to a conventional optical microscope. The thesis also contains detailed analysis of the performance of the system. From this analysis, it is concluded that greater resolution improvement can be achieved by using appropriate material for the optical thin film.
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Iqbal, Tahir. "Nanoplasmonic grating coupler for transducer applications." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602547.
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This thesis investigates the excitation of surface plasmon polaritons (SPPs) on a one dimensional (ID) grating etched in a gold film on a (high-index) gallium phosphide (GaP) substrate. The experimental component of the work addresses the design and building of an optical set-up for the far-field characterization of the spatially confined (-20 x 20μm) gratings in transmission, with better than 2° angular resolution, and the commissioning and use of a WiTec scanning near-field optical microscope (with bespoke modification) for near-field analysis. The purpose of the latter is to track the propagation of SPPs on the planar gold film region beyond the grating launch site. Both the far- and near-field experimental data are interpreted with reference to modelled results generated by using COMSOL, a commercial, finite-element analysis software package. Coupling efficiency of the incident light to the SPP is studied as a function of slit width where the grating periodicity and the (optimized) gold thickness remain constant. Defining a simple and convenient measure of the coupling efficiency the optimum slit width is found to be between 1/3 and 1/2 of the grating period. Such grating devices support only the fundamental mode and offer less radiative scattering of SPPs. The experimental results are in agreement with the far-field modelling results and the optimum slit-width range in the grating devices is close to that suggested by near-field analysis. The (maximum) propagation length, Lspp, just outside the grating device is found to be -13.33 ± 0.13μm under excitation by laser light of 785 nm wavelength. The Lspp is associated with the full width at half maximum (FWHM) of the SPP resonance. The grating on high refractive index substrate described above has intended application in heat assisted magnetic recording where it is envisaged that the focussing of optical energy to nanoscale dimensions will take place using SPPs generated by using a grating coupler integrated on a semiconductor laser chip. In addition, an optimal 1 D grating was designed and fabricated on a 50 nm Au film on a (low-index) glass substrate for application as a highly sensitive biosensor. The sensitivity was found to be 524 nm per refractive index unit (RIU) which is highly competitive with many other plasmon-based biosensors while being of simpler geometrical structure and more economical design.
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Mokhtar, Mohd Ridzuan. "Bragg grating filters for optical networks." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/15462/.
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This thesis focuses on the exploitation of fibre Bragg gratings in optical communication networks. New designs, as well as procedures for dynamically altering grating characteristics are proposed for several important functions. We begin with designing gratings for flattening the gain profile of an erbium-doped fibre amplifier. The design process uses an alternative method to the inverse scattering method, but produces a similar spectral response quality. These gratings have either modulated refractive index or chirp rate. Then, we propose a reconfigurable phase-code encoder. The device is composed of a uniform grating, with a number of equidistant fine wires for the purpose of modulating the phase via the thermo-optic effect. Error free data transmission is demonstrated in several optical code-division multiple access architectures. The characteristics of the device are also theoretically modelled. Next, we construct a simple package for continuous tuning of fibre gratings, which adopts the beam bending technique. It demonstrates over 110 nm tuning range and the operational wavelength can be accurately predicted. Its spectral response and limitations are also studied. This device has been incorporated into several optical systems, which include tunable distributed feedback fibre laser, add-drop multiplexer and high power fibre laser. Finally, we present a package for varying the dispersion of a fibre grating. The package deforms a beam into a cubic function shape with a contra-flexure point at the middle. Consequently, this allows changes in the grating delay characteristic without shifting its centre wavelength. This device has achieved dispersion compensation of an 80 km non-zero dispersion-shifted fibre in a 10 Gb/s system. Additionally, since its bandwidth also changes with the stress gradient, it has also been utilised as a bandwidth-variable bandpass filter at the receiving terminal of a spectrum-sliced wavelength-division multiplexed system.
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Yeung, Wings T. "Accurate characterization of nanophotonic grating structures." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129848.
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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, February, 2020Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (page 75).
Augmented reality waveguides are designed to have grating regions to in-couple, out-couple, and propagate light from a light engine to the user. This thesis develops two reliable systems to qualify manufactured waveguides. The first system determines grating quality by measuring grating pitch and orientation uniformity across grating regions. The system uses scatterometry in Littrow configuration and captures both the reflected zeroth and first order diffracted light. The second system determines the overall quality of a waveguide by measuring the resolution of the device using a Modulation Transfer Function, MTF, technique. MTF is commonly measured using either the line pair method or the slant edge method. This thesis proposes a new method to measure MTF using single pixel illumination and point spread function. Results from the two systems are presented, and the capabilities and limitations of each system are explored.
by Wings T. Yeung.
M. Eng.
M.Eng. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
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Johnson, Ian Paul. "Grating devices in polymer optical fibre." Thesis, Aston University, 2012. http://publications.aston.ac.uk/18094/.
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This thesis presents the fabrication of fibre Bragg gratings (FBGs) and long period gratings (LPGs) in polymer optical fibre (POF). Possible fabrication techniques were discussed to fabricate FBGs in polymer optical fibre including a detailed description of the phase mask inscription technique used to fabricate FBGs in both single and multi mode microstructured polymer optical fibre (mPOF). Complementing the fabrication of polymer optical fibre Bragg gratings (POFBGs), a technique has been developed to permanently splice POF to silica optical fibre with the use of an optical adhesive. This allowed for the fabricated POFBGs to be characterised away from the optical table, allowing for application specific characterisation. Furthermore Bragg gratings have been fabricated in polymer POF with a Bragg response within the 800nm spectral region. Within this spectral region, POF predominantly manufactured from PMMA experiences considerably smaller attenuation losses when compared to the attenuation losses within the 1550nm spectral region. The effect of thermally annealing fabricated POFBGs has been studied. This included demonstrating the ability to tune the Bragg wavelength of a POFBG sensor to a desired wavelength. Thermal annealing has also been used to manufacture wavelength division multiplexed sensors with the use of a single phase mask. Finally POFBGs have been fabricated in Topas Cyclic Olefin Copolymer. Fabrication of Bragg gratings within this copolymer allowed for the first demonstration of near immunity to relative humidity whilst monitoring changes in temperature of the environment the POFBG sensor was in. Bragg gratings fabricated in the Topas copolymer demonstrated sensitivity to relative humidity which was 65 times less than that of a PMMA based POFBG sensor. This decrease in sensitivity has the potential to significantly reduce the potential of cross sensitivity to relative humidity whilst being employed to monitor measurands such as temperature and axial strain.
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Stanford, Christopher J. "Highly sensitive fiber bragg grating biosensors." College Park, Md.: University of Maryland, 2008. http://hdl.handle.net/1903/8988.
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Thesis (M.S.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of Electrical and Computer Engineering . Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Aikio, Mauri. "Hyperspectral prism-grating-prism imaging spectrograph /." Espoo [Finland] : Technical Research Centre of Finland, 2001. http://www.vtt.fi/inf/pdf/publications/2001/P435.pdf.
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Diéguez, Moure Lorena. "Optical grating coupler biosensor and biomedical applications." Doctoral thesis, Universitat de Barcelona, 2012. http://hdl.handle.net/10803/101149.
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Biosensors are nowadays a powerful tool to enable the detection of specific biological interactions and to evaluate the concentration dependence in the response. A biosensor usually consists of three different parts: the sample to be measured, the transducer and the electronic system that amplifies the signal, analyzes the data and brings a result to the final user. The transducer includes the bioreceptor (which specifically interacts with the sample) and the interface that transforms the recognition from the bioreceptor into a measurable signal. When the analyte interacts with the bioreceptor, the transducer sends a signal that is processed by the electronics. All this process occurs in an efficient, quick, cheap, easy, simple and specific way. Regarding the type of the transductor, the biosensors can be electrochemical, optical, acoustic, magnetic or thermometric; but overall the most powerful ones are the optical biosensors, and among them the grating coupler. As a technique for investigating processes at the solid/liquid interface, presents high mechanical stability, immunity to electromagnetic interferences and pushes the sensitivity to levels even higher than other techniques and allows for the direct monitoring of macromolecular adsorption. Taking advantage of the last advances in nanotechnology, the goal of this thesis is to study the versatility of an Optical Grating Coupler Biosensor. The design of new grating sensor chips will be investigated, a new calibration technique for the sensors will be proposed and, taking advantage of the technique, different biomedical scenarios will be tested.Esta tesis consiste en el diseño, fabricación y test de un Biosensor Óptico basado en redes de difracción y sus aplicaciones en biomedicina. Los biosensores ópticos son dispositivos que detectan interacciones biomoleculares específicas mediante un transductor óptico. Exhiben alta sensibilidad, alta estabilidad mecánica, son inmunes a las interferencias electromagnéticas y permiten medidas no destructivas. En los Biosensores Ópticos por Onda Evanescente un modo guiado se propaga a lo largo de la guía de ondas mientras que la onda evanescente interactúa con la superficie del sensor, reconociendo cualquier interacción biomolecular que provoque una modificación en el índice de refracción efectivo de la guía óptica. En este caso, la inserción de luz láser en la guía óptica se produce con ayuda de una red de difracción grabada en la superficie del sensor. Para un ángulo muy preciso se excita un modo guiado. Como consecuencia de las reacciones en la superficie se produce un cambio en el ángulo de acoplo. La medida en tiempo real del ángulo de acoplo, en función de la actividad bioquímica en la superficie es la base de este tipo de biosensor óptico. El objetivo es fabricar sensores de bajo coste en polímero y también en distintos materiales que permitan calibrar otras técnicas. Otro objetivo de esta tesis es la calibración de los sensores y de las distintas soluciones buffer comúnmente usadas en biosensado. Como aplicación, se ha usado un equipo comercial (Optical Waveguide Lightomode Spectroscopy, OWLS, MicroVacuum) para estudiar, mediante control electroquímico, el crecimiento y la liberación de multicapas de PLL/DNA para aplicaciones en administración de fármacos. También se ha usado el OWLS para optimizar la inmovilización de receptores olfativos en un dispositivo biosensor para el desarrollo de una nariz bioelectrónica.
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Henkel, Carsten, Jean-Yves Courtois, and Alain Aspect. "Atomic diffraction by a thin phase grating." Universität Potsdam, 1994. http://opus.kobv.de/ubp/volltexte/2010/4226/.
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We present a semiclassical perturbation method for the description of atomic diffraction by a weakly modulated potential. It proceeds in a way similar to the treatment of light diffraction by a thin phase grating, and consists in calculating the atomic wavefunction by means of action integrals along the classical trajectories of the atoms in the absence of the modulated part of the potential. The capabilities and the validity condition of the method are illustrated on the well-known case of atomic diffraction by a Gaussian standing wave. We prove that in this situation the perturbation method is equivalent to the Raman-Nath approximation, and we point out that the usually-considered Raman-Nath validity condition can lead to inaccuracies in the evaluation of the phases of the diffraction amplitudes. The method is also applied to the case of an evanescent wave reflection grating, and an analytical expression for the diffraction pattern at any incidence angle is obtained for the first time. Finally, the application of the method to other situations is briefly discussed.
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Shams-Zadeh-Amiri, Ali M. "Modeling of circular-grating surface-emitting lasers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0023/NQ30644.pdf.
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Rausch, Kameron Wade. "Broadband Arrayed Waveguide Grating Multiplexers on InP." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1319%5F1%5Fm.pdf&type=application/pdf.
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Park, Jung Won. "Fast spinning-top dynamics of photorefractive grating /." Available to subscribers only, 2006. http://proquest.umi.com/pqdweb?did=1140193991&sid=24&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Lam, Suk Yee. "Gain grating techniques in solid state dyes." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420431.
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Lin, John Chin-Hsiang. "Integrated optical sensors using waveguide grating reflectors." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239280.
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Chan, Gordon Siu Fan. "Vertical grating assisted coupling between waveguide layers." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282414.
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Stevens, Robert Edward. "Laser-induced grating techniques for combustion diagnostics." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413212.
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Nash, David James. "Grating and prism coupling to surface plasmons." Thesis, University of Exeter, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337803.
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Chen, Zhuo. "Grating coupled surface plasmons in metallic structures." Thesis, University of Exeter, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441770.
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KAWASE, LILIANA ROCHA. "BRAGG GRATING IN OPTICAL FIBERS AND APPLICATIONS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1997. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8454@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINANCIADORA DE ESTUDOS E PROJETOS
O objetivo principal deste trabalho foi o de estudar as redes de Bragg em fibras ópticas e suas principais aplicações, com especial interesse na compensação de dispersão de pulsos ópticos em sistemas de telecomunicações, onde uma implementação original foi construída. Faz-se uma revisão geral das técnicas existentes para fabricá-las e caracterizá-las, além de suas principais aplicações, não somente na área de telecomunicações mas também na área sensoriamento óptico. São mostrados os resultados experimentais obtidos nas montagem realizadas para escrever redes de Bragg em fibras ópticas e para caracterizá-las. Algumas experiências usando redes de Bragg para o controle do comprimento de onda de emissão de um laser de semicondutor e para medição de força aplicada numa estrutura são mostradas. São mostrados também os resultados experimentais inéditos obtidos com a compensação de dispersão de pulsos ópticos em enlaces de telecomunicações, onde várias montagens foram realizadas para comprovar a superioridade da utilização da redes de Bragg para esse fim. Demonstra-se também um sistema para gerar pulsos solitônicos sintonizável em comprimento de onde numa faixa de MHZ. Finalmente são mostrados os resultados obtidos com a utilização de fibras ópticas para chaveamento interferométrico de luz. Neste sistema são utilização como elemento óptico não linear fibras tipo D, com e sem redes de Bragg, revestidas com filme de materiais semicondutores amorfos.
Bragg grating in optical fibers are used to compensate the dispersion of optical pulses in telecommunication systems. Initially, an overview is presented of the existing fabrication techniques of such gratings, as well as the techniques used for characterization. Some useful applecations in telecommunications and sensing are also shown. The results obtained in the set-up to write and to characterize Bragg gratings are presented. Some measurements were also done with typical applications such as controlling the emitting wavelength in semiconductors lasers, and monitoring the applied pressure in an optical fiber. Some new results are described on dispersion compensation in fibers. Using specially chirped Bragg gratings to pre- compensatedispersion of an optical pulse in a 80 km fiber link, we demonstrated that the poor quality of the input laser pulses has little impact on the duration of the pulses recovered after transmission. Finally, an interferometric switching arrangement using a semiconductor coated D fiber as nonlinear control element, is presented. The configuration uses infrared optical pulses to control a continuous wave light signal. It is also shown that the original reflected wavelength of a semiconductor coated D-fiber with Bragg grating can be shited with an external optical control signal.
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Vassilopoulos, Christos Elia. "Fibre grating reflectors and backward-wave couplers." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/46860.
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Park, Ray J. "Multi-Grating Demultiplexer Utilizing Chirped Grating." Thesis, 2005. http://hdl.handle.net/10125/10454.
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Praveen, A. Vishnu. "Investigation of Multi-Axis Beam Steering using Diffraction Grating." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4419.
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Optical beam-steering is becoming a key optical functionality in free space optical links used for communication and sensing. For example, in recent times, compact, wide-angle, fast, multi-axis beam steering is used extensively for LiDAR system in automotive vehicles, remote sensing platforms and deep-space optical communication. The state-of-the-art beam steering optics are typically based on mechanical, optical and/or electronic array designs. The present work investigates alternate schemes to perform multi-axis beam steering using one-dimensional diffraction gratings. Various schemes to perform multi-axis steering utilizing spectral scanning, pitch tuning and grating azimuthal rotation are discussed.
More specifically, rigid silicon nitride gratings on glass substrate are designed for polarization-independent, spectrally scanned steering. The silicon nitride structures are optimized to achieve high diffraction efficiency for both linear polarizations by interfacing MATLAB based Genetic Algorithm Optimization and Lumerical FDTD based optical simulations. The dynamic steering is studied by varying the wavelength of incidence beam and azimuthal rotation of the grating about the normal to the grating. In diffraction gratings, the change in wavelength has the same effect as the change in pitch of the grating. Thereby flexible silicone material, Polydimethylsiloxane (PDMS) based grating is designed and optimized for polarization insensitive, high diffraction efficiency into a particular order and simulated for pitch tuning and azimuthal rotation. Lastly, experimental study of multi-axis beam steering using glass blazed gratings by incorporating spectral scanning and azimuthal rotation is discussed.
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Mahesh, Kondiparthi. "Novel Methods To Interrogate Fiber Bragg Grating Sensors." Thesis, 2010. https://etd.iisc.ac.in/handle/2005/1926.
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A novel detection technique to estimate the amount of chirp in fiber Bragg gratings (FBGs) is proposed. This method is based on the fact that reflectivity at central wavelength of FBG reflection changes with strain/temperature gradient (linear chirp) applied to the same. Transfer matrix approach was used to vary different grating parameters (length, strength and apodization) to optimize variation of reflectivity with linear chirp. Analysis is done for different sets of ‘FBG length-refractive index strength’ combinations for which reflectivity vary linearly with linear chirp over a decent measurement range. This work acts as a guideline to choose appropriate grating parameters in designing sensing apparatus based on change in reflectivity at central wavelength of FBG reflection.
A novel high sensitive FBG strain sensing technique using lasers locked to relative frequency reference is proposed and analyzed theoretically. Static strain on FBG independent of temperature can be measured by locking frequency of diode laser to the mid reflection frequency of matched reference FBG, which responds to temperature similar to that of the sensor FBG, but is immune to strain applied to the same. Difference between light intensities reflected from the sensor and reference FBGs (proportional to the difference between respective pass band gains at the diode laser frequency) is not only proportional to the relative strain between the sensor and reference FBGs but also independent of servo residual frequency errors. Usage of relative frequency reference avoids all complexities involved in the usage of absolute frequency reference, hence, making the system simple and economical. Theoretical limit for dynamic and static strain sensitivities
considering all major noise contributions are respectively of the order of 25 pε/ Hz and
1.2nε /
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Mahesh, Kondiparthi. "Novel Methods To Interrogate Fiber Bragg Grating Sensors." Thesis, 2010. http://etd.iisc.ernet.in/handle/2005/1926.
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A novel detection technique to estimate the amount of chirp in fiber Bragg gratings (FBGs) is proposed. This method is based on the fact that reflectivity at central wavelength of FBG reflection changes with strain/temperature gradient (linear chirp) applied to the same. Transfer matrix approach was used to vary different grating parameters (length, strength and apodization) to optimize variation of reflectivity with linear chirp. Analysis is done for different sets of ‘FBG length-refractive index strength’ combinations for which reflectivity vary linearly with linear chirp over a decent measurement range. This work acts as a guideline to choose appropriate grating parameters in designing sensing apparatus based on change in reflectivity at central wavelength of FBG reflection.
A novel high sensitive FBG strain sensing technique using lasers locked to relative frequency reference is proposed and analyzed theoretically. Static strain on FBG independent of temperature can be measured by locking frequency of diode laser to the mid reflection frequency of matched reference FBG, which responds to temperature similar to that of the sensor FBG, but is immune to strain applied to the same. Difference between light intensities reflected from the sensor and reference FBGs (proportional to the difference between respective pass band gains at the diode laser frequency) is not only proportional to the relative strain between the sensor and reference FBGs but also independent of servo residual frequency errors. Usage of relative frequency reference avoids all complexities involved in the usage of absolute frequency reference, hence, making the system simple and economical. Theoretical limit for dynamic and static strain sensitivities
considering all major noise contributions are respectively of the order of 25 pε/ Hz and
1.2nε /
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Cheng, Sheng-Tai, and 程聲泰. "Analysis of Grating-assisted Directional Couplers with Arbitrary Grating Profiles." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/00812574845570690057.
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碩士義守大學
電機工程學系
89
The purpose of the thesis is to analyze the coupling properties of grating-assisted directional couplers(GADC) with arbitrary grating profiles. From the papers reviewed, studies of GADC were based on rectanguler corrugations. In this thesis, we propose five different shapes of grating structures including rectanguler, triangular, parallelogram, trapezium and sinusoidal corrugations, and design GADC with arbitrary shapes by various duty cycles. Coupling conditions, coupling length and coupling efficiency for five structures of gratings were compared with each other. We hope that this study is helpful in fabrication of couplers devices.