Letteratura scientifica selezionata sul tema "Coupled waveguides"

La integració de tots els components bàsics per a la generació, manipulació i detecció de llum en xips òptics està impulsant avenços científics i tecnològics, per exemple, en el desenvolupament de tecnologies de la informació o de dispositius de detecció per a les tecnologies quàntiques. Degut a la seva flexibilitat, escalabilitat i la possibilitat d’observar directament l’evolució de la funció d’ona utilitzant senzilles tècniques de tractament d’imatges, les estructures fotòniques integrades són una plataforma ideal per a la simulació quàntica, és a dir, per emular fenòmens quàntics que apareixen en altres branques de la física. A més, aquestes analogies òptiques-quàntiques també permeten dissenyar circuits fotònics integrats amb propietats excepcionals. En aquesta tesi aprofitem propietats no trivials de la física quàntica per dissenyar nous dispositius fotònics integrats amb funcionalitats avançades i rendiments millorats, així com nous simuladors fotònics. Específicament, explotem les similituds entre les equacions de Helmholtz i de Schrödinger, que permeten reproduir la dinàmica temporal d’una partícula atrapada en un potencial periòdic amb l’evolució espacial de la llum propagant-se en guies d’ona acoblades, per aplicar transformacions supersimètriques i processos adiabàtics així com explorar geometries topològiques no trivials en sistemes de guies d’ona òptiques acoblades. En aquesta línia, la primera part de la tesi està dedicada a introduir els conceptes físics i matemàtics que descriuen les guies d’ona òptiques acoblades, les analogies òptiques-quàntiques i la supersimetria en òptica. La segona part de la tesi engloba el disseny de nous dispositius fotònics integrats combinant l’aplicació de transformacions supersimètriques per manipular modes espacials amb tècniques de passatge adiabàtic per introduir la robustesa. Primer presentem un nou mètode per a la multiplexació de modes espacials basat en guies d’ona supersimetriques, que filtren els modes, en combinació amb la tècnica de passatge adiabàtic espacial que es fa servir per transmetre eficient i robustament els modes escollits entre guies. De manera similar, mantenint-nos en la idea d’aplicar protocols d’enginyeria quàntica per dissenyar nous dispositius fotònics amb rendiments millorats, proposem connectar de manera adiabàtica estructures supersimètriques al llarg de la distància de propagació. En particular, aquesta tècnica l’utilitzem per dissenyar guies d’ona còniques, filtres de modes, divisors de feixos i interferòmetres, eficients i robustos. Finalment, la tercera part de la tesi està dedicada a la simulació de diferents fenòmens quàntics utilitzant sistemes fotònics. Per començar aquesta part, explorem els efectes que les transformacions supersimètriques indueixen en sistemes amb propietats topologies no trivials, les quals estan intrínsecament lligades a les simetries internes del sistema. Amb aquest objectiu, considerem el sistema més simple amb propietats topològiques no trivials i demostrem en sistemes de guies d’ona acoblades com la protecció topològica d’un estat pot ser suspesa i restablerta utilitzant transformacions supersimètriques. A més, per accedir a aquestes fases topològiques no trivials, un element clau és la introducció de camps artificials gauge (AGF) que controlen la dinàmica de partícules no carregades que d’una altra manera eludeixen la influència dels camps electromagnètics estàndards. En aquesta línia, investiguem la possibilitat d’induir AGF utilitzant llum amb moment orbital angular en comptes de manipular la geometria del sistema. Específicament, mesurem l’efecte de gàbia d’Aharonov-Bohm que està lligat amb la presència d’un camp magnètic. Aquesta tècnica permet accedir a diferent règims topològics en una sola estructura, un pas important per a la simulació quàntica utilitzant sistemes fotònics.<br>La integración de todos los componentes básicos para la generación, manipulación y detección de luz en chips ópticos está impulsando avances científicos y tecnológicos, por ejemplo, en el desarrollo de tecnologías de la información o en los dispositivos de detección para las tecnologías cuánticas. Debido a su flexibilidad, escalabilidad y a la posibilidad de observar directamente la evolución de la función de onda utilizando senzillas técnicas de trata, las estructuras fotónicas son ideales para la simulación cuántica, es decir, para emular fenómenos cuánticos que aparecen en otras ramas de la física. Es más, estas analogías ópticas-cuánticas también permiten diseñar nuevos circuitos fotónicos integrados con propiedades excepcionales. En esta tesis, aprovechamos propiedades no triviales que emergen de la física cuántica para diseñar nuevos dispositivos fotónicos integrados con funcionalidades avanzadas y rendimientos mejorados, así como nuevos simuladores fotónicos. Específicamente, explotamos las similitudes entre las ecuaciones de Helmholtz y de Schrödinger, que permiten reproducir la dinámica temporal de una particula atrapada en un potencial periódico con la evolución espacial de la luz propagándose en guías de onda, para aplicar transformaciones supersimétricas y procesos adiabáticos así como explorar geometrías topológicas no triviales en sistemas de guías de onda ópticas acopladas. La primera parte de la tesis está dedicada a introducir los conceptos matemáticos y físicos que describen las guías de onda ópticas acopladas, las analogías ópticas-cuánticas y la supersimetria óptica. La segunda parte de la tesis engloba el diseño de nuevos dispositivos fotónicos integrados basados en combinar transformaciones supersimétricas para manipular los modos espaciales con las técnicas adiabáticas para introducir robustez. Primero presentamos un nuevo método para la multiplexación de modos espaciales basado en guías de onda supersimétricas, que filtran los modos, en combinación con la técnica de pasaje adiabático espacial que se usa para transmitir de manera eficiente y robusta los modos escogidos entre guías. De manera similar, manteniéndonos en la idea de aplicar protocolos de ingeniería cuántica para diseñar nuevos dispositivos fotónicos con rendimientos superiores, proponemos conectar de manera adiabática estructuras supersimétricas a lo largo de la propagación. En particular, ésta técnica la utilizamos para diseñar guías de onda cónicas, filtros modales, divisores de haz e interferómetros. Finalmente, la tercera parte de la tesis está dedicada a la simulación de diferentes fenómenos físicos utilizando sistemas fotónicos. Para empezar, exploramos los efectos que las transformaciones supersimétricas inducen en sistemas con propiedades topológicas no triviales, las cuales están intrínsecamente ligadas a las simetrías internas del sistema. Con este objetivo, consideramos el sistema más simple con propiedades topológicas no triviales y demostramos en un sistema de guías de onda acopladas cómo la protección topológica de un estado puede ser suspendida y restablecida utilizando transformaciones supersimétricas. Además, para acceder a las fases topológicas no triviales, un elemento clave es la introducción de campos artificiales de gauge (AGF) que controlan la dinámica de partículas no cargadas que de otra manera eluden la influencia de los campos electromagnéticos. Es esta línea, investigamos la posibilidad de inducir AGF utilizando luz con momento orbital angular en lugar de manipular la geometría del sistema. Específicamente, medimos el fenómeno de jaula de Aharonov-Bohm que está ligado a la presencia de un campo magnético sintético. Esta técnica permite acceder a diferentes regímenes topológicos en una sola estructura, un paso importante para la simulación cuántica utilizando sistemas fotónicos.<br>The integration of all the basic components for light generation, manipulation and detection in optical chips is boosting scientific and technological advances, for instance, in the development of information technology and data communications or of sensing devices for quantum technologies. Due to its flexibility, scalability and of the possibility of directly observing the wavefunction evolution using simple imaging techniques, integrated photonic structures are an ideal playground for quantum simulation i.e., for emulating quantum phenomena appearing in other branches of physics. Moreover, these quantum-optical analogies also allow to design novel integrated photonic circuits with exceptional properties. In this context, in this thesis we harness non-trivial properties stemming from quantum physics to design novel integrated photonic devices with advanced functionalities and enhanced performances as well as to engineer novel photonic simulators. Specifically, we exploit the similarities between the Helmholtz and the Schrödinger equations, which allow to mimic the temporal dynamics of a single particle trapped in a lattice potential with the spatial evolution of a light beam propagating in an array of optical waveguides, to apply supersymmetric (SUSY) transformations and adiabatic passage processes as well as to explore non-trivial topological geometries in systems of coupled optical waveguides. In this vein, the first part of the thesis is devoted to introduce the mathematical concepts and physical ideas behind coupled optical waveguides, quantum-optical analogies and optical SUSY. After that, the second part of the thesis encompasses the design of novel integrated photonic devices by combining the spatial modal content manipulation offered by SUSY transformations with the robustness supplied by adiabatic passage techniques. In this regard, we start by presenting a novel method for mode division (de)multiplexing rooted on SUSY waveguides, which provide the mode filtering capabilities, in combination with a Spatial Adiabatic Passage protocol, which is used to efficiently and robustly transfer the desired modes between waveguides. Similarly, keeping on the idea of applying quantum engineering protocols to design novel photonic devices with enhanced performances, we also propose to connect, in an adiabatic fashion, SUSY structures along the propagation direction. In particular, this technique is used to engineer efficient and robust tapered waveguides, mode filters, beam splitters and interferometers. Finally, the third part of the thesis is dedicated to the photonic simulation of different phenomena. We explore first the effect that SUSY transformations induce in systems with non-trivial topological properties, which are intrinsically connected with the system's internal symmetries. To this aim, we consider the simplest system with non-trivial topological properties and demonstrate in waveguide arrays how the topological protection of a targeted state can be suspended and reestablished by applying SUSY transformations. Moreover, to access these non-trivial topological phases, a key step is the introduction of Artificial Gauge Fields (AGF) controlling the dynamics of uncharged particles that otherwise elude the influence of standard electromagnetic fields. To this end, we investigate the possibility of inducing AGF by injecting light beams carrying Orbital Angular Momentum, rather than manipulating the geometry of the system. Specifically, we measure the Aharonov-Bohm caging effect, which is directly related with the presence of a synthetic magnetic flux, in an array of coupled optical waveguides. This technique paves the way towards accessing different topological regimes in one single structure, representing an important step forward for quantum simulation in photonic structures.

Lorsqu'un défaut est introduit dans un cristal phononique, des états apparaissent dans les bandes interdites et se localisent au niveau des défauts. Ils décroissent rapidement loin du défaut. Par conséquent, il est possible de localiser et de guider la propagation des ondes en concevant des défauts dans un cristal phononique parfait. Le guide d’onde à résonateurs couplés, fondé sur le couplage d'une séquence de cavités, présente simultanément un fort confinement des ondes et une faible vitesse de groupe ; il peut être utilisé pour concevoir des circuits plutôt arbitraires. En outre, la propagation des ondes élastiques dans une matrice solide peut être contrôlée en remplissant des cavités d'un fluide, sur la base des systèmes couplés fluides-solides. Ils ont des applications essentielles pour la réduction des vibrations et l’isolation acoustique. Dans cette thèse, les ondes acoustiques et élastiques se propageant dans les guides d’ondes à résonateurs couplés périodiques et apériodiques sont étudiées. L’interaction fluide-solide dans les cristaux phononiques fluide / solide est étudiée. Les travaux sont menés en combinant simulation numérique, analyse par modèles théoriques et investigation expérimentale<br>When a defect is introduced into a phononic crystal, states localized at the defect appear in the band gaps. They decay rapidly far away from the defect. Therefore, it is possible to localize and guide wave propagation by designing defects in the perfect phononic crystal. Coupled-resonator waveguides based on the coupling effect between a sequence of defect cavities have simultaneously strong wave confinement and low group velocity, and can be used to design rather arbitrary circuits. Furthermore, the propagation of elastic waves in a solid matrix can be controlled through changing fluid fillings based on fluid-solid interaction. Thus, they have essential applications in vibration reduction and noise isolation. In this thesis, the acoustic and elastic waves propagating in both periodic and aperiodic coupled-resonator waveguides are investigated. The fluid-solid interaction in fluid/solid phononic crystals is studied. The work is conducted by combining numerical simulations, theoretical model analysis and experimental investigations

The characteristics of slotted circular waveguides with different dimensions, including cutoff frequencies of TE and TM modes, impedance and modal field distributions will be analyzed using the generalized spectral domain approach. The Method of Moment will be applied, basis functions that include the edge conditions will be used and a computer program will be developed. Obtained results will be presented for different number, depth and thickness of coupling slots, and compared with available data to demonstrate the accuracy and the efficiency of the approach. Plots of the electric and magnetic field lines corresponding to the dominant as well as a number of higher order modes will be presented for quadruple ridge case.

There exists substantial applications motivating the study of nonlinear longitudinal wave propagation in layered (or laminated) elastic waveguides, in particular within areas related to non-destructive testing, where there is a demand to understand, reinforce, and improve deformation properties of such structures. It has been shown [76] that long longitudinal waves in such structures can be accurately modelled by coupled regularised Boussinesq (cRB) equations, provided the bonding between layers is sufficiently soft. The work in this thesis firstly examines the initial-value problem (IVP) for the system of cRB equations in [76] on the infinite line, for localised or sufficiently rapidly decaying initial conditions. Using asymptotic multiple-scales expansions, a nonsecular weakly nonlinear solution of the IVP is constructed, up to the accuracy of the problem formulation. The asymptotic theory is supported with numerical simulations of the cRB equations. The weakly nonlinear solution for the equivalent IVP for a single regularised Boussinesq equation is then constructed; constituting an extension of the classical d'Alembert's formula for the leading order wave equation. The initial conditions are also extended to allow one to separately specify an O(1) and O(ε) part. Large classes of solutions are derived and several particular examples are explicitly analysed with numerical simulations. The weakly nonlinear solution is then improved by considering the IVP for a single regularised Boussinesq-type equation, in order to further develop the higher order terms in the solution. More specifically, it enables one to now correctly specify the higher order term's time dependence. Numerical simulations of the IVP are compared with several examples to justify the improvement of the solution. Finally an asymptotic procedure is developed to describe the class of radiating solitary wave solutions which exist as solutions to cRB equations under particular regimes of the parameters. The validity of the analytical solution is examined with numerical simulations of the cRB equations. Numerical simulations throughout this work are derived and implemented via developments of several finite difference schemes and pseudo-spectral methods, explained in detail in the appendices.

In this work we propose the apodization or windowing of the coupling coefficients of the unit cells conforming a coupled resonator device as a mean to reduce the level of secondary sidelobes in the case of SCISSOR configuration [7] or reducing the passband ripples in the case of CROW configuration [8]. This technique is regularly employed in the design of digital filters [18] and has been applied as well in the design of other photonic devices such as corrugated waveguide filters [9] and fiber Bragg gratings [19]. We also propose a novel technique for the apodization of coupled resonator structures by applying a longitudinal offset between resonators in order to modify the power coupling constant, which alleviates the technical requirements required for the production of these devices. We will demonstrate the design, fabrication and characterization of CROW structures employing the apodization through the aforementioned technique.<br>Doménech Gómez, JD. (2013). Apodized Coupled Resonator Optical Waveguides: Theory, design and characterization [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/32278<br>TESIS

Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution); and, (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.<br>Includes bibliographical references (p. 149-151).<br>Despite the great achievements obtained with fast-field and parabolic equation models, normal mode programs still remain a very efficient, simple and practical tool for describing ocean acoustics in range-independent environments. Numerical implementations of wave-theory solutions for range-dependent acoustic problems can be classified as: normal-mode techniques (adiabatic or coupled modes); parabolic-approximation techniques (narrow- or wide-angle parabolic equations solved by split-step or finite-difference techniques); and finite-element/finite- difference solutions of the full wave equation. The mode techniques provide approximate field solutions if implemented in the adiabatic approximation, while complete wave theory solutions can be obtained by including full mode coupling. Parabolic approximations to the elliptic wave equation have been extensively studied over the past 10 years([15], [23]). The advantage of using a parabolic wave equation is that it can be efficiently solved by noniterative forward marching techniques. However, any form of the parabolic equation is an approximate wave equation derived under the assumptions of: (1) forward propagation only, and (2) that energy is propagating within a limited angular spectrum around the main propagation direction. The last category of models based on finite-difference and finite-element solutions of the full wave equation([22]) is well suited for providing solutions for propagation in general range-dependent environments.<br>(cont.) The existing codes, however, are extremely computer intensive. My thesis focuses on a two-dimensional two-way coupled modes model, and then expend it to a three-dimensional coupled modes model for two-dimensional, range- dependent waveguides. Numerical examples of two-dimensional and three-dimensional problems are presented, and comparisons with the results from analytical solution, as well as from COUPLE are also considered.<br>by Wenyu Luo.<br>S.M.