Bandpass microwave filters are often modeled as a set of coupled discrete and localized resonators. This model is adequate in the narrow-band case. It, however, fails to describe accurately compact structures where stray couplings can be strong. To address this problem, a new view is proposed in this thesis. Instead of basing the model on localized discrete resonances, we start by constructing a model that is based on the global resonances of the structure. These are the resonances that the ports see and emerge when the entire structure is treated as a single unit. The resulting circuit, the transversal circuit, is universal. It is valid for any coupled resonator filter. The circuit is used in optimization of compact and ultra wideband suspended stripline filters and excellent results were obtained. In order to relate the global-eigen modes model to the conventional model, the issue of representation of microwave filters is investigated in detail. It is shown that a microwave filter can be represented by an infinite number of similar coupling matrices by using different modes as basis. According to this new view, a similarity transformation in microwave coupled resonator filters is interpreted as a change of basis. Two circuits that are related by a similarity transformation represent the same filter structure by using different sets of modes as basis. These conclusions were exploited in establishing a design theory for filters with dual-mode cavities. The new theory leads to direct and accurate design techniques that need no, or minimal, optimization. No tuning is used in the CAD steps. Tuning may only be required to account for manufacturing tolerances. A new tuning configuration is described and validated by computer simulation. A novel dual-mode filter with improved quality factor and reduced sensitivity is developed and designed within the same approach. The filter is fabricated and measured and excellent results are achieved. The same design methodology was used to introduce a new class of dual-mode dual-band microwave filters with improved sensitivity. It is also shown that canonical dual-mode filters can be designed within the same view with minimal local optimization of the input cavity. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2010-03-31 01:33:36.818

Coupled whispering-gallery-mode (WGM) optical microcavities have been extensively explored to tune the resonant eigenfrequencies and spatial distributions of the optical modes, finding many unique photonic applications in a variety of fields, such as nonlinear optics, laser physics, and non-Hermitian photonics. As one type of WGM microcavities, microtube cavities with axial potential wells support 3D confined resonances by circulating light along the microtube cross-section and axis simultaneously, which offers a promising possibility to explore multidimensional and multichannel optical coupling. In this thesis, the optical coupling of 3D confined resonant modes is investigated in coupled microtube cavities fabricated by self-rolling of prestrained nanomembranes. In the first coupling system, multiple sets of 3D optical modes are generated in a single microtube cavity owing to nanogap induced resonant trajectory splitting. The large overlap of optical fields in the split resonant trajectories triggers strong optical coupling of the 3D confined resonant modes. The spectra anticrossing feature and changing-over of one group of coupled fundamental modes are demonstrated as direct evidence of strong coupling. The spatial optical field distribution of 3D coupling modes was experimentally mapped upon the strong coupling regime, which allows direct observation of the energy transfer process between two hybrid states. Numerical calculations based on a quasi-potential model and the mode detuning process are in excellent agreement with the experimental results. On this basis, monolithically integrated twin microtube cavities are proposed to achieve the collective coupling of two sets of 3D optical modes. Owing to the aligned twin geometries, two sets of 3D optical modes in twin microtubes are spectrally and spatially matched, by which both the fundamental and higher-order axial modes are respectively coupled with each other. Multiple groups of the coupling modes provide multiple effective channels for energy exchange between coupled microcavities, which are illustrated by the measured spatial optical field distributions. The spectral anticrossing and changing-over features of each group of coupled modes are revealed in experiments and calculations, indicating the occurrence of strong coupling. In addition, the simulated 3D mode profiles of twin microcavities confirm the collective strong coupling behavior, which is in good agreement with the experimental results. Our work provides a compact and robust scheme for realizing 3D optical coupling, which is of high interest for promising applications such as 3D non-Hermitian systems and multi-channel optical signal processing.

Optical microcavities (OMs) are receiving increasing attention owing to their potential applications ranging from cavity quantum electrodynamics, optical detection to photonic devices. Recently, rolled-up structures have been demonstrated as OMs which have gained considerable attention owing to their excellent customizability. To fully exploit this customizability, asymmetric and topological rolled-up OMs are proposed and investigated in addition to conventional rolled-up OMs in this thesis. By doing so, novel phenomena and applications are demonstrated in OMs. The fabrication of conventional rolled-up OMs is presented in details. Then, dynamic mode tuning by a near-field probe is performed on a conventional rolled-up OM. Next, mode splitting in rolled-up OMs is investigated. The effect of single nanoparticles on mode splitting in a rolled-up OM is studied. Because of a non-synchronized oscillating shift for different azimuthal split modes induced by a single nanoparticle at different positions, the position of the nanoparticle can be determined on the rolled-up OM. Moreover, asymmetric rolled-up OMs are fabricated for the purpose of introducing coupling between spin and orbital angular momenta (SOC) of light into OMs. Elliptically polarized modes are observed due to the SOC of light. Modes with an elliptical polarization can also be modeled as coupling between the linearly polarized TE and TM mode in asymmetric rolled-up OMs. Furthermore, by adding a helical geometry to rolled-up structures, Berry phase of light is introduced into OMs. A -π Berry phase is generated for light in topological rolled-up OMs so that modes have a half-integer number of wavelengths. In order to obtain a deeper understanding for existing rolled-up OMs and to develop the new type of rolled-up OMs, complete theoretical models are also presented in this thesis.

In this thesis we have presented a thorough study on the optical and sensoristic properties of SRSN Mu-disks, in an isolated configuration and when coupled to a passive Si3N4 waveguide placed underneath. The whole structure of the device have been previously simulated in order to study the behavior of the supported WGM when subject to a geometrical variation (i.e.: radius, thickness, shape of the edge of the isolated Mu-disk): the obtained results granted the realization of Mu-resonators with Q factor exceeding 104. The coupled structure have been then simulated with the main goal of maximizing the WGM intensity transmitted at the end of the WG. This task has been fulfilled through a careful optimization of the geometrical parameters (i.e.: X-Gap and Z-Gap). The subsequent step, involving the fabrication process of the sample - realized in the Centro Nacional de Microelectronica (CNM) of Bellaterra - has been carried out using standard CMOS compatible process. The deposition and the implantation of the Si3N4 has been performed by means of LPCVD technique, while for the SiO2 deposition the PECVD. Finally the optical elements has been defined by means of a two level photolithographic mask. On the produced samples we have performed a superficial analysis (SEM, AFM) with the aim of evaluate the presence of geometrical imperfections and estimation of the superficial roughness. Furthermore the EFTEM analysis revealed the absence of Si-nc inside the active layer. Using the Cut-back technique, low losses under 1 dB/cm have been found in both VIS and IR spectral range in the passive WG of different width. On the other hand, applying the SES technique on an Si-rich WG structure we have been able to extract the losses value of active material in a wide and continuous range of wavelength, defined inside the PL spectrum. As a result of a careful optimization of the active SRSN in terms of PL intensities and optical losses, we have been able to produce bright and high Q isolated Mu-disks, achieving maximum values about 1.4x104 in a wide spectral range in the VIS and emitting up to few nW on a single resonance. The reported Q values are the best ever reported in circular Si-based light emitting Mu-cavities and are just limited by the spectral resolution of our experimental setup. The coupled structures demonstrated Q values up to 1.48x103, which are susceptible to be greatly improved through optimization of the fabrication process. Through a prof of concept , we have demonstrated that these structures are very sensible to the surrounding material and are able to detect refractive index changes with sensitivities of 51.79 nm/RIU and minimum measured refractive index change of 1.15x10-3 RIU. / En esta tesis, realizada en el departament d' Electrònica de la Universitat de Barcelona se ha presentado un estudio detallado the las propiedades ópticas y sensoras de estructuras resonantes tipo micro-disco fabricados íntegramente en nitruro de silicio enriquecido con silicio (SRSN). El estudio se ha llevado a cabo bien en estructuras aisladas o en una configuración acoplada con una guía de onda passiva situada debajo de la cavidad. La totalidad de la estructura ha sido simulada con el fin de estudiar el comportamiento de los modos resonantes WGM soportados cuando se cambian las condiciones de contorno geómetricas y del material. Los resultado obtenidos han permitido la realización de estructuras resonantes con factores de calidad superiores a 104. El objetivo de las simulaciones ha sido el de maximizar la intensidad transmitida de los modos soportados (WGM) al final de la guía de onda. Este hito ha sido cumplido gracias a la optimización de los parámetros geómetricos relativos (el X-gap y el Z-gap). Una vez producidas las muestras, se procedió a la realización de un análisis de superficie (SEM, AFM) para evaluar la rugosidad efectiva de las estructuras y las eventuales imperfecciones geométricas. Como resultado de la optimización del material activo en términos de intensidad de fotoluminiscencia y pérdidas ópticas, se consiguieron realizar cavidades resonantes de alta emisión luminosa y buenos factores de calidad. En un nuevo montaje experimental de u-PL desarrollado íntegramente para el estudio de estos dispositivos, se obtuvieron valores máximos de Q = 1.4x104 en un rango espectral ancho en el visible. La potencia emitida en cada resonancia ha sido medida y cuantificada en un valor de nW. Este valor permite la utilización de detectores de silicio integrados. Con el fin de evaluar la sensitividad del dispositivo, se han llevado a cabo medidas de u-PL cambiando el entorno del microdisco y monitorizando el desplazamiento espectral que sufre una determinada resonancia. El resultado de estas medidas muestra un desplazamiento de 1.37 nm como consecuencia de un índice de refracción de An = 0.0038 RIU (refractive index unit).

This diploma thesis deals with the spectrum analysis, frequency characteristics, Chladni figures and simulation of modal and harmonic analysis of an acoustic guitar in ANSYS program interface. In the acoustic guitar analysis, various details that can influence the instrument spectrum are discussed. Especially on its performance over time, the number of generated harmonic components and their performance. Then the guitar bracing innovation of the dreadnought guitar was created from the measured, simulated and calculated data. Four acoustic guitars with the innovation were then made. These innovated instruments were further analyzed and compared with the acoustic guitar before the innovation and with a competitor’s guitar. Furthermore, the thesis describes parts of an acoustic guitar, wood properties, theoretical background and measurement methods.

Optical microcavities (OMs) are receiving increasing attention owing to their potential applications ranging from cavity quantum electrodynamics, optical detection to photonic devices. Recently, rolled-up structures have been demonstrated as OMs which have gained considerable attention owing to their excellent customizability. To fully exploit this customizability, asymmetric and topological rolled-up OMs are proposed and investigated in addition to conventional rolled-up OMs in this thesis. By doing so, novel phenomena and applications are demonstrated in OMs. The fabrication of conventional rolled-up OMs is presented in details. Then, dynamic mode tuning by a near-field probe is performed on a conventional rolled-up OM. Next, mode splitting in rolled-up OMs is investigated. The effect of single nanoparticles on mode splitting in a rolled-up OM is studied. Because of a non-synchronized oscillating shift for different azimuthal split modes induced by a single nanoparticle at different positions, the position of the nanoparticle can be determined on the rolled-up OM. Moreover, asymmetric rolled-up OMs are fabricated for the purpose of introducing coupling between spin and orbital angular momenta (SOC) of light into OMs. Elliptically polarized modes are observed due to the SOC of light. Modes with an elliptical polarization can also be modeled as coupling between the linearly polarized TE and TM mode in asymmetric rolled-up OMs. Furthermore, by adding a helical geometry to rolled-up structures, Berry phase of light is introduced into OMs. A -π Berry phase is generated for light in topological rolled-up OMs so that modes have a half-integer number of wavelengths. In order to obtain a deeper understanding for existing rolled-up OMs and to develop the new type of rolled-up OMs, complete theoretical models are also presented in this thesis.

Tesis por compendio / [EN] Phononic crystals are artificial materials formed by a periodic arrangement of inclusions embedded into a host medium, where each of them can be solid or fluid. By controlling the geometry and the impedance contrast of its constituent materials, one can control the dispersive properties of waves, giving rise to a huge variety of interesting and fundamental phenomena in the context of wave propagation. When a propagating wave encounters a medium with different physical properties it can be transmitted and reflected in lossless media, but also absorbed if dissipation is taken into account. These fundamental phenomena have been classically explained in the context of homogeneous media, but it has been a subject of increasing interest in the context of periodic structures in recent years as well. This thesis is devoted to the study of different effects found in sonic and phononic crystals associated with transmission, reflection and absorption of waves, as well as the development of a technique for the characterization of its dispersive properties, described by the band structure. We start discussing the control of wave propagation in transmission in conservative systems. Specifically, our interest is to show how sonic crystals can modify the spatial dispersion of propagating waves leading to control the diffractive broadening of sound beams. Making use of the spatial dispersion curves extracted from the analysis of the band structure, we first predict zero and negative diffraction of waves at frequencies close to the band-edge, resulting in collimation and focusing of sound beams in and behind a 3D sonic crystal, and later demonstrate it through experimental measurements. The focusing efficiency of a 3D sonic crystal is limited due to the strong scattering inside the crystal, characteristic of the diffraction regime. To overcome this limitation we consider axisymmetric structures working in the long wavelength regime, as a gradient index lens. In this regime, the scattering is strongly reduced and, in an axisymmetric configuration, the symmetry matching with acoustic sources radiating sound beams increase its efficiency dramatically. Moreover, the homogenization theory can be used to model the structure as an effective medium with effective physical properties, allowing the study of the wave front profile in terms of refraction. We will show the model, design and characterization of an efficient focusing device based on these concepts. Consider now a periodic structure in which one of the parameters of the lattice, such as the lattice constant or the filling fraction, gradually changes along the propagation direction. Chirped crystals represent this concept and are used here to demonstrate a novel mechanism of sound wave enhancement based on a phenomenon known as "soft" reflection. The enhancement is related to a progressive slowing down of the wave as it propagates along the material, which is associated with the group velocity of the local dispersion relation at the planes of the crystal. A model based on the coupled mode theory is proposed to predict and interpret this effect. Two different phenomena are observed here when dealing with dissipation in periodic structures. On one hand, when considering the propagation of in-plane sound waves in a periodic array of absorbing layers, an anomalous decrease in the absorption, combined with a simultaneous increase of reflection and transmission at Bragg frequencies is observed, in contrast to the usual decrease of transmission, characteristic in conservative periodic systems at these frequencies. For a similar layered media, backed now by a rigid reflector, out-of-plane waves impinging the structure from a homogeneous medium will increase dramatically the interaction strength. In other words, the time delay of sound waves inside the periodic system will be considerably increased resulting in an enhanced absorption, for a broadband spectral range. / [ES] Los cristales fonónicos son materiales artificiales formados por una disposición periódica de inclusiones en un medio, pudiendo ambos ser de carácter sólido o fluido. Controlando la geometría y el contraste de impedancias entre los materiales constituyentes se pueden controlar las propiedades dispersivas de las ondas. Cuando una onda propagante se encuentra un medio con diferentes propiedades físicas puede ser transmitida y reflejada, en medios sin pérdidas, pero también absorbida, si la disipación es tenida en cuenta. La presente tesis está dedicada al estudio de diferentes efectos presentes en cristales sónicos y fonónicos relacionados con la transmisión, reflexión y absorción de ondas, así como el desarrollo de una técnica para la caracterización de sus propiedades dispersivas, descritas por la estructura de bandas. En primer lugar, se estudia el control de la propagación de ondas en transmisión en sistemas conservativos. Específicamente, nuestro interés se centra en mostrar cómo los cristales sónicos son capaces de modificar la dispersión espacial de las ondas propagantes, dando lugar al control del ensanchamiento de haces de sonido. Haciendo uso de las curvas de dispersión espacial extraídas del análisis de la estructura de bandas, se predice primero la difracción nula y negativa de ondas a frecuencias cercanas al borde de la banda, resultando en la colimación y focalización de haces acústicos en el interior y detrás de un cristal sónico 3D, y posteriormente se demuestra mediante medidas experimentales. La eficiencia de focalización de un cristal sónico 3D está limitada debido a las múltiples reflexiones existentes en el interior del cristal. Para superar esta limitación se consideran estructuras axisimétricas trabajando en el régimen de longitud de onda larga, como lentes de gradiente de índice. En este régimen, las reflexiones internas se reducen fuertemente y, en configuración axisimétrica, la adaptación de simetría con fuentes acústicas radiando haces de sonido incrementa la eficiencia drásticamente. Además, la teoría de homogenización puede ser empleada para modelar la estructura como un medio efectivo con propiedades físicas efectivas, permitiendo el estudio del frente de ondas en términos refractivos. Se mostrará el modelado, diseño y caracterización de un dispositivo de focalización eficiente basado en los conceptos anteriores. Considérese ahora una estructura periódica en la que uno de los parámetros de la red, sea el paso de red o el factor de llenado, cambia gradualmente a lo largo de la dirección de propagación. Los cristales chirp representan este concepto y son empleados aquí para demostrar un mecanismo novedoso de incremento de la intensidad de la onda sonora basado en un fenómeno conocido como reflexión "suave". Este incremento está relacionado con una ralentización progresiva de la onda conforme se propaga a través del material, asociado con la velocidad de grupo de la relación de dispersión local en los planos del cristal. Un modelo basado en la teoría de modos acoplados es propuesto para predecir e interpretar este efecto. Se observan dos fenómenos diferentes al considerar pérdidas en estructuras periódicas. Por un lado, si se considera la propagación de ondas sonoras en un array periódico de capas absorbentes, cuyo frente de ondas es paralelo a los planos del cristal, se produce una reducción anómala en la absorción combinada con un incremento simultáneo de la reflexión y transmisión a las frecuencias de Bragg, de forma contraria a la habitual reducción de la transmisión, característica de sistemas periódicos conservativos a estas frecuencias. En el caso de la misma estructura laminada en la que se cubre uno de sus lados mediante un reflector rígido, la incidencia de ondas sonoras desde un medio homogéneo, cuyo frente de ondas es perpendicular a los planos del cristal, produce un gran incremento de la fuerza de / [CA] Els cristalls fonònics són materials artificials formats per una disposició d'inclusions en un medi, ambdós poden ser sòlids o fluids. Controlant la geometría i el contrast d'impedàncies dels seus materials constituents, és poden controlar les propietats dispersives de les ondes, permetent una gran varietatde fenòmens fonamentals interessants en el context de la propagació d'ones. Quan una ona propagant troba un medi amb pèrdues amb propietats físiques diferents es pot transmetre i reflectir, però també absorbida si la dissipació es té en compte. Aquests fenòmens fonamentals s'han explicat clàssicament en el context de medis homogenis, però també ha sigut un tema de creixent interés en el context d'estructures periòdiques en els últims anys. Aquesta tesi doctoral tracta de l'estudi de diferents efectes en cristalls fonònics i sònics lligats a la transmissió, reflexió i absorció d'ones, així com del desenvolupament d'una tècnica de caracterització de les propietats dispersives, descrites mitjançant la estructura de bandes. En primer lloc, s'estudia el control de la propagació ondulatori en transmissió en sistemes conservatius. Més específicament, el nostre interés és mostrar com els cristalls sonors poden modificar la dispersió espacial d'ones propagants donant lloc al control de l'amplària per difracció dels feixos sonors. Mitjançant les corbes dispersió espacial obtingudes de l'anàlisi de l'estructura de bandes, es prediu, en primer lloc, la difracció d'ones zero i negativa a freqüències próximes al final de banda. El resultat és la collimació i focalització de feixos sonors dins i darrere de cristalls de so. Després es mostra amb mesures experimentals. L'eficiència de focalització d'un cristall de so 3D està limitada per la gran dispersió d'ones dins del cristall, que és característic del règim difractiu. Per a superar aquesta limitació, estructures axisimètriques que treballen en el règim de llargues longituds d'ona, i es comporten com a lents de gradient d'índex. En aquest règim, la dispersió es redueix enormement i, en una configuració axisimètrica, a causa de l'acoblament de la simetría amb les fonts acústiques que radien feixos sonors, l'eficiència de radiació s'incrementa significativament. D'altra banda, la teoria d'homogeneïtzació es pot utilitzar per a modelar, dissenyar i caracteritzar un dispositiu eficient de focalització basat en aquests conceptes. Considerem ara una estructura periòdica en la qual un dels seus paràmetres de xarxa, com ara la constant de xarxa o el factor d'ompliment canvia gradualment al llarg de la direcció de propagació. Els cristalls chirped representen aquest concepte i s'utilitzen ací per a demostrar un mecanisme nou d'intensificació d'ones sonores basat en el fenòmen conegut com a reflexió "suau". La intensificació està relacionada amb la alentiment progressiva de l'ona conforme propaga al llarg del material, que està associada amb la velocitat de grup de la relació de dispersió local en els diferents plànols del cristall. Es proposa un model basat en la teoria de modes acoblats per a predir i interpretar este efecte. Dos fenòmens diferents cal destacar quan es tracta d'estructures periòdiques amb dissipació. Per un costat, al considerar la propagació d'ones sonores en el plànol en un array periòdic de capes absorbents, s'observa una disminució anòmala de l'absorció i es combina amb un augment simultani de reflexió i transmissió en les freqüències de Bragg que contrasta amb la usual disminució de transmissió, característica dels sistemes conservatius a eixes freqüències. Per a un medi similar de capes, amb un reflector rígid darrere, les ones fora del pla incidint l'estructura des de un medi homogeni, augmentaran considerablement la interacció. En altres paraules, el retràs temporal de les ones sonores dins del sistema periòdic augmentarà significativament produint un augmen / Cebrecos Ruiz, A. (2015). Transmission, reflection and absorption in Sonic and Phononic Crystals [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/56463 / TESIS / Premios Extraordinarios de tesis doctorales / Compendio