Thesis (M.S.)--Ohio University, June, 2009. / Title from PDF t.p. Includes bibliographical references.

Microelectronics has enjoyed great success in the past century. As the technology node progresses, the complementary metal-oxide-semiconductor scaling has already reached a wall, and serious challenges in high-bandwidth interconnects and fast-speed signal processing arise. The incorporation of photonics to microelectronics provides potential solutions. The theme of this thesis is focused on the novel applications of travelling-wave microresonators such as microdisks and microrings for the on-chip optical interconnects and signal processing. Challenges arising from these applications including theoretical and experimental ones are addressed. On the theoretical aspect, a modified version of coupled mode theory is offered for the TM-polarization in high index contrast material systems. Through numerical comparisons, it is shown that our modified coupled mode theory is more accurate than all the existing ones. The coupling-induced phase responses are also studied, which is of critical importance to coupled-resonator structures. Different coupling structures are studied by a customized numerical code, revealing that the phase response of symmetric couplers with the symmetry about the wave propagating direction can be simply estimated while the one of asymmetric couplers is more complicated. Mode splitting and scattering loss, which are two important features commonly observed in the spectrum of high-Q microresonators, are also investigated. Our review of the existing analytical approaches shows that they have only achieved partial success. Especially, different models have been proposed for several distinct regimes and cannot be reconciled. In this thesis, a unified approach is developed for the general case to achieve a complete understanding of these two effects. On the experimental aspect, we first develop a new fabrication recipe with a focus on the accurate dimensional control and low-loss performance. HSQ is employed as the electron-beam resist, and the lithography and plasma etching steps are both optimized to achieve vertical and smooth sidewalls. A third-order temperature-insensitive coupled-resonator filter is designed and demonstrated in the silicon-on-insulator (SOI) platform, which serves as a critical building block element in terabit/s on-chip networks. Two design challenges, i.e., a broadband flat-band response and a temperature-insensitive design, are coherently addressed by employing the redundant bandwidth of the filter channel caused by the dispersion as thermal guard band. As a result, the filter can accommodate 21 WDM channels with a data rate up to 100 gigabit/s per wavelength channel, while providing a sufficient thermal guard band to tolerate more than ±15°C temperature fluctuations in the on-chip environment. In this thesis, high-Q microdisk resonators are also proposed to be used as low-loss delay lines for narrowband filters. Pulley coupling scheme is used to selectively couple to one of the radial modes of the microdisk and also to achieve a strong coupling. A first-order tunable narrowband filter based on the microdisk-based delay line is experimentally demonstrated in an SOI platform, which shows a tunable bandwidth from 4.1 GHz to 0.47 GHz with an overall size of 0.05 mm². Finally, to address the challenges for the resonator-based delay lines encountered in the SOI platform, we propose to vertically integrate silicon nitride to the SOI platform, which can potentially have significantly lower propagation loss and higher power handling capability. High-Q silicon nitride microresonators are demonstrated; especially, microresonators with a 16 million intrinsic Q and a moderate size of 240 µm radius are realized, which is one order of magnitude improvement compared to what can be achieved in the SOI platform using the same fabrication technology. We have also successfully grown silicon nitride on top of SOI and a good coupling has been achieved between the silicon nitride and the silicon layers.

Optical resonators are structures that allow light to circulate and store energy for a duration of time. This work primarily looks at the fabrication, characterization, and application of whispering gallery mode microresonators and the analysis of organic photonic crystal-like structures and simulation of their resonant effects. Whispering gallery mode (WGM) microresonators are a class of cylindrically symmetric optical resonator which light circulates around the equator of the structure. These resonators are named after acoustic whispering galleries, where a whisper can be heard anywhere along the perimeter of a circular room. These optical structures are known for their ultra high Q-factor and their low mode volume. Q-factor describes the photon lifetime in the cavity and is responsible for the energy buildup within the cavity and sharp spectral characteristics of WGM resonators. The energy buildup is ideal for non-linear optics and the sharp spectral features are beneficial for sensing applications. Characterization of microbubble resonators is done by coupling light from a tunable laser source via tapered optical fiber into the cavity. The fabrication of quality tapered optical fiber on the order of 1-2 μm is critical to working on WGM resonators. The measurement of Q-factors up to 2x10⁸ and mode spectra are possible with these resonators and experimental techniques. This work focuses on microdisk and microbubble WGM resonators. The microdisk resonators are fabricated by femtosecond laser micromachining. The micromachined resonators are fabricated by ablating rotating optical fiber to generate the disk shape and then heated to reflow the surface to improve optical quality. These resonators have a spares mode spectrum and display a Q factor as high as 2x10⁶. The microbubble resonators are hollow microresonators fabricated by heating a pressurized capillary tube which forms a bubble in the area exposed to heat. These have a wall thickness of 2-5 μm and a diameter of 200-400 μm. Applications in pressure sensing and two-photon fluorescence of dye in microbubble resonators is explored. Photonic crystals can have engineered resonant properties by tuning photonic band gaps and introducing defects to create cavities in the photonic structure. In this work, a natural photonic crystal structure is analyzed in the form of diatoms. Diatoms are a type of phytoplankton which are identified by unique ornamentation of each species silica shell, called a frustule. The frustule is composed of a quasi-periodic lattice of pores which closely resembles manmade photonic crystals. The diatom frustules are analyzed using image processing techniques to determine pore-to-pore spacing and identify defects in the quasi-periodic structure which may contribute to optical filtering and photonic band gap effects. The data gathered is used to simulate light propagation through the diatom structure at different incident angles and with different material properties and to verify data gathered experimentally.

Orientador: Newton Cesário Frateschi / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-02T20:57:13Z (GMT). No. of bitstreams: 1 Souza_MarioCesarMendesMachadoDe_D.pdf: 15167961 bytes, checksum: b18ee3c5c89a54254813d054e000f1d7 (MD5) Previous issue date: 2017 / Resumo: Após duas décadas de progresso contínuo, a fotônica integrada apresenta-se como uma tecnologia indispensável, exibindo soluções para importantes demandas tecnológicas atuais como o tráfego e processamento de sinais ópticos ultra-rápidos. Ao mesmo tempo, ela permite avanços substanciais em áreas emergentes como o "laboratório-no-chip" (lab-on-a-chip). No entanto, enquanto funcionalidades básicas necessárias para a maioria das aplicações (fontes de luz, moduladores, filtros, linhas de atraso, detectores, etc.) já estão disponíveis em uma variedade de dispositivos e plataformas, alguns desafios ainda permanecem. Nos últimos quatro anos, estivemos interessados em identificar alguns desses desafios e fornecer abordagens interessantes para enfrentá-los. Esta tese, que engloba uma parcela importante dessas investigações, pode ser dividida em dois tópicos. No primeiro, apresentamos microresonadores acoplados como dispositivos que permitem um controle espectral flexível e reconfigurável. Explorando as características desses dispositivos, demonstramos novas funcionalidades como o controle reconfigurável do "splitting" entre ressonâncias, fornecemos novas ferramentas de modelagem como uma teoria de modos acoplados modificada e propomos um modulador que emprega anéis acoplados, capaz de superar a limitação entre eficiência de modulação e largura de banda enfrentada por moduladores baseados em um único anel. No segundo tópico apresentamos o desenvolvimento de um espectrômetro a transformada de Fourier integrado em um chip, utilizando fotônica de silício. Os desafios para obter esse dispositivo, como a não-idealidade inerente à plataforma de silício (dispersão e não-linearidade termo-ótica) são discutidos em detalhe, além da demonstração experimental que indica como tal dispositivo pode abrir caminho para espectrômetros portáteis robustos e econômicos / Abstract: After two decades of continuous progress, integrated photonics has proven its indisputable role as an enabling technology. It addresses important technological demands of our time such as ultrafast optical data transfer and processing while allowing substantial progress in emerging areas, including lab-on-a-chip. Although the basic functionalities required for most applications (light sources, modulators, filters, delay lines, detectors, etc.) are now available in a variety of designs and platforms, a few challenges remain and room for improvement can still be found. During the last four years, we have been interested in identifying some of these challenges and in providing interesting approaches to tackle a handful. This thesis, encompassing an important share of such investigations, can be divided into two topics. First, we present coupled microresonators as devices allowing for flexible and reconfigurable spectral control. Exploiting these devices, we demonstrate novel functionalities like the reconfigurable resonance-splitting control, we provide novel modeling tools such as a modified coupled mode theory, and we propose a coupled-ring modulator that overcomes the trade-off between modulation efficiency and bandwidth faced by single microrings modulators. The second topic addresses the realization of an on-chip Fourier transform spectrometer using silicon photonics. We discuss the challenges of realizing such device due to non-idealities inherent to the silicon platform (dispersion and thermo-optic non-linearity) and we provide an experimental demonstration indicating how this device can pave the way for robust and cost-effective portable spectrometers / Doutorado / Física / Doutor em Ciências / 156281/2013-9 / 2014/04748-2, 2015/20525-6 / CNPQ / FAPESP

Kinetic inductance detectors (KIDs) are superconducting thin-film microresonators that are sensitive photon detectors. These detectors are a candidate for the next generation of experiments designed to measure the polarization of the cosmic microwave background (CMB). I discuss the basic theory needed to understand the response of a KID to light, focusing on the dynamics of the quasiparticle system. I derive an equation that describes the dynamics of the quasiparticle number, solve it in a simplified form not previously published, and show that it can describe the dynamic response of a detector. Magnetic flux vortices in a superconducting thin film can be a significant source of dissipation, and I demonstrate some techniques to prevent their formation. Based on the presented theory, I derive a corrected version of a widely-used equation for the quasiparticle recombination noise in a KID. I show that a KID consisting of a lumped-element resonator can be sensitive enough to be limited by photon noise, which is the fundamental limit for photometry, at a level of optical loading below levels in ground-based CMB experiments. Finally, I describe an ongoing project to develop multichroic KID pixels that are each sensitive to two linear polarization states in two spectral bands, intended for the next generation of CMB experiments. I show that a prototype 23-pixel array can detect millimeter-wave light, and present characterization measurements of the detectors.

Microresonators are devices that confine light in small volumes through total internal reflection. Introducing an emissive species into a microresonator allows for resonance enhanced emission at frequencies where the spectrum of the emissive species overlaps with the resonant frequencies of the microresonator. Previous research has led to a good understanding of these phenomena in 1D and 2D microresonators, but many 3D microresonator geometries have not yet been investigated. This work details the successful creation and demonstration of a cubic polymeric optical microresonator.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Prof. Ali Adibi; Committee Member: Prof. Joseph Perry; Committee Member: Prof. Stephen Ralph; Committee Member: Prof. Thomas Gaylord. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Orientador: Newton Cesário Frateschi / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-28T23:46:00Z (GMT). No. of bitstreams: 1 Rezende_GuilhermeForniasMachadode_M.pdf: 3592220 bytes, checksum: e91127c5e777f7e4dfeeff9c5257f907 (MD5) Previous issue date: 2015 / Resumo: Microrressonadores óticos são blocos fundamentais para a integração fotônica. A busca por transmissão de sinais cada vez mais rápidos (atualmente, em dezenas de Gbps) faz com que novos projetos de combinações topológicas entre microanéis sejam exigidos constantemente. Quando aplicados ao processamento de sinais fotônicos, as características de um microrressonador ¿ a saber, espaçamento espectral livre, fator de qualidade e finesse ¿ costumam funcionar como figuras de mérito para avaliar sua capacidade de processamento, filtragem e modulação. Uma estratégia para o aumento da densidade espectral de resposta de transmissão utilizada neste trabalho consiste em acoplar microanéis menores no interior de um maior, mantendo-se o tamanho compacto original do ressonador maior. Neste trabalho, elaboramos uma ferramenta de projeto objetivando prever e descrever as características espectrais deste tipo de dispositivo. Para tanto, foram utilizados o Método de Matriz de Espalhamento, a Teoria de Modos Acoplados e a generalização e sistematização da Regra de Mason para o Ganho de Grafos Direcionais. Nossa ferramenta permite compreender as diferentes combinações de caminhos óticos executados pela luz no interior das cavidades, resolve analiticamente o espectro de transmissão de microanéis acoplados e providencia uma análise da potência ótica no interior de cada cavidade, provendo uma comparação eficiente com os resultados da Teoria de Modos Acoplados. Comparando as previsões teóricas com medidas de caracterização de dispositivos fabricados, encontramos a necessidade de reformulação das ideias dos chamados modos escuros ¿ os quais não são excitados dependendo da forma na qual o sistema é bombeado ¿ para descrição destes sistemas fotônicos / Abstract: Microring resonators are building block for photonic integration. The demand for faster signal transfer (nowadays, in the orders of Gbps) constantly requires new designs of topological combinations between microrings. When applied to photonic signal processing, their characteristics of free spectral range, quality factor and finesse are used as figure of merit in order to evaluate their capacity of processing, filtering and modulation. A strategy for enhancing the spectral density of transmission response, used in this work, consists in coupling smaller microrings inside a bigger one, keeping the original compact size of the bigger resonator unchanged. In this work, we elaborated a design tool in order to predict and describe the behavior of spectral characteristics of this kind of device. For that purpose, it was used the Scattering Matrix Method, the Coupled Mode Theory and the generalization and systematization of Mason¿s Rule for the Gain of Directional Graphs. Our tool provides a full understanding of all combinations of optical path inside the cavities, solve analytically the transmission spectrum of the coupled microrings and provides an optical power analysis inside each cavity, implying an efficient comparison with the results of Coupled Mode Theory. By comparing theoretical predictions with the measurements of characterization of fabricated devices, we found the necessity of reformulation of the ideas of the so-called dark states ¿ those which are not excited depending the way the system is pumped ¿ for describing theses photonic systems / Mestrado / Física / Mestre em Física / 131434-6/2013 / CNPQ

Kerr frequency combs enable compact and robust platforms for applications such as data communications and spectroscopy. Initial demonstrations used dissipative soliton combs operating in the anomalous group velocity dispersion (GVD) regime to illustrate the promising capabilities of Kerr-comb-based technologies. However, many real-world applications, such as wavelength division multiplexing and LiDAR, benefit from higher comb-line powers that are inherently inaccessible to Kerr frequency combs. Nevertheless, nonsolitonic Kerr combs operating in the normal GVD regime offer promise as a platform for the integration of such applications due to their ability to easily access high pump-to-comb conversion efficiencies and spectral profiles with slower power falloffs. Unlike a dissipative Kerr soliton which is a single cycle periodic pattern on top of a homogenous background, a nonsolitonic Kerr comb arises through the interlocking of two switching waves of opposite polarity, each of which connects the two homogenous state solutions of the bistable cavity response. Here, we present a systematic approach for turn-key generation of Kerr combs in the normal GVD regime. We use a coupled ring geometry to induce and control avoided mode crossings for the generation of low-noise frequency combs with conversion efficiencies of up to 57%. Moreover, we explore the regime of synchronization for these nonsolitonic Kerr combs. Synchronization is a universal mechanism of coupled nonlinear oscillators that manifests itself as the spontaneous appearance of order within nature's tendency for disorder and chaos. It is a process by which the natural rhythms of interacting oscillators adjust to a common frequency and produce a mutually phase-locked state. In the realm of Kerr frequency combs, synchronization allows for the repetition rates, or equivalently the comb-line spacings, of individual Kerr combs to become identical. We reveal the universality of Kerr comb synchronization by synchronizing two nonsolitonic Kerr combs and thereby extending the scope of synchronization beyond the soliton regime. Furthermore, we introduce a method to overcome the inherently low output power of Kerr combs while maintaining the high conversion efficiency of a normal GVD Kerr comb. We demonstrate efficient comb-line power enhancement by coherently combining two nonsolitonic Kerr combs via on-chip synchronization. Our on-chip synchronization design removes the requirement for dispersion compensation of the coupling signal while increasing the overall stability of the system. Our techniques of comb generation, synchronization, and coherent combining enable nonsolitonic Kerr combs as a platform to achieve a fully integrated, high-power Kerr comb source.

In recent years, there has been significant progress in the development of integrated photonic circuits (PICs). Matured fabrication and simulation techniques have enabled the development of novel devices and system architectures. Ideally, these newly developed technologies are put to test in the lab, both to verify that they perform as simulated and to demonstrate the viability of the technology. Testing the increasingly complex optical circuits brings various challenges. One of these challenges is the sensitivity to temperature changes of many optical circuits, especially micro ring and micro disk resonators (MRRs and MDRs). Due to the nature of these resonators, slight deviations in the material properties have a large impact on their resonant frequency. Despite this, their small footprint and wavelength selectivity makes them promising components for many future technologies, especially Dense Wavelength Division Multiplexed (DWDM) communication links. Multiple resonators cascaded on a single bus waveguide can operate on multiple wavelengths simultaneously with relatively few components and in a small combined area. Since every extra connection to a PIC has a footprint similar to that of a micro resonator, a packaging optimized thermal control scheme is needed to fully leverage all advantages of micro resonators. This work will focus on the thermal stabilization of cascaded micro resonators and how thermal control can be optimized to simplify the packaging of PIC prototypes. This simplification enables the demonstration of complex systems and more realistic scenarios for thermal control of both resonators and other circuits. It will first show how a number of PICs and their respective packages were built, keeping subsequent testing in mind. Then, it demonstrates automatic initialization of cascaded MRR and how stable operation, while undergoing large temperature swings, can be achieved using a minimum number of connections to the PIC. Next, it shows stable operation of an eight-wavelength receiver, operating uncooled at 16 Gb/s/?, over a record 75 °C. Finally, it presents how all the learned lessons are brought together to built a 2.5D integrated SiPh transceiver that is capable of transmitting 512 Gb/s bidirectionally. This transceiver can be plugged into Field Programmable Gate Arrays (FPGAs), which can then be used to implement accelerators for real computing problems, used as a PCIe bridge to a standard compute server, or both. The transceiver is also designed to work with many types of optical switches, allowing demonstrations of novel switching algorithms and network architectures. The contributions discussed in this thesis can assist in enabling future high bandwidth optical interfaces by optimizing the thermal control strategy and may be used at all stages of PIC design and packaging to facilitate the development of new technologies.