Dissertations / Theses on the topic 'Photonics'

Les cristaux photoniques à gradient (CPG) permettent une ingénierie de leur indice effectif, ce qui offre de nouveaux degrés de liberté pour la conception de dispositifs photoniques. Ils s’appréhendent par l’optique à gradient d’indice (GRIN optics), qui décrit des milieux inhomogènes dans lesquels la lumière ne se propage pas rectilignement. Il est ainsi possible d’envisager tout profil d’indice. Les CPG sont donc particulièrement attractifs pour la miniaturisation des composants optiques, notamment en photonique sur Silicium. Ils sont fondés sur la variation d’un paramètre de la maille élémentaire du cristal photonique (CP); ici, c’est le facteur de remplissage qui varie afin que l’indice effectif du CPG réalise le profil d’indice souhaité. Le but de cette thèse est d’explorer le potentiel des CPG en concevant des dispositifs à gradient d’indice sur la "plateforme" Silicium sur isolant (SOI) aux longueurs d’onde pour les télécommunications. C’est la chaine complète qui va de la conception à la caractérisation du dispositif, en passant par la simulation et la fabrication, qui est mise en œuvre. Nous nous sommes principalement concentrés sur deux instruments typiques de l’optique à gradient d’indice : la lentille de Mikaelian et le Half Maxwell Fish Eye (HMFE). Dans cette thèse, nous proposons une nouvelle méthode d’approximation de l’indice effectif adaptée à la "plateforme" SOI, que nous avons validée en concevant une lentille de Mikaelian (à profil d’indice sécante hyperbolique). Pour de tels dispositifs, il faut en effet tenir compte de deux indices effectifs : celui du mode guidé dans la couche de Silicium et celui du CP. Dans cette méthode, l’indice effectif du CP est d’abord calculé pour remplacer l’indice de la couche du mode guidé ; puis l’indice effectif de cette couche est calculé. Les résultats de simulation obtenus au moyen d’un logiciel commercial (méthode FDTD) montrent que la lentille ainsi conçue satisfait les prévisions analytiques, contrairement à ce que donnent les méthodes couramment utilisées. Nous l’avons alors appliquée au HMFE. Les dispositifs ont ensuite été fabriqués en salle blanche par lithographie par faisceau d’électrons (EBL) et par gravure plasma (ICP). Les différents CPG fabriqués consistent en des trous d’air répartis périodiquement dans la couche de Silicium, dont le diamètre minimal est d’environ 40 nm. Puis, ils ont été caractérisés en deux temps, notamment par microscopie en champ proche (SNOM). L’épaisseur de ces dispositifs est de quelques longueurs d’onde (3 ou 5 λ_0 environ), tandis la largeur de leur tâche focale est proche de la limite de diffraction (0.5 λ_0 environ). Ils fonctionnent sur une plage de longueurs d’onde de 150 nm environ. Les résultats de la lentille de Mikaelian ont été utilisés pour développer un convertisseur de taille de mode (taper) effectif sur quelques longueurs d’onde. Il est dix fois plus court qu’un convertisseur classique. Dans cette thèse, nous montrons aussi comment il est possible d’interpréter la propagation de l’onde EM dans ces composants à gradient d’indice sur "plateforme" SOI au moyen du principe de l’interféromètre multimode. En se propageant, les différents modes accumulent une différence de phase, qui se traduit par un battement qui modifie la distribution du champ EM, conduisant à la focalisation. La longueur caractéristique de ce battement est égale à la distance focale. Tous ces dispositifs sont étudiés pour s’intégrer dans des circuits de photonique intégrée
Gradient photonic crystals (GPhCs) enable the engineering of their effective index, opening up new degrees of freedom in photonic device design. They can be understood through gradient index optics (GRIN optics), which describe inhomogeneous media in which light does not propagate along straight paths. This makes it possible to consider any index profile. This makes GPhCs particularly attractive for the miniaturization of optical components, especially in silicon photonics. They are based on the variation of a parameter of the photonic crystal elemental cell (PhC); here, the filling factor is varied so that the effective index of the GPhC achieves the desired index profile. The aim of this thesis is to explore the potential of GPhCs by designing graded-index devices on the Silicon-On-Insulator (SOI) "platform" at telecom wavelengths. The complete chain from design to device characterization, including simulation and manufacturing, is implemented. We focused on two typical gradient index optics instruments: the Mikaelian lens and the Half Maxwell Fish Eye (HMFE). In this thesis, we propose a new effective index approximation method for the SOI "platform", which we have validated by designing a Mikaelian lens (with a hyperbolic secant index profile). For such devices, two effective indices need to be taken into account: that of the guided mode in the Silicon layer and that of the PhC. In this method, the effective index of the PhC is first calculated to replace the index of the guided mode layer; then the effective index of this layer is calculated. Simulation results obtained using commercial software (FDTD method) show that the lens designed in this way satisfies the analytical predictions, contrary to the results obtained with commonly used methods. We then applied it to HMFE.The devices were then fabricated in the cleanroom by electron beam lithography (EBL) and plasma etching (ICP). The individual GPhCs consisted of periodically distributed air holes in the Silicon layer, with a minimum diameter of around 40 nm. They were then characterized in two stages, notably by near-field microscopy (SNOM). These devices are only a few wavelengths thick (approx. 3 or 5 λ_0), while their focal spot width is close to the diffraction limit (approx. 0.5 λ_0). They operate over a wavelength range of around 150 nm. The Mikaelian lens results have been used to develop a mode size converter (taper), which is effective over a few wavelengths. It is ten times shorter than a conventional converter. In this thesis, we also show how it is possible to interpret EM wave propagation in these graded-index components on the SOI platforms using the multimode interferometer principle. As they propagate, the different modes accumulate a phase difference, resulting in a mode beat that modifies the EM field distribution, leading to focusing. The characteristic length of this mode beat is equal to the focal length. All these devices are studied for integration into integrated photonics circuits

Thanks to its compatibility with the current CMOS technology and its potential of seamless integration with electronics, silicon photonics has been attracting an ever-increasing interest in recent years from both the academia and industry. By applying silicon photonic technology in microwave photonics, on-chip integration of microwave photonic systems could be implemented with improved performance including a much smaller size, better stability and lower power consumption. This thesis focuses on developing silicon-based photonic integrated circuits for microwave photonic applications. Two types of silicon-based on-chip devices, waveguide Bragg gratings and optical micro-cavity resonators, are designed, developed, and characterized, and the use of the developed devices in microwave photonic applications is studied. After an introduction to silicon photonics and microwave photonics in Chapter 1 and an overview of microwave photonic signal generation and processing in Chpater2, in Chapter 3 a silicon-based on-chip phase-shifted waveguide Bragg grating (PS-WBG) is designed, fabricated and characterized, and its use for the implementation of a photonic temporal differentiator is experimentally demonstrated. To have a waveguide grating that is wavelength tunable, in Chapter 4 a tunable waveguide grating is proposed by incorporating a PN junction across the waveguide grating, to use the free-carrier plasma dispersion effect in silicon to achieve wavelength tuning. The use of a pair of wavelength-tunable waveguide gratings to form a wavelength-tunable Fabry-Perot resonator for microwave photonic signal processing is studied. Thanks to its electrical tunability, a high-speed electro-optic modulator, a tunable fractional-order photonic temporal differentiator and a tunable optical delay line are experimentally demonstrated. To increase the bandwidth of a waveguide grating, in Chapter 5 a linearly chirped waveguide Bragg grating (LC-WBG) is designed, fabricated and evaluated. By incorporating two LC-WBGs in two arms of a Mach-Zehnder interferometer (MZI) structure, an on-chip optical spectral shaper is produced, which is used in a photonic microwave waveform generation system based on spectral-shaping and wavelength-to-time (SS-WTT) mapping for linearly chirped microwave waveform (LCMW) generation. To enable the LC-WBG to be electrically tuned, in Chapter 6 a lateral PN junction is introduced in the grating and thus an electrically tunable LC-WBG is realized. By incorporating two tunable LC-WBGs in a Michelson interferometer structure, an electrically tunable optical spectral shaper is made. By applying the fabricated spectral shaper in an SS-WTT mapping system, a continuously tunable LCMW is experimentally generated. Compared with a waveguide Bragg grating device, an on-chip optical micro-cavity resonator usually has a much smaller dimension, which is of help to increase the integration density and reduce the power consumption. Different on-chip optical micro-cavity resonators are studied in this thesis. In Chapter 7, an on-chip symmetric MZI incorporating multiple cascaded microring resonators is proposed. By controlling the radii of the rings, the MZI could be designed to have a spectral response with a linearly-varying free spectral range (FSR), which could be used in photonic generation of an LCMW, and to have a multi-channel spectral response with identical channel spacing, which could be used in the implementation of an independently tunable multi-channel fractional-order temporal differentiator. To further reduce the footprint of an optical micro-cavity resonator, in Chapter 8 an ultra-compact microdisk resonator (MDR) with a single-mode operation and an ultra-high Q-factor is proposed, fabricated and evaluated, and its use for the implementation of a microwave photonic filter and an optical delay line is experimentally demonstrated. To enable the MDR to be electrically tunable, in Chapter 9 an electrically tunable MDR is realized by incorporating a lateral PN junction in the disk. The use of the fabricated MDR in microwave photonic applications such as a high-speed electro-optic modulator, a tunable photonic temporal differentiator and a tunable optical delay line is experimentally demonstrated.

Chip scale photonic integrated circuits can provide important new functions in communications, signal processing and sensing. Recent research on microwave photonics (MWPs) and integrated optical sensors using the silicon photonic devices has opened up new opportunities for signal processing and sensing applications. MWPs brings together the world of microwave engineering and optoelectronics, which provides solutions for processing high frequency microwave signals. It has attracted significant interest in many different areas including communications, sensors, radar systems and defence applications. The use of photonic integrated circuit enhances functionalities and flexibilities as well as enabling a reduction of size and weight for MWP applications. The high integratablity of the photonic circuit not only boosts the filtering, time delay and phase shifting functionalities, but also enables the sensing applications in the nano-scale range. Integrated sensors are under high demand in many environmental chemical and biomedical applications. The mass fabricated integrated sensor provides opportunities for multi-functional sensor array with minimized volume. The research work presented in this thesis aims to investigate silicon photonics applications in MWP signal processing and different sensing circumstances. Firstly, the MWP filter based on the SOI microring resonator with phase compensation method is demonstrated. In addition, instantaneous frequency measurement based on frequency to time mapping is presented. Then, a novel integrated optical sensor system based on SOI add drop microring resonator structure is presented. The MWP techniques for high performance sensing application is explored. Lastly, to address the multi-functionality of silicon photonics based sensor, an application of integrated ultrasound optical sensor is demonstrated. It is expected the work provided in this thesis can assist in the emergence of real-world silicon photonic applications. (1992 out of 2000 characters)

The mid-infrared wavelength region (2-20 µm) is of great utility for a number of applications, including chemical bond spectroscopy, trace gas sensing, and medical diagnostics. Despite this wealth of applications, the on-chip mid-IR photonics platform needed to access them is relatively undeveloped. Silicon is an attractive material of choice for the mid-IR, as it exhibits low loss through much of the mid-IR. Using silicon allows us to take advantage of well-developed fabrication techniques and CMOS compatibility, making the realization of on-chip integrated mid-IR devices more realistic. The mid-IR wavelengths also afford the opportunity to exploit Si's high third-order optical nonlinearity for nonlinear frequency generation applications. In this work, we present a Si-based platform for mid-IR photonics, with a special focus on micro-resonators for strong on-chip light confinement in the 4-5 μm range. Additionally, we develop experimental optical characterization techniques to overcome the inherent difficulties of working in this wavelength regime. First, we demonstrate the design, fabrication, and characterization of photonic crystal cavities in a silicon membrane platform, operational at 4.4 μm (Chapter 2). By transferring the technique known as resonant scattering to the mid-IR, we measure quality (Q) factors of up to 13,600 in these photonic crystal cavities. We also develop a technique known as scanning resonant scattering microscopy to image our cavity modes and optimize alignment to our devices. Next, we demonstrate the electro-optic tuning of these mid-IR Si photonic crystal cavities using gated graphene (Chapter 3). We demonstrate a tuning of about 4 nm, and demonstrate the principle of on-chip mid-IR modulation using these devices. We then investigate the phenomenon of optical bistability seen in our photonic crystal cavities (Chapter 4). We discover that our bistability is thermal in origin and use post-processing techniques to mitigate bistability and increase Q-factors. We then demonstrate the design, fabrication, and characterization grating-coupled ring resonators in a silicon-on-sapphire (SOS) platform at 4.4 μm, achieving intrinsic Q-factors as high as 278,000 in these devices (Chapter 5). Finally, we provide a quantitative analysis of the potential of our SOS devices for nonlinear frequency generation and describe ongoing experiments in this regard (Chapter 6).
Engineering and Applied Sciences

The American Institute for Manufacturing Integrated Photonics (AIM Photonics) is focused on developing an end- to- end integrated photonics ecosystem in the U.S., including domestic foundry access, integrated design tools, automated packaging, assembly and test, and workforce development. This paper describes how the institute has been structured to achieve these goals, with an emphasis on advancing the integrated photonics ecosystem. Additionally, it briefly highlights several of the technological development targets that have been identified to provide enabling advances in the manufacture and application of integrated photonics.

We have performed a theoretical study into silicon-on-insulator photonic waveguide arrays. Such waveguides are capable of high levels of light confinement which reinforces the already strong nonlinear response of silicon, making systems involving the waveguidcs ideal for the study of non-linear effects. This study is focussed on two nonlinear processes in relation to the waveguide arrays: optical soli tans and modulational instability, which are often related effects themselves. Optical solitons are pulses localised ill Due or more spatial and/or temporal dimensions which propagate through media -in a. robust, self-reinforcing manner. They require a balance between nonlinearity, diffraction and dispersion. Modulational instability is related to wave-mixing processes whereby photons of a certain frequency arc converted to photons of different frequencies, depending on phase matching and conservation laws. The instability causes the growth of spectral sidebands about a pump pulse, and is often found to occur during soliton propagation. In this thesis a study of the propagation of light within arrays of waveguides is presented, wherein conditions are tuned to promote soliton formation and an emphasis is placed on investigating discrete spatiotemporal solitons. Advantages and disadvantages of employing silicon waveguides for soliton formation are noted with suggestions given to enable minimising of the latter. It is shown that silicon-on-insulator waveguides can provide an excellent medium for supporting discrete spatiotemporal solitons, and where applicable theoretical results have been related to experimental ones performed in tandem . Similar arrays to used to study modulational instability. It is shown that, through exploitation of the supermodes supported by a waveguide array, different degrees of instability, quantified by an amount of 'gain', are possible within the same array. Depending on the initial excitation conditions it is possible for a pulse to experience either large or insignificant amounts of the gain.

El silicio es la plataforma más prometedora para la integración fotónica, asegurando la compatibilidad con los procesos de fabricación CMOS y la producción en masa de dispositivos a bajo coste. Durante las últimas décadas, la tecnología fotónica basada en la plataforma de silicio ha mostrado un gran crecimiento, desarrollando diferentes tipos de dispositivos ópticos de alto rendimiento. Una de las posibilidades para continuar mejorando las prestaciones de los dispositivos fotónicos es mediante la combinación con otras tecnologías como la plasmónica o con nuevos materiales con propiedades excepcionales y compatibilidad CMOS. Las tecnologías híbridas pueden superar las limitaciones de la tecnología de silicio, dando lugar a nuevos dispositivos capaces de superar las prestaciones de sus homólogos electrónicos. La tecnología híbrida dióxido de vanadio/ silicio permite el desarrollo de dispositivos de altas prestaciones, con gran ancho de banda, mayor velocidad de operación y mayor eficiencia energética con dimensiones de la escala de la longitud de onda. El objetivo principal de esta tesis ha sido la propuesta y desarrollo de dispositivos fotónicos de altas prestaciones para aplicaciones de conmutación. En este contexto, diferentes estructuras basadas en silicio, tecnología plasmónica y las propiedades sintonizables del dióxido de vanadio han sido investigadas para controlar la polarización de la luz y para desarrollar otras funcionalidades electro-ópticas como la modulación.
Silicon is the most promising platform for photonic integration, ensuring CMOS fabrication compatibility and mass production of cost-effective devices. During the last decades, photonic technology based on the Silicon on Insulator (SOI) platform has shown a great evolution, developing different sorts of high performance optical devices. One way to continue improving the performance of photonic optical devices is the combination of the silicon platform with another technologies like plasmonics or CMOS compatible materials with unique properties. Hybrid technologies can overcome the current limits of the silicon technology and develop new devices exceeding the performance metrics of its counterparts electronic devices. The vanadium dioxide/silicon hybrid technology allows the development of new high-performance devices with broadband performance, faster operating speed and energy efficient optical response with wavelength-scale device dimensions. The main goal of this thesis has been the proposal and development of high performance photonic devices for switching applications. In this context, different structures, based on silicon, plasmonics and the tunable properties of vanadium dioxide, have been investigated to control the polarization of light and for enabling other electro-optical functionalities, like optical modulation.
El silici és la plataforma més prometedora per a la integració fotònica, assegurant la compatibilitat amb els processos de fabricació CMOS i la producció en massa de dispositius a baix cost. Durant les últimes dècades, la tecnologia fotònica basada en la plataforma de silici ha mostrat un gran creixement, desenvolupant diferents tipus de dispositius òptics d'alt rendiment. Una de les possibilitats per a continuar millorant el rendiment dels dispositius fotònics és per mitjà de la combinació amb altres tecnologies com la plasmònica o amb nous materials amb propietats excepcionals i compatibilitat CMOS. Les tecnologies híbrides poden superar les limitacions de la tecnologia de silici, donant lloc a nous dispositius capaços de superar el rendiment dels seus homòlegs electrònics. La tecnologia híbrida diòxid de vanadi/silici permet el desenvolupament de dispositius d'alt rendiment, amb gran ample de banda, major velocitat d'operació i major eficiència energètica en l'escala de la longitud d'ona. L'objectiu principal d'esta tesi ha sigut la proposta i desenvolupament de dispositius fotònics d'alt rendiment per a aplicacions de commutació. En este context, diferents estructures basades en silici, tecnologia plasmònica i les propietats sintonitzables del diòxid de vanadi han sigut investigades per a controlar la polarització de la llum i per a desenvolupar altres funcionalitats electró-òptiques com la modulació.
Sánchez Diana, LD. (2016). High performance photonic devices for switching applications in silicon photonics [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/77150
TESIS

Integrated microwave photonics changes the scaling laws of information and communication systems offering architectural choices that combine photonics with electronics to optimize performance, power, footprint and cost. Application Specific Photonic Integrated Circuits, where particular circuits/chips are designed to optimally perform particular functionalities, require a considerable number of design and fabrication iterations leading to long-development times and costly implementations. A different approach inspired by electronic Field Programmable Gate Arrays is the programmable Microwave Photonic processor, where a common hardware implemented by the combination of microwave, photonic and electronic subsystems, realizes different functionalities through programming. Here, we propose the first-ever generic-purpose Microwave Photonic processor concept and architecture. This versatile processor requires a powerful end-to-end field-based analytical model to optimally configure all their subsystems as well as to evaluate their performance in terms of the radiofrequency gain, noise and dynamic range. Therefore, we develop a generic model for integrated Microwave Photonics systems. The key element of the processor is the reconfigurable optical core. It requires high flexibility and versatility to enable reconfigurable interconnections between subsystems as well as the synthesis of photonic integrated circuits. For this element, we focus on a 2-dimensional photonic waveguide mesh based on the interconnection of tunable couplers. Within the framework of this Thesis, we have proposed two novel interconnection schemes, aiming for a mesh design with a high level of versatility. Focusing on the hexagonal waveguide mesh, we explore the synthesis of a high variety of photonic integrated circuits and particular Microwave Photonics applications that can potentially be performed on a single hardware. In addition, we report the first-ever demonstration of such reconfigurable waveguide mesh in silicon. We demonstrate a world-record number of functionalities on a single photonic integrated circuit enabling over 30 different functionalities from the 100 that could be potentially obtained with a simple seven hexagonal cell structure. The resulting device can be applied to different fields including communications, chemical and biomedical sensing, signal processing, multiprocessor networks as well as quantum information systems. Our work is an important step towards this paradigm and sets the base for a new era of generic-purpose photonic integrated systems.
Los dispositivos integrados de fotónica de microondas ofrecen soluciones optimizadas para los sistemas de información y comunicación. Generalmente, están compuestos por diferentes arquitecturas en las que subsistemas ópticos y electrónicos se integran para optimizar las prestaciones, el consumo, el tamaño y el coste del dispositivo final. Hasta ahora, los circuitos/chips de propósito específico se han diseñado para proporcionar una funcionalidad concreta, requiriendo así un número considerable de iteraciones entre las etapas de diseño, fabricación y medida, que origina tiempos de desarrollo largos y costes demasiado elevados. Una alternativa, inspirada por las FPGA (del inglés Field Programmable Gate Array), es el procesador fotónico programable. Este dispositivo combina la integración de subsistemas de microondas, ópticos y electrónicos para realizar, mediante la programación de los mismos y sus interconexiones, diferentes funcionalidades. En este trabajo, proponemos por primera vez el concepto del procesador de propósito general, así como su arquitectura. Además, con el fin de diseñar, optimizar y evaluar las prestaciones básicas del dispositivo, hemos desarrollado un modelo analítico extremo a extremo basado en las componentes del campo electromagnético. El modelo desarrollado proporciona como resultado la ganancia, el ruido y el rango dinámico global para distintas configuraciones de modulación y detección, en función de los subsistemas y su configuración. El elemento principal del procesador es su núcleo óptico reconfigurable. Éste requiere un alto grado de flexibilidad y versatilidad para reconfigurar las interconexiones entre los distintos subsistemas y para sintetizar los circuitos para el procesado óptico. Para este subsistema, proponemos el diseño de guías de onda reconfigurables para la creación de mallados bidimensionales. En el marco de esta tesis, hemos propuesto dos nuevos nodos de interconexión óptica para mallas reconfigurables, con el objetivo de obtener un mayor grado de versatilidad. Una vez escogida la malla hexagonal para el núcleo del procesador, hemos analizado la configuración de un gran número de circuitos fotónicos integrados y de funcionalidades de fotónica de microondas. El trabajo se ha completado con la demonstración de la primera malla reconfigurable integrada en un chip de silicio, demostrando además la síntesis de 30 de las 100 funcionalidades que potencialmente se pueden obtener con la malla diseñada compuesta de 7 celdas hexagonales. Este hecho supone un record frente a los sistemas de propósito específico. El sistema puede aplicarse en diferentes campos como las comunicaciones, los sensores químicos y biomédicos, el procesado de señales, la gestión y procesamiento de redes y los sistemas de información cuánticos. El conjunto del trabajo realizado representa un paso importante en la evolución de este paradigma, y sienta las bases para una nueva era de dispositivos fotónicos de propósito general.
Els dispositius integrats de Fotònica de Microones oferixen solucions optimitzades per als sistemes d'informació i comunicació. Generalment, estan compostos per diferents arquitectures en què subsistemes òptics i electrònics s'integren per a optimitzar les prestacions, el consum, la grandària i el cost del dispositiu final. Fins ara, els circuits/xips de propòsit específic s'han dissenyat per a proporcionar una funcionalitat concreta, requerint així un nombre considerable d'iteracions entre les etapes de disseny, fabricació i mesura, que origina temps de desenrotllament llargs i costos massa elevats. Una alternativa, inspirada per les FPGA (de l'anglés Field Programmable Gate Array), és el processador fotònic programable. Este dispositiu combina la integració de subsistemes de microones, òptics i electrònics per a realitzar, per mitjà de la programació dels mateixos i les seues interconnexions, diferents funcionalitats. En este treball proposem per primera vegada el concepte del processador de propòsit general, així com la seua arquitectura. A més, a fi de dissenyar, optimitzar i avaluar les prestacions bàsiques del dispositiu, hem desenrotllat un model analític extrem a extrem basat en els components del camp electromagnètic. El model desenrotllat proporciona com resultat el guany, el soroll i el rang dinàmic global per a distintes configuracions de modulació i detecció, en funció dels subsistemes i la seua configuració. L'element principal del processador és el seu nucli òptic reconfigurable. Este requerix un alt grau de flexibilitat i versatilitat per a reconfigurar les interconnexions entre els distints subsistemes i per a sintetitzar els circuits per al processat òptic. Per a este subsistema, proposem el disseny de guies d'onda reconfigurables per a la creació de mallats bidimensionals. En el marc d'esta tesi, hem proposat dos nous nodes d'interconnexió òptica per a malles reconfigurables, amb l'objectiu d'obtindre un major grau de versatilitat. Una vegada triada la malla hexagonal per al nucli del processador, hem analitzat la configuració d'un gran nombre de circuits fotónicos integrats i de funcionalitats de fotónica de microones. El treball s'ha completat amb la demostració de la primera malla reconfigurable integrada en un xip de silici, demostrant a més la síntesi de 30 de les 100 funcionalitats que potencialment es poden obtindre amb la malla dissenyada composta de 7 cèl·lules hexagonals. Este fet suposa un rècord enfront dels sistemes de propòsit específic. El sistema pot aplicarse en diferents camps com les comunicacions, els sensors químics i biomèdics, el processat de senyals, la gestió i processament de xarxes i els sistemes d'informació quàntics. El conjunt del treball realitzat representa un pas important en l'evolució d'este paradigma, i assenta les bases per a una nova era de dispositius fotónicos de propòsit general.
Pérez López, D. (2017). Integrated Microwave Photonic Processors using Waveguide Mesh Cores [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/91232
TESIS

In this dissertation, the prospect of a quantum technology based on a photonic crystal chip hosting a quantum network made of quantum dot spins interacting via single photons is investigated. The mathematical procedure to deal with the Liouville-Von Neumann equation, which describes the time-evolution of the density matrix, was derived for an arbitrary system, giving general equations. Using this theoretical groundwork, a numerical model was then developed to study the spatiotemporal dynamics of entanglement between various qubits produced in a controlled way over the entire quantum network. As a result, an efficient quantum interface was engineered allowing for storage qubits and traveling qubits to exchange information coherently while demonstrating little error and loss in the process; such interface is indispensable for the realization of a functional quantum network. Furthermore, a carefully orchestrated dynamic control over the propagation of the flying qubit showed high-efficiency capability for on-chip single-photon transfer. Using the optimized dispersion properties obtained quantum mechanically as design parameters, a possible physical structure for the photonic crystal chip was constructed using the Plane Wave Expansion and Finite-Difference Time-Domain numerical techniques, exhibiting almost identical transfer efficiencies in terms of normalized energy densities of the classical electromagnetic field. These promising results bring us one step closer to the physical realization of an integrated quantum technology combining both semiconductor quantum dots and sub-wavelength photonic structures.
ID: 029049734; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 247-254).
Ph.D.
Doctorate
Optics and Photonics

The content of this thesis encompasses the fundamentals, modelling, chip design, nanofabrication process, measurement setup, and experimental results of devices exploiting the optical properties of phase-change chalcogenide materials. Special attention is paid to integrated Si₃N₄ nanophotonic circuits for optical switching and memory applications, as well as to multilayer stacks for colour modulation. Herein, the implementation of the first robust, non-volatile, phase-change photonic memory is presented. By utilising optical near-field effects for Read, Write and Erase operations, bit storage of up to eight transmission levels is demonstrated in a single device employing Ge₂Sb₂Te₅ as the active material. These on-chip memory cells feature single-shot read-out of the transmission state and switching energies as low as 13.4pJ at speeds approaching 1GHz. The capability to readily switch between intermediate states is also demonstrated, a feature that requires complex iteration-based algorithms in electronic phase-change memories. This photonic memory is not only the first truly non-volatile memory---a long-term elusive goal in integrated photonics---but could also potentially represent the first multi-level memory, including electronic counterparts, that requires no computational post-processing or drift correction. These findings provide a pathway towards solving the throughput limitations of current computer architectures by eliminating the so-called von-Neumann bottleneck and portend a new paradigm in all-photonic memory, non-conventional computing, and tunable photonic devices. Finally, novel capabilities in electro-optic colour modulation using phase-change materials are demonstrated. In particular, this thesis offers the first implementation of Ag₃In₄Sb₇₆Te₁₇-based optical cavities for colour modulation on low-dimensional multilayer stacks. Moreover, "gray-scale" image writing is demonstrated by establishing intermediate levels of crystallisation via voltage modulation. This finding, in turn, corresponds to the first demonstration of nonvolatile colour-depth modulation in the emerging phase-change materials nanodisplay technology, featuring resolutions down to 50nm. Furthermore, a comprehensive comparison is carried out for two types of materials: growth- (Ag₃In₄Sb₇₆Te₁₇) and nucleation-dominated (Ge₂Sb₂Te₅) alloys in terms of colour, energy efficiency, and resolution. These results provide new tools for the new generation of bistable and ultra-high-resolution displays and smart glasses while allowing for other potential applications in photonics and optoelectronics.

Esta tesis doctoral tiene como objetivo el diseño y la implementación de dispositivos ópticos novedosos capaces de realizar tareas de procesado de señales de rediofrecuencia, concretamente en las bandas de microondas y milimétricas, explotando para ello efectos de luz lenta que tienen lugar sobre algunos medios físicos que presentan características especiales. Con este propósito, se han investigado estructuras basadas en tecnología de semiconductor en guiaonda, además de estructuras de naturaleza resonante sobre circuitos en silicio y compuestos híbridos fabricados con materiales activos pertenecientes a los grupos III-V sobre silicio. En concreto, se han prouestos diferentes circuitos ópticos capaces de desarrollar tareas propias de desfasador y retardadeo verdadero de banda ancha para señales de radiofrecuncia. El comportamiento de dichos circuitos ópticos bajo estudio se ha caracterizado mediante modelado teórico, quedando éstos adecuadamente validados a través de resultados experimentales. En primer lugar, se han llevado a cabo estudios concernientes a la degradación producida por ruido en estructuras desfasadores formadas por amplificadores ópticos de semiconductor. Como resultado, se ha propuesto una nueva estructura que ha revertido en un rendimiento optimizado en términos de ruido sin que ello suponga una alteración en su funcionnalidad básica como desfasador. Esta estructura desfasadora ha sido el elemento clave en el ensamblado de un filtro elimina banda sintonizable. En segundo lugar, se han utilizado diferentes configuraciones basadas en anillos de silicio con dimensiones micrométricas para el desarrollo e implementación de diferentes procesadores de señal, tales como filtros reconfigurables y sintonizables y retardadores multicanal. Concretamente, se ha introducido un nuevo concepto inspirado en la técnica conocida como SCT, cuyo beneficio redunda en un aumento considerable del ancho de banda útil de las señales de radiofrecuencia a procesar gracias a
Lloret Soler, JA. (2012). Slow Light Effects in Photonic Integrated Circuits with Application to Microwave Photonics [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/16472
Palancia

Nanophotonics is an emerging research field that deals with interaction between light and matter in a sub-micron length scale. Nanophotonic devices have found an increasing number of applications in many areas including optical communication, microscopy, sensing, and solar energy harvesting especially during the past two decades. Among all nanophotonic devices, three main areas, namely photonic crystals, optical metamaterials and plasmonic devices, gain dominant interest in the photonic society owning to their potential impacts. This thesis studies the fabrication and characterization of three types of novel devices within the above-mentioned areas. They are respectively photonic-crystal (PhC) surface-mode microcavities, optical metamaterial absorbers, and plasmonic couplers. The devices are fabricated with modern lithography-based techniques in a clean room environment. This thesis particularly describes the critical electron-beam lithography step in detail; the relevant obstacles and corresponding solutions are addressed. Device characterizations mainly rely on two techniques: a vertical fiber coupling system and a home-made optical transmissivity/reflectivity setup. The vertical fiber coupling system is used for characterizing on-chip devices intended for photonic integrations, such as PhC surface-mode cavities and plasmonic couplers. The transmissivity/reflectivity setup is used for measuring the absorbance of metamaterial absorbers. This thesis presents mainly three nanophotonic devices, from fabrication to characterization. First, a PhC surface-mode cavity on a SOI structure is demonstrated. Through a side-coupling scheme, a system quality-factor of 6200 and an intrinsic quality-factor of 13400 are achieved. Such a cavity can be used as ultra-compact optical filter, bio-sensor and etc. Second, an ultra-thin, wide-angle metamaterial absorber at optical frequencies is realized. Experimental results show a maximum absorption peak of 88% at the wavelength of ~1.58μm. The ultra-fast photothermal effect possessed by such noble-metal-based nanostructure can potentially be exploited for making better solar cells. Finally, we fabricated an efficient coupler that channels light from a conventional dielectric waveguide to a subwavelength plasmonic waveguides and vice versa. Such couplers can combine low-loss dielectric waveguides and lossy plasmonic components onto one single chip, making best use of the two.
QC 20110524

The work presented in this thesis is derived from experimentation in the field of molecular organic photonics. This is done from the standpoint that devices cannot be understood without recourse to the molecular properties and vice versa. A background of nonlinear optics and a brief introduction to the origins of molecular organic nonlinearity is given to aid understanding of the main points of the argument. The dipole moment of several organics was calculated using a simple capacitance method which has been successfully applied to reactive species. These dipole moment results were necessary in the extraction of βʷ from the µβʷ extracted from the EFISH technique. This experiment was performed at 1.064µm and 1.907µm with the latter wavelength being applied to the first in a new class of organic molecules. Results of the work on a number of techniques relevant to thin film devices are also presented. This culminated in an amplitude modulator case study that brought all the techniques together. Finally a discussion on the links between molecular and device related properties justifies the approach taken.

Recent interest in conical diffraction (CD) has led to a large increase in experimental and theoretical investigations over the last two decades, a marked change from the previous 160 quiet years in the field. Once dismissed as an optical curiosity, the phenomenon has emerged as a fascinating area with potential for a large number of practical applications many of which have been realised while others are still being discovered. In this thesis a number of aspects of the theory as recently described are experimentally investigated with a view to strengthening the current theoretical understanding of the phenomenon. Developing from single crystal CD (the simplest case), through cascade CD, nonlinear CD, and with a particular emphasis on the polarisation effects of the phenomenon, a number of areas are investigated. Single crystal CD with circularly (CPL), linearly (LPL), azimuthally and radially polarised light (APL and RPL) is examined. The effect of LPL in removing a section of the ring orthogonally polarised to the incident beam is shown, along with the first investigation into the effects of RPL and APL polarisation effects in CD. The effect of the incident beam spot size on the pattern developed is also investigated and shown to conform to the theory. All findings show good agreement with the current theory. Cascade CD with various numbers of crystals and incident beam polarisations is investigated. Included in these experiments are a variable two crystal cascade and the first demonstration of the different patterns produced for a three crystal cascade when left and right circularly polarised light (LCPL and RCPL, respectively) are used, as recently predicted. As with the single crystal case, results are in agreement with theory. In both the single and cascade cases a cross section of the beam is captured to demonstrated the free space evolution of a CD beam. Simultaneous second harmonic generation (SHG) and CD from a single crystal is described in an update of Bloembergen et al.'s pioneering 1970's investigations with added emphasis on polarisation. SHG in non-phase matched conditions, as well as the influence of incident polarisation on the pattern and type of SHG, are observed. And finally a sensor based on CD demonstrating a simple, practical application of the phenomenon is outlined and a prototype device made and trialled. Using the effect of LPL described earlier to determine the polarisation angle of an incident beam, the device's use as a polarimeter is also tested to determine the specific rotation introduced by optically active liquids with the initial prototype showing results comparable to current methods. This work contains 7 chapters. The first is an introduction to the history of the phenomenon along with a thesis statement. Chapter 2 deals with single crystal CD, chapter 3 contains the expansion from single to cascade CD. The complexities introduced by various types of polarisation are described in chapter 4 for both single and cascade setups. Chapter 5 deals with SHG using a CD crystal and chapter 6 outlines the design and operation of the novel sensor based on the phenomenon. The final chapter is a summary of the work and outlook on the future of the field.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 181-190).
In recent years, quantum cascade lasers have emerged as mature semiconductor sources of light in the terahertz range, the frequency range spanning 1 to 10 THz. Though technological development has pushed their operating temperatures up to 200 Kelvin and their power levels up to Watt-level, they have remained unsuitable for many applications as a result of their narrow spectral coverage. In particular, spectroscopic and tomographic applications require sources that are both powerful and broadband. Having said that, there is no fundamental reason why quantum cascade lasers should be restricted to narrowband outputs. In fact, they possess gain spectra that are intrinsically broad, and beyond that can even be tailored to cover an octave-spanning range. This thesis explores the development of broadband sources of terahertz radiation based on quantum cascade lasers (QCLs). The chief way this is done is through the development of compact frequency combs based on THz QCLs, which are able to continuously generate milliwatt levels of terahertz power covering a fractional bandwidth of 14% of their center frequency. These devices operate on principles similar to microresonator-based frequency combs, and make use of the quantum cascade laser's fundamentally large nonlinearity to phase-lock the cavity modes. These devices will enable the development of ultra-compact dual comb spectrometers based on QCLs, and will potentially even act as complete terahertz spectrometers on a chip. This thesis also uses broadband terahertz time-domain spectroscopy to analyze the behavior of THz QCLs. By using QCLs as photoconductive switches, the usual limitations imposed by optical coupling are circumvented, and properties of the laser previously inaccessible can be directly observed. These properties include the gain and absorption of the laser gain medium, the populations of the laser's subbands, and properties of the waveguide like its loss and dispersion. Knowledge of these properties were used to guide frequency comb design, and were also used to inform simulations for designing better lasers.
by David Patrick Burghoff.
Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 183-197).
Silicon photonics promises to revolutionize the field of optics by allowing for cheap, compact, low-power and low-noise optical systems on chip. In the past decade and a half, the basic functionality and acceptable performance of many individual integrated photonic components have been demonstrated, particularly in the digital regime. However, there are several challenges remaining before these advances can truly be exploited to create large-scale, commercial, analog integrated photonic systems. In this thesis, we address three of these challenges: (1) managing photonic layout and design of large-scale, complex systems jointly with CMOS driving circuitry, (2) integrating analog optical components in silicon, and (3) integrating photonic light sources in silicon. First, we present a comprehensive VerilogA modeling toolkit for the simulation of large, joint photonic plus CMOS systems as part of the creation of a full photonic process design kit (PDK) and demonstrate its use. Other smaller contributions to the PDK and process are also described. Next, we describe the development of two modulators meant for analog applications: an integrated, linearized Mach-Zehnder modulator and an integrated single-sideband modulator, both of which are measured to have impressive performance. Then, we discuss the development of an integrated mode-locked laser to serve as an on-chip light source for precision, low-noise optical applications. Finally, we describe preliminary work toward creating fully integrated analog systems, with the ultimate aim of demonstrating a compact, low-noise microwave oscillator.
by Cheryl M. Sorace-Agaskar.
Ph. D.

Until recently, quantum photonic architecture comprised of large-scale (bulk) optical elements, leading to severe limitations in miniaturization, scalability and stability. The development of the first integrated quantum optical circuitry removes this bottleneck and allows realization of quantum optical schemes whose greatly increased capacity for circuit complexity is crucial to the progress of experimental quantum information science and the development of practical quantum technologies. Integrated quantum photonic circuits within Silica-on-Silicon waveguide chips were simulated, designed and tested. Hundreds of devices have been fabricated with the core components found to be robust and highly repeatable. Amongst these demonstrations, all the basic components required for quantum information applications are shown. The first integrated quantum metrology experiments are demonstrated by beating the standard quantum limit with two- and four-photon entangled states while providing the first re-configurable integrated quantum circuit capable of adaptively controlling levels of non-classical interference of photons. The tested integrated devices show no limitations to obtain high quality performances. It is reported near-unity visibility of two-photon non-classical interference and a Controlled-NOT gate that could in principle work in the fault tolerant regime. It is demonstrated the realization of a compiled version of Shors quantum factoring algorithm on an integrated waveguide chip. This demonstration serves as an illustration to the importance of using integrated optics for quantum optical experimentsThe first integrated optical circuits fabricated in the laser direct-write technology are reported in this Thesis. The quality quantum effects, together with a rapid turnaround process and the capability of writing complex 3D structures are promising for future quantum optical networks. The advent of integrated quantum photonics is necessary for the progression of quantum information science. The results reported in this Thesis provides fundamental building blocks from which future quantum devices will be constructed and presents high-fidelity quantum optics platforms for fundamental investigation

Ce travail de thèse apporte une contribution au domaine émergent de la photonique de Josephson en étudiant des corrélations entre photons émis par effet tunnel inélastique à travers une jonction Josephson soumise à une différence de potentiel électrique. Nous démontrons la possibilité de modifier fortement la statistique de ces photons en incorporant la jonction dans un environnement électromagnétique soigneusement conçu. Dans ce contexte, nous avons élaboré et mesuré une source de rayonnement micro-onde de forte intensité, capable d'émettre des photons dont les statistiques dites « de groupement » et « de dégroupement » ne dépendent que d'un seul paramètre modifiable in situ.Afin de réaliser cette expérience, nous avons mis en place un montage de type Hanbury-Brown & Twiss pour mesurer les corrélations entre photons à l'aide d'amplificateurs linéaires dans un cryostat à dilution. De plus, nous avons conçu des circuits micro-onde où la jonction est exposée à des impédances dépendant spécifiquement de la fréquence. Pour réaliser ces dispositifs, nous avons développé un procédé de nano-fabrication de jonctions Josephson verticales à base de nitrure de niobium utilisant de l'oxyde de magnésium comme barrière tunnel. Enfin, en vue d'une meilleure compréhension de nos échantillons, nous avons contribué aux avancées théoriques liées à l'extension de la théorie dite P(E) de l'effet tunnel inélastique de paires de Cooper, dans le but de décrire les corrélations entre événements tunnel.Ces résultats ouvrent la voie, non seulement à une évolution de ces sources de lumière vers le domaine fréquentiel du THz, mais aussi à l'élaboration d'autres dispositifs basés sur la même physique, tels que des détecteurs et des amplificateurs proches de la limite quantique
This thesis contributes to the emerging field of Josephson photonics through the study of correlations between microwave photons emitted by inelastic Cooper pair tunneling across a voltage-biased Josephson junction. We show that the photon statistics can be strongly modified by embedding the junction into a carefully engineered electromagnetic environment. Doing so, we have elaborated and measured a bright on-demand radiation source, capable of emitting bunched and anti-bunched microwave photons depending only on a single in-situ tunable parameter.In order to conduct this experiment, we have implemented a Hanbury-Brown & Twiss setup for photon correlation measurements using linear amplifiers in a dilution refrigerator. Furthermore, we have designed microwave circuits presenting specific frequency-dependent impedances to the junction. To build these devices we have developed a nano-fabrication process for vertical Josephson junctions made from niobium nitride and using magnesium oxide as a tunnel barrier. Finally, we have contributed to the theoretical advances associated with the understanding of these devices, which extend the so-called P(E) theory of inelastic Cooper pair tunneling to include correlations between tunneling events.These results pave the way for further developments, notably with the possibility to extend the frequency range of these radiation sources to the THz domain but also in view of other devices based on the same physics, such as detectors and amplifiers close to the quantum limit

This thesis presents an investigation into some of the structural colours that are produced in nature. There are many animals and plants that produce structural colour, with a particularly high structural colour diversity in insects. Of the species that exhibit structural colours, three species are the subjects for investigation of this thesis. Those comprise a group of beetles from South-East Asia, Torynorrhina flammea, a buttery, Parides sesostris and a fruit, Margaritaria nobilis, both from South American rainforests. The structures that produce the vivid colours of these species were analysed using electron microscopy. This information aided the design and creation of three inorganic, synthetic replicas of the natural structures. The fruit of Margaritaria nobilis was structurally analysed, yielding the discovery of a novel multilayer fibre. These fibres were cylindrical in design and were found to be layered together producing the epidermis of the fruit. The multilayer structure produced a vivid blue colour appearance, which is believed to offer a selective advantage because the colour deceives birds into thinking that the fruit contains nutritious flesh. This selective advantage earns M. nobilis the label of mimetic fruit. The structure found within the M. nobilis fruit epidermis inspired the synthesis of a structure which comprises single cylindrical multilayer fibres. The synthetic fibres were manufactured from elastic materials which allow the structure to be deformed under strain and, therefore, a change in colour can be observed. As the structure was stretched, this made the layers get thinner and, therefore, the colour of the fibre blue-shifted. The fibre was able to be stretched to over twice its original length which yields a shift in peak reflected wavelength of over 200 nm. Four beetles from the Torynorrhina flammea species were investigated with the aim of replicating the nanostructures responsible for their colour appearance. The initial interest in the beetles came from their strikingly vivid colour appearances. The structure responsible for the vivid colours in all four of the subspecies is a multilayer with high structural order and over 100 laminae. Both of these attributes contribute to the saturation of the colours exhibited. The multilayer was found to be intersected by an array of rods, the long axis of which is orthogonal to the surface. The rods are believed to be the cause of an interesting diffraction phenomenon exhibited by the beetles. Using imaging scatterometry, the structure was found to diffract the colour produced by the multilayers into an annulus around a specularly reflected white spot. This inspired the synthesis of a multilayer permeated with an array of holes with the aim of replicating a system that could reproduce the annular pattern of colour reflection. The initial synthesised system comprised a quarter-wave stack with a perfectly ordered hexagonal array of holes permeating the surface orthogonally. The sample displayed the scattering characteristics of a hexagonal array, and the reflection spectra of the multilayer stack. When disordered hexagonal arrays were milled into the structure with a focussed ion beam, the scattering pattern started to show more of the green colour from the multilayer and less of the ordered scattering pattern. The highly disordered, synthesised structure displayed no hexagonal scattering pattern, but instead it showed a highly scattered bluish-green colouration. One sample was created by directly mapping out the array of holes using an image of the original array from one of the beetle samples. This sample was expected the same annular diffraction pattern as the beetles, however, the sample instead exhibited the same scattering pattern as the highly disordered array. Some structurally coloured systems in nature have more than one light scattering structure, all of which contribute to the overall colour of the system. For complicated systems such as this, it is necessary to devise a technique to characterise the individual scattering structures separately. One such species that displays a complex, multicomponent system is Parides sesostris. The male of the species displays bright green patches on the dorsal side of the forewings which are made up of thousands of green wing scales. These green scales contain a 3D gyroid poly-crystal at centre with a membrane layer surrounding the underside of each scale and a scattering structure on top. Using focussed ion beam milling techniques allowed the individual characterisation of each of these structures. The gyroid poly-crystal was found to reflect not green but blue wavelengths. This led to the discovery by another group [1] that the scales contain at least one type of fluorophore. The removal of the membrane structure and some of the gyroid poly-crystal from the base of the scale resulted in the change of the overall scale structure from green to cyan. This suggests that the membrane maybe a significant source of fluorescence. Computational modelling, without fluorescence, suggests that the addition of the membrane layer to the gyroid does not shift the band-gap wavelengths; however, the overall reflection intensity does increase. The scattering structure on the top side of each scale is comprised a bi-grating which sits on top of the 3D gyroid structure. The long periodicity of the bi-grating protrudes above the surface, resulting in the very top layer of the scale to be a mono-grating. This whole structure decreases the angular-dependence of the colour by efficiently scattering the incident light into the gyroid and also scattering the reflected light from the gyroid, resulting in a double-scattering. FIB-milling was used to isolate the scattering part of the structure. Analysis of this component of the structure revealed that it was not a source of the green colour itself; however, it did show the characteristic scattering pattern of a mono-grating. The small periodicity of the bi-grating did not produce a scattering pattern since the periodicity is too small to produce optical diffraction at normal incidence. To characterise the effect of the fluorophores, the whole scale structure was photo-bleached using ultra-violet radiation for two months with the aim of destroying the fluorophores contained within the structure. The expected result occurred which was the blue-shifting of the peak reflected wavelengths. However, it could not be confirmed whether or not the photo-bleaching reduced the physical size of the light scattering structures which would, in theory, result in a blue-shift of the peak reflected wavelengths. The male P. sesostris green wing scales were also the subject for investigation for trying to make inorganic replicas of the gyroid-polycrystal. A surface sol-gel coating process was utilised to coat the green wing scales with titania. This coating process was performed using a few different methods. Half of the samples were coated with TiO2 and the other half with tin-doped TiO2. Half of each of these samples had their surfaces dendritically amplified before the coating processes and the other half were left untreated. The samples were coated with 25 surface sol-gel (SSG) cycles of each treatment at a time. After each 25 cycle treatment the samples were optically characterised. The total number of cycles applied to the samples at the end was 150. The addition of layers of titania resulted in a general red-shift that was higher for the tin-doped titania samples than for the titania samples. Another general trend found was that the samples that had their surfaces dendritically amplified, produced a lower red-shift in peak wavelength. This was contrary to the hypothesis that the amplification process was supposed to aid the SSG coating process and, therefore, increases the red-shift in peak wavelength.

Photonic signal processing has been considered a promising solution to overcome the inherent bandwidth limitations of its electronic counterparts. Over the last few years, an impressive range of photonic integrated signal processors have been proposed with the technological advances of III-V and silicon photonics, but the signal processors offer limited tunability or reconfigurability, a feature highly needed for the implementation of programmable photonic signal processors. In this thesis, tunable and reconfigurable photonic signal processors are studied. Specifically, a photonic signal processor based on the III-V material system having a single ring resonator structure for temporal integration and Hilbert transformation with a tunable fractional order and tunable operation wavelength is proposed and experimentally demonstrated. The temporal integrator has an integration time of 6331 ps, which is an order of magnitude longer than that provided by the previously reported photonic integrators. The processor can also provide a continuously tunable fractional order and a tunable operation wavelength. To enable general-purpose signal processing, a reconfigurable photonic signal processor based on the III-V material system having a three-coupled ring resonator structure is proposed and experimentally demonstrated. The reconfigurability of the processor is achieved by forward or reverse biasing the semiconductor optical amplifiers (SOAs) in the ring resonators, to change the optical geometry of the processor which allows the processor to perform different photonic signal processing functions including temporal integration, temporal differentiation, and Hilbert transformation. The integration time of the signal processor is measured to be 10.9 ns, which is largely improved compared with the single ring resonator structure due to a higher Q-factor. In addition, 1st, 2nd, and 3rd of temporal integration operations are demonstrated, as well as a continuously tunable order for differentiation and Hilbert transformation. The tuning range of the operation wavelength is 0.22 nm for the processor to perform the three functions. Compared with the III-V material system, the CMOS compatible SOI material system is more cost effective, and it offers a smaller footprint due to the strong refractive index contrast between silicon and silica. Active components such as phase modulators (PMs) can also be implemented. In this thesis, two photonic temporal differentiators having an interferometer structure to achieve active and passive fractional order tuning are proposed and experimentally demonstrated. For both the active and passive temporal differentiators, the fractional order can be tuned from 0 to 1. For the active temporal differentiator, the tuning range of the operation wavelength is 0.74 nm. The use of the actively tunable temporal differentiator to perform high speed coding with a data rate of 16 Gbps is also experimentally demonstrated.

Las fases geométricas son tema de investigación actual en diversas áreas de la física. Interesa investigarlas tanto por razones de carácter teórico, cuanto por razones ligadas a sus aplicaciones. Entre estas últimas resaltan las aplicaciones en información cuántica. Un computador cuántico está basado en la posibilidad de generar, almacenar y manipular bits de información codificados en los grados de libertad de sistemas cuánticos. Estos son llamados qubits. Los qubits son superposiciones coherentes de dos estados fundamentales. Mientras su contraparte clásica puede valer 0 o 1 excluyentemente, el qubit puede tomar ambos valores 0 y 1 simultáneamente. Esto hace posible procesar información con mucha mayor rapidez en comparación a una computadora clásica. El problema central con los qubits es que son sumamente frágiles, de modo que su tiempo de vida media es muy pequeño. El fenómeno que lleva a un estado de superposición hacia un estado clásico se llama decoherencia. Para que un computador cuántico sea viable, es necesario contar con qubits cuya vida media sea mayor que el tiempo que toma realizar operaciones sobre ellos (computación). Una ruta muy promisoria es la que se basa en las fases geométricas. Ellas permiten realizar operaciones que, de un lado, pueden ser muy rápidas y, de otro lado, pueden ser inmunes o muy robustas frente a la decoherencia. Para implementar computación cuántica geométrica, es entonces necesario ser capaz de manipular fases geométricas con gran versatilidad. Contribuyendo a este ín, esta tesis presenta nuevos resultados en la manipulación de fases geométricas que aparecen cuando el qubit está codificado en fotones polarizados. Esta tesis contiene dos partes principales. En la primera parte hacemos un intento preliminar en manipular fases en estados de polarización. Específicamente, tratamos a la fase de Pancharatnam (fase total) que resulta de evoluciones unitarias arbitrarias. Discutimos los aspectos teóricos involucrados y mostramos en detalle como hacer que un estado de polarización siga cualquier curva sobre la esfera de Poincaré. Luego presentamos los métodos utilizados para llevar a cabo las mediciones de la fase total acumulada a lo largo de la evolución del estado. En la segunda parte de esta tesis, extendemos nuestros métodos y desarrollamos técnicas para suprimir localmente las fases dinámicas que puedan aparecer durante la evolución del estado de polarización. Esto nos permite observar y medir fases geométricas. Usando métodos similares a los discutidos en la primera parte, mostramos finalmente que las fases geométricas observadas experimentalmente coinciden con las predicciones teóricas con buena aproximación.
Tesis

Silicon photonics technologies have the potential to overcome the bandwidth limitations inherent in electrical interconnect technology. Modulation technology which is efficient both in terms of size and energy is required if silicon photonics are to replace electronics for interconnect communications. Silicon germanium technologies have the potential to not only improve the performance of current semiconductor devices but to also extend the reach of semiconductor technology into new areas such as development of a room temperature THz laser. A novel process that allows easy fabrication of Ohmic contacts to moderately doped n-type Germanium has been developed. This process has the potential to allow the realization of new devices which have been previously hampered by non-Ohmic contacts or dopant segregation problems. This work reported in this thesis also includes the design and fabrication of Ge/SiGe QCSE devices. Thin barrier QCSE designs have been put forward as a potential way to produce a more energy efficient modulator. Simulations of the devices show that a design with 16 nm Ge QWs and 8 nm SiGe barriers can provide effective modulation covering the entire optical communications C band with less than 3 V DC offset and achieve a contrast ratio across the band of over 3 dB. It was also shown that despite the thin barriers the wavefunctions remain well confined to the QWs suggesting that even thinner barriers are possible. MQW structures with thin barriers were grown and photodiodes fabricated from them. While the wafers did not have barriers as thin as designed they were thinner than devices previously demonstrated. From photocurrent measurements it was shown that these MQW structures were able to effectively modulate light near the 1550 nm wavelength with better performance than devices found in the literature.

This manuscript investigates the use of microring resonators to create all-optical reservoir-computing networks implemented in silicon photonics. Artificial neural networks and reservoir-computing are promising applications for integrated photonics, as they could make use of the bandwidth and the intrinsic parallelism of optical signals. This work mainly illustrates two aspects: the modelling of photonic integrated circuits and the experimental results obtained with all-optical devices. The modelling of photonic integrated circuits is examined in detail, both concerning fundamental theory and from the point of view of numerical simulations. In particular, the simulations focus on the nonlinear effects present in integrated optical cavities, which increase the inherent complexity of their optical response. Toward this objective, I developed a new numerical tool, precise, which can simulate arbitrary circuits, taking into account both linear propagation and nonlinear effects. The experimental results concentrate on the use of SCISSORs and a single microring resonator as reservoirs and the complex perceptron scheme. The devices have been extensively tested with logical operations, achieving bit error rates of less than 10^−5 at 16 Gbps in the case of the complex perceptron. Additionally, an in-depth explanation of the experimental setup and the description of the manufactured designs are provided. The achievements reported in this work mark an encouraging first step in the direction of the development of novel networks that employ the full potential of all-optical devices.

In this work, I studied the hybrid system based on self-assembled guanosine crystal (SAGC) conjugated to wide-bandgap semiconductor gallium nitride (GaN). Guanosine is one of the four bases of DNA and has the lowest oxidation energy, which favors carrier transport. It also has large dipole moment. Guanosine molecules self-assemble to ribbon-like structure in confined space. GaN surface can have positive or negative polarity depending on whether the surface is Ga- or N-terminated. I studied SAGC in confined space between two electrodes. The current-voltage characteristics can be explained very well with the theory of metal-semiconductor-metal (MSM) structure. I-V curves also show strong rectification effect, which can be explained by the intrinsic polarization along the axis of ribbon-like structure of SAGC. GaN substrate property influences the properties of SAGC. So SAGC has semiconductor properties within the confined space up to 458nm. When the gap distance gets up to 484nm, the structure with guanosine shows resistance characteristics. The photocurrent measurements show that the bandgap of SAGC is about 3.3-3.4eV and affected by substrate properties. The MSM structure based on SAGC can be used as photodetector in UV region. Then I show that the periodic structure based on GaN and SAGC can have photonic bandgaps. The bandgap size and the band edges can be tuned by tuning lattice parameters. Light propagation and emission can be tuned by photonic crystals. So the hybrid photonic crystal can be potentially used to detect guanosine molecules. If guanosine molecules are used as functional linker to other biomolecules which usually absorb or emit light in blue to UV region, the hybrid photonic crystal can also be used to tune the coupling of light source to guanosine molecules, then to other biomolecules.

Thesis (Ph. D.)--School of Materials Science and Engineering, Georgia Institute of Technology, 2006.
Summers, Christopher, Committee Chair ; Chang, Gee-Kung, Committee Member ; Carter, Brent, Committee Member ; Wang, Zhong Lin, Committee Member ; Meindl, James, Committee Member ; Li, Mo, Committee Member.

Optical microresonators (OMRs) have been widely applied in various sensing applications. However, the sensing performances of conventional OMR-based sensors are subject to resonance parameters and fabrication accuracy and are further restricted by the interrogation scheme used. Recently, microwave photonic (MWP) techniques have been used to realize high-speed and high-resolution OMR-based sensors. So far, those MWP schemes are either still fabrication dependent or only applicable to specific uses, and rare attention has been paid to achieving multi-parameter sensing that is indispensable in real-life applications. The thesis proposes novel OMR-based MWP sensing schemes with improved sensing performances. Based on the MWP sideband processing technique, a new MWP interrogation scheme, which features a high resolution regardless of the OMR parameters and fabrication imperfections, is proposed and demonstrated in the sensing of temperature, humidity, and magnetic field, respectively, with high sensitivity and high resolution, where an automatic correction mechanism is added to compensate for resonance lineshape variation automatically. Next, the high-resolution MWP sensing scheme is extended to cascaded OMRs to enable multi-parameter sensing capability. The simultaneous high-resolution MWP sensing of temperature and humidity with two cascaded OMRs is demonstrated. Lastly, machine learning (ML) and deep learning (DL) techniques are applied to MWP sensing to reduce the complexity further. The temperature-insensitive MWP humidity sensor is first achieved with the support vector regression. Then, a new MWP multi-parameter sensing paradigm with the least requirement on the OMR structure is proposed by incorporating DL to process the raw interrogation results directly. The simultaneous MWP sensing of temperature and humidity with a single optical resonance using the convolutional neural tangent kernel is demonstrated.

In der vorliegenden Arbeit werden ZnO-Mikronadeln bezüglich ihrer Anwendbarkeit als Mikroresonatoren untersucht. Dabei stehen Kavitätsmoden im Fokus der Untersuchungen, die sich nur senkrecht zur Nadelachse ausbreiten, sprich innerhalb der hexagonalen Nadelquerschnittsfläche. Folglich wird der Einfluss der Gestalt der Querschnittsfläche auf Resonatoreigenschaften wie Propagation, Form, Direktionalität und Qualität der Kavitätsmoden sowohl theoretisch simuliert als auch experimentell nachgewiesen. Die dabei beobachteten hohen Qualitätsfaktoren von Flüstergalerie-Moden ermöglichen es darüberhinaus, Wechselwirkungseffekte zwischen Kavität und Mode zu beobachten. Der erste Teil der Arbeit beschäftigt sich mit der regulären, polygonalen Resonatorform und deren Einfluss auf die Dimensionalität von Kavitätsmoden sowie deren mögliche Wechselwirkung mit dem elektronischen System des Resonators. Beispielhaft wird ein hexagonaler Resonator zur Veranschaulichung gewählt, wie er durch ZnO-Mikronadeln gegeben ist, undmittels Finite-Difference-Time-Domain (FDTD)-Simulationen sowie winkelaufgelöster Photolumineszenz (PL)-Spektroskopie untersucht. Die aufgenommenen PL-Spektren können unter Zuhilfenahme photonischer Dispersionskurven von ein- und zwei-dimensionalen Kavitätsmoden reproduziert werden. Basierend auf diesen Ergebnissen wird der Einfluß der Resonatorecken auf die Lichtauskopplung diskutiert und mittels winkelaufgelöster, anregungsabhängiger und temperaturabhängier PL-Spektroskopie nachgewiesen. Desweiteren wird auf die Wechselwirkung zwischen dem Resonator und den Kavitätsmoden eingegangen, imSpeziellen auf die starke Kopplung zwischen Flüstergalerie-Moden und freien Exzitonen imResonatormaterial. Bereits erschienende Publikationen zu diesemThema werden präsentiert und kritisch hinterfragt. Dabei wird ein Leitfaden aufgestellt, der eine Evaluierung möglicher Polaritonen-Phänomene ermöglicht. Um Wechselwirkungen dieser Art auch in den hier untersuchtenMikronadeln nachzuweisen, werden Hochanregungs-PL-Messungen durchgeführt. Dabei werden Messungen in der Mitte der Nadel sowie in der Nähe ihrer Ecken getätigt, um spezielle Polaritonen-Propagationseffekte beobachten zu können. Im zweiten Teil der Arbeit wird der Einfluß von irregulären und inhomogenen Resonatorformen auf die Bildung von Flüstergalerie-Moden diskutiert. Dafür werden elongierte Teile der Nadeln, die durch laterale Auswüchse entstehen, winkelaufgelöst bezüglich einer gerichteten Auskopplung von Kavitätsmoden vermessen und verzerrte Mikronadeln, wie sie beim Biegen entstehen, bezüglich der entstehenden Deformationseffekte und deren Einfluss auf die Kavitätsmoden mittels hochaufgelöster Mikro-PL untersucht. Die experimentellen Ergebnisse zu irregulären Resonatoren können durch FDTD-Simulationen bestätigt werden. Desweiteren wurden Mikronadel- und Nanonadel-Quantengraben-Heterostrukturen hergestellt und deren Lumineszenzeigenschaften diskutiert. Dabei wird speziell auf die Homogenität der Quantengrabenemission eingegangen und Strategien zur Realisierung einer starken Kopplung zwischen Flüstergalerie-Moden und Quantengraben-Exzitonen aufgestellt. Diese Strategien werden experimentell umgesetzt und deren Ergebnisse anhand von Kathodolumineszenzmessungen vorgestellt.

Stimulated Brillouin scattering (SBS) involves nonlinear interaction of an optical wave with material, which under the phase-matching condition results in generation of an acoustic wave. In turns, part of the optical wave is scattered by the acoustic wave through an inelastic scattering process. SBS enables unique applications in optical fibers and more recently in on-chip photonic waveguides, ranging from RF-signal processing to lasing, frequency combs, RF sources, and light storage. Harnessing on-chip SBS paves the way to photonic integration by enabling powerful functionalities in an integrated, scalable, energy-efficient and potentially CMOS-compatible platform. In this thesis, we explore the possibility of enabling SBS in a silicon-based platform by designing, fabricating and characterizing a hybrid silicon-chalcogenide waveguide, which shows significant improvement in terms of nonlinear losses and SBS gain compared to a standard silicon waveguide. The SBS response in photonic waveguides including the silicon-chalcogenide platform is subject to spectral broadening which influences the quality of the devices whose performance are relying on the narrow linewidth of SBS. The spectral broadening is mainly due to structural non-uniformities along the waveguides which affect the local SBS response and consequently deteriorates the strength of the integrated SBS response. Therefore, characterizing those waveguides is of great importance. To address this issue, we employed the principle of distributed SBS sensing to monitor the on-chip waveguides. However, since the waveguides length is on the order of cm and mm, the spatial resolution of the distributed technique needs to be very high, preferably in the sub-mm regime, which is the main goal of this thesis.

Silicon based integrated circuits has been dominating the electronics technology industry in the last few decades. As the telecommunications and the computing industry slowly converges together, the need for a material to build photonics integrated circuits (PIC) that can be cost-effective and be produced in mass market has become very important. This thesis describes and outlines the characteristics of high index contrast waveguides as a building blocks that can be designed, fabricated and employed on devices in silicon photonics. Initially in this work, a fully vectorial H-field based finite element method has been used to obtain the modal characteristics of high index contrast bent waveguide to get a better understanding of the curved section. Through the beam propagation method, the propagation losses and the spot-size along the propagation distance are obtained when a mode from the straight guide is launched into a bent guide. It is also learnt that mode beating exists at the junction of a straight-to-bent waveguide, in which higher order modes will also be generated. It will be shown in this work that power do exchange between the two polarization states, therefore the polarization conversion, the power losses and the bending losses will be investigated. It will also shown in here that by applying lateral offsets with coupled waveguides of unequal widths, the insertion loss can be reduced. Secondly, for a high index contrast waveguide such as the silicon strip waveguide with a nanoscale cross-section, modes in such waveguide are not purely TE or TM but hybrid in nature, with all the six components of their E and H-fields being present. Therefore a detail analysis of the modal field profiles along with the Poynting vector profile will be shown. The effects of waveguide's width and height on the effective indices, the hybridness, the modal effective area and the power confinement in the core or cladding has been studied. Furthermore the modal birefringence of such strip waveguide will be shown. It will be presented that for a strip waveguide with height of 260 nm, single mode exists in the region of the width being 200 nm to 400 nm and that the modal effective is at its minimum when width is around 320 nm for both polarization states. Thirdly, a compact polarization rotator with an asymmetric waveguide structure design, suitable for fabrication that does not require a slanted side wall or curved waveguide is considered in this work. It will be shown in here that due to the hybrid nature of the asymmetric waveguide design, maximum polarization rotation (from TE to TM) will be achieve by enhancing the non-dominant field profile of both polarized fundamental mode. As the modal hybridness and the propagation constants of both polarized modes will be obtained, the half-beat length, polarization conversion and polarization cross-talk will be calculated by using the FEM and the least squares residual boundary method (LSBR). It is learnt that a compact single stage polarization rotator with a device length of 48 μm with more than 99% of polarization conversion is achieved in this work. Finally, a study of vertical and horizontal slot waveguide will be shown. Based on silicon strip waveguide, a detail modal characteristics of E and H-fields along with the Poynting vectors are presented. It will be shown that for slot waveguide, high power confinement and power density will be achieved in the slot area. It will be presented that by optimising the waveguide and slot dimension, the performance of the power confinement and power density in the slot region can be improved.

Cryptosporidium is a protozoan parasite causing cryptosporidiosis; a diarrheal disease of varying severity. The infection is transmitted by tiny spores called oocysts resistant to harsh environmental conditions and various disinfectants. Cryptosporidium infection and recovery from the illness is dependent on the body's immune system. It is important to be able to detect these parasites quickly to reduce the risk of infection. Multiple-angle light scattering systems have been developed for detecting cryptosporidium oocysts suspended in water. The proposed systems were set up with a single wavelength (red AlGaInP laser: 658.4 nm) and two wavelength (violet InGaN laser: 405.7 nm and red AlGalnP laser: 658.4 nm) sources. The single wavelength system was developed for measuring particle concentration and particle size and refractive index. It combined multiple-angle scattering detection, to collect angle- resolved scattered intensities from suspensions, and the partial least square regression method (PLS-R) to predict characterizing information of samples under investigation based on calibration models. The calibration models were composed from the calibration data generated from the experiments for particle concentration measurement and according to Mie theory with refraction and transmission corrections included for particles' size and refractive index measurements. The dual wavelength system was set up for particle identification by using relative wavelength scattered intensity as the identifying means. Measurement of particle concentration, size and refractive index by the single multiple angle light scattering system was validated using polystyrene spheres in aqueous suspensions. Applying the systems to cryptosporidium oocyst suspensions, the concentration measurement results had lowest errors from the references 9.5 % at concentration of 2.00x10600cysts/ml in mono-dispersion and 3.6 % at concentration of 7.50x105 oocysts/ml for cryptosporidium and mixed suspensions with polystyrene sphere suspensions. The measured cryptosporidium oocysts' size and refractive index were 4.37 ± 0.16!-Lm and 1.38 ± 0.05 which also had good agreement to the reference value (size: 4.38 ± 0.23 urn, refractive index: 1.37). The dual wavelength multiple-angle light scattering system collected the relative wavelength scattered intensities from suspensions of the cryptosporidium oocysts comparing to polystyrene spheres and E.coli. The relative wavelength multiple-angle scattered intensity of cryptosporidium oocysts suspension showed a characteristic scattering pattern and significantly different pattern from the polystyrene spheres and bacteria E.coli. The results presented in this research have demonstrated that the proposed multiple-angle light scattering systems have the capability to initially detect cryptosporidium oocysts in suspension. These systems could be further developed for online cryptosporidium detection by combination with pattern recognition techniques.

We investigate the design, fabrication, and experimental characterization of high quality factor photonic crystal nanobeam cavities, with theoretical quality factors of \(1.4 × 10^7\) in silicon, operating at ~1550 nm. By detecting the cross-polarized resonantly scattered light from a normally incident laser beam, we measure a quality factor of nearly \(7.5 × 10^5\). We show on-chip integration of the cavities using waveguides and an inverse taper geometry based mode size converters, and also demonstrate tuning of the optical resonance using thermo-optic effect. We also study coupled cavities and show that the single nanobeam cavity modes are coupled into even and odd superposition modes. Using electrostatic force and taking advantage of the highly dispersive nature of the even mode to the nanobeam separation, we demonstrate dynamically reconfigurable optical filters tunable continuously and reversibly over a 9.5 nm wavelength range. The electrostatic force, obtained by applying bias voltages directly to the nanobeams, is used to control the spacing between the nanobeams, which in turn results in tuning of the cavity resonance. The observed tuning trends were confirmed through simulations that modeled the electrostatic actuation as well as the optical resonances in our reconfigurable geometries. Finally we demonstrate reconfiguration of coupled cavities by using optical gradient force induced mechanical actuation. Propagating waveguide modes that exist over wide wavelength range are used to actuate the structures and in that way control the resonance of a localized cavity mode. Using this all-optical approach, more than 18 linewidths of tuning range is demonstrated. Using an on-chip temperature self-referencing method that we developed, we determined that 20% of the total tuning was due to optomechanical reconfiguration and the rest due to thermo-optic effects. By operating the device at frequencies higher than the thermal cut-off, we show high speed operation dominated by just optomechanical effects. Independent control of mechanical and optical resonances of our structures, by means of optical stiffening, is also demonstrated.
Engineering and Applied Sciences

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.
26
Title as it appears in MIT degrees awarded booklet, February 19, 2014: Multiwavelength integrated ring laser. Cataloged from PDF version of thesis.
Includes bibliographical references (pages 151-153).
In this thesis, an interesting approach for a photonic laser source is presented. By using integrated photonic resonators with an external gain medium, we are able to build a laser that offers a number of advantages including reducing the electrical and thermal load on the integrated chip socket, eliminating the challenges of integrating gain mediums into CMOS processes, allowing for lasing at virtually arbitrary wavelengths, the possibility of multiwavelength operation with a shared gain medium, elimination of closed-loop control of wavelength tuning, ability to control laser output and wavelength on-chip, and the potential for wavelength modulation using novel resonator tuning designs. Several iterations of the laser were built and characterized culminating in a final integrated laser that showed a wall-plug efficiency of 1.10% at a maximum output power of 6 mW. We demonstrate even higher wall-plug efficiencies using commercial filters. We also demonstrate wavelength modulation and open eye diagrams for data rates up to 5 Gb/s using the laser in a communications link. Simulations of birefringent filters are performed to model wavelength dependence on polarization which when manipulated can give rise to single or multiwavelength lasing. Finally, the power spectral density is simulated by assuming uncorrelated phase between lasing modes.
by Johanna S. Chong.
M. Eng.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 173-183).
As raw compute power of a single chip continues to scale into the multi-teraflop regime, the processor I/O communication fabric must scale proportionally in order to prevent a performance bottleneck. As electrical wires suffer from high channel losses, pin-count constraints, and crosstalk, they are projected to fall short of the demands required by future memory systems. Silicon-photonic optical links overcome the fundamental tradeoffs of electrical wires; dense wavelength division multiplexing (DWDM) - where multiple data channels share a single waveguide or fiber to greatly extend bandwidth density - and the potential to combine at chip-scale with a very large scale integrated (VLSI) CMOS electrical chip make them a promising alternative for next-generation processor I/O. The key device for VLSI photonics is the optical microring resonator, a compact micrometer-scale device enabling energy-efficient modulation, DWDM channel selection, and sometimes even photo-detection. While these advantages have generated considerable interest in silicon-photonics, present-day integration efforts have been limited in scale owing to the difficulty of integration with advanced electronics and the sensitivity of microring resonators to both process and thermal variations. This thesis develops and demonstrates the pieces of a photonically-interconnected processor-to-memory system. We demonstrate a complete optical transceiver platform in a commercial 45 nm SOI process, showing that optical devices can be integrated into an advanced, commercial CMOS SOI process even without any changes to the manufacturing steps of the native process. To show that photonic interconnects are viable even for commoditized and cost-sensitive memory, we develop the first monolithic electronic-photonic links in bulk CMOS. As the stabilization of ring resonators is critical for use in VLSI systems, we contribute to the understanding of process and thermal variations on microring resonators, leading to the demonstration of a complete auto-locking microring tuning system that is agnostic to the transmitted data sequence and suitable for unencoded low-latency processor-to-memory traffic. Finally, the technology and methods developed in this work culminate in the demonstration of the world's first processor chip with integrated photonic interconnects, which uses monolithically integrated photonic devices to optically communicate to main memory.
by Chen Sun.
Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 137-142).
Silicon photonics is moving fast toward industrialization. It satisfies the increasing demand for higher speed, larger bandwidth communication. Thus it has a wide range of applications including high-performance computing, data center, telecom etc.. However, the on-chip (waveguide) and off-chip (fiber) components for silicon photonics have quite different characteristics for the polarizations of light. The polarization dependence of on-chip silicon photonics components still remains a bottleneck for the real application of it. Efficient devices for manipulating polarizations are highly demanded. Herein, we present the designs of adiabatic polarization rotator (PR) and polarization splitter and rotator (PSR) to deal with this issue. With their adiabatic nature, larger bandwidth (>100 nm) and better fabrication tolerance have been achieved. Besides, the effort toward the realization of a full-functional two-input two-output PBS, which is an exact correspondent of the traditional cube PBS in free space is presented. The structure was fabricated in a commercial state-of-art CMOS foundry and has a bandwidth of over 150 nm and less than -10dB crosstalk level. Though its application in traditional communication can be replaced by PS, PR or PSR, its application in more accurate systems such as polarization-entangled states generation and manipulation in quantum optics or on-chip heterodyne interferometers. Moreover, original compact-ring resonator based even-dropping optical bus system is proposed and analyzed in detail. Large free-spectral range offered by small radius micro-ring gives more communication channels to fully utilize the power of wavelength division multiplexing (WDM). Furthermore, a multi-channel WDM broadcasting system is proposed using the optical bus design. We have demonstrated a two-channel broadcasting system, which can be further increased to more than 16 channels.
by Zhan Su.
S.M.

Many applications in photonics rely on the ability to confine light in small volumes. This is commonly achieved by utilizing two or more materials with a large refractive index contrast, such as silicon and silicon dioxide, diamond and air, etc. However, techniques available to fabricate sub-wavelength structures in these materials, including electron beam lithography followed by etching, or focused ion beam milling, are often costly and time consuming. In addition, there are few options to tune the optical response of fabricated devices. A panoply of new photonic applications can be unlocked by taking advantage of the versatility of so-called ”soft” materials. Though they typically have a lower index contrast, they can be manipulated by a variety of accurate and rapid techniques, in addition to the standard cleanroom approaches. Polymers and colloids are thus attractive materials for photonics because of the large toolbox available for their fabrication on length scales comparable to the wavelength of light. In this thesis, photonic applications based on three different platforms are presented, each of which comes with a unique fabrication approach: (1) colloidal self-assembly of three dimensional periodic structures, (2) roll-to-roll nano-imprint lithography (R2RNIL) of polymers towards functional photonic devices such as colorimetric sensors and on-chip spectrometers and (3) biopolymer (silk) microspheres. Spherical polystyrene colloids are self-assembled into a 3D face-centered cubic (fcc) lattice and are embedded in SiO2 or TiO2. Once the colloids are burnt out, a porous structure which preserves the fcc arrangement remains. It possesses optical properties of a photonic crystal, which are modified by infiltrating liquids that create partially filled patterns throughout the structure. The evolution of the photonic properties are investigated as deviations from perfect periodicity increase. Furthermore, the opportunity to realize optically pumped lasers (e.g. band edge or random lasers) in this material platform is discussed. Polymers have numerous desirable properties for the future of photonic devices. However, they suffer from a low refractive index contrast. The ability to create functional polymer photonic devices for chip-scale operation is demonstrated, and simulations and experiments are conducted for various photonic components, including waveguides, gratings, and ring resonators. Two dimensional photonic crystals with 100 nm feature sizes are produced by the R2RNIL and they display tunable structural color. Photonic elements for on-chip photonic integration are also fabricated with R2RNIL. S-shaped waveguides are coupled to ring resonators and ring resonator quality (Q) factors close to 60,000 are measured. A grating coupler setup is built and tested by measuring silicon-on-insulator devices featuring rings coupled to the waveguide, and Qs of 20,000- 30,000 are obtained. Silk is a special polymer in the sense that it is biocompatible and thus interfacing photonic components with internal organs can be envisaged. Here, investigations of silk’s photonic properties in the context of microspheres are performed. A tapered fiber is used to couple in and out of the whispering gallery optical resonances of silk microspheres. Qs of 500-1000 are determined from transmission measurements; simulations and scanning electron micrographs confirm that the reduction in Q is due to deviations from a completely spherical shape.
Chemistry and Chemical Biology

Integrated photonics is a promising technology which has applications in many areas such as biomedical, aero-space, radar, distributed computing, sensors and high speed signal processing. The aim is to reduce the cost, size and power consumption of optical devices and components by integrating them on a nano-scale. Currently silicon (Si) is the main material of choice in integrated photonics, however it has drawbacks which limit its uses in particular for high efficiency optical sources and detectors. The focus of this thesis will therefore be on finding an optimized integrated photonics platform which can support the integration of an optical source, photodetector, optical modulator and waveguides with matched confinement factors, whilst maintaining compatibility with existing CMOS fabrication processes and techniques used in the microelectronics industry. Some potential materials include gallium arsenide (GaAs), silicon carbide (SiC), indium phosphide (InP), gallium nitride (GaN) and silicon germanium (SiGe).

The microwave photonics (MWP) is a promising technology in recent years in terms of processing high frequency microwave signals. It offers some advantages over electronic signal processing. Some of its advantages are high speed, low loss, wide range, light weight and immunity from electromagnetic interference. Because of these advantages, integrated MWP circuits can be used in many applications such as filters, phase shifters and time delay devices. Moreover, with the development of complementary metal-oxide semiconductor technology, MWP circuits can be integrated on a compact silicon-on-insulator platform. In this thesis, a new tunable single passband MWP filter based on on-chip silicon photonics technology and integrated MWP technology is designed. The new method has a great improvement in the selectivity of the filter by employing a dual-parallel Mach–Zehnder modulator (DPMZM). It simultaneously achieves the generation of phase-modulated signal and compensation for the undesired phase. The results show that the designed single passband MWP filter based on a DPMZM and an SOI single ring resonator, has a narrowband radio frequency response, where an average 10-dB bandwidth of 5.12 GHz is achieved. Another challenge for photonic circuit integration is coupling lights from optical fibers into photonic chips because of the spot size difference between fiber optical mode and waveguide mode. In this thesis, a simple solution is designed to achieve a horizontal integration of a fiber-chip spot size converting edge coupler, which only requires an inverse taper and a linear mode expander to couple light from a fiber and laterally expand the mode. Optimizing inverse taper parameters yields a 90% coupling efficiency from fiber to coupler output end for both the transvers electric and the transverse magnetic polarizations, which can be used for horizontal integration with a 50:50 polarization splitter.

Observing and controlling solid state quantum systems is an area of intense research in quantum science today. Such systems offer the natural advantage of being bound into a solid device, eliminating the need for laser cooling and trapping of atoms in free space. These solid state "atoms" can interface directly with photonic channels designed to efficiently couple into larger networks of interacting quantum systems. With all of the tools of semiconductor fabrication technology available, the idea of scalable, chip-based quantum networks is a tantalizing prospect.
Physics

An optical beamforming network that uses an uncooled Fabry-Perot laser is demonstrated. This is achieved by using a fast-scanning, high-resolution optical spectrum analyzer to track the frequency and power shift of the uncooled laser, and then reconfiguring a programmable Fourier-domain optical processor to provide compensation. In this way, the need for temperature control of the laser is eliminated, and the number of optical sources is reduced by using the output spectral lines of the laser. The system realizes six wideband microwave photonic phase shifters, and the resulting magnitude and phase responses vary within a 2σ deviation of 6.1dB and 14.8°, respectively, even when the laser current is changed during measurement. A microwave photonic filter is presented based on a feedback structure, which uses a Fourier-domain optical processor as the control element and the fast-scanning optical spectrum analyzer as the feedback component. This system provides low-pass RF response. Experimental results demonstrate a 6-tap microwave photonic filter with a free spectral range of 2.5GHz. The power fluctuation of the first-order passband in RF response is within ±1dB over 20 minutes. A novel tunable all-optical microwave photonic mixer is presented based on serial phase modulation and an on-chip notch filter. The notch filter breaks the out-of-phase symmetry between the upper and lower sidebands generated from phase modulation, resulting in bandpass response of frequency selection. This system is achieved through an all-optical approach, which does not require electrical components, thus increasing the operation bandwidth of the system. The tunability of frequency selection is achieved through adjusting the wavelength of the optical source. Experimental results verify the technique with a 3rd-order SFDR of 91.7dBm/Hz2/3.

This thesis concerns some experimental and theoretical issues in fiber optics. In particular, properties and devices based on photonic crystal fibers (PCFs) are investigated.

The work can be grouped into three parts. In the first part we use sound to control light in PCFs. The lowest order flexural acoustic mode of various PCFs is excited using an acoustic horn. The acoustic wave acts as a traveling long-period grating. This is utilized to couple light from the lowest order to the first higher order optical modes of the PCFs. Factors affecting the acoustooptic coupling bandwidth are also investigated. In particular, the effect of axial variations in acoustooptic phase-mismatch coefficient are studied.

In the second part of the thesis we use an electric field to control transmission properties of PCFs. Tunable photonic bandgap guidance is obtained by filling the holes of an initially index-guiding PCF with a nematic liquid crystal and applying an electric field. The electric field introduces a polarization-dependent change of transmission properties above a certain threshold field. By turning the applied field on/off, an electrically tunable optical switch is demonstrated.

The third part consists of two theoretical works. In the first work, we use relativistic causality, i.e. that signals cannot propagate faster than the vacuum velocity of light, to show that Kramers-Kronig relations exist for waveguides, even when material absorption is negligible in the frequency range of interest. It turns out that evanescent modes enter into the Kramers-Kronig relations as an effective loss term. The Kramers-Kronig relations are particularly simple in weakly guiding waveguides as the evanescent modes of these waveguides can be approximated by the evanescent modes of free space. In the second work we investigate dispersion properties of planar Bragg waveguides with advanced cladding structures. It is pointed out that Bragg waveguides with chirped claddings do not give dispersion characteristics significantly different from Bragg waveguides with periodic claddings.

The focus of this thesis is to investigate the implementation of Radio Frequency (RF) In-Phase and Quadrature-Phase (I/Q) vector modulation through the use of modern photonic components and sub-systems which offer extremely wide RF intrinsic bandwidths. All-electronic vector modulators suffer from frequency coverage limitations and amplitude and phase instability due to components such as phase shifters and variable gain controllers operating at or near 100\% bandwidth. In stark contrast, once an RF signal has been modulated onto an optical carrier, the percent bandwidth of the RF to carrier is typically less than 0.01\% percent. The fundamental mechanisms and basic electronic and photonic components needed to achieve vector modulation is introduced first. The primary electrical component required in most architectures is the 90° RF hybrid coupler, which is required to generate the RF I and Q terms. The two primary photonic building blocks, aside from the laser, electro-optic modulator and demodulator, are Mach-Zehnder Modulators (MZM) and Variable Optical Attenuators (VOA). Through the utilization of these components, multiple past architectures are explored and multiple new architectures are designed simulated. For each architecture, there is a discussion on the practical implementation. Considerations such as system complexity, integration, and sensitivity to unwanted environmental stimuli are taken into account with potential solutions to alleviate these risks. In closing, the noise figure and its impact on Spur-Free Dynamic Range (SFDR) for a basic RF photonic link is derived to provide a system-level figure of merit that can be used, in most RF applications, to determine the overall performance utility current and future designs.

Silicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 – 5 ?m). In this wavelength range, the omnipresent hurdle of nonlinear silicon photonics in the telecommunication band, i.e., nonlinear losses due to two-photon absorption, is inherently nonexistent. With the lack of efficient light-emission capability and second-order optical nonlinearity in silicon, heterogeneous integration with other material systems has been another direction pursued. Finally, several approaches have been proposed and demonstrated to address the energy efficiency of silicon photonic devices in the near-infrared wavelength range. In this dissertation, theoretical and experimental works are conducted to extend applications of integrated photonics into mid-infrared wavelengths based on silicon, demonstrate heterogeneous integration of tantalum pentoxide and lithium niobate photonics on silicon substrates, and study two-photon photovoltaic effect in gallium arsenide and plasmonic-enhanced structures. Specifically, performance and noise properties of nonlinear silicon photonic devices, such as Raman lasers and optical parametric amplifiers, based on novel and reliable waveguide technologies are studied. Both near-infrared and mid-infrared nonlinear silicon devices have been studied for comparison. Novel tantalum-pentoxide- and lithium-niobate-on-silicon platforms are developed for compact microring resonators and Mach-Zehnder modulators. Third- and second-harmonic generations are theoretical studied based on these two platforms, respectively. Also, the two-photon photovoltaic effect is studied in gallium arsenide waveguides for the first time. The effect, which was first demonstrated in silicon, is the nonlinear equivalent of the photovoltaic effect of solar cells and offers a viable solution for achieving energy-efficient photonic devices. The measured power efficiency achieved in gallium arsenide is higher than that in silicon and even higher efficiency is theoretically predicted with optimized designs. Finally, plasmonic-enhanced photovoltaic power converters, based on the two-photon photovoltaic effect in silicon using subwavelength apertures in metallic films, are proposed and theoretically studied.
Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics and Photonics

This thesis explains and implements the Finite Difference Method to simulate for the propagating modes in integrated waveguides. The equidistant and non-equidsitant methods are explained and implemented. A shape recognition engine is implemented to recognize rectangular waveguide structures provided by the user in the form of images. A geometric meshing algorithm is developed to improve accuracy.
Cette thèse explique et met en oeuvre la méthode des diffrences finis pour simuler la propagation de modes de guides d'ondes intgré. La méthode équidistante et non-équidistante est expliquée et mise en oeuvre. Un moteur de reconnaissance de formes est mise en oeuvre pour reconnaître la structure des guides d'ondes rectangulaire prévues par l'utilisateur sous forme d'images. Un algorithme géomtrique de maillage est développé pour améliorer l'exactitude.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references.
In 2020, 1Tb/s on-/off-chip communication bandwidth and ~100fJ/bit total energy in a point to point link is predicted by Moore's law for high performance computing applications. These requirements are pushing the limits of on-chip silicon CMOS transistors and off-chip VCSELs technology. The major limitation of the current systems is the lack of ability to enable more than a single channel on a single wire/fiber. Silicon photonics, offering a solution on the same platform with CMOS technology, can enable Wavelength Division Multiplexed (WDM) systems. However, Silicon photonics has to overcome the wafer level, fabrication variations and dynamic temperature fluctuations, induced by processor cores with low-energy high-speed resonators. In this work, we offer a solution, called as Automated Wavelength Recovery (AWR), to these limitations. In order to demonstrate AWR, we design and demonstrate high performance active silicon resonators. A microdisk modulator achieved open eye-diagrams at a data rate of 25Gb/s and error-free operation up to 20Gb/s. A thermo-optically tunable microdisk modulator with Low power modulation (1 If/bit) at a data rate of 13-Gb/s, a 5.8-dB extinction ratio, a 1.22-dB insertion loss and a record-low thermal tuning (4.9-[mu].W/GHz) of a high-speed modulator is achieved. We demonstrated a new L-shaped resonant microring (LRM) modulator that achieves 30 Gb/s error-free operation in a compact (< 20 [mu]m²) structure while maintaining single-mode operation, enabling direct WDM across an uncorrupted 5.3 THz FSR. We have introduced heater elements inside a new single mode filter, a LRM filter, successfully. The LRM filter achieved high-efficiency (3.3[mu]W/GHz) and high-speed ([tau]f ~1.6 [mu]s) thermal tuning and maintained signal integrity with record low thru to drop power penalty (<1.1 dB) over the 4 THz FSR and <0.5dB insertion loss. We have integrated a heater driver and adiabatic resonant microring (ARM) filter in a commercial bulk CMOS deep-trench process for the first time. The proposed AWR algorithm is implemented with an ARM multiplexer. An advanced method for AWR is also introduced and demonstrated with passive resonators.
by Erman Timurdogan.
S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 109-114).
We present results on the development of integrated erbium-doped aluminum oxide lasers on a silicon photonics platform. A key achievement in this work is a scalable laser design for high output power and ultra-narrow linewidth performance. Using a novel wavelength-insensitive design, a CMOS compatible waveguide structure is proposed to achieve high confinement factor and intensity overlap for both the pump (980 nm) and signal (1550 nm) wavelengths. Laser operation in the C- and L- bands of the erbium gain spectrum is obtained with both a distributed Bragg reflector and a distributed feedback structure. We demonstrate power scaling with output power greater than 75 mW and obtain an ultra-narrow linewidth of 5.3 t 0.3 kHz. We investigate the influence of gain film thickness uniformity in distributed feedback laser performance and show a compensation scheme based on a curved cavity design. We then consider the application in optical communications by demonstrating a multiwavelength cascaded laser to generate wavelength division multiplexing (WDM) light sources. Finally, we propose an integration scheme of laser in full silicon photonics platform by using an erbium trench. The approach is alignment free and allows the erbium-doped film deposition to be the last backend process, providing a pathway to a scalable CMOS compatible laser device.
by Purnawirman.
Ph. D.