The exponential rise in global data traffic and the growing reliance on digital applications is pushing the bandwidth demands within data centers. The traditional hierarchical network architecture of data centers, primarily relying on electrical interconnects, faces scalability challenges including power dissipation, bandwidth limitations, and cooling requirements. Optical interconnects, using fibers and pluggable transceivers, emerge as a promising solution to these challenges, offering advantages such as electromagnetic interference resistance, high bandwidth, and efficient energy usage. This thesis explores the design, fabrication, and characterization of opto-electronic devices to be used as components for optical transceivers on a silicon photonics platform, which leverages the mature complementary metal-oxide semiconductor fabrication technology. Chapter 2 introduces the basics of waveguide theory alongside the principles behind defect-based avalanche photodiodes, phototransistors, and two-level system optical amplifiers. Chapter 3 details the design, simulation, and characterization of a high-responsivity silicon/germanium phototransistor, achieving over 1000 A/W in performance. Chapter 4 discusses the design and measurement of an all-silicon avalanche photodetector for near-infrared wavelengths mediated by deep-level defects. In Chapter 5, the focus shifts to enhancing the previously mentioned photodetector’s responsivity through slow light gain with subwavelength grating waveguide structures, with details on its design, simulation, fabrication, and characterization. Chapter 6 explores the development and analysis of an erbium-doped waveguide amplifier on a hybrid silicon nitride - tellurite platform, incorporating erbium ions via ion implantation. This thesis makes contributions toward realizing efficient silicon photonics-based data communication infrastructure, supporting the escalating demand for bandwidth while mitigating power consumption and improving system scalability. / Dissertation / Doctor of Philosophy (PhD)

Recent impactful advances in integrated photonics undoubtedly owe much to silicon and its associated enabling platform (SOI). Although silicon has proved to be an indispensable element in many photonic systems yet it seems that it is not the ultimate solution to address all the challenges facing the photonics community. Therefore, integration of silicon with other optical materials featuring diverse properties is highly desirable. Such integration will be conducive to platforms which are naturally more capable and are suited for implementation of a wider range of optical devices and diverse functionalities. This dissertation is dedicated to design and implementation of integrated optical elements for hybrid material platforms. The basic theoretical foundation of integrated photonics is laid out in Chapter 2. In Chapter 3, an interlayer grating coupler for a specific hybrid material platform is designed, and demonstrated. Considering the fact that in almost all integrated photonic platforms, fabrication imperfections lead to an unpredictable shift in the wavelength of operation of individual devices, post fabrication tuning/trimming is inevitable. A number of widely used post fabrication trimming/tuning methods are briefly reviewed in Chapter 4 with special emphasis on a method based on electron beam exposure. In Chapter 5, an ultra-fast, low-power, and self-trimmable electro-optic modulator in demonstrated on a Si-based multilayer platform. Due to its remarkable optical and electronic properties, graphene has become a valuable material for opto-electronic applications. Integration of this novel 2D material with SOI platform is investigated in Chapter 6. Graphene-based electro-optic modulation through absorption and refractive-index change is successfully demonstrated using electrostatic gating mechanism. Chapter 7 is devoted to demonstration of a field-programmable 2 by 2 optical switch on a vertically stacked Si/SiO2/SOI platform. In Chapter 8, the peak-dragging phenomenon in a nanobeam photonic crystal cavity is studied. The optical bistability associated with this nonlinear phenomenon is of great interest for all-optical processing and sensing application. Future directions of this thesis are also discussed in the last Chapter.

The fundamental limits of electronic systems in communication networks motivated scholars to think of an alternative approach to overcome problems such as demand for wider bandwidths and heat dissipation. All-optical signal processing is demonstrated as a potential solution. A major improvement in cost and speed of networking systems is expected through replacing microelectronics by photonic chips. However, the variety of operations essential to perform all-optical signal processing cannot be handled by a single material platform yet. Several III-V semiconductors, such as AlGaAs, have demonstrated potentials for photonic integration; nevertheless, there is still lack of data in literature on nonlinear optical properties of these materials. In this thesis, we extend the quest to evaluate more candidates from this class of semiconductors. Moreover, we are aiming for demonstrating the potentials of various III-V compounds for nonlinear photonics on-a-chip. In this thesis, we propose several optical waveguide designs based on quaternary III-V semiconductors AlGaAsSb and InGaAsP. We present modal analysis for waveguide designs and show that effective mode area much less than 1 $\mu m^{2}$ can be obtained. We also report specific waveguide designs that display zero-dispersion points at the specific wavelength ranges of interest. The designed waveguides are thus expected to demonstrate efficient nonlinear optical interactions. Next step is the fabrication of these devices with the goal to experimentally assess their nonlinear optical performance. The fabrication process of InGaAsP/InP strip-loaded waveguide is briefly reviewed. Following that, we report on the first, to the best of our knowledge, demonstration of third-order nonlinear optical interactions in InGaAsP/InP strip-loaded waveguides. We have performed self-phase modulation, nonlinear absorption measurements, and four-wave mixing experiments at the telecom wavelength range. The nonlinear phase shift up to 2.5 $\pi$ has been observed. Following that, we use Monte-Carlo method for design optimization and tolerance analysis of a multi-step lateral taper Spot-Size Converter in indium phosphide. An exemplary four-step lateral taper design featuring 0.35 dB coupling loss at optimal alignment of a standard single-mode fiber, $>$7 $\mu m$ 1-dB displacement tolerance in any direction of in a facet plane, and a great stability against manufacturing variances demonstrated.

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

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This Master’s dissertation focuses on exploring optical nonlinearities in IIIV semiconductors. This work covers a range of III-V materials and a few devices. To begin with, optical characterization of Aluminium Gallium Arsenide (AlGaAs) waveguides with enhanced nonlinear optical interactions was carried out. We have experimentally demonstrated wide conversion ranges andhigh conversion efficiencies for four-wavemixing inAlGaAswaveguides with three different geometries. In addition to that, both linear and nonlinear losses in each of these geometries were explored. AlGaAs represents only one compound of the large group of III-V semiconductors. To explore the potentials of other semiconductors compounds of this group for nonlinear optics, it is imperative to have information about refractive indices of different III-V compounds. This refractive index information is only available for some binary compounds in isolated spectral windows. In this thesis, we developed a model capable of predicting the values of the refractive indices of binary, ternary and quaternary III-V semiconductor compounds from the values of their band-gap energies. We compared the value predicted by our proposed model with existing experimental data and it was found not only is the predicted values in good agreement with the known values, but also has a lower error margin when compared to previously reported models. Finally, in quest for more suitable material platform for nonlinear photonic integration at different wavelength ranges, a detailed analysis of other potential III-V compounds not previously explored for photonic integration is presented.

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 µm). 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.

In this thesis, I report on how to use Single Photon Entanglement for generating certified quantum random numbers. Single Photon Entanglement is a particular type of entanglement which involves non-contextual correlations between two degrees of freedom of a single photon. In particular, here I consider momentum and polarization. The presence of the entanglement was validated using different attenuated coherent and incoherent sources of light by evaluating the Bell inequality, a well-known entanglement witness. Different non-idealities in the calculation of the inequality are discussed addressing them both theoretically and experimentally. Then, I discuss how to use the Single Photon Entanglement for generating certified quantum random numbers using a semi-device independent protocol. The protocol is based on a partial characterization of the experimental setup and the violation of the Bell's inequality. An analysis of the non-idealities of the devices employed in the experimental setup is also presented In the last part of the thesis, the integrated photonic version of the previously introduced experiments is discussed: first, it is presented how to generate single photon entangled states exploiting different degrees of freedom with respect to the bulk experiment. Second, I discuss how to perform an integrated test of the Bell's inequality.

In the thesis is described the development of two platforms to optogenetically induce single neuron excitation and formation of memory in biological in-vitro neuronal networks.One platform is a photonic chip, with aperiodic grating scatterers able to create a specific light distribution on the surface of the chip. The second platform is a digital light processor device integrated in a microscopy setup, able to create on the sample plane whatever pattern with 3 um resolution. Stimulating simultaneously many neurons, it was demonstrated the ability of this system to induce potentiation on the illuminated cells, and thus engram formation.

L’inscription par laser femtoseconde directe dans les cristaux laser offre une nouvelle opportunité de conception et développement de sources laser intégrées. Elle conduit à un prototypage rapide et à un bon rapport coût-efficacité, conformément aux futures feuilles de route de la photonique. Cependant, les défis liés au dépôt d’énergie d’un laser intense dans des milieux transparents et les modifications qui s’ensuivent restent encore des questions ouvertes. Ces défis ont été relevés en partie grâce à une étude minutieuse et systématique des zones modifiées par laser femtoseconde dans les matériaux transparents. Le fluorure de calcium (CaF2), en raison de sa symétrie cubique et de ses excellentes propriétés de luminescence en tant que cristal laser, a été choisi comme matériaux de référence dans cette thèse. L’inscription laser en régime femtoseconde de guides d’ondes à l’intérieur de ce cristal a été réalisée pour une conception future de source laser intégrée. Pour la première fois, des écritures laser « lisses » et non réciproques ont été observées à l’intérieur de certains échantillons « coupés spécialement » de cristaux de CaF2. De plus, un guidage de la lumière dépendant de la polarisation a été identifié et est présenté. Un modèle et une méthode ont été développés pour caractériser quantitativement et qualitativement ces guides d’ondes, en particulier pour les mesures de perte de transmission, ainsi que les cartographies tridimensionnelles de l’indice de réfraction des zones modifiées. / Femtosecond laser micromachining inside laser crystals offers a new platform to miniaturize highly compact laser sources. It leads to rapid prototyping and cost-effectiveness in line with the future photonics roadmaps. However, the challenges in relation to an intense laser pulse energy deposition within transparent media and the modifications that follow still remain open-ended questions. These challenges have been addressed with a careful and systematic study of femtosecond modified zones inside transparent materials. Due to its cubic symmetry and excellent luminescence properties as laser crystal, Calcium Fluoride (CaF2) was selected, and ultrafast laser inscription of waveguides inside this crystal was realized. Smooth and non-reciprocal writings were observed inside certain “specially cut” samples of the CaF2 crystals for the first time. Additionally, polarization dependent guiding is identified and presented. Furthermore, an authentic model and concept was engaged for the quantitative and qualitative characterization of the waveguides, particularly for the transmission loss measurements and the three-dimensional refractive index mappings of the modified zones.