Chalcogenide based Phase Change Materials are currently of great technological interest in the growing field of optoelectronics. Ge₂Sb₂Te₅ (GST) is the most widely studied phase change material, and it has been commercially used in both optical and electronic data storage applications, due to its ability to switch between two different atomic configurations, at high speed and with low power consumption, as well as its high optical and electrical contrast between amorphous and crystalline states. Despite its well-known optical and electrical properties, the operation in combination of optical and electrical domains has not yet been fully investigated. This work studies the operation of GST nano-devices exposed to a combination of optical and electrical stimuli or mixed mode by asking, is it possible to electrically measure an optically induced phase change, or vice versa? If so, how do the optical and electrical responses relate to each other, and is it possible to operate GST with a combination of optical and electrical signals? What are the technical constraints that need to be considered in order to fabricate GST devices that could be operated either optically or electrically? In order to answer these questions, experiments that characterized the optical and electrical responses of GST based nano-devices were performed. It was found that different crystallization mechanisms may have influence in the response, and that the thermal and optical design characteristics of the device play a key role in its operation. Finally a proof of principle, of an opto-electonic memory device that can be read electrically, reset optically and write electrically, is presented. This opens up possibilities for the development of new opto-eloectronic applications such as non-volatile interfaces between future photonics and electronics, high speed optical communication detectors, high speed cameras, artificial retinas and many more.

Ces travaux de thèse ont porté sur des matériaux constitués de dispersions de particules colloïdales nanométriques, issues d'un matériau ferroélectrique, dans un cristal liquide chiral à phase smectique ferroélectrique. Ils ont pour but d'étudier les effets occasionnés par ces dispersions sur les propriétés du nanocolloïde, notamment celles liées à leur ferroélectricité. Cette étude a montré que les comportements mésomorphes et ferroélectriques de ces matériaux sont conservés. Une baisse de polarisation spontanée ainsi qu'un recul des températures des transitions ont été mis en évidence pour des faibles concentrations en NPs. Une "transition" de ces comportements a été observée pour une concentration critique au-delà de laquelle les particules s'agrègent pour former des amas au sein du milieu cristal liquide. Nous nous sommes intéressés ensuite à deux modes de relaxation diélectriques. Le premier lié aux mouvements de distorsions de l'hélice dans la phase ferroélectrique, le second aux mouvements de compression des couches smectiques de part et d'autre de la transition ferroélectrique-paraélectrique. Les comportements observés semblent être gouvernés par les modifications des propriétés visco-élastiques des nanocolloïdes, occasionnés par l'intercalation des nanoparticules entre les couches smectiques. / The present thesis work concerns materials made of dispersions of nanometric colloidal particles, from a bulk ferroelectric material, dispersed within a chiral smectic phase of a ferroelectric liquid crystal. The goal of this work is to study the effect of the dispersed nanoparticles over the nanocolloïd properties, specially the ones related to ferroelectricity. This study showed no change over mesomorphic and ferroelectric behavior of the materials. A decrease in spontaneous polarization and phase transition temperatures was found for low nanoparticle concentrations. A "transition" of these behaviors was observed for a critical concentration, beyond which, nanoparticles aggregate and form clusters inside the liquid crystal matrix. Afterwards, we have studied two dielectric relaxation modes. The first one related to distorsions of the helix in the ferroelectric phase and the second one to the compression movements of the smectic layers around the ferroelectric-paralectric transition. The observed behaviors seem to be due to modifications of the visco-elastic properties of nanocolloids, produced by intercalation of nanoparticles between the smectic layers.

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[EN] Optical technologies are the backbone of modern communication systems providing high-speed access to the Internet, efficient inter and intra-data center interconnects and are expending towards growing research fields and new markets such as satel- lite communications, LIDARs (Laser Imaging Detection and Ranging) applications, Neuromorphic computing, and programable photonic circuits, to name a few. Be- cause of its maturity and low-cost, silicon photonics is being leveraged to allow these new technologies to reach their full potential.As a result, there is a strong need for innovative, high-speed and energy-efficient photonic integrated building blocks on the silicon platform to increase the readiness of silicon photonic integrated circuits. The work developed and presented in this thesis is focused on the design and char- acterization of advanced passive and active devices, for photonic integrated circuits. The thesis consists of three main chapters as well as a motivation and concluding sections exposing the rationale and the accomplishments of this work. Chapter one describes the design and characterization of an electro-optical Mach-Zehnder mod- ulator embedded in highly efficient vertical pn junction exploiting the free-carrier dispersion effect in the O-band.. Chapter two is devoted to the design and charac- terization of a novel geometry of asymmetrical multimode interference device and its implementation in a Mach-Zehnder modulator. Chapter three is dedicated to the design and characterization of innovative 1-dimensional photonic crystal designs for slow- lightmodulation applications. An extensive analysis of the main trade-off arising from the use of slow light is presented. / [ES] Las tecnologías ópticas son el eje vertebrador de los sistemas de comunicación mod- ernos que proporcionan acceso de alta velocidad a la Internet, interconexiones efi- cientes entre centros de datos y dentro de ellos. Además, se están expandiendo hacia campos de investigación crecientes y nuevos mercados como son las aplicaciones de comunicaciones por satélite, los LIDAR (Laser Imaging Detection and Ranging), la computación neuromórfica y los circuitos fotónicos programables, por nombrar algunos. La fotónica de silicio está considerada y aceptada ampliamente como una de las tecnologías clave para que dichas aplicaciones puedan desarrollarse. Como resultado, hay una fuerte necesidad de estructuras fotónicas básicas integradas que sean innovadoras, que soporten altas velocidades de transmisión y que sean más eficientes en términos de consumo de potencia, a fin de aumentar la capacidad de los circuitos integrados fotónicos de silicio. El trabajo desarrollado y presentado en esta tesis se centra en el diseño y la car- acterización de dispositivos avanzados pasivos y activos, para circuitos fotónicos integrados. La tesis consta de tres capítulos principales, así como de sendas sec- ciones de motivación y conclusiones que exponen los fundamentos y los logros de este trabajo. El capítulo uno describe el diseño y la caracterización de un modulador electro-óptico Mach-Zehnder incorporado en una unión pn vertical altamente eficien- ciente que explota el efecto de dispersión de plasma en banda O. El capítulo dos está dedicado al diseño y caracterización de una nueva geometría de dispositivo de interferencia multimodo asimétrico y su aplicación en un modulador Mach-Zehnder. El capítulo tres está dedicado al diseño y caracterización de innovadores cristales fotónicos unidimensionales para aplicaciones de modulación con luz lenta. Se pre- senta un amplio análisis de los principales retos derivados del uso de la misma. / [CA] Les tecnologies òptiques són l'eix vertebrador d'aquells sistemes de comunicació moderns que proporcionen accés d'alta velocitat a la Internet, així com intercon- nexions eficients inter i entre centres de dades. A més a més, s'estan expandint cap a camps d'investigació creixents i nous mercats com són les aplicacions de co- municacions per satèl·lit, els LIDAR (Laser Imaging Detection and Ranging), la computació neuromòrfica i els circuits fotònics programables, entre d'altres. La fotònica de silici és considerada i acceptada àmpliament com una de les tecnologies clau i necessàries perquè aquestes aplicacions puguen desenvolupar-se. Per aquest motiu, es fa necessària l'existència d'estructures fotòniques bàsiques integrades que siguen innovadores, que suporten altes velocitats de transmissió i que siguen més eficients en termes de consum de potència, a fi d'augmentar la capacitat dels cir- cuits integrats fotònics de silici. El treball desenvolupat i presentat en aquesta tesi se centra en el disseny i la caracterització de dispositius avançats passius i actius, per a circuits fotònics integrats. La tesi consta de tres capítols principals, així com d'una secció de motivació i una altra de conclusions que exposen els fonaments i els assoliments d'aquest treball. El capítol u descriu el disseny i la caracterització d'un modulador electro-òptic Mach-Zehnder incorporat en una unió pn vertical d'alta efi- ciència que explota l'efecte de dispersió de plasma en la banda O. El capítol dos està dedicat al disseny i caracterització d'una nova geometria de dispositiu d'interferència multimode asimètric així com a la seua aplicació en un modulador Mach-Zehnder. El capítol tres està dedicat al disseny i caracterització d'innovadors cristalls fotònics unidimensionals per a aplicacions de modulació amb llum lenta. S'inclou també una anàlisi detallada dels principals reptes derivats de l'ús d'aquest tipus de llum. / I want to thank you the Generelitat Valenciana and the European Project L3MATRIX for the funding, without them my doctorate would not taken place. / Zanzi, A. (2020). Passive and active silicon photonics devices at TLC telecommunication wavelengths for on-chip optical interconnects [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/149377 / TESIS

A monolithically integrated broadly tunable MQW laser that utilizes a combined impurity-free vacancy disordering (IFVD) of quantum wells and optical beam steering techniques is proposed and investigated experimentally. The device consists of a beam-steering section and an optical amplifier section fabricated on a GaAs/AlGaAs quantum well (QW) p-i-n heterostructure. The beam steering section forms a reconfigurable optical waveguide that can be moved laterally by applying separately controlled electrical currents to two parallel contact stripes. The active core of the gain section is divided in into selectively intermixed regions. The selective intermixing of the QW in the gain section results in neighboring regions with different optical bandgaps. The wavelength tuning is accomplished by steering the amplified optical beam through the selected region where it experiences a peak in the gain spectrum determined by the degree of intermixing of the QW. The laser wavelength tunes to the peak in the gain spectrum of that region. The IFVD technique relies on a silica (SiO2) capped rapid thermal annealing and it has been found that the degree of intermixing of the QW with the barrier material is dependent on the thickness of the SiO2 film. The QW sample is first encapsulated with a 400nm thick SiO2 film grown by plasma enhanced chemical vapor deposition (PECVD). In the gain section, the SiO2 film is selectively etched using multiple photolithographic and reactive ion etching steps whereas the SiO2 film is left intact in all the remaining areas including the beam-steering section. The selective area quantum well intermixing is then induced by a single rapid thermal annealing step at 975°C for a 20s duration to realize a structure with quantum well that has different bandgaps in the key regions. Optical characterizations of the intermixed regions have shown a blue shift of peak of the electroluminescence emission of 5nm, 16nm and 33nm for the uncapped, 100nm and 200nm iv respectively when compared to the as grown sample. The integrated laser exhibited a wavelength tuning range of 17nm (799nm to 816nm). Based on the same principle of QW selective intermixing, we have also designed and fabricated a monolithically integrated multi-wavelength light emitting diode (LED). The LED emits multiple wavelength optical beams from one compact easy to fabricate QW structure. Each wavelength has an independent optical power control, allowing the LED to emit one or more wavelengths at once. The material for the LED is the same AlGaAs/GaAs QW p-i-n heterostructure described above. The device is divided into selectively intermixed regions on a single QW structure using IFVD technique to create localized intermixed regions. Two different designs have been implemented to realize either an LED with multiple output beams of different wavelengths or an LED with a single output beam that has dual wavelength operation capabilities. Experimental results of the multiple output beams LED have demonstrated electrically controlled optical emission of 800nm, 789nm and 772nm. The single output LED has experimentally been shown to produce wavelength emission of 800nm and/or 772nm depending on electrical activation of the two aligned intermixed regions.

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Optical interconnects based on CMOS compatible photonic integrated circuits are regarded as a promising technique to tackle the issues traditional electronics faces, such as limited bandwidth, latency, vast energy consumption and so on. In recent years, plasmonic integrated components have gained great attentions due to the properties of nano-scale confinement, which may potentially bridge the size mismatch between photonic and electronic circuits. Based on silicon nanowire platform, this thesis work studies the design, fabrication and characterization of several integrated plasmonic components, aiming to combine the benefits of Si and plasmonics. The basic theories of surface plasmon polaritons are introduced in the beginning, where we explain the physics behind the diffraction-free confinement. Numerical methods frequently used in the thesis including finite-difference time-domain method and finite-element method are then reviewed. We summarize the device fabrication techniques such as film depositions, e-beam lithography and inductively coupled plasma etching as well as characterization methods, such as direct measurement method, butt coupling, grating coupling etc. Fabrication results of an optically tunable silicon-on-insulator microdisk and III-V cavities in applications as light sources for future nanophotonics interconnects are briefly discussed. Afterwards we present in details the experimental demonstrations and novel design of plasmonic components. Hybrid plasmonic waveguides and directional couplers with various splitting ratios are firstly experimentally demonstrated. The coupling length of two 170 nm wide waveguides with a separation of 140 nm is only 1.55 µm. Secondly, an ultracompact polarization beam splitter with a footprint of 2×5.1 μm2 is proposed. The device features an extinction ratio of 12 dB and an insertion loss below 1.5 dB in the entire C-band. Thirdly, we show that plasmonics offer decreased bending losses and enhanced Purcell factor for submicron bends. Novel hybrid plasmonic disk, ring and donut resonators with radii of ~ 0.5 μm and 1 μm are experimentally demonstrated for the first time. The Q-factor of disks with 0.5 μm radii are                         , corresponding to Purcell factors of . Thermal tuning is also presented. Fourthly, we propose a design of electro-optic polymer modulator based on plasmonic microring. The figure of merit characterizing modulation efficiency is 6 times better comparing with corresponding silicon slot polymer modulator. The device exhibits an insertion loss below 1 dB and a power consumption of 5 fJ/bit at 100 GHz. At last, we propose a tightly-confined waveguide and show that the radius of disk resonators based on the proposed waveguide can be shrunk below 60 nm, which may be used to pursue a strong light-matter interaction. The presented here novel components confirm that hybrid plasmonic structures can play an important role in future inter- and intra-core computer communication systems. / <p>QC 20140404</p>

<p>Electro-optic phase modulation can be used to generate high repetition rate optical frequency combs. The optical frequency comb (OFC) has garnered much attention upon its inception, acting as a crucial component in applications ranging from metrology and spectroscopy, to optical communications. Electro-optic frequency combs (EO combs) can be generated by concatenating an intensity modulator and phase modulator together. The first part of this work focuses on broadening the modest bandwidth inherent to the EO combs. This is achieved by propagation in a nonlinear medium, specifically propagation in a nonlinear optical loop mirror (NOLM). This allows for broadening the EO frequency comb spectrum to a bandwidth of 40 nm with a spectral power variation of < 10 dB. This spectrally broadened EO comb is then used in dual comb interferometry measurements to characterize the single soliton generated in an anomalous dispersion silicone-nitride microresonator. This measurement allows for rapid characterization with low average power. Finally, electro-optic phase modulation is used in a technique to prove frequency-bin entanglement. A quantum network based on optical fiber will require the ability to perform phase modulation independent of photon polarization due to propagation in optical fiber scrambling the polarization of input light. Commercially available phase modulators are inherently dependent on the polarization state of input light making them unsuited to be used in such a depolarized environment. This limitation is overcome by implementing a polarization diversity scheme to measure frequency-bin entanglement for arbitrary orientations of co- and cross- polarized frequency-bin entangled photon pairs.</p>

Ce travail de thèse porte sur la réalisation d’un nouveau modulateur électro-optique pouvant s’intégrer sur un substrat SOI. Le modulateur proposé utilise une structure dite à fente ou SLOT formée verticalement par la couche superficielle de silicium du matériau SOI sur laquelle on dépose la couche de BTO puis une couche de silicium amorphe. Le confinement latéral dans ce guide de lumière est réalisé par gravure de la couche de silicium amorphe supérieure. La géométrie du ruban de silicium amorphe est optimisée pour obtenir un mode SLOT en polarisation TM (Transverse Magnétique) pour lequel la quasi-totalité de l’énergie lumineuse est confinée dans la couche active de BTO, ce qui permet d’augmenter l’efficacité du modulateur par rapport à une structure conventionnelle. La conception d’un tel modulateur a nécessité l’élaboration d’un outil numérique multi-physique lors de ce travail de thèse afin de prendre en compte rigoureusement les propriétés d’anisotropie des matériaux ferroélectriques, rarement disponibles dans les logiciels de simulation photonique commerciaux. Plus précisément, nous combinons un solveur de mode optique FVFD avec un solveur radiofréquence de Laplace. Il permet des calculs précis de la modulation d'indice de réfraction et de la réponse électro-optique induite par l’effet Pockels des matériaux anisotropes qui présentent une variation non-diagonale du tenseur de permittivité. L’optimisation du modulateur est réalisée, tant du point de vue optique qu’électrique en radiofréquence. Notamment, pour obtenir un modulateur rapide, il est nécessaire de concevoir une électrode qui possède une onde radiofréquence de même constante de propagation que le mode SLOT optique. Le travail de thèse est aussi consacré à la conception des briques de bases d’optique intégrée passive nécessaires à la réalisation des modulateurs: guides droits, diviseurs de faisceaux de type MMI (MultiMode Interference), de virages et de coupleurs directionnels. Un solveur de mode en coordonnées cylindriques a permis de concevoir des virages à très faibles rayons de courbure de 3,6 µm avec des pertes de radiation inférieures à 0.1 dB/90°. Étonnamment, pour des guides en arête, la réduction du rayon de courbure d’un virage n’implique pas forcément une augmentation des pertes de radiation et conduit à une amélioration des performances du dispositif. Ce résultat est très important parce que le virage est la brique de base qui est la plus difficile à miniaturiser en optique intégrée. Actuellement, les rayons de courbures sont limités à 15 µm dans les technologies utilisant les guides en arête. Ce résultat validé expérimentalement, montre qu’il est possible d’obtenir une densité d’intégration 4 à 5 fois plus importante sans modification de la technologie de fabrication. Le deuxième résultat innovant pour la photonique sur silicium porte sur l’obtention de diviseurs de faisceaux très compacts et insensibles à la polarisation (2.0 x 3.6 µm²). / The aim of this thesis is to explore a new electro-optic modulator which could be integrated on SOI substrate. The ferroelectric material BaTiO3 (BTO) is potentially the most interesting because it has highest linear electro-optic coefficient among perovskite materials, and its monolithic integration on a SOI substrate as a crystalline thin film was demonstrated in INL. The proposed modulator uses a structure SLOT formed vertically through the silicon layer of the SOI on which is deposited the layer of BTO then an amorphous silicon layer. The lateral confinement in the light guiding is formed by etching of the upper amorphous silicon layer. The geometry of the strip-loaded amorphous silicon is optimized to obtain a SLOT TM (Transverse Magnetic) polarization mode in which substantially all of the light energy is confined in the active layer of BTO, thereby increasing the efficiency of modulator with respect to a conventional structure. The design of such a modulator requirs the development of a multi-physics numerical tool to consider carefully anisotropic properties of ferroelectric materials, rarely available in commercial photonics simulation softwares. Specifically, we combine a FVFD optical mode solver with a radiofrequency Laplace solver. It allows precise calculation of the modulation of refractive index and the electro-optical response induced by Pockels effect of anisotropic materials exhibiting non-diagonal change in the permittivity tensor. The optimization of the modulator is carried out, from both aspects optical and electrical in radiofrequency. In particular, to obtain a rapid modulator, it is necessary to design a radiofrequency electrode that has a same wave propagation constant of optical SLOT mode. The thesis is as well devoted to the design of passive building blocks in integrated optics, which are necessary for the implementation of modulators: straight waveguides, beam splitters of type MMI (MultiMode Interference), turns and directional couplers. A cylindrical coordinate’s mode solver realizes the design of turns of very low bending radii of 3.6 microns with radiation losses less than 0.1dB/90°. Surprisingly, for strip-loaded guides, reducing the cornering radius of turns does not necessarily imply an increase in losses of radiation, and so leading to improved device performance. This result is very important because the turns is a basic building block the most difficult to be miniaturized in integrated optics. Currently, the radii of curvature are limited to 15 microns in waveguide technology. The experimental validation shows that it is possible to obtain a 4-5 times larger integration density without changing the manufacturing technology. The second result for innovative silicon photonics is about obtaining very compact and polarization insensitive beam splitters (2.0 x 3.6 μm²).

The behaviour of electrons in nanostructures such as quantum wells is of interest for the design of new electronic and electro-optic devices, and also for exploration of basic many-body physics. This thesis develops and tests improved methods for describing such electronic behaviour. The system used for this work was the parabolic quantum well (PQW), an important special system which has recently attracted much experimental and theoretical attention. We firstly report self-consistent nonlinear groundstate solutions of the Poisson equation together with the Thomas-Fermi (TF) hydrostatic equations. In contrast to most previous solutions, all the electron density profiles were inhomogeneous and continuous. We also added a von Weizsacker term with and without the exchange/exchange-correlation to the above treatment, using a novel numerical approach allowing for wider electron gases than previously possible. We also report for the first time the effects of spatially varying effective mass and dielectric function in theories of this type. To investigate infrared response of these systems, we apply new hydrodynamic theories recently proposed by Dobson. By using this type of theory, we simultaneously satisfy the Harmonic Potential Theorem (extended generalized Kohn theorem) and obtain the correct 2D plasmon dispersion, as well as obtaining the correct spacing of standing plasmons. Other inhomogeneous hydrodynamic theories do not achieve this. We also showed analytically an exact solution for a plasmon mode at the Kohn frequency in addition to one found in the Harmonic Potential Theorem. An open hydrodynamic theory was then developed based on this type of mode. Numerical application of Kohn Frequency Theorem theory was shown and the results were compared with other existing hydrodynamic theories.