abstract: Optical metasurfaces, i.e. artificially engineered arrays of subwavelength building blocks supporting abrupt and substantial light confinement, was employed to demonstrate a novel generation of devices for circularly polarized detection, full-Stokes polarimetry and all-optical modulation with ultra-compact footprint and chip-integrability. Optical chirality is essential for generation, manipulation and detection of circularly polarized light (CPL), thus finds many applications in quantum computing, communication, spectroscopy, biomedical diagnosis, imaging and sensing. Compared to natural chiral materials, chiral metamaterials and metasurfaces enable much stronger chirality on subwavelength scale; therefore, they are ideal for device miniaturization and system integration. However, they are usually associated with low performance due to limited fabrication tolerance and high dissipation mainly caused by plasmonic materials. Here, a bio-inspired submicron-thick chiral metamaterial structure was designed and demonstrated experimentally with high contrast (extinction ratio >35) detection of CPL with different handedness and high efficiency (>80%) of the overall device. Furthermore, integration of left- and right-handed CPL detection units with nanograting linear polarization filters enabled full-Stokes polarimetry of arbitrarily input polarization states with high accuracy and very low insertion loss, all on a submillimeter single chip. These unprecedented highly efficient and high extinction ratio devices pave the way for on-chip polarimetric measurements. All-optical modulation is widely used for optical interconnects, communication, information processing, and ultrafast spectroscopy. Yet, there’s deficiency of ultrafast, compact and energy-efficient solutions all in one device. Here, all-optical modulation of light in the near- and mid-infrared regimes were experimentally demonstrated based on a graphene-integrated plasmonic nanoantenna array. The remarkable feature of the device design is its simultaneous near-field enhancement for pump and probe (signal) beams, owing to the localized surface plasmon resonance excitation, while preserving the ultrafast photocarrier relaxation in graphene. Hence, a distinct modulation at 1560nm with record-low pump fluence (<8μJ/cm^2) was reported with ~1ps response time. Besides, relying on broadband interaction of graphene with incident light, a first-time demonstration of graphene-based all-optical modulation in mid-infrared spectral region (6-7μm) was reported based on the above double-enhancement design concept. Relying on the tunability of metasurface design, the proposed device can be used for ultrafast optical modulation from near-infrared to terahertz regime. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2020

Optical electroabsorption modulators (EAMs) that utilize quantum wells (QWs) are known to exhibit high modulation sensitivity, which is required for the analog optical fiber link application, compared to other types of optical modulators. QW-EAMs utilize the change of absorption coefficients that depends on the change of electric field across the QW for the optical intensity modulation. This dissertation focuses on the theoretical analysis of the optical properties of asymmetric double QWs (ADQWs) and the systematic optimization of modulation sensitivity in low-voltage EAMs that incorporate ADQWs. In this structure, the accurate calculation of excitons is especially important because the excitonic as well as the band-to-band optical transitions dominate the optical properties at the operating wavelength. The complex linear optical susceptibility was calculated within the density matrix approach in the quasi-equilibrium regime for the low excitation power and through a thorough treatment of line broadening. Transition strengths were calculated in the wavevector space, which effectively includes valence subband mixing with the warping of the subbands, excitonic mixing effects, and possible optical selection rules (e.g., light polarization, spin of excitons). The calculated transmission properties of the waveguide EAMs were almost identical to the experimental data at the device operating bias range. The mixing of excitons in ADQWs was analyzed in detail in momentum space, which was demonstrated to be very important in the process of structural optimization of ADQWs. The optimization of the structural parameters revealed that at an adequate barrier position and well width, the barrier thickness affects the modulation efficiency the most. Subsequently, in InGaAsP-based waveguide type QW-EAMs that operate at 1550 nm, the optimization of only one variable the thickness of the coupling barrier of the ADQWs shows 380 % enhancement in the modulation sensitivity at a much lower bias field (70->35 kV/cm) compared with that of single-QW structures. This enhancement is found to be caused by the strong mixing of the two exciton states originating in different subband pairs.

<p>  </p> <p>Integrated photonics has provided an elegant way to bring the table-top bulky optical systems from the research lab to our daily life, thanks to its compact size, robustness, and low power consumption. Over the past decade, Silicon Nitride (Si3N4) photonics has become a leading material platform, benefiting from its record-low loss, large Kerr nonlinearity, and compatibility with the foundry process. However, the lack of electro-optical effect makes it challenging to actively tune the Si3N4 photonic circuits for advanced applications, such as LiDAR, spectroscopy, and atomic clocks. During my PhD research, I have developed a new platform of piezoelectric control of Si3N4 photonics through stress-optical effect. By integrating an<br> Aluminum Nitride (AlN) piezoelectric actuator, I demonstrated the tuning of Si3N4 optical microring resonator at sub-microsecond speed with nano-Watt power consumption. Microwave frequency (GHz) acousto-optic modulation (AOM) is realized by exciting high-overtone bulk acoustic wave resonant modes (HBAR), which are tightly confined in an acoustic Fabry-Pérot cavity. Maximum of 9.2 GHz modulation is achieved which falls into the microwave X-band. </p> <p><br></p> <p>The applications of the Piezo-on-Photonic platform are extensively explored in the quasi-DC and high frequency regimes. By working as a stress-optical tuner at low frequency, it allows me to actively tune a Kerr frequency comb into different states, and stabilize it over several hours, which can serve as the light source for the next-generation chip-based LiDAR engine. On the other hand, the GHz frequency AOM has helped me demonstrate a magnetic-free integrated optical isolator, a device that transmits light in only one direction. Three AlN HBAR actuators are integrated closely on the same Si3N4 microring resonator, which generate an effective rotating acoustic wave and break the transmission reciprocity of the light. A maximum of 10 dB isolation is achieved under 300 mW total radiofrequency power, with minimum insertion loss of 0.1 dB. Finally, the application of the same technique in quantum microwave to optical converter is theoretically analyzed, showing potential for building future quantum networks. The initial experimental attempt and outlook for future improvements are investigated. </p> <p><br></p> <p>In conclusion, this thesis investigated a novel Piezo-on-Photonic platform for flexible and efficient control of the Si3N4 photonic system, and its applications in a wide variety of advanced devices are demonstrated, with the potential of being key building blocks for future optical systems on-chip.  </p>

O trabalho de doutorado teve como objetivo desenvolver um modulador óptico baseado em filme magnetostrictivo para aplicação como magnetômetro. A modelagem e simulação do dispositivo foi realizada utilizando software com cálculo por método dos elementos finitos (MEF) e teve como finalidade auxiliar iterativamente os processos de projeto e fabricação do modulador. A originalidade da proposta baseia-se na construção de um guia de onda em óptica integrada recoberto por um filme magnetostrictivo para permitir a modulação , via efeito elasto-óptico, da onda guiada pela aplicação de campos magnéticos externos. O campo magnético aplicado provoca a deformação o material magnetostrictivo que induz uma modificação no perfil de esforço aplicado ao substrato. O substrato tem suas propriedades ópticas alteradas devido ao efeito elasto-óptico, o que provoca mudanças nas propriedades da luz transmitida. O trabalho tem seu início com o estudo e a caracterização de filmes magnetostrictivos de Tb25F275 e Tb23Co77 depositados por sputtering sobre substratos de silício. Uma técnica para preparação das amostras e medição da magnetostricção foi estabelecida e os coeficientes de magnetostrição dos filmes foram determinados a partir das medições diretas dos deslocamentos das amostras, em função dos campos magnéticos aplicados, utilizando a técnica de Atomic Force Microscopy (AFM). Os resultados experimentais obtidos permitiram a realização de simulações por MEF para verificação dos modos de guiamento da luz gerados pelo perfil de esforços induzidos termicamente no processo de deposição do filme magnetostrictivo sobre substrato de B12GeO4 (BGO). Foi modelado e simulado também o efeito da aplicação do campo magnético sobre o guia óptico obtido inicialmente pelo efeito de esforço térmico. No resultado das simulações foi possível verificar as alterações do índice de refração efetivo e da intensidade óptica do modo guiado em função de campos magnéticos aplicados ao modulador. Ao final do trabalho realizaram-se a fabricação de alguns protótipos. Os resultados das caracterizações dos moduladores construídos permitirão, no futuro, ajustar os modelos de simulação elaborados. / The doctoral work aims are the development and simulation of an optical modulator based on the effect of magnetostriction for application as magnetometer. The multiphysics simulations were performed using the Finite Elements Method (FEM). In the manufacturing process of optical modulator integrated optics techniques were applied. The originality of the proposal is based on the construction of an integrated optical waveguide covered by a magnetostrictive film to allow the modulation of the guided wave, through the elasto-optical effect, by the application of external magnetic fields. The applied magnetic field causes deformation of the magnetostrictive material that induces a modification of the stress profile produced in substrate. The substrate has its optical properties altered due to the elasto-optical effect, which causes changes in the properties of transmitted light. The work begins with the study and characterization of TbFe and TbCo2 magnetostrictive films deposited by sputtering on silicon substrates. A method for sample preparation and measurement of magnetostriction was established. The magnetostrictive coefficient of the films was determined from the direct measurement of displacements of samples by AFM technique for magnetic fields applied. The experimental results obtained allowed to perform MEF simulations to verify the light guided modes generated by the profile of thermally induced stress created by deposition process of magnetostrictive film on B12GeO4 (BGO) substrate. It was also modeled and simulated the effect of the application of magnetic field on the optical guide obtained initially by the effect of thermal stress. In simulation results, it was possible to verify the changes of effective refractive index and optical intensity of guided modes as functions of magnetic fields applied to the modulator. At the end of the work, some prototypes were fabricated. The results of characterizations of the built modulators will allow, in the future, adjustments in simulation models.

O trabalho de doutorado teve como objetivo desenvolver um modulador óptico baseado em filme magnetostrictivo para aplicação como magnetômetro. A modelagem e simulação do dispositivo foi realizada utilizando software com cálculo por método dos elementos finitos (MEF) e teve como finalidade auxiliar iterativamente os processos de projeto e fabricação do modulador. A originalidade da proposta baseia-se na construção de um guia de onda em óptica integrada recoberto por um filme magnetostrictivo para permitir a modulação , via efeito elasto-óptico, da onda guiada pela aplicação de campos magnéticos externos. O campo magnético aplicado provoca a deformação o material magnetostrictivo que induz uma modificação no perfil de esforço aplicado ao substrato. O substrato tem suas propriedades ópticas alteradas devido ao efeito elasto-óptico, o que provoca mudanças nas propriedades da luz transmitida. O trabalho tem seu início com o estudo e a caracterização de filmes magnetostrictivos de Tb25F275 e Tb23Co77 depositados por sputtering sobre substratos de silício. Uma técnica para preparação das amostras e medição da magnetostricção foi estabelecida e os coeficientes de magnetostrição dos filmes foram determinados a partir das medições diretas dos deslocamentos das amostras, em função dos campos magnéticos aplicados, utilizando a técnica de Atomic Force Microscopy (AFM). Os resultados experimentais obtidos permitiram a realização de simulações por MEF para verificação dos modos de guiamento da luz gerados pelo perfil de esforços induzidos termicamente no processo de deposição do filme magnetostrictivo sobre substrato de B12GeO4 (BGO). Foi modelado e simulado também o efeito da aplicação do campo magnético sobre o guia óptico obtido inicialmente pelo efeito de esforço térmico. No resultado das simulações foi possível verificar as alterações do índice de refração efetivo e da intensidade óptica do modo guiado em função de campos magnéticos aplicados ao modulador. Ao final do trabalho realizaram-se a fabricação de alguns protótipos. Os resultados das caracterizações dos moduladores construídos permitirão, no futuro, ajustar os modelos de simulação elaborados. / The doctoral work aims are the development and simulation of an optical modulator based on the effect of magnetostriction for application as magnetometer. The multiphysics simulations were performed using the Finite Elements Method (FEM). In the manufacturing process of optical modulator integrated optics techniques were applied. The originality of the proposal is based on the construction of an integrated optical waveguide covered by a magnetostrictive film to allow the modulation of the guided wave, through the elasto-optical effect, by the application of external magnetic fields. The applied magnetic field causes deformation of the magnetostrictive material that induces a modification of the stress profile produced in substrate. The substrate has its optical properties altered due to the elasto-optical effect, which causes changes in the properties of transmitted light. The work begins with the study and characterization of TbFe and TbCo2 magnetostrictive films deposited by sputtering on silicon substrates. A method for sample preparation and measurement of magnetostriction was established. The magnetostrictive coefficient of the films was determined from the direct measurement of displacements of samples by AFM technique for magnetic fields applied. The experimental results obtained allowed to perform MEF simulations to verify the light guided modes generated by the profile of thermally induced stress created by deposition process of magnetostrictive film on B12GeO4 (BGO) substrate. It was also modeled and simulated the effect of the application of magnetic field on the optical guide obtained initially by the effect of thermal stress. In simulation results, it was possible to verify the changes of effective refractive index and optical intensity of guided modes as functions of magnetic fields applied to the modulator. At the end of the work, some prototypes were fabricated. The results of characterizations of the built modulators will allow, in the future, adjustments in simulation models.

En premier lieu, des couches minces épitaxiales ont été obtenues sur des substrats de silicium grâce à l’utilisation de l’épitaxie par jets moléculaire et de couches tampons de titanate de strontium SrTiO3. Une technique de croissance par co-déposition a été développée de manière à obtenir un rapport Ba:Ti proche de la stoechiométrie, et ce afin d’éviter la formation de défauts cristallins dans la couche de BaTiO3. Le matériau déposé cristallise dans une structure de symétrie quadratique, ce qui est unpré-requis pour l’obtention de propriétés électro-optiques. De plus, selon les conditions de croissance, l’axe c de la maille élémentaire quadratique a pu être ajusté de manière à être aligné parallèlement ou perpendiculairement à la surface du substrat. L’utilisation d’une mince couche tampon de nucléation a également permis de croitre des films mincesBaTiO3 épitaxiées par pulvérisation, technique largement répandue en milieu industriel.Un coefficient de Pockels élevé a par la suite été obtenu sur de tellescouches épitaxiées. La valeur mesurée de 148pmV est clairement supérieure aux valeurs admises dans la littérature pour d’autres matériaux nonlinéairestels que le niobate de lithium, pour lequel un coefficient de31pmV est rapporté. La méthode de caractérisation électro-optique développée à cette occasion révèle également le caractère ferroélectrique des couches de BaTiO3, observé pour la première fois dans de tels matériaux épitaxiés sur silicium.Finalement, ces couches minces électro-optiquement actives ont été intégrées dans des dispositifs photoniques sur silicium. Dans cette optique,une structure de guide d’onde à fente a été utilisée en insérant 50nm deBaTiO3 entre deux couches de silicium. Dans ce type de structure, le confine mentoptique est 5 fois supérieur à celui obtenu pour des guides d’onde en silicium avec une gaine à base de BaTiO3. Des guides d’ondes rectilignesont tout d’abord été fabriqués, pour lesquels des pertes optiques del’ordre de 50−100 dB/cm ont été mesurées. Par la suite, des composants passifs fonctionnels ont été fabriqués, tels que des interféromètres typeMach-Zehnder, des résonateurs circulaires et des coupleurs. Finalement,la fonctionnalité de composants actifs a été démontrée pour la première fois, en se basant notamment sur des résonateurs ayant un facteur de qualité Q d’environ 5000, et pour lequel la résonance varie en fonction du champ électrique transverse. L’origine physique de cette variation n’a cependant pas pu être expliquée sur la seule base de l’effet Pockels. Cette thèse démontre que l’utilisation de nouveaux matériaux électro optiquement actifs au coeur de dispositifs photoniques sur silicium créede nouvelles opportunités pour la conception et l’ingénierie de circuitsphotoniques. L’intégration d’oxydes tels que barium titanate permet d’envisager de nouveaux concepts de dispositifs pour ajuster, moduler ou commuter la lumière au sein de circuits photoniques denses. De nouveaux défis et perspectives s’ouvrent également aux scientifiques pour modifier artificiellement les propriétés électro-optiques de ces matériaux, que ce soit par contrainte, dopage ou par l’ingénierie de multicouches. De telles avancées pourront sans aucun doute fortement améliorer les performances des dispositifs. / A novel concept of utilizing electro-optical active oxides in silicon photonic devices is developed and realized in the frame of this thesis. The integration of such oxides extends the silicon photonics platform by non-linear materials, which can be used for ultra-fast switching or low-power tuning applications. Barium titanate is used as active material as it shows one of the strongest Pockels coefficients among all oxides. Three major goals are achieved throughout this work: First, thin films of BaTiO3 are epitaxially grown on silicon substrates via molecular beam epitaxy (MBE) using thin SrTiO3 buffer layers. A shuttered co-deposition growth technique is developed in order to minimize the formation of defects in the BaTiO3 films by achieving a 1:1 stoichiometry between barium and titanium. The layers show a tetragonal symmetry and are therefore well-suited for electro-optical applications. The orientation of the long c -axis of the BaTiO3 crystal can be tuned to point perpendicular or parallel to the film surface, depending on the growth conditions. In addition, thin MBE-grown seed layers are combined with rf-sputter deposition. With this hybrid growth approach, rather thick ( > 100 nm), epitaxial BaTiO3 layers on silicon substrates are obtained with a commercially available, wide spread deposition technique. As a second goal, a strong Pockels coefficient of reff = 148 pm/V is determined in the epitaxial BaTiO3 films. This first experimental result on the electro-optical activity of BaTiO3 layers on silicon shows a clear enhancement compared to alternative non-linear materials such as lithium niobate with reff = 31 pm/V. By means of the electro-optical characterization method, also the presence of ferroelectricity in the films is demonstrated. Third, the electro-optical active BaTiO3 layers are embedded into silicon photonic devices. For this purpose, a horizontal slot-waveguide structure with a ~50 nm-thick BaTiO3 film sandwiched between two silicon layers is designed. With this design, the optical confinement in the active BaTiO3 layer is enhanced by a factor of 5 compared to Si-waveguide structures with a standard cross section and BaTiO3 as cladding. Straight BaTiO3 slot-waveguides with propagation losses of 50 − 100 dB/cm as well as functional passive devices such as Mach-Zehnder-interferometers, couplers, and ring resonators are experimentally realized. Additionally, first active ring resonators with Q-factors of Q~5000 are fabricated. The physical origin of the observed resonance shift as a function of the applied bias voltage, however, can not be conclusively clarified in the present work. The combination of high-quality, functional BaTiO3 layers with silicon photonic devices as demonstrated in this thesis offers new opportunities by extending the design palette for engineering photonic circuits with the class of electro-opticalactive materials. The integration of oxides such as BaTiO3 enables novel device concepts for tuning, switching, and modulating light in extremely dense photonic circuits. The integration also opens exciting challenges for material scientists to tailor the electro-optical properties of those oxides by strain engineering or fabrication of superlattice structures, which could ultimately lead to another boost of their electro-optical properties.

No description available.

Tesis por compendio / [ES] La fotónica de silicio es una tecnología emergente clave en redes de comunicación e interconexiones de centros de datos de nueva generación, entre otros. Su éxito se basa en la utilización de plataformas compatibles con la tecnología CMOS para la integración de circuitos ópticos en dispositivos pequeños para una producción a gran escala a bajo coste. Dentro de este campo, los interferómetros integrados juegan un papel crucial en el desarrollo de diversas aplicaciones fotónicas en un chip como sensores biológicos, moduladores electro-ópticos, conmutadores totalmente ópticos, circuitos programables o sistemas LiDAR, entre otros. Sin embargo, es bien sabido que la interferometría óptica suele requerir caminos de interacción muy largos, lo que dificulta su integración en espacios muy compactos. Para mitigar algunas de estas limitaciones de tamaño, surgieron varios enfoques, incluyendo materiales sofisticados o estructuras más complejas, que, en principio, redujeron el área de diseño pero a expensas de aumentar los pasos del proceso de fabricación y el coste. Esta tesis tiene como objetivo proporcionar soluciones generales al problema de tamaño típico de los interferómetros ópticos integrados, con el fin de permitir la integración densa de dispositivos basados en silicio. Para ello, aunamos los beneficios tanto de las guías de onda bimodales como de las estructuras periódicas, en términos de la mejora del rendimiento y la posibilidad para diseñar interferómetros monocanal en áreas muy reducidas. Más específicamente, investigamos los efectos dispersivos que aparecen en estructuras menores a la longitud de onda y en las de cristal fotónico, para su implementación en diferentes configuraciones interferométricas bimodales. Además, demostramos varias aplicaciones potenciales como sensores, moduladores y conmutadores en tamaños ultra compactos de unas pocas micras cuadradas. En general, esta tesis propone un nuevo concepto de interferómetro integrado que aborda los requisitos de tamaño de la fotónica actual y abre nuevas vías para futuros dispositivos basados en funcionamiento bimodal. / [CA] La fotònica de silici és una tecnologia emergent clau en xarxes de comunicació i interconnexions de centres de dades de nova generació, entre altres. El seu èxit es basa en la utilització de plataformes compatibles amb la tecnologia CMOS per a la integració de circuits òptics en dispositius diminuts per a una producció a gran escala a baix cost. Dins d'aquest camp, els interferòmetres integrats juguen un paper crucial en el desenvolupament de diverses aplicacions fotòniques en un xip com a sensors biològics, moduladors electro-òptics, commutadors totalment òptics, circuits programables o sistemes LiDAR, entre altres. No obstant això, és ben sabut que la interferometría òptica sol requerir camins d'interacció molt llargs, la qual cosa dificulta la seua integració en espais molt compactes. Per a mitigar algunes d'aquestes limitacions de grandària, van sorgir diversos enfocaments, incloent materials sofisticats o estructures més complexes, que, en principi, van reduir l'àrea de disseny però a costa d'augmentar els processos de fabricació i el cost. Aquesta tesi té com a objectiu proporcionar solucions generals al problema de grandària típica dels interferòmetres òptics integrats, amb la finalitat de permetre la integració densa de dispositius basats en silici. Per a això, combinem els beneficis tant de les guies d'ones bimodals com de les estructures periòdiques, en termes de funcionament d'alt rendiment per a dissenyar interferòmetres monocanal compactes en àrees molt reduïdes. Més específicament, investiguem els efectes dispersius que apareixen en estructures menors a la longitud d'ona i en les de cristall fotònic, per a la seua implementació en diferents configuracions interferomètriques bimodals. A més, vam demostrar diverses aplicacions potencials com a sensors, moduladors i commutadors en grandàries ultres compactes d'unes poques micres cuadrades. En general, aquesta tesi proposa un nou concepte d'interferòmetre integrat que aborda els requisits de grandària de la fotònica actual i obri noves vies per a futurs dispositius basats en funcionament bimodal. / [EN] Silicon photonics is a key emerging technology in next-generation communication networks and data centers interconnects, among others. Its success relies on the ability of using CMOS-compatible platforms for the integration of optical circuits into small devices for a large-scale production at low-cost. Within this field, integrated interferometers play a crucial role in the development of several on-chip photonic applications such as biological sensors, electro-optic modulators, all-optical switches, programmable circuits or LiDAR systems, among others. However, it is well known that optical interferometry usually requires very long interaction paths, which hinders its integration in highly compact footprints. To mitigate some of these size limitations, several approaches emerged including sophisticated materials or more complex structures, which, in principle, reduced the design area but at the expense of increasing fabrication process steps and cost. This thesis aims at providing general solutions to the long-standing size problem typical of optical integrated interferometers, in order to enable the densely integration of silicon-based devices. To this end, we combine the benefits from both bimodal waveguides and periodic structures, in terms of high-performance operation and compactness to design single-channel interferometers in very reduced areas. More specifically, we investigate the dispersive effects that arise from subwavelength grating and photonic crystal structures for their implementation in different bimodal interferometric configurations. Furthermore, we demonstrate various potential applications such as sensors, modulators and switches in ultra-compact footprints of a few square microns. In general, this thesis proposes a new concept of integrated interferometer that addresses the size requirements of current photonics and open up new avenues for future bimodal-operation-based devices. / Financial support is also gratefully acknowledged through postdoctoral FPI grants from Universitat Politècnica de València (PAID-01-18). European Commission through the Horizon 2020 Programme (PHC-634013 PHOCNOSIS project). The authors acknowledge funding from the Generalitat Valenciana through the AVANTI/2019/123, ACIF/2019/009 and PPC/2020/037 grants and from the European Union through the operational program of the European Regional Development Fund (FEDER) of the Valencia Regional Government 2014–2020. / Torrijos Morán, L. (2021). Photonic Applications Based on Bimodal Interferometry in Periodic Integrated Waveguides [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172163 / Compendio