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Physical Review B, 107 (22), ISSN:1098-0121, ISSN:0163-1829, ISSN:1550-235X, ISSN:0556-2805, ISSN:2469-9969, ISSN:1095-3795, ISSN:2469-9950

Since the beginning of the 20th century with the development of telecommunications, new designs and materials were studied for the search oflow power consumption photonic devices on silicon-based platforms for applications such data-com, telecom, sensing, or quantum optics. Due to its indirect bandgap, silicon is a non-efficient light emitting material. For this reason, hybrid integration of other materials for optical amplification has been studied. One of the main handicaps for crystalline materials implementation on silicon platforms is found in the lattice mismatch imposed by silicon which introduces constraints and defects in the material lattice. For this purpose, engineering optical materials for photonic integration has become a hot research topic aiming at providing additional functionalities. In this regard, functional oxides are a very interesting class of materials due to their singular properties. Material engineering is commonly employed to tune and manipulate such properties at will, thus being functional oxides often used to build active reconfigurable elements in complex systems. Transparent oxides with moderate refractive indexes are targeted for hybrid integration due to the rewarding benefits envisioned. Lattice adaptation using a buffing layer between silicon and the functional oxide is an elegant solution to epitaxially grow high-quality crystalline functional oxide films and to avoid interdiffusion between substrate and oxide material. This technique requires a buffer layer to envision defect-free thin films interfaces light scattering and defect density kept to minima. Yttria-Stabilized Zirconia (YSZ) isawell-known buffer oxide for other functional oxides. Among its properties should be noted : chemical stability, transparency range from the visible to the mid-IR, a refractive index around 2.15, which makes this functional oxide interesting for the development of low-loss waveguides when grown over a low contrast substrate. While these optical properties are very interesting for various applications, including on-chip optical communications and sensing, YSZ has remained almost unexplored in photonics. After proving low propagation losses of 2 dB/cm at a wavelength of 1380 nm in highly monocrystalline YSZ waveguides, we intended to explore this material for optical amplification. In this thesis, we explore the deposition of Er³⁺-doped YSZ thin layers by pulsed layer deposition (PLD) on a multilayer and mono layer approach providing luminescence in correspondence with C-band of telecommunication window (λ=1.5 μm) and in the visible range of wavelengths. Structural and optical characterization lead to a highly optical efficient material showing enhanced photoluminescence at 1530 and 1535 nm wavelengths. After characterization, we integrated our material as cladding on SiNx waveguides. Propagation losses and optical amplification at 1530 and 1535 nm using different pumping techniques are discussed in this thesis. Moreover, multilayer approach used for Er³⁺ has been explored for other rare-earth materials such as Pr³⁺.On this subject, structuraland optical characterization results on Pr³ -doped YSZ emission at 1350 nm in the O-band of telecomm window (λ=1.3μm) paves the way towards implementation and interaction of near-IR emitting rare-earth materials in YSZ.; Depuis le début du 20e siècle avec le développement des télécommunications, de nouveaux designs et matériaux ont été étudiés pour la recherche de dispositifs photoniques à faible consommation d'énergie sur des plateformes à base de silicium pour des applications en data-com, télécommunications, détection ou optique quantique. En raison de sa bande interdite indirecte, le silicium est un matériau photoluminescent très peu efficace. Pour cette raison, l'intégration hybride d'autres matériaux pour l'amplification optique est l’objet d’études actuelles. L'un des principaux handicaps de la croissance de matériaux cristallins sur des plateformes silicium se trouve dans le désaccord de paramètre de maille avec le silicium qui introduit des contraintes et des défauts dans le matériau intégré. À cette fin, l'ingénierie des matériaux optiques pour l'intégration photonique est devenue un sujet de recherche intense visant à fournir des fonctionnalités supplémentaires. À cet égard, les oxydes fonctionnels constituent une classe de matériaux très intéressante en raison de leurs propriétés pour la photonique. L'ingénierie des matériaux est couramment utilisée pour régler et manipuler ces propriétés à volonté, les oxydes fonctionnels étant souvent utilisés pour construire des éléments reconfigurables actifs dans des systèmes complexes. Les oxydes transparents avec des indices de réfraction modérés sont ciblés pour l'intégration hybride en raison des avantages envisagés. L'adaptation des réseaux cristallins à l'aide d'une couche possédant un paramètre de maille entre celui du silicium et de l'oxyde fonctionnel est une solution élégante pour faire croître par épitaxie des films d'oxydes fonctionnels cristallins de haute qualité et pour éviter l'interdiffusion entre le substrat et le matériau oxyde. Cette technique nécessite une couche tampon pour garantir des interfaces de qualité, en maintenant la diffusion de la lumière et la densité de défauts au minimum. La zircone stabilisée à l'yttria (YSZ) est un oxyde tampon bien connu pour d'autres oxydes fonctionnels. Parmi ses propriétés, il faut noter : la stabilité chimique, la transparence du visible au moyen-IR, un indice de réfraction autour de 2,15, ce qui rend cet oxyde fonctionnel intéressant pour le développement de guides d'ondes à faibles pertes lorsqu'il est déposé sur un substrat à faible contraste. Bien que ces propriétés optiques soient très intéressantes pour diverses applications, y compris les communications et la détection optiques sur puce, YSZ est resté presque inexploré en photonique. Après avoir démontré de faibles pertes de propagation de 2 dB / cm à une longueur d'onde de 1380 nm dans des guides d'ondes de YSZ hautement monocristallins, nous avons envisagé d'explorer ce matériau pour l'amplification optique. Dans cette thèse, nous explorons le dépôt de couches minces d’YSZ dopées Er³⁺ par ablation laser pulsé (PLD) en monocouche et en multicouche fournissant une luminescence dans la bande C de la fenêtre de télécommunications (λ= 1,5 μm) et dans le domaine du visible de longueurs d'onde. Les caractérisations structurale et optique ont montré que ce matériau est efficace optiquement et présente une forte photoluminescence à des longueurs d'onde de 1530 et 1535 nm. Après ces caractérisations, nous avons intégré ce matériau comme «cladding» sur des guides d'ondes SiNx. Les pertes de propagation et l'amplification optique à 1530 et 1535 nm en utilisant différentes techniques de pompage sont discutées dans cette thèse. De plus, l'approche multicouche utilisée pour Er³⁺ a été explorée pour d'autres terres rares tels que le Pr³⁺. À ce sujet, les résultats de caractérisation structurale et optique de l'émission d’YSZ dopé Pr³⁺ à 1350 nm dans la bande O de la fenêtre de télécommunication (λ= 1,3 μm) ouvrent la voie à la mise en œuvre et à l'interaction de matériaux terres rares dopés dans YSZ émettant dans le proche-IR.

International audience

International audience; Near-infrared (near-IR) integrated photonic devices in silicon based platforms have been studied over the last decades for applications such as on-chip optical communications and sensing. Hybrid integration of functional oxides to search the limits of low power consumption has been a challenge overcome by material engenieering. In this regard, Yttria-Stabilized Zirconia (YSZ) stands as an interesting material for its structural, chemical and optical properties which includes transparency range from the visible to the mid-IR wavelength range. In this regard, we recently demonstrated YSZ waveguides with propagation losses as low as 2 dB/cm at a wavelength of 1380 nm [2]. Based on the encouraging preliminary results, we have recently explored the possibility to introduce active rare-earth dopants into YSZ waveguides to demonstrate on-chip optical amplifiers based on YSZ. In this study, we introduced multilayer approach depositing by pulsed laser deposition (PLD) technique by Er 3+ ions, providing outstanding luminescence around λ = 1.54 µm, in correspondence with C-band of telecommunications. Such active layers have been grown onto different platforms, including SiN and sapphire. The optical properties of Er-doped YSZ thin films growth on waveguides under resonant pumping will be discussed in this paper. These results pave the way towards the implementation of new rare-earth-doped functional oxides into hybrid photonic platforms in a customized and versatile manner, adding light amplification functionalities.

International audience; Due to the strong evolution of data transmission worldwide, silicon photonics needs to provide low power consuming and ultra-fast modulators. Pockels effect is known to answer both these demands. However, silicon is a centrosymmetric crystal, which makes it inadequate to use Pockels effect. Nonetheless, by straining a silicon waveguide, it is possible to unlock second order nonlinear optics effects, enabling electro-optic modulation through Pockels effect. In our work, we experimentally demonstrated a high-speed strain-induced Pockels effect based electro-optic modulation in a Mach-Zehnder silicon modulator. We also present a complete analysis of Pockels, Kerr, and free carriers effects.

International audience

International audience; We report on the first demonstration of high-speed optical modulation based on Pockels effect in strained silicon waveguides. Bandwidths higher than 20GHz and low insertion loss have been achieved at a wavelength of 1550nm.

International audience; En déformant de façon hétérogène la maille cristalline du silicium, un effet Pockels a été démontré pour des fréquences au-delà de 20GHz. Ce travail ouvre la voie vers le développement de nouvelles générations de composants photoniques Si.

International audience; Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. Numerous demonstrations of optoelectronic devices have been reported including plasma dispersion effect based optical modulators, germanium photodetectors or III-V laser on silicon (Si) platform. Nevertheless, the strong evolution of silicon photonics towards very low power consumption circuits call upon new strategies to be developed, especially for power-hungry components such as optical modulators. One strategy is to use Pockels effect in Si waveguides. However, bulk Si is a centrosymmetric semiconductor, which cannot exhibit any second order optical nonlinearities. Nonetheless, under a strain gradient, generated by depositing a stressed layer, typically by silicon nitride (SiN)on Si waveguides, this restriction vanishes. Over the years, many attempts to characterize the second order nonlinear susceptibility tensor through Pockels effect have been performed. However, the semiconductor nature of Si, hinders correct analysis. Indeed, carriers in Si, at the Si/SiN interface and in SiN have a screening effect when performing electro-optic modulation. This yields to the fact that the first works in the field largely overestimate the second order nonlinear susceptibility. On the other hand, it is also possible to characterize the second order susceptibility tensor through second harmonic generation (SHG). This way, we are able to highlight a second order nonlinearity effect, yet without applying an external field which would suffer from the screening effect from the Si/SiN interface. In this study we explore the design of SHG devices using dispersion engineered strained silicon waveguides. Modal methods exploiting both the phase-matching and thequasi-phase-matching approach taking into account the overlaps between strain gradient profiles and optical modes. Recent experimental result on SHG in strained silicon waveguides will also be discussed.

International audience; Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. However, Silicon is a centrosymmetric semiconductor, which cannot exhibit any second order optical nonlinearities, like second harmonic generation nor the linear electro-optic effect (i.e. Pockels effect). Nonetheless, by means of strain gradients, generated by depositing a stressed layer (typically SiN) on silicon waveguides, this restriction vanishe. Hence, for years, many attempts on characterizing the second order nonlinear susceptibility tensor through Pockels effect have been performed. However, due to the semiconductor nature of silicon, its analysis has been wrongly carried out. Indeed, carriers in Si, at the Si/SiN interface and in SiN have a screening effect when performing electro-optic modulation, which have led to overestimations of the second order nonlinear susceptibility and eventually rose a controversy on the real existence of Pockels effect in strained silicon waveguides. Here, we report on unambiguous experimental characterization of Pockels effect in the microwave domain, by taking advantage of the inherent limitation of carrier effect in high frequency range. Recent results on high-speed measurements will be presented and discussed. Both charge effects and Pockels effect induced under an electric field will be also analysed.

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Any: 2014, Tutores: Francesca Peiró Martínez i Sonia Estradé Albiol, Er-doped silicon nanocrystal-based oxides/nitrides have been investigated. These layers are grown between a polycrystalline silicon electrode and a monocrystalline silicon substrate to allow electrical injection. Energy Filtered (EF-) and High Resolution (HR-) TEM characterization has been performed to provide microscopic insight onto the macroscopic optoelectronic properties of the samples. Evident Er-clustering has been observed in silicon dioxides but not in silicon nitrides, suggesting a better Er solubility and local environment when nitrogen is incorporated. Silicon nanocrystals have been observed in silicon-rich nitride layers, as expected, but also in a region close to the silicon dioxide-polysilicon interface in a layer with no nitrogen or Si excesses. This unexpected Si clusterization has been attributed to Si diffusion from the polycrystalline silicon electrode into the silicon dioxide as a consequence of the annealing treatment. The structural characterization carried out by HRTEM and EFTEM has been correlated with the optoelectronic properties of the devices.