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On-chip spatial and polarization multiplexing have emerged as a powerful strategy to boost the bandwidth of integrated optical transceivers. State-of-the-art multiplexers require accurate control of the relative phase or the spatial distribution among different guided optical modes, seriously compromising the bandwidth and performance of the devices. To overcome this limitation, we propose a new approach based on the coupling between guided modes in integrated waveguides and optical beams free-propagating on the chip plane. The engineering of the evanescent coupling between the guided modes and free-propagating beams allows spatial and polarization multiplexing with state-of-the-art performance. To demonstrate the potential and versatility of this approach, we have developed a two-polarization multiplexed link and a three-mode multiplexed link using standard 220-nm-thick silicon-on-insulator technology. The two-polarization link shows a measured -35 dB crosstalk bandwidth of 180 nm, while the three-mode link exhibits a -20 dB crosstalk bandwidth of 195 nm. These bandwidths cover the S, C, L, and U communication bands. We used these links to demonstrate error-free transmission (bit-error-rate < 10-9) of two and three non-return-to-zero signals at 40 Gbps each, with power penalties below 0.08 dB and 1.5 dB for the two-polarization and three-mode links respectively. The approach demonstrated here for two polarizations and three modes is also applicable to future implementation of more complex multiplexing schemes.

Silicon photonics holds the promise for large-scale and low-cost production of high-performance optoelectronic circuits. Driven by the impressive technology development in the recent years, silicon photonics is expanding its frontiers towards new applications beyond datacom, including among others, sensing, radio-over-fiber and quantum. Aiming to meet the requirements of these new applications, the Si photonics community is exploring alternative wavelength ranges and physical phenomena, with a particular interest in the mid-infrared (2-20 µm wavelength), and Kerr nonlinearities. Patterning Si with features smaller than half of the wavelength has proven to be a simple and powerful tool to overcome performance limitations of conventional silicon photonic devices. This PhD is devoted to the use of Si subwavelength engineering to develop novel devices and circuits for spectroscopy applications in the near-IR and mid-IR and supercontinuum generation exploiting Kerr nonlinearities. The main results obtained in this PhD include: i) first demonstration of Jaquinot's advantage with integrated Fourier transform spectrometer made in silicon photonics, ii) demonstration of silicon Fourier transform spectrometer for wavelength near 5.5 µm, the longest reported for silicon, and iii) supercontinuum generation expanding 2.35 octaves, between two 1.55 µm and 7.5 µm wavelength. This is, to the best of our knowledge, the widest supercontinuum generation in silicon., La photonique au silicium est prometteuse pour la production à grande échelle et à faible coût de circuits optoélectroniques de haute performance. Grâce à l'impressionnant développement technologique de ces dernières années, la photonique au silicium élargit ses frontières vers de nouvelles applications au-delà des communications de données, y compris, entre autres, la détection, la radio sur fibre et la quantique. Afin de répondre aux exigences de ces nouvelles applications, la communauté de la photonique au silicium explore de nouvelles gammes de longueurs d'onde et de nouveaux phénomènes physiques, avec un intérêt particulier pour l'infrarouge moyen (longueur d'onde de 2 à 20 µm) et les non-linéarités Kerr. L'application de motifs sur le Si avec des caractéristiques inférieures à la moitié de la longueur d'onde s'est avérée être un outil simple et puissant pour surmonter les limites de performance des dispositifs photoniques au silicium conventionnels. Cette thèse est consacrée à l'utilisation de l'ingénierie des sous-longueurs d'onde du silicium pour développer de nouveaux dispositifs et circuits pour les applications de spectroscopie dans l'infrarouge proche et moyen et la génération de supercontinuum exploitant les non-linéarités Kerr. Les principaux résultats obtenus dans le cadre de cette thèse sont les suivants : i) première démonstration de l'avantage de Jaquinot avec un spectromètre intégré à transformée de Fourier fabriqué en photonique de silicium, ii) démonstration d'un spectromètre à transformée de Fourier en silicium pour une longueur d'onde proche de 5,5 µm, la plus longue rapportée pour le silicium, et iii) génération de supercontinuum s'étendant sur 2,35 octaves, entre deux longueurs d'onde de 1,55 µm et 7,5 µm. Il s'agit, à notre connaissance, de la plus large génération de supercontinuum dans le silicium.

Fabrication of core/shell-structured Y 2 O 3 :Bi, Eu/SiO 2 nanophosphors was presented. The core nanophosphors, Y 2 O 3 :Bi, Eu, were synthesized by urea precipitation and annealing. The silica shell was formed by modified Stober method and its thickness was controlled by the amount of TEOS. Additional heat-treatment was applied on the core-shell particles in order to remove any residual impurities. Size and shape of core and core/shell particles were investigated by SEM analysis.