Owing to its centrosymmetric structure, the critical optical component of a silica fiber cannot to possess a second-order nonlinear optical susceptibility, Χ(²), preventing a silica fiber from many potential applications. Here, we theoretically and experimentally demonstrate a new technique to generate large and thermodynamically stable second-order nonlinearity into silica optical tapered fibers without breaking the centrosymmetry of the silica glass. The nonlinearity is introduced by surface layers with high polar-ordering fabricated by a novel hybrid covalent/ionic self-assembly multilayer technique. Despite the overall rotational symmetry of the nonlinear fiber, we observe significant second harmonic generation with ~ 400–500 fold enhancement of the SHG power compared to the traditional tapers. Phase matching for a SHG process in second-order nonlinear tapered fibers is also realized by the compensation of waveguide modal dispersion with material chromatic dispersion, which occurs only for submicron tapers where the modal dispersion is large. In addition, quasi-phase-matching for a nonlinear taper can be accomplished by introducing a periodic pattern into the nonlinear film coating. We use UV laser ablation for the controlled removal of particular nonlinear film segments on a taper surface in order to produce a Χ(²) grating structure. A resulting SHG enhancement from quasi-phase-matching is observed over a broadband spectrum of the pump light mainly due to the non-uniform shape of a taper waveguide. The laser ablation is a clean and fast technique able to produce well-define patterns of polymer films on either flat or curved substrate geometry. With surface layers containing reactive functional groups e.g. primary amines, we demonstrate that the resulting patterned film obtained from the laser ablation can be used as a template for further self-assembly of nanoparticles with high selectivity. A pattern feature size down to ~ 2μm or smaller can be fabricated using this approach. We also discuss preliminary results on a novel technique to further improve spatial accuracy for selective self-assembly of nanoparticles at an unprecedented level. Different types of nanoparticles are joined in order to form well-defined, molecular-like superstructures with nanoscale accuracy and precision. The technique is based on a selective surface functionalization of photosensitive molecules coated on metallic nanoparticles utilizing enhanced two-photon photocleavage at the plasmonically-active sites (hot spots) of the nanoparticles in resonance with an applied electromagnetic wave. As a result, the surface functional groups at the nanoparticle hot spots are different from the the other areas, allowing other kinds of nanoparticles to self-assemble at the hot spots with high degree of selectivity. / Ph. D.

Layer-by-layer deposition techniques were used to fabricate films with second order nonlinear optical (NLO) properties. These materials are key to the development of electro-optic modulators used in fiber optic communication systems. Performance benefits and lower manufacturing costs are driving the development of organic NLO materials as replacements for inorganic crystalline materials such as lithium niobate. The layer-by-layer deposition technique in which polyelectrolytes are deposited on a surface by electrostatic effects is called the Ionically Self-Assembled Monolayer or ISAM method. The role of the optically inactive polycation's structure on deposition and chromophore orientation was studied by fabricating films with several different polycations. While the specific interactions responsible for chromophore orientation in ISAM films remains unclear, hydrogen bonding and electrostatic effects are ruled out as the sole sources of orientation. The highest values of χ(2) were observed under pH conditions that resulted in flat and thin layers. The relationship between pH and the optical homogeneity of the film was also explored. Deposition of polymers under pH conditions in which the polymer chains were aggregated in solution results in films that are not suitable for use in devices. In this work, a new layer-by-layer deposition technique was developed. Coined hybrid deposition, it relies on covalent bonds and electrostatic interactions for film fabrication. Optically inactive polyamines were used as sources of positive charges and as binding sites with optically active low molecular weight chromophores functionalized with a reactive triazine ring and negative charged sulfonate groups. Polar ordering of the chromophores was obtained when the deposition was done under conditions in which covalent bonding was the preferred attachment mechanism for the chromophore molecules. pH conditions in which electrostatic attachment dominated resulted in poorer orientation. The effect of adding ionic salts to the dye solutions was studied, with hopes of increasing the chromophore density in the film by shielding inter-dye electrostatic repulsions. A linear relationship in deposited amount, as characterized by absorbance/bilayer, was observed as the salt concentration was increased. Little effect on χ;(2) was observed for films made with the as-received Procion Red MX-5B chromophore. However, films fabricated from purified Procion Brown MX-GRN showed a definite dependence on added salt. Exceptional χ(2) values were obtained for Procion Brown films deposited using 0.5 M NaCl and PAH. The importance of depositing from non-aggregated solutions was again highlighted, as films made with the less soluble Procion Orange were significantly less homogeneous than those made from Procion Red and Procion Brown which were highly soluble. The role of polycation structure on the deposition and orientation of Procion Brown and Red was examined. / Ph. D.

Les molécules organométalliques présentant d’intéressantes propriétés, notamment en optique non linéaire (ONL), en luminescence et en photovoltaïque, trouvent leur utilité dans la préparation de nouveaux matériaux pour des applications dans les domaines de l’optoélectronique, de la photonique et des cellules solaires à colorant photosensible (DSSC). Ce manuscrit de thèse présente la synthèse et les résultats des propriétés ONL du second ordre de nouveaux complexes dissymétriques push-pull de motif D–π–M–π–A et basés sur les diacétylures de platine (II), les diacétylures de ruthénium (II) et les dérivés du ferrocène. Ces complexes sont constitués de ligands du méthylènepyrane en tant que groupes électrodonneurs pro-aromatiques (D) et de ligands formaldéhyde, indane-1,3-dione, pyrazine, pyrimidine ou iodure de pyrimidinium en tant que groupes électroattracteurs (A), ces deux groupes étant séparés par le centre métallique et différents espaceurs π-conjugués. La réponse en optique non linéaire (ONL) du second ordre des complexes a été mesurée à l’aide de la méthode EFISH (Electric-Field-Induced Second Harmonic) et a été comparée à celle de leurs analogues tout organiques. Tous les complexes ont donné des valeurs µβ de la réponse ONL, fortement augmentées par la méthylation de la pyrimidine. En utilisant les mêmes types de groupes électrodonneurs et électroattracteurs, les plus fortes réponses ONL ont été obtenues avec les complexes de ruthénium. Pour l’un d’entre-eux, une valeur µβ0 particulièrement élevée de 6000.10-48 esu a pu être mesurée. / Organometallic molecular systems exhibiting interesting properties, such as non-linear optical (NLO) responses, luminescence and energy photoconversion, are of great interest in the preparation of novel materials with potential applications in opto-electronics, photonics and Dye-Sensitized Solar Cells (DSSC). This manuscript highlights the synthesis, characterization and the second-order NLO properties of new asymmetrical D–π–M–π–A push–pull dialkynyl ruthenium- and platinum-based as well as dialkenyl ferrocene-based complexes. All complexes incorporate pyranylidene ligands as pro-aromatic donor groups (D) and formaldehyde, indane-1,3-dione pyrazine, pyrimidine or pyrimidinium iodide as electron-withdrawing groups (A) separated by the metal fragment and various π-linkers. The second order nonlinear optical (NLO) properties of all complexes were measured by the electric-field-induced second harmonic generation (EFISH) technique and compared to those of their purely organic analogs. All complexes exhibited µβ values, which dramatically increased upon methylation of the pyrimidine group. With the same donor–acceptor group combination, the strongest NLO response was obtained with the ruthenium complexes, which exhibited a remarkably high µβ0 value of 6000.10-48 esu.

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