Etude et caractérisation de composants d’optique intégrée exploitant les propriétés électro-optiques d’oxydes fonctionnels épitaxiés

摘要

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).