Conception de micro-nano cavités à base de cristaux photoniques en silicium et nitrure de silicium en vue d’application en optique intégrée et non linéaire

Abstract

The ability to develop innovative photonic devices enabling the controlling of the flow of light at the nanoscale, has motivated a growing interest. In particular, planar photonic crystal cavities (PhCs) based struc tures are promising candidates for such applications. The aim of this thesis is to study and design silicon (Si) and silicon nitride (SiN)-based planar photonic crystal (PhC) micro-nano cavities (planar technology). These cavities were designed to reduce the radiation losses (improve the quality factor Q) and strong confinement of the light (reduce the mode volume V). First, we studied the dispersion diagram of photonic band-gap structures incorporated into a planar optical waveguide. Numerical models by plane waves (PWE-3D) are developed, the aim is to optimize the geometrical parameters of lattice of air holes etched in a layer of silicon (Si) or silicon nitride (SiN) that gives a wide band gap. In order to explore the potential of planar structures to strong vertical confinement of the light, different configurations were proposed and studied to determine the impact of symmetry and refractive index of the cladding on the band-gap. Next, we study and design micro-nanocavities implemented in a planar photonic crystal surrounded with various high and low refractive index cladding materials. Such structures can be used both in integrated and non linear optics. We have shown theoretically that, at the wavelength scale, the physics of light confinement in the vertical direction is substantially controlled by the geometry of the surrounding (bottom and top) claddings. We have also studied and designed hybrid (Si-PS) and silicon nitride (SiN) cavities realized in planar PhC suspended on a silicon-on-insulator substrate (SOI). Such cavities show efficient nonlinear optical properties. The design of the proposed cavities is based on an engineering technique of defect which consists of tuning the position and radius of the lateral, upper, and lower boundary holes near the cavity edge. This technique allows to give a gradual change of the envelope function of the electric field at the edges of the cavity. This latter allows to minimizes the radiative component in the light cone and reduce the optical loss in the vertical direction. Interesting and important results are reported for the design of cavities with high (Q/V). Furthermore, the small perturbations theory enables to determine the shift of the resonant wavelength of the proposed cavities induced by a small change of the dielectric constant of the order of 10− 4. The optical sensitivity of the optimized cavities was studied and discussed in the case of the presence of different gaseous environments and temperature change. Due to their high quality factor and small mode volume, we have shown that the optimized cavities are well suited for the design of Gas and temperature sensor operating both in the visible and mid-infrared range.