Hybrid laser design for a silicon photonics platform

Silicon Photonics is a new technology that allows to create photonic devices that use silicon as an optical medium, with the final goal of integrating photonic and electronic devices on the same silicon chip. Although various passive optical devices have been successfully demonstrated in the context of Silicon Photonics, the most important building block of an optical system, i.e. an efficient laser source, monolithically integrated on Si, is still missing. This is due to the fact that silicon is an indirect band-gap material. Nowadays, several technological solutions are available to overcome this problem. An overview of the state-of-the-art of the available techniques for laser integration on silicon is presented in the first part of this work. Approaches such as hybrid integration, heterogeneous integration through wafer bonding, direct hetero-epitaxial growth on silicon are investigated, highlighting advantages and disadvantages for all of these techniques. Also, the most important features of two mature platforms for photonic integration, i.e. SOI and SiN-on-silica, are discussed and compared. In the second part of this work, after a brief theoretical review of microring resonators and the Vernier effect, the structure of an hybrid laser, based on the edge-coupling between a III-V Reflective Semiconductor Optical Amplifier (RSOA) and an external photonic integrated circuit (PIC), designed as the front mirror of the laser cavity, is presented. The performances of this device, in terms of Wall-Plug Efficiency (WPE), effective length (Leff) and linewidth, are analyzed as the linear losses of the waveguides change, when 1) the PIC is realized using a SOI Platform and 2) a SiN Platform. In particular, two types of designs are investigated: one maximizes the WPE, the other minimizes the linewidth. The final part of this work is dedicated to the introduction of non-linear effects, like Two Photon Absorption (TPA) and Free Carrier Absorption (FCA), in silicon waveguides. First of all, nonlinearities are introduced in microring resonators, then in straight waveguides and finally, an overall model of the entire PIC is built in such a way that it is possible to compute the optical electric field reflectivity at the RSOA. Once this reflectivity is known, the influence of these non-linear effects on the performances of the device is discussed.