Tunable Laser in Silicon Photonic platform exploiting ring resonators: overview and modelization.

Thanks to its important features in the field of integrated electronic circuits and CMOS processes, Silicon is one of the most used semiconductor in electronic industry. Actually, research is moving in the direction of using this material also for photonic application, trying to integrate photonic devices over semiconductor platforms, with the purpose to improve integrated circuits performances, for example increasing transmission velocity. Silicon Photonics studies how efficiently embed photonic components in silicon integrated circuits. The main drawback of using Silicon-based technology in photonic circuits, is that Silicon is and indirect band-gap semiconductor, this means that is not perfectly suitable to fabricate active optical devices, like lasers, since during recombination processes there is not energy-momentum conservation. For this reason, in this thesis integration technologies of photonic devices are firstly analysed, pointing out benefits and drawbacks of monolithic and heterogeneous integration methods, focusing then on platforms that can guarantee effective integration, and are always scalable and CMOS compatible, including SiO2, Silicon Nitride and Indium Phosphide platforms. The state of the art currently proposes solutions for Silicon Photonic mainly with heterogeneous integration, ensuring that the performance of lasers are satisfactory in terms of very narrow linewidth, suitably high optical power output and very low losses. In order to achieve these goals, two research groups are analysed, which have in common the use of ring resonators as resonant cavities in lasers, which are useful to increase the effective cavity length, favouring light emission with very narrow linewidth and, above all, making the laser tunable guaranteeing a wide frequency span of the emitted light. The purpose of this thesis is to simulate the static and dynamic behaviour of an integrated laser on a Silicon Nitride platform, consisting of a reflective outer section, waveguide, phase section and two coupled ring resonators. In particular, the emission spectrum was obtained, the device's response to a current intensity modulation (small-signal) has been simulated, the Relative Intensity Noise (RIN) and the spectrum of the integrated RIN were retrieved. Finally, the dynamic behaviour of the laser has been analysed by plotting the eye diagram stimulating the laser with square wave modulation of current and a pseudo-random bit stream. Each simulation has been done for different coupling coefficient values, producing different FWHM values. In conclusion, the structure analysed and simulated is confirmed as a valid possibility for the integration of optoelectronic devices on Silicon. In fact, the dynamic and static behaviour of the device is satisfactory and comparable with the state of the art, so the characteristic of the analysed device are promising. Considering the compatibility of materials taken in consideration with the CMOS process, good scalability characteristics are also guaranteed. The analysis performed can be developed and extended by considering other non-linear effects introduced by the use of Silicon, e.g. the Kerr Effect and Two-Photon Absorption, so that more realistic simulations can be performed.