Delayed Differential Equation Analysis of Harmonic Mode Locking in Quantum Dot Ring Lasers

The demand for ultrafast and broad band communication has opened an active research topic in order to improve the telecommunications performances. In particular, in the last 25 years the requested bandwidth has doubled every 18 months with an increase of the data rates that are expected to grow beyond 10 Gb/s in the nearly future. In this sense, sub-Tera Hertz spectrum (0.1THz-0.3THz) has become more and more attractive. More specifically, quantum dots structures are predicted to have superior properties with respect to their bulk counterpart. These zero-dimensional devices are already capable to emits in pulsed regime at hundreds of Gigahertz and they find wide uses in various field, not only as RF sources but also in biomedical applications. Among the advantages it is noticeable the presence of a minor size, less power consumption, and a higher bandwidth. Mode locking technique is one of the possibilities to exploit the above stated pulsed regime to establish a basis for the future 5G and 6G transmissions. In this thesis, numerical simulations of a quantum dot ring cavity laser are performed in order to demonstrate the possibility to emit frequencies of 150-160GHz. To this aim, a preexisting MATLAB code is used to solve a set of rate equations with a Multi Sections Differential Delayed Equations Approach (MS-DDE). A considerable effort was spent to find the geometrical and optical parameters to exploit a stable harmonic mode locking regime in the sub-tera hertz range. Furthermore, the implications of these parameters on the photocurrent and on the efficiency were investigated. This model could be used to perform a preliminary analysis in the design of Quantum Dot Lasers based devices in passive or harmonic mode locking regime. Moreover, it could provide a general overview on performances of bias and geometrical parameters.