Inside this thesis, a Multi-Section Delayed Differential Equation model has been used to perform the numerical analysis of a passively mode locked quantum dot lasers produced by the german company Nanoplus Nanosystems and Technologies GmbH. In particular, the device analyzed has been created for pumping single photon source and so it's characterised by a very low repetition rate (extremely long cavity) which makes quite trivial its analysis. We've started by providing the theoretical background required to model the QD-based lasers focussing our attention mainly: on the QD electronic structure, on their features and on their rate equations (both under current injection and under reverse voltage).