We develop a new general model for rigorous theoretical description of circularly polarised ultrashort optical pulse interactions with the resonant non-linearities in semiconductor QDs embedded in optical waveguides and semiconductor microcavities. The method is based on the self-consistent FDTD-solution of the vector Maxwell equations coupled via macroscopic polarisation to the originally derived time-evolution equations of a discrete four-level quantum system in terms of the real pseudospin (coherence) vector exploiting the SU(4) group formalism. Selective excitation of specific spin-states with predefined helicity of the optical pulse and formation of polarised Self-Induced Transparency (SIT)-solitons in a specially prepared degenerate four-level system is numerically demonstrated. The model is applied to the stimulated optical dipole transitions of the trion state in a singly charged QD taking into account the spin relaxation dynamics. Our theoretical and numerical approach yields the time evolution of the spin population of the trion state which is in good agreement with the time-resolved polarised photoluminescence experimental data.