  We studied theoretically coherent phenomena in the multimode dynamics of
single section semiconductor ring lasers with Quantum Dots (QDs) active region.
In the unidirectional ring configuration our simulations show the occurrence of
self-mode-locking in the system leading to ultra-short pulses (sub-picoseconds)
with a THz repetition rate. As confirmed by the Linear Stability Analysis (LSA)
of the Traveling Wave (TW) Solutions this phenomenon is triggered by the
analogous of the Risken-Nummedal-Graham-Haken (RNGH) instability affecting the
multimode dynamics of two-level lasers.
