Ultrafast dynamics of quantum dots

The physics of quantum dot (QD) photonic devices has been a subject of great interest since the development of self-assembly growth techniques. One of the principle motivating factors for the study of QD lasers was the possibility of substantially reducing the phase-amplitude coupling (alpha-factor) of semiconductor lasers from values in the region of 3-5 for quantum well devices. Amongst the expected benefits of such a reduction were low modulation chirp, reduced filamentation in high power devices and reduced sensitivity to optical feedback.

To date, QD lasers have displayed a wide range of alpha-factors, the value displaying a strong dependence on the measurement conditions. Recent analysis has shown that the low ground state (GS) gain saturation of QD devices coupled with a large amount of non-resonant carriers in the QD's excited states (ES) and barrier states can result in large values above threshold and as a consequence, directly phase modulated devices have been demonstrated. In addition, it has been proposed that the unique carrier dynamics of QD semiconductor optical amplifiers (SOAs) would lead to a reduction of patterning effects compared to conventional devices, for both linear and non-linear applications. As the understanding of relevant carrier relaxation processes in QD structures improves, additional device functionalities will be realised. 

The work on quantum dot dynamics is carried out in collaboration with the Photonics Device Dynamics group, CIT and Tyndall National Institute. For recent publications, please see the various researcher pages on this site.