How Many Longitudinal Modes Can Oscillate in a Quantum-Dot Laser: An Analytical Estimate

Multilongitudinal-mode oscillation in a quantum-dot (QD) laser is studied. The number of modes is shown to remain limited with increasing injection current. The maximum number of modes that can oscillate in a QD laser is analytically estimated. While this number increases with increasing surface density of QDs or cavity length, it remains limited (first increases and then decreases) with increasing scatter in the QD size. The critical tolerable values of the structure parameters are derived beyond which higher order longitudinal modes cannot oscillate. It is notable that, in addition to the maximum tolerable scatter, there also exists the minimum scatter in the QD size for each higher order mode to start lasing.