The Effect of Cavity Length on Two-State Quantum Dot Laser Performance

Abstract

we have investigated an accurate rate equation model to examine the laser cavity length-dependent characteristics of two-state-lasing 1.55μm-InAs–InP (113) B quantum-dot laser (QDL). The rate equations model considered both the ground state (GS) lasing, the excited state (ES) lasing, and the inhomogeneous and homogeneous broadenings. Results demonstrate that with an increase in cavity length, the threshold gain is decreased, the output power spectrum is broadened, the turn-on delay is decreased, and the threshold current is increased for both the GS and ES emissions. Also, the direct relaxation channel does not lead to a saturation of emitted photons of the GS. As the ES starts to lase, the photon numbers slope efficiency of the GS emission is reduced, which is more evident for shorter cavity lengths. In addition, With a shorter cavity length, the 3-dB modulation bandwidth increases for both the ground and excited states emissions, accompanied by more output photons. Moreover, as the ES lasing began, the 3-dB modulation bandwidth slop of the GS with the increase in bias current decreases until it remains almost constant. Also, the 3-dB modulation bandwidth of the GS is larger than ES at the same bias current, where the trend is opposite for larger cavity lengths. The 3-dB modulation responses bandwidth of ~ 26GHz and ~17GHz have been achieved for GS and ES emission at a bias current of 50mA for 300μm cavity length.