Effect of carrier transition mechanisms and gain compression on relative intensity noise of 1.55 µm QD lasers

Abstract

The impacts of gain compression and direct carrier transition on relative intensity noise (RIN) characteristics of 1.55µm QD lasers have been investigated theoretically. The auto and cross correlation coefficients are calculated through small signal linearization of rate equations for carriers and photon numbers in presence of Langevin noise sources. Calculations reveal that gain nonlinearity reduces RIN level of QD lasers while increases damping factor. These results show good agreement with experimental measurements of RIN spectrum in 1.55µm QD lasers which is flat up to 10GHz. Evaluations demonstrate that among wetting layer, Quantum and Photon shot noises, the second and third one have essential role in overall value of RIN in both linear and nonlinear QD lasers. Moreover, calculations indicate that by increasing the direct carrier transition time, RIN level of auto and cross correlations resulted from wetting layer and ground state carriers increases. Finally, it is shown that the RIN level declines in nonlinear QD lasers by working at higher injection currents which is in confirmation with recent experimental reports. Though, it is demonstrated that considering nonlinear gain and direct carrier transition play essential role on correct modeling of RIN characteristics in 1.55µm QD lasers.