Analytical investigation of relative intensity noise properties of injection-locked mid-IR quantum cascade lasers

Abstract

In this paper, we develop an analytical approach by linearization of small-signal rate equations in the presence of the Langevin noise sources to investigate the noise properties of mid-IR optically injected locked quantum cascade lasers. Excellent agreement between the reported numerical results and our developed analytical method have been obtained with the advantage of drastic calculation time reduction and deeper system performance knowledge. Then, a comprehensive study has been performed which reveals notable noise reduction, especially near the threshold current. It is shown that increasing the phase difference between the slave and master lasers enhances the corresponding noise term and makes this term the dominant noise-generating process near the locking edges. Additionally, by introducing relative intensity noise (RIN) maps, we demonstrate that increasing the bias current leads to lower RIN and frequency detuning range, while increasing the optical injection power eventuates wider frequency range and also, lower RIN. It has also been discussed that higher linewidth enhancement factors enhance the locking range and decreases the RIN near the positive frequency detuning boundaries. RIN reduction efficiency versus total injected power to the slave laser has been also introduced as a measure of effectiveness of optical injection locking.