Gain saturation and optical feedback mediated semiconductor laser statistics, dynamics, and intensity noise

In this work, we systematically studied the effects of gain saturation or nonlinear Gain (NLG) and optical feedback (OFB) on the dynamics, intensity noise, and probability density distributions (PDDs) of semiconductor lasers (SLs). By examining the temporal trajectory of photon numbers and bifurcation diagrams, we shed light on laser behavior under varying conditions. Our simulations reveal that including NLG and OFB in the rate equations leads to substantial changes in operational states and noise characteristics. Notably, when lasers operate in continuous wave (CW) or periodic oscillation (PO) modes, relative intensity noise (RIN) is suppressed when NLG is considered. As OFB strength increases, PDDs transition from symmetric to asymmetric forms. In chaotic regions, these PDDs exhibit a peak at low intensity, decreasing at multiples of the average photon number. Additionally, under strong OFB, incorporating NLG can shift laser dynamics from chaotic behavior to POs or CW operation. The presence of NLG further enhances stability and accentuates this behavior by displaying a peak near the average photon number, which is notably diminished without NLG. By incorporating NLG, we find a reduction in the standard deviation of fluctuations. Overall, our findings highlight the importance of NLG and OFB for reducing instability in SLs, paving the way for the development of higher-performance laser systems.