Dynamics, Statistical Analysis, and Spectral Line-Shape of Semiconductor Lasers Subject to Optical Feedback

We explore how optical feedback (OFB) strength affects the dynamics, noise (such as relative intensity noise (RIN) and frequency noise (FN)), probability density distribution (PDD), and spectral line-shape characteristics of semiconductor lasers (SLs). We examined photon number (PN) fluctuations, frequency shift (FS) fluctuations, and the corresponding RIN and FN spectra, along with PN-PDD and FS-PDD, across six operating states. Our findings clearly demonstrate that OFB strength transforms operational states, noise characteristics, and PDD shape and width. In CW modes, both RIN and FN decrease near the solitary noise level, especially in the strong OFB CW state, which has lower noise than the weak OFB state. By increasing OFB, the PDD shape shifts from a symmetric Gaussian to an asymmetric non-Gaussian distribution, with the chaotic condition showing a peak at low intensity. Strong OFB yields sharply defined central and satellite peaks with narrowed linewidths of approximately 571 Hz and 48 Hz, while moderate OFB results in coherence collapse and broadened peaks.