Influence of the gain bandwidth on the intensity noise properties of a multi-longitudinal-mode semiconductor laser subject to optical feedback

Using a partial differential equations (PDE) model, we have numerically investigated the intensity noise properties of a multi-longitudinal-mode semiconductor laser subject to optical feedback. We have studied the relative intensity noise spectrum (RIN(v)) for a broad range of feedback strengths, and have analysed its dependence on the value of the gain bandwidth by computing the frequency averaged RIN in two different ranges: below 90 GHz, which we name low-frequency averaged RIN, and also considering all the frequencies of the intensity fluctuations (total averaged RIN), which include the beating of the longitudinal modes well in the THz range. We observe how the low-frequency averaged RIN provides information on the dynamics of the emission in the chaotic region and depends on the value of the gain bandwidth. We also show that the total averaged RIN at low feedback levels may be useful to study the amount of longitudinal modes involved in the emission.