Theory of delayed optical feedback in lasers

A tutorial introduction to the dynamical behavior of lasers is presented. Simple physical pictures explain the essential ingredients that determine the dynamical properties. The relevant dynamical equations are derived for a laser with delayed external optical feedback, possibly spectrally filtered before re-entry into the laser. Focusing on semiconductor lasers the steady-state solutions are derived and discussed as to their stability, whereafter the various different types of dynamics predicted by the model are presented, highlighting Low-Frequency Fluctuations.