Simulation of the frequency behavior of external-cavity semiconductor lasers

A theoretical model of semiconductor lasers mounted in external cavities is developed. The modes' frequencies and gains are calculated. We study the frequency of the oscillating mode versus the laser injection current. We explain its hysteresis behavior by introducing in the model the coupling between the semiconductor gain and its index of refraction induced by fluctuations in carrier density. We also determine the influence of the laser diode output facet reflection coefficient on mode hops and frequency tuning. Theoretical simulations coincide well with experimental observations.