Influence of an external feedback on the tuning of the emission frequency of a semiconductor laser

A study was made of the tuning of the emission frequency of a semiconductor laser matched to an external resonator by a microlens made of a chalcogenide glass. It was found that heating of the active region during a current pulse resulted in frequency hopping between the modes of the intrinsic (internal) laser resonator and the direction of such hopping was governed by the relative positions of the internal and external resonator modes. This direction depended periodically on the length of the external resonator and the period was a multiple of the optical length of the active part of the laser.