Characteristics of semiconductor lasers operating near threshold with external light injection

Abstract

Static and dynamic properties of semiconductor lasers biased from below to above threshold are presented on the basis of a unified treatment of semiconductor lasers with external light injection. The performances of such a laser are depending on both the gain change due to external light injection and the gain difference between actual free-running laser gain and threshold gain. The stable locking range is asymmetric even for a DFB laser since one of the most distinguishing features for a laser biased near threshold is that the optical injection level is high, compared with that for a laser biased far above threshold. If the optical injection level is higher than a critical value: the locking is unconditionally stable because the relaxation resonance of a free-running laser is severely damped by external light injection. Therefore, the stable locking range can be divided into three parts according to the optical injection level. The modulation bandwidth of such a laser has a minimum value with respect 10 the bias current.