The static and dynamic properties of injection-locked semiconductor lasers considering the influence of nonlinear gain are presented systematically. Depending on locking conditions, the modulation bandwidth of a semiconductor laser may be increased or decreased by external light injection. However, the relaxation resonance frequency and the damping rate as defined for a solitary Fabry-Perot (FP) laser are always enhanced by injection locking. That is, contrary to that in a solitary FP laser, the modulation bandwidth in an injection-locked laser is not determined solely by the relaxation resonance frequency, because an injection-locked laser is a third-order system. Therefore, a new definition of the modulation bandwidth is presented for such a laser. The performances of injection-locked distributed feedback (DFB) lasers are also discussed. The theory is in good agreement with the experiments.
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