Measurement of linewidth enhancement factor of semiconductor lasers by modified direct frequency-modulation method

摘要

The frequency modulation characteristics of 1.3 mu m DFB lasers below the relaxation resonance reveal two different types of response: the in-phase response between the frequency modulation (FM) and the amplitude modulation (AM), and the out-of-phase response between them. In both cases, the ratio of the FM index to the AM index is strongly dependent on the modulation frequency; however, when the modulation frequency is increased beyond the relaxation resonance, this value approaches the linewidth enhancement factor. On the basis of this result, the linewidth enhancement factors of 1.3 mu m DFB lasers with different amounts of wave-length detuning are determined.