Generation of frequency comb and its dependence on gain suppression in directly modulated semiconductor laser

摘要

This paper presents a theoretical study on the generation of optical frequency combs (OFCs) using direct modulation of semiconductor laser. Influence of gain suppression on characteristics of the generated OFCs is investigated. The study includes intensive and comprehensive investigations of the temporal and spectral characteristics of the generated OFCs as a function of the gain suppression over a wide range of the bias current. We report on generation of short optical pulses and large numbers of comb lines with low-power flatness under weak gain suppression and/or strong modulation depth when the laser is biased near the threshold. The influence of gain suppression becomes more robust when the laser is biased far above threshold. By adopting the operating parameters, we predict pulses with 60 ps width and 10 comb lines with 2.1 dB flatness when the gain suppression is ignored. Under strong gain suppression, broader pulses (132 ps width) and only five lines with higher flatness of 4.99 dB could be obtained.