Bandwidth-enhanced LFM signal generation by period-one dynamics in a directly modulated semiconductor laser

Period-one (P1) laser dynamics provide effective methods for radar signal generation. However, the linearly frequency-modulated (LFM) signal bandwidth generated by P1 dynamics is constrained by the limited variation range of the injection strength. In this Letter, a bandwidth-enhanced LFM signal generation method by P1 dynamics in an optically injected directly modulated semiconductor laser (DM-SL) is proposed. In addition to controlling the injection strength via electro-optical modulation, which is the same as the previous schemes, the bias current of the DM-SL is regulated via direct modulation. By interaction between the carrier effect and temperature effect in the optically injected DM-SL, the P1 oscillation frequency is increased under the same optical injection strength, leading to the generation of LFM signals with enlarged bandwidth. In the experiment, the maximum signal bandwidth reaches 21 GHz (11.7-32.7 GHz), which is enhanced by 11 GHz compared with that generated without bias current regulation. The proposed method is a promising technique for ultra-wideband radar signal generators.