Generation of picosecond optical pulses with highly RF modulated AlGaAs DH laser

Abstract

AlGaAs DH lasers with strong RF modulation superimposed on the relatively low dc bias below the oscillation threshold were demonstrated to be feasible for generation of a train of approximately 30 ps optical pulses at a repetitive frequency of sub-GHz range. The pulse envelope width was measured by three different methods: a fast response photodetector, the second-harmonic generation (SHG) correlation method, and an ultrafast streak camera. The results of the SHG correlation and the streak camera agreed fairly well. In order to explain the generation mechanism and the characteristics of these ultrashort optical pulses in a highly RF modulated semiconductor diode laser, the rate equation analysis was performed and the results were generally in good agreement with the experiment. Furthermore, from the computer simulation for the analysis of the SHG correlation traces, it was inferred that an individual ultrashort optical pulse has internal substructures made of fluctuating fields whose spike widths were of the order of subpicoseconds, due to the randomness of the phases among lasing modes.