Dynamics of gain-switching operation in gain-coupled distributed-feedback semiconductor lasers with absorptive grating

Very-low-chirping optical short-pulse generation in gain-coupled (GC) distributed-feedback (DFB) semiconductor lasers of absorptive-grating type is investigated. First, we have observed time-resolved spectra of gain-switched optical pulses. The GC DFB laser has shown a very small and characteristic lasing wavelength shift with time. Moreover, we have noticed uncommon bias-dependence of the pulse width and pulse tailing at high bias regime. Then, we have examined spontaneous emission from the grating to probe carrier generation by the optical pulse. Next, we have conducted a rate equation analysis to understand the uncommon pulse dynamics of the GC DFB laser by taking the carrier generation in the grating into account, consequently, all the anomalies observed in the GC DFB laser have successfully been explained. Finally, by making use of the analysis, we have shown a guideline to further improve the pulse shape without sacrificing the low chirping property