Picosecond pulse analysis of gain-switched 1.55 µm InGaAsP laser

Results of computer simulation of gain-switched pulses from InGaAsP lasers emitting at 1.55 μm are reported. Multimode rate equations are solved for short triangular current pulses of large amplitude superimposed on a dc bias close to threshold. Lasers of conventional length (200μm) and with short cavity (50 μm) are analyzed. The effect of wavelength chirp on time-resolved and the time-averaged multimode spectra is demonstrated. Optical pulses as short as 10 ps are predicted for short-cavity lasers with reflective coatings. While the number of longitudinal modes in gain-switched spectrum is efficiently reduced for short-cavity lasers, the dynamic linewidth of each mode remains of a similar magnitude (up to 140 GHz) as for standard-cavity lasers. It is expected that gain saturation effects could reduce the calculated values of dynamic linewidth.