Isolated picosecond pulses obtained by spectral selection from gain-switched semiconductor lasers

摘要

The possibility of obtaining time-isolated picosecond high power optical pulses by the spectral selection of a Gain-switched semiconductor laser was proved experimentally and by simulation. In the experiments, optical pulses with a peak power ofabout 15-20 W and FWHM about 25 PS were obtained from an AlGaAs double heterostructure laser with a nominal power of 45 W. The pumping current had a rise-time around 200 PS and an amplitude of 20 A. The current amplitude exceeded the threshold valueapproximately 20-fold. It was shown that the lasing spectrum is considerably wider than that of steady state generation under these conditions. Both high and low-energy tails appear in the spectrum, and spectral time-resolved measurements indicate thatthese correspond to very short optical pulses. The high-energy short-pulsed part of the laser emission was isolated using spectral selective filters. A simple model considering time-dependent spectral gain was developed which describes adequately both the spectral and transient features of the observed phenomena. It follows from the simulation that intensive time-isolated picosecond optical pulses can be obtained with any semiconductor laser in Gain-switched mode, provided that the rise time of the current pulse is fairly short and an appropriate optical filter is chosen.