Generation of short optical pulses in semiconductor lasers by combined dc and microwave current injection

Picosecond pulse generation in low threshold buried optical guide lasers is obtained by using combined direct and microwave current excitation. The pulse widths are obtained from the second harmonic autocorrelation and are a function of direct current for several levels of RF exitation using lasers 125 and 380 microns long. The pulses have a Gaussian shape, whose width has a complex functional dependence on the applied currents. Results show that increasing dc and microwave current, and decreasing laser length, decreases the pulse width. A 125 micron long laser using 0.25 W RF at 1 GHz and 35 mA dc bias provides the shortest pulses. Using this laser at the indicated current levels the emission consists of a burst of approximately 10 pulses separated by 30 ps, and has an approximately exponentially decaying amplitude. Degradation introduces saturable absorption in the lasers and results in shortening the pulses. In addition, reduced pulse widths are obtained for short current pulse excitation.