Abstract

In order to get short pulses from semiconductor lasers, an extremely short and intense pumping signal has to be applied to the device. Optical switches have proved to be efficient sources for providing electrical pulses with risetime as short as the incident optical beam and thus equal to 1 ps or less. The exponential decay time depends on the recovery time of the switch and ranges from the ns to ps time scale. We have theoretically investigated the optical response of a semiconductor laser to such electrical short pulses (<25 ps). For this an extension of the common rate equations have been used where forward and backward travelling beams are separately calculated. The approximation of distributed loss valid on a time scale larger than the roundtrip time T_r is not needed, and multireflection effects can be studied. Fig.l-a gives the result of gain switching in a semiconductor laser with a pulse of 25 ps full width at half maximum (FWHM) with a total increase of carriers equal to 5xl0¹⁸cm^-3 and a rise time of 1 ps. A first pulse arises with a FWHM (6 ps) slightly smaller than T_r (7 ps). The reflections of the pulse on the facets create a tail that depends on how fast the gain is saturated. Therefore, both a short electrical pump and a large differential gain are required.

© 1990 Optical Society of America