Abstract

The production of ultrashort optical pulses from GaAs vertical-cavity surface-emitting lasers (VCSELs) has been demonstrated by electrical and optical gain switching. The monolithically grown devices have four quantum wells in the active region, and have dimensions and mirror reflectivities (distributed Bragg reflector stacks) optimized for cw operation under current injection. Pulses as short as 24 ps were produced by electrical gain switching and optical gain switching. The pulse durations were determined by the photon lifetime of the VCSEL, whose value is constrained by the requirements for cw operation under current injection. Thus, there are design tradeoffs for VCSELs between short pulse production versus efficient cw electrical operation. Measurements of the optical spectra show the time-bandwidth product can be as small as 0.6, suggesting very small chirp for a gain-switched laser. This is a consequence of the small thickness of the active region of the VCSEL. Also, for lasers operating at different wavelengths, there is an increase in pulse duration as the wavelength increases, which results from band-filling effects.

© 1992 Optical Society of America