Electrically Gain-Switched Vertical-Cavity Surface-Emitting Lasers

We report electrical gain-switching of a packaged vertical-cavity surface-emitting laser (VCSEL). Pulse durations as short as 24 ps at repetition rates up to 2 GHz were obtained from a four quantum well GaAs/AlGaAs VCSEL, which emits 0.8 mW continuous wave power in a single mode at room temperature and has a current threshold of 6 mA. Simultaneous measurement of the optical spectrum showed an almost transform limited line-width indicating ultralow chirp. Optical pumping with subpicosecond pulses of the same packaged devices, held at a constant electrical bias, yielded 22 ps pulses, in good agreement with the electrical pumping. Simple calculations show that the pulse duration obtained by gain-switching is limited by the design constraints necessary to operate the VCSEL continuous wave at room temperature with low-threshold current, high-quantum efficiency, and reasonable output power.