Control and Generation of Localized Pulses in Passively Mode-Locked Semiconductor Lasers

We show experimentally and theoretically that localized pulses can be generated from an electrically biased 200 μm multitransverse-mode vertical-cavity surface-emitting laser. The device is passively mode-locked using optical feedback from a distant resonant saturable absorber mirror and is operated below its threshold. We observe multistability between the nonlasing (off) solution and a large variety of pulsating solutions which have a different number and arrangement of pulses per round trip, thus indicating that the mode-locked pulses are localized, i.e., mutually independent. We show that modulation of the bias current allows control of the number and the location of the pulses traveling within the cavity, thus suggesting that our system can be operated as an arbitrary pattern generator of mode-locked pulses.