Picosecond pulses from mode-locked quantum well semiconductor lasers

Semiconductor diode lasers can provide compact sources of ultrashort light pulses [1-2]. Our research efforts are aimed at the development of a widely tunable, diode laser source for the generation of picosecond, and ultimately sub-picosecond, pulses. The InGaAsP/InGaAs active region of the diode is composed of two quantum wells [3-4] grown lattice matched to GaAs. Work is done using both symmetric and asymmetric structures. All laser structures are grown using the McMaster molecular beam epitaxy facility. Mode-locking is achieved with the diodes in an external cavity configuration. The two different quantum wells allow a 64 nm tuning range centered at 985 nm. Typical pulse durations measured directly from the diode are found to be between 3 and 15 ps. The mode-locked output from the external cavity laser is then coupled into a semiconductor optical amplifier to increase the pulse power. The active regions of the amplifiers are based on the same InGaAsP/InGaAs material as for the oscillators. Our initial amplification work focuses on narrow stripe geometries. This provides large bandwidth, single pass traveling wave amplification. The effect of amplification on pulse shape is measured using a cross-correlation technique. In this technique, the ps pulses are frequency mixed through a nonlinear crystal with 80 fs, 795 nm pulses from a mode-locked Ti: Sapphire laser.