Passively mode-locked InAs quantum dot lasers on a silicon substrate by Pd-GaAs wafer bonding

We demonstrate an electrically pumped InAs quantum dot (QD) two-section passively mode-locked laser (MLL) on a silicon substrate by low temperature (250 °C) Pd-GaAs wafer bonding technology. The saturable absorber of the QD-MLL is electrically isolated by a 15-μm wide dry-etching gap which resulted in ∼30 kΩ resistance from the gain regions of the MLL. At room temperature, the laser operates in the O-band (1.3 μm) telecommunication wavelength regime with a threshold current of 94 mA and laser bar cavity and absorber lengths of 6 mm and 300 μm, respectively. The optimum mode-locked conditions are observed under injection current and reverse bias voltage of 124 mA and −7 V, which generates pulses at a repetition rate of 7.3 GHz, an optical bandwidth of 0.97 nm, and a nearly transform limited pulse width of 2 ps (sech2 pulse profile). These results enable QD-MLLs to be integrated with silicon photonic integrated circuits, such as optical time division multiplexing and optical clocks.