摘要： Passively mode-locked (PML) InAs/InGaAs quantum dot (QD) lasers directly grown on silicon and emitting at 1310 nm are promising sources for high-speed, high-capacity communication applications. To overcome the low light generation efficiency of silicon, QD are directly grown on Si [1]. Their ultrafast carrier dynamics, broadband gain spectra and easily saturated gain and absorption allow for the generation of ultra-short optical pulses as demonstrated very recently [2]. The QD laser epitaxial growth was completed on an on-axis (001) Si substrate with a 45 nm GaP buffer layer by solid-source molecular beam epitaxy [3]. In this contribution, the pulse train stability of a PML QD laser consisting of a five-stack InAs/InGaAs dots-in-a-well structure is experimentally studied. The total length of the laser was designed to be 4.5 mm with a saturable absorber length corresponding to 18 %. The isolation length between gain and absorber section is 10 μm. The laser emits optical pulse trains at a repetition rate (RR) of 9.4 GHz. Fig. 1a depicts the pulse-to-pulse timing jitter (TJ) σpt p = 0.5 [4] with Δν being the RR line width in the radio-frequency (RF) spectrum and ν0 being the RR. The TJ is calculated from the timing phase noise (TPN) power spectral densities (PSD) [5] in dependence on the absorber reverse bias voltage and the gain current. Low TJ values of around 100 fs to 200 fs can be identified in the majority of biasing regimes. In the regime for shortest pulses with pulse widths below 5 ps, located just above lasing threshold and at gain currents below 120 mA, very low TJ values (color coded purple) are obtained. A lowest TJ of 9 fs (-3 dB fundamental RR beat note line width of 400 Hz) is obtained at a gain current of 105 mA and an absorber reverse bias voltage of 0.6 V, slightly above lasing threshold. The corresponding TPN PSD is depicted in Fig. 1b. The optical pulse train amplitude jitter (AJ) is quantified as a relative standard deviation of the pulse intensity variations [6]. As indicated in Fig. 1c, an AJ below 5 % is attained in the short pulse regime which is located at gain currents below 120 mA and at higher currents and low saturable absorber voltages (color coded purple). Such low AJ denotes excellent stable operation. Fig. 1d depicts the nonlinear intensity auto-correlation signal representing the shortest deconvoluted pulse width of 1.7 ps at 125 mA and 2.6 V absorber reverse bias voltage. The corresponding time-bandwidth product amounts to 1.1. Pulses with pulse widths shorter than 10 ps where obtained at all biasing conditions except for high gain currents above 140 mA and small absorber reverse bias voltages below 0.6 V. In this small regime pulse widths of 10 ps to 18 ps are obtained. In conclusion, stable optical pulse train generation by a monolithic passively mode-locked InAs/InGaAs quantum dot laser directly grown on silicon with a lowest optical pulse width of 1.7 ps, a lowest timing jitter of 9 fs (400 Hz RR beat note line width) and a negligible relative amplitude jitter are experimentally reported.