Fig. 1. (a) 1.7 μm epitaxy structure with high-strained InGaAs/InGaAsP multi-quantum wells; (b)The scanning electron microscope (SEM) picture of the cross-section of the device, the inset shows fundamental transverse mode of the ridge waveguide; (c) Top view of colliding-pulse mode-locked laser

Fig. 2. Schematic diagram of measuring RF spectrum

Fig. 3. (a) A typical cavity length dependence of the inverse external differential quantum efficiency; (b) P-I curves of mode-locked laser at different reverse bias voltage V_SA

Fig. 4. (a) The RF spectrum measured at a driving current of 520 mA and a reverse bias voltage of −1.6 V. The inset shows the RF peak at the fundamental repetition frequency; (b) The pulse train measured at a driving current of 520 mA and a reverse bias voltage of −1.6 V

Fig. 5. RF spectrum maps in dBm scale as a function of driving current at different reverse bias voltages. (a) RF spectrum map at reverse bias voltage of −1.4 V; (b) RF spectrum map at reverse bias voltage of −1.6 V; (c) RF spectral map at reverse bias voltage of −1.8 V; (d) RF spectrum map at reverse bias voltage of −2 V

Fig. 6. (a) Emission spectra of the laser measured at a reverse bias voltage of −1.6 V for different driving currents; (b) Emission spectra of the laser measured at a driving current of 520 mA for different reverse bias voltages