Passively Mode-Locked Quantum-Well Laser With a Saturable Absorber Having Gradually Varied Bandgap

We report a novel passively mode-locked quantum-well laser, which have an asymmetric colliding pulse mode-locked structure. The saturable absorber (SA) multi-quantum wells (MQWs) of the laser have bandgap, which is gradually varied along the ridge direction realized by selective area growth technique, forming a broadband absorber. As a result, light pulses are obtained at a repetition frequency of 226 GHz with a minimum pulse width of 605 fs under an appropriate current bias. Because of the continuous variation of the SA MQW bandgap, the SA absorption peak covers a wide range of wavelength, which makes the device more immune to SA bandgap change resulted from SA reverse bias or light absorption-induced heating of the SA, compared with traditional MQW mode-locked lasers.