1.8-THz-wide optical frequency comb emitted from monolithic passively mode-locked semiconductor quantum-well laser.

We report on an optical frequency comb with 14 nm (∼1.8  THz) spectral bandwidth at a -3  dB level that is generated using a passively mode-locked quantum-well laser in photonic integrated circuits fabricated through an InP generic photonic integration technology platform. This 21.5-GHz colliding-pulse mode-locked laser cavity is defined by on-chip reflectors incorporating intracavity phase modulators followed by an extracavity semiconductor optical amplifier as a booster amplifier. A 1.8-THz-wide optical comb spectrum is presented with an ultrafast pulse that is 0.35 ps wide. The radio frequency beat note has a 3-dB linewidth of 450 kHz and 35-dB SNR.