Highly-Stable Integrated InGaAsP/InP Mode-Locked Laser and Optical Phase-Locked Loop

We demonstrate an integrated InGaAsP/InP mode-locked laser that is stabilized with an optical phase-locked loop (OPLL). Using the OPLL, a single comb line is locked to a reference oscillator (a 200 Hz linewidth Brillouin laser). The comb linewidth is reduced from 100 MHz (unlocked) to <; 550 Hz (locked) using the OPLL. The rms phase error between the comb and reference laser is 20°. The linewidth of the adjacent comb lines is <; 1 kHz, and the comb spans 430 GHz.