Investigations of Repetition Rate Stability of a Mode-Locked Quantum Dot Semiconductor Laser in an Auxiliary Optical Fiber Cavity

We have investigated experimentally the pulse train (mode beating) stability of a monolithic mode-locked multi-section quantum-dot laser with an added passive auxiliary optical fiber cavity. Addition of the weakly coupled (${\approx}-24$ dB) cavity reduces the current-induced shift $d\nu/dI$ of the principal peak in the RF spectrum (the effective pulse repetition frequency) by more than an order of magnitude, from ${-}39.5$ to ${-}2.3$ kHz/mA. The rms timing jitter of the pulse train is simultaneously reduced from 1.4 to 0.9 ps.