Monolithically Integrated Gain-Flattened Ring Mode-Locked Laser for Comb-Line Generation

We demonstrate broadband comb-line generation from an integrated multiple quantum well InGaAsP/InP passively mode-locked laser (MLL) with a gain flattening filter (GFF) based on an asymmetric Mach-Zehnder interferometer. The intracavity filter flattens the nonuniform gain profile of the semiconductor material providing a more uniform net cavity gain. The GFF MLL has a -10 dB comb span of 15 nm (1.88 THz), the widest spectral width yet demonstrated for an integrated QW MLL at 1.55 μm . The measured optical linewidth at the center of the comb is 29 MHz, the -20 dB RF linewidth 500 KHz, while the output spectrum is phase-locked to produce 900 fs pulses at a repetition rate of 30 GHz with 4.6 ps integrated jitter from 100 Hz to 30 MHz.