Monolithic Mode-Locked Laser With an Integrated Optical Amplifier for Low-Noise and High-Power Operation

High-power 40 GHz 1.55 μm passively mode-locked surface-etched distributed Bragg reflector lasers monolithically integrated with semiconductor optical amplifiers (SOAs) are reported. These are based on an optimized AlGaInAs/InP epitaxial structure with a three quantum-well active layer and a far-field reduction layer. The device produces near transform-limited sech² pulses with the shortest measured pulse duration at 3.19 ps, and the narrowest measured radio frequency linewidth at 110 kHz. The highest average output power at ~155 mW with a peak power of >0.6 W was attained from the SOA-end facet while mode-locked. The beam divergences from the SOA side were narrow and symmetric (26.7° × 26.8°), which is highly desirable for butt coupling to a single-mode fiber.