Mode-locked laser diodes and their monolithic integration

We describe mode locked laser diodes (MLLDs) operating from 40 GHz to >1 THz. Below 40 GHz, operation at the fundamental cavity frequency is appropriate, but at higher frequencies harmonic mode-locking (HML) is used. To increase output power and control nonlinear behavior, the gain needs to be modified, and an AlGaInAs/InP structure with a three-quantum-well active layer and passive far-field reduction layer is presented. In 40-GHz all-active MLLDs, this structure offers improvements in internal loss, slope efficiency, mode locking (ML) range, RF linewidth, timing jitter, far field pattern, and coupling efficiency to a single-mode fiber. By creating a transparent passive waveguide in part of the cavity, a 490-fs pulse width was achieved, the shortest reported from any quantum well MLLD. Several approaches are described for HML: colliding pulse ML operating up to 240 GHz, coupled cavity ML up to 160 GHz, and sampled Bragg grating constructions up to 1.28 THz. This latter approach offers stable HML over a wide range of bias conditions. Finally, we report a synchronized multicolor ML laser array, containing four 40-GHz lasers with designated wavelength registration for optical code division multiple access or optical time division multiple access applications