Picosecond dynamics of semiconductor Fabry-Perrot lasers: A simplified model.

A simplified semiconductor laser model that is sufficient to describe laser dynamics on a picosecond time scale is presented. The model prescribes a time-domain differential equation regarding thecomplex amplitude of the light field. The simplification comes from an approximation of the semiconductor optical gain dynamics that typically exhibits two distinct time scales with a slow component on the order of hundreds of picoseconds and a fast component on the order of a few picoseconds or subpicoseconds. For laser dynamics concerning mainly the picosecond time scale, the slow component of the material gain dynamics can be treated as a static effect and the fast component can be treated as instantaneous. Such treatment also shines light on relations between semiconductor optical amplifier nonlinearities such as self-phase modulation and device parameters such as the linewidth enhancement factor and confinement factors. The model correctly predicts various picosecond laser dynamics of semiconductor lasers including the preference of a constant-power, FM mode-locking operation once the correct chirp condition is first established. A coupled multispatial mode (MSM) model based on the simplified time-domain laser model is used to successfully explain self-start AM mode-locking operations of single-contact Fabry-Perot laser diodes (FP-LDs) that have been observed experimentally. A mechanism for establishing the needed condition for single-contact FP-LD's self-FM mode-locking operations is also proposed based on the understanding of the MSM AM mode-locking operations.