Contents 1. Introduction
Single-contact Fabry-Perot (FP) semiconductor laser diodes (LDs) do not usually self-mode-lock. The multi-longitudinal-mode (MLM) operation is often the type of mode competition, exhibiting the well-known mode-partition noise behavior rather than mode locking (ML). Recently, however, some single-contact FP LDs are experimentally demonstrated to be self-FM ML as well as self-AM ML [1]–[4]. MLM coupled-mode theories [5]–[6] are explored to explain the possible self-FM and self-AM ML operations, but conditions under which these highly coherent ML operations are preferred to other chaotic mode-competition operations are not all clear. In this report, we provide a time-domain analysis of single-contact FP LDs, which is capable to treat multi-spatial-mode (MSM) cavities. The model clearly differentiates different MLM regimes and attributes the ML action of single-contact FP LDs to the active MSM coupling. The critical self-AM ML action, namely, the saturable absorption (SA), is also prescribed in terms of the spatial hole burning, the linewidth enhancement factor (LEF), and the fast gain saturation.
