Passively modelocked lasers with semiconductor saturable absorption mirrors (SESAMs) are attractive comb sources since they can be made environmentally stable, but they become unstable when the group velocity dispersion is too low or the gain is too high due to modes that grow in the wake of the modelocked pulse. Here, we investigate the wake mode dynamics in detail using a combination of evolutionary and dynamical methods. We find the stationary pulse when it is stable and we describe the evolution of the wake mode instability when the pulse is unstable. We then calculate the dynamical spectrum of the modelocked pulse, and we show that it has six discrete eigenmodes, two of which correspond to wake modes. The wake modes are unstable when the wake mode eigenvalues have a positive real part. We also show that even when stable the wake modes lead to experimentally-observed sidebands.
Citation: Optics Letters
Pub Type: Journals