Underlying dynamics of the pedestal components in a modulated laser diode with noise

We demonstrate that the pedestal components observed in the power spectra o f a directly modulated laser diode, which were interpreted as a sign of ins tability of the periodic regime, are an indication of the coexistence of a chaotic regime with the periodic one. We present the underlying dynamics be hind the rise of these pedestals, showing two different situations in which the pedestals appear. In both, a periodic regime coexists with another att ractor, a saddle cycle in one case and a chaotic attractor in the other. Th e random fluctuations included in the laser diode model allow the coexistin g attractors to merge in the observed behavior of the laser. (C) 1999 Optic al Society of America.