We introduce the simplest one-dimensional model of a dispersive optical med
ium with saturable dissipative nonlinearity and filtering (dispersive loss)
which gives rise to stable solitary pulses (autosolitons). In the particul
ar case when the dispersive loss is absent, the same model may also be inte
rpreted as describing a stationary field in a planar optical waveguide with
uniformly distributed saturable gain and absorption. In a certain region o
f the model's parameter space, two coexisting solitary-pulse solutions are
found numerically, one of which may be stable. Solving the corresponding li
nearized eigenvalue problem, we identify stability borders for the solitary
pulses in their parametric plane. Beyond one of the borders, the symmetric
pulse is destroyed by asymmetric perturbations, and at the other border it
undergoes a Hopf bifurcation, which may turn it into a breather. (C) 2000
Elsevier Science B.V. All rights reserved.