  A new type of transverse instability in dispersively nonlinear optical
cavities, called the optical whistle, is discussed. This instability occurs in
the mean-field, soliton forming limit when the cavity is driven with a
finite-width Gaussian beam, and gives rise to oscillation, period doubling, and
chaos. It is also seen that bistability is strongly affected due to the
oscillation within the upper transmission branch. The phenomenon is interpreted
as a mode-mismatch in the soliton formation process and is believed to have
broad applicability.
