Oscillating dark cavity solitons

We show that oscillating dark solitons exist on a stable continuous plane-w ave background in a cavity with a saturable defocusing nonlinearity. These oscillations can be attributed to a linear internal mode of the soliton wit h a complex eigenvalue emerging above a definite input field intensity. Usi ng a simple analytical model, we find that the self-oscillations appear as a consequence of an interaction between the center of the soliton and the s urrounding ring. (C) 1998 Optical Society of America.