  We report on the experimental observation of stable dark solitons in an all
normal dispersion fiber laser. We found experimentally that dark soliton
formation is a generic feature of the fiber laser under strong continuous wave
(CW) emission. However, only under appropriate pump strength and negative
cavity feedback, stable single or multiple dark soliton could be achieved.
Furthermore, we show that the features of the observed dark solitons could be
well understood based on the nonlinear Schrodinger equation (NLSE).
