  We experimentally observe soliton self-organization and pulsation in a
passively mode-locked fiber laser. The optomechanical interaction in the
optical fiber is key to the formation of equidistant soliton bunches. These
solitons simultaneously undergo a pulsation process with a period corresponding
to tens of the cavity round trip time. Using the dispersive Fourier
transformation technique, we find that the Kelly sidebands in the shot-to-shot
spectra appear periodically, synchronizing with the pulsation.
