  We report numerical and experimental studies of dissipative-soliton-resonance
(DSR) in a fiber laser with a nonlinear optical loop mirror. The DSR pulse
presents temporally a flat-top profile and a clamped peak power. Its spectrum
has a rectangle profile with characteristic steep edges. It shows a unique
behavior as pulse energy increases: The rectangle part of the spectrum is
unchanged while the newly emerging spectrum sits on the center part and forms a
peak. Experimental observations match well with the numerical results.
Moreover, compression of the DSR pulses is both numerically and experimentally
demonstrated for the first time. An experimentally obtained DSR pulse of 63 ps
duration is compressed down to 760 fs, with low-intensity pedestals using a
grating pair. Before being compressed to its narrowest width, the pulse firstly
evolves into a cat-ear profile, and the corresponding autocorrelation trace
shows a crown shape, which distinguishes itself from properties of other
solitons formed in fiber lasers.
