  We study the excitations of dark solitons in a nonlinear optical fiber with
the second- and fourth-order dispersion, and find the emergence of striped dark
solitons (SDSs) and some multi-dark-soliton bound states. The SDSs can exhibit
time-domain oscillating structures on a plane wave, and they have two types:
the ones with or without the total phase step, while the multi-dark-soliton
bound states exhibit different numbers of amplitude humps. By the modified
linear stability analysis, we regard the SDSs as the results of the competition
between periodicity and localization, and analytically give their existence
condition, oscillation frequency, and propagation stability, which show good
agreements with numerical results. We also provide a possible interpretation of
the formation of the existing striped bright solitons (SBSs), and find that SBS
will become the pure-quartic soliton when its periodicity and localization keep
balance. Our results provide the theoretical support for the experimental
observation of striped solitons in nonlinear fibers, and our method can also
guide the discovery of striped solitons in other physical systems.
