Few-cycle solitons that do not want to be too short in duration

We review recent achievements in theory of ultrashort optical pulses propagating in nonlinear fibers. In particular we are interested in the shortest duration (the highest peak power) of an optical soliton. Optical solitons are found to cannot go beyond the critical single-cycle duration even for the most favorable medium dispersion. A formation of singular cusps prohibits the existence of too short solitons, which seems to be unavoidable universal feature of bright solitons.