Abstract

For both their fundamental and applied interests, optical dark solitons have attracted growing attention in recent years. In view of their potential application to fiber-based communication systems, several techniques were proposed for the generation of continuous-wave (cw) odd-symmetry dark soliton pulse trains. Two of these techniques are based on the direct modulation of a cw laser beam by a Mach-Zehnder interferometer [1] or a phase-modulated fiber loop mirror [2]. These methods suffer the limitation of the typical electronic bandwidths and are therefore adapted to repetition-rates in the GHz range. Other approaches involve the adiabatic transformation of a dual-frequency signal in a dispersion decreasing fiber with normal dispersion [3], and the passive Fourier filtering of standard mode-locked bright pulse trains [4]. Thanks to the absence of electrooptic components, the last two techniques are suitable for ultra-high repetition rates. However, because of important technical obstacles, they were demonstrated only with multi-Gigahertz repetition rates. In this work we analyze and demonstrate a new passive technique for cw dark soliton train generation, which is based on the phenomenon of modulational instability (MI) and therefore naturally leads to THz repetition rates.

© 1998 Optical Society of America