Abstract

Modulation instability (Ml) refers to a process in which a weak time modulation (from the noise) grows exponentially as a result of an interplay between nonlinearity and group velocity dispersion. This amplitude modulation corresponds to the generation of picosecond and femtosecond subpulses in the time domain and frequency sidelobes in the spectral domain. We report the first observation of Ml in the normal-dispersion regime. This new kind of Ml, induced by cross-phase modulation, was recently predicted.¹ In this work, Ml is observed at 532 nm by propagating intense picosecond or nanosecond pulses in short lengths of a single-mode optical fiber. It has been found that sidelobes appear about the pump frequency as a result of the cross-phase modulation induced by the simultaneously generated stimulated Raman scattering pulses. Sidelobe shifts ranged from 1.5 to 8.5 nm, which corresponded to the generation of 670–120-fs time-duration subpulses. The Ml results are in good agreement with theory.

© 1988 Optical Society of America