Observation of modulation instability in a fibre soliton laser

Modulation instability is the well-known tendency in anomalous dispersion fibres for small variations in an almost constant power level to grow exponentially. For an erbium doped fibre soliton laser, although it operates in the anomalous dispersion regime of the fibre used and a strong internal gain exits in it, because a soliton pulse is inherently stable against modulation instability, normally no modulation instability can be observed. In this paper we report on an experimental observation of modulation instability in a passively mode-locked fibre soliton ring laser. We show that due to modulation instability, dispersive waves of the laser can become unstable and consequently result in the generation of new spectral components in the soliton spectrum.