Spatio-temporal observation of higher-order modulation instability in a recirculating fiber loop

Modulation instability (MI) in fiber optics is a nonlinear process in which a monochromatic signal wave propagating along with a continuous pump wave initially experiences exponential growth, provided that its frequency detuning relative to the pump falls within the MI gain bandwidth [1] . This eventually leads to the formation of pulse trains with characteristic repetition rate. In practice, spectral noise surrounding the pump might itself be amplified by MI in the so-called "noise-induced" or “spontaneous” scenario and lead to the complete breakup of the wavefield. In this work, we report single-shot experimental observations of higher-order MI in a recirculating optical fiber loop. This regime corresponds to the case where instability harmonics also fall in the MI gain bandwidth which result in a succession of pulse splitting in the spatio-temporal dynamics of the wave system [2] . We observe evidence of an interplay with the spontaneous MI that critically depends on the pump-signal frequency detuning.