We experimentally study the fluctuation properties of a scalar fourth-order modulation instability (MI) process obtained by pumping a photonic crystal fiber in the normal dispersion region. We observe large wavelength-dependent pulse-to-pulse fluctuations that cannot be significantly reduced by stimulating the process with a single seed. Their reduction requires two seeds slightly detuned from the maximum gain frequency in order to also stimulate the second-order MI process cascaded from the fourth-order one. This concept is validated by experiments and numerical simulations.
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