Statistical characterization of the internal structure of noiselike pulses using a nonlinear optical loop mirror

•A technique is proposed to estimate the statistics of a bunch of short pulses.•The technique relies on the ultrafast response of a nonlinear optical loop mirror.•The inner statistics of noise-like pulses from a figure-8 fiber laser is measured.•A non-gaussian distribution is obtained, with a heavy high-amplitude tail.•The existence of intense spikes compatible with optical rogue waves is revealed.

In this work we study statistically the internal structure of noiselike pulses generated by a passively mode-locked fiber laser. For this purpose, we use a technique that allows estimating the distribution of the amplitudes of the sub-pulses in the bunch. The technique takes advantage of the fast response of the optical Kerr effect in a fiber nonlinear optical loop mirror (NOLM). It requires the measurement of the energy transfer characteristic of the pulses through the NOLM, and the numerical resolution of a system of nonlinear algebraic equations. The results yield a strongly asymmetric distribution, with a high-amplitude tail that is compatible with the existence of extreme-intensity sub-pulses in the bunch. Following the recent discovery of pulse-energy rogue waves and spectral rogue waves in the noiselike pulse regime, we propose a new way to look for extreme events in this particular mode of operation of mode-locked fiber lasers, and confirm that rogue wave generation is a key ingredient in the complex dynamics of these unconventional pulses.