Experimental investigation of spontaneous and seeded modulation instability competition: route to the thermalization of the Fermi Pasta Ulam Tsingou recurrences

We experimentally investigate the noise-driven thermalization of the Fermi Pasta Ulam Tsingou (FPUT) recurrences. In fiber optics, such dynamic is observed when the spontaneous modulation instability (MI), generating noise floor amplification, is able to compete with seeded MI, at the origin of the coherent energy transfers between the Fourier modes. An input noise tuning setup is implemented, combined with a heterodyne time domain reflectometer which allows to record the power and phase distributions of the Fourier modes. By also recording the fiber output spectra, we highlight a progressive loss of the process coherence and the breakup of the FPUT recurrences.