Observation of the noise-driven thermalization of the Fermi-Pasta-Ulam-Tsingou recurrence in optical fibers

TL;DR

This paper demonstrates the thermalization process of the Fermi-Pasta-Ulam-Tsingou recurrence in optical fibers, showing the transition from reversible to irreversible states driven by noise and active loss compensation.

Contribution

It provides the first experimental observation of noise-driven thermalization of FPUT recurrence in optical fibers, highlighting the transition to a spectrally thermalized state.

Findings

Up to four recurrences observed at low noise levels

Higher noise levels lead to irreversible thermalization

Active loss compensation enables multiple recurrence observations

Abstract

We report the observation of the thermalization of the Fermi-Pasta-Ulam-Tsingou recurrence process in optical fibers. We show the transition from a reversible regime to an irreversible one, revealing a spectrally thermalized state. To do so, we actively compensate the fiber loss to make the observation of several recurrences possible. We inject into the fiber a combination of three coherent continuous waves, which we call Fourier modes, and a random noise. We enhance the noise-driven modulation instability process against the coherent one by boosting the input noise power level to speed up the evolution to the thermalization. The distributions of the Fourier modes power along the fiber length are recorded thanks to a multi-heterodyne time-domain reflectometer. At low input noise levels, we observe up to four recurrences. Whereas, at higher noise levels, the Fourier modes fade into the noise-driven modulation instability spectrum revealing that the process reached an irreversible thermalized state.