Experimental observation of the spatio-temporal dynamics of breather gases in a recirculating fiber loop

We report the experimental observation of breather gases (BGs) in optics, realized in a recirculating fiber loop that enables virtually lossless propagation over 1200 km. Initiated by a slowly modulated optical background perturbed by noise, the BGs form through a nonlinear fission process and demonstrate spatiotemporal dynamics that align closely with numerical simulations of the focusing one-dimensional nonlinear Schrödinger equation. The minimal dissipation in our setup enables a statistical characterization of the BGs and confirms the theoretically predicted doubling of kurtosis during the evolution of the BGs. To our knowledge, these results open new avenues for experimental studies of integrable turbulence involving solitons on a finite background.