7.9km
The article links to their paper 'Petabit-per-second data transmission using a chip-scale microcomb ring resonator source'[1]
> We experimentally demonstrate transmission of 1.84 Pbit s–1 over a 37-core, 7.9-km-long fibre using 223 wavelength channels derived from a single microcomb ring resonator producing a stabilized dark-pulse Kerr frequency comb.