Fig. 2: Mode-to-mode verification of comb-to-comb stabilization.

a The slave comb is connected to the master comb through a short fiber line for back-to-back evaluation. Mode-to-mode relative stability is monitored for two in-loop frequencies (ν₁, ν₂) and one out-of-loop frequency (ν₃). b Optical spectra of the master comb (f_r = 100.0 MHz) and two distinct slave combs (f_r′ = 100.0 MHz and f_r″ = 203.8 MHz). The original spectrum of f_r″ is given in dark green while its broadened spectrum in light blue. c RF spectrum of the mode-to-mode error signal for the in-loop frequency ν₁. d Allan deviations of the in-loop and out-of-loop frequencies. e Modal linewidth measurement. f Multi-heterodyne modal linewidth measurements at three different filter frequencies (orange:1530 nm, green: 1540 nm, blue: 1560 nm). TFBG Tunable fiber Bragg grating, PD Photo-detector, and RFSA Radio frequency spectrum analyzer