Fig. 1
From: Free-space transfer of comb-rooted optical frequencies over an 18 km open-air link
Phase-coherent transfer of comb-rooted optical frequencies over an 18-km free space link. a Multiple optical carriers are extracted from a frequency comb in stabilization to a high-finesse cavity and transmitted from Site A to Site B. The second carrier λc is selected as the feedback compensation channel of atmospheric optical phase noise, while other carriers λt1, λt2 and λt3 are dedicated channels for optical frequency transfer. b Refractive indices of air and fiber in the infrared range are compared in the inset. c Optical power scintillation at Site B observed at a sampling rate of 3 ms over an interval of 300 s. d Scintillation frequency spectrum. AOM acousto-optic modulator, C optical circulator, EDFA erbium-doped fiber amplifier, PLL phase-locked loop, T telescope, M flat mirror, OC optical coupler, PD photodetector, WDM wavelength division multiplexer
