Optical frequency transfer with below 10−21 uncertainty using a DFB–laser-based fiber Brillouin amplifier

Exploiting the outstanding performance of optical atomic clocks for improved timekeeping, relativistic geodesy, and fundamental physics beyond standard model demands comparing distant state-of-the-art clocks. Interferometric fiber links have been demonstrated as an eminent method such frequency comparisons over distances up to thousands kilometers. However, distances, attenuation mandates signal amplification. Fiber Brillouin amplification (FBA) has proven efficient technique coherent transfer. Demonstrated FBA schemes designed based on costly narrow-linewidth pump lasers analog pump-to-signal phase locking schemes. Furthermore, high power requirement these FBAs hinders integration FBA-based dissemination connections shared telecommunication signals in C-band. In this paper, we propose experimentally demonstrate a novel module (FBAM) employing cost-effective distributed feedback (DFB) assisted by digital scheme field programmable gated array. The new FBAM is compact, cost-effective, directly applicable different bands, which opens opportunities establish metrology infrastructure within existing networks. Additionally, small-footprint DFB-FBAM allows frequent stages with lower reach continental scale optimized signal-to-noise ratio. We characterized DFB-FBAM’s transfer uncertainty using two-way layout in-lab 100 km long link fractional instability 9.3 × 10−22 at 10 ks time. characterizations show contributions (−2.1 ± 3.3) below averaging times >100 ks. For first time, assess temporal shift variations underground implement track changes remote FBAM.