Temperature-Induced Noise-Insensitive Laser Repeater Station for Optical Frequency Transfer

We report on the realization of a temperature-induced noise-insensitive laser repeater station (TiLRS), which can effectively remove the annoying out-of-loop phase noise existing in the conventional laser repeater station (LRS). TiLRS is able to achieve the same capability as the conventional LRS including power amplification, signal regeneration, and phase noise compensation. More importantly, based on the out-of-loop noise inline detection and the active noise compensation (ANC) setup, our system gets rid of the need for the sophisticated temperature control system and precise out-of-loop path matching. In addition, we also design the temperature-induced noise-insensitive local station (TiLS) and remote station (TiRS) as well as the modified two-way comparison (MTWC) method for the instability evaluation. The phase-temperature coefficient of the proposed cascaded system can achieve 9.1 as/K, which is three orders of magnitude lower than the same configuration suffering from the out-of-loop noise and is the best value reported so far for the fiber-optic interferometer. We experimentally demonstrate the cascaded optical frequency transfer system by using one TiLRS connecting the 460-km commercial fiber link with the fractional frequency instability of about $1.01 \times 10^{-15}$ at 1 s and $1.20 \times 10^{-19}$ at 10 000 s. This technology paves the way for the optical frequency transfer networks with high accuracy, high robustness, and low temperature sensitivity.