All-optical link for direct comparison of distant optical clocks

Abstract

We developed an all-optical link system for making remote comparisons of two distant ultra-stable optical clocks. An optical carrier transfer system based on a fiber interferometer was employed to compensate the phase noise accumulated during the propagation through a fiber link. Transfer stabilities of $2\times 10^{-15}$ at 1 second and $4\times 10^{-18}$ at 1000 seconds were achieved in a 90-km link. An active polarization control system was additionally introduced to maintain the transmitted light in an adequate polarization, and consequently, a stable and reliable comparison was accomplished. The instabilities of the all-optical link system, including those of the erbium doped fiber amplifiers (EDFAs) which are free from phase-noise compensation, were below $2\times 10^{-15}$ at 1 second and $7\times 10^{-17}$ at 1000 seconds. The system was available for the direct comparison of two distant ${}^{87}$Sr lattice clocks via an urban fiber link of 60 km. This technique will be essential for the measuring the reproducibility of optical frequency standards.

References in corpus (3)

• Sr lattice clock at 1x10^{-16} fractional uncertainty by remote optical evaluation with a Ca clock
• Cascaded multiplexed optical link on a telecommunication network for frequency dissemination
• Direct Comparison of Distant Optical Lattice Clocks at the $10^{-16}$ Uncertainty

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