A Precise Frequency Comparison System Using an Optical Carrier.

SUMMARY We have investigated the performance of an optical carrier transfer system for remote comparison of optical clocks. In the frequency transfer system, technical problems and fundamental principles limit coherent transfer on a long-haul optical fiber. They contribute to noise processes that come from the propagation delay in the fiber, the design of the interferometer, burst length fluctuations of the fiber, asymmetrical propagation characteristics, and so on. The feasibility of a full optical link with high stability is discussed. Phase detection with a high degree of precision and cancelation of the fiber-induced noise on the round-trip light are achieved with a well-known standard technique using an all-fiber-based interferometer. We report the characteristics of these noise processes with results on a spooled fiber. The Allan deviation of the compensated link which is extended to 90 km reaches 5 × 10⁻¹⁸, close to the theoretical limit imposed by the delay-unsuppressed fiber noise at an averaging time of 103 s. [ABSTRACT FROM AUTHOR]