Exploring High-Precision Transmission of Optical Reference Frequencies via Wavelength Division Multiplexing

Transmitting an ultra-high precision frequency of an optical clock via wavelength division multiplexing (WDM) is a key technology for economically realizing innovative applications enabled by significantly accurate and stable time and frequency. In this study, we investigated an optical frequency transmission method using a commercial WDM system, employing our highly stable optical frequency repeater systems with a fiber noise compensation (FNC) function. For the 20-km WDM transmission, we achieved the frequency instability of 4 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–15</sup> at an averaging time of 1 second (s) and reaches ~ 1 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–18</sup> at 34,000 s. This frequency stability enables optical clock reference frequencies to be transmitted over long distances, demonstrating the potential of our WDM link to enable the widespread deployment of the optical clock frequency at the frontier of precision.