High-precision Joint Time and Frequency Transfer over a Fiber-optic Telecom Testbed

Abstract: It is highly desired to operate a joint time and frequency transfer over the exiting fiber-optic telecom networks with the commercial data transmission. Previously, we proposed a time transfer scheme based on bidirectional time division multiplexing transmission over a single fiber with the same wavelength (BTDM-SFSW), and an optical amplification scheme of single-fiber bidirectional-transmission unidirectional optical amplifier (SFBT-UOA). The effects of excess noises like Rayleigh backscattering etc. on the received time signals can be efficiently suppressed for an accepted timing jitter. Simultaneously, the bidirectional propagation delay symmetry can be guaranteed for an expected uncertainty without requiring complicated and expensive link calibration. In this paper, we propose a high-precision joint BTDM-SFSW based time and unidirectional frequency transfer over conventional telecom networks. A stable frequency signal is achieved by compensating the fiber temperature dependent phase variation according to the time transfer. The proposed joint transfer scheme is demonstrated over a 320 km fiber-optic telecom testbed with two 10 Gb/s data transmission channels. The time transfer stabilities (time deviation, TDEV) of 23.2 ps/s and 5.4 ps/10^5 s, respectively, and the frequency transfer stabilities (Allan deviation, ADEV) of 5.4X10^-13/s and 9.5X10^-17/10^5 s, respectively, are reached. The measured bit error rates (BER) of the 10 Gb/s communication data are well below 10^-13.