Development Of Frequency Transfer Via Optical Fiber Link at NICT

摘要

NICT in Japan has developed a radio frequency (RF) dissemination system using an optical fiber link. The phase noise induced during the transmission through the optical fiber is actively cancelled by a compensation system. A proving test has been conducted on the 114-km urban telecom optical fiber link in Tokyo. The transfer stability in the 10-18 level at an averaging time of 1 day was achieved. In the last few years, optical frequency standards have improved significantly and attained high frequency stability. Such significant improvements make it difficult to compare the optical clocks between distant laboratories without performance degradation by using conventional time transfer methods via a satellite link. A low-noise frequency distribution system is demanded in the field of astronomy and particle accelerators, as well as time and frequency metrology. Frequency distribution using an optical fiber link has attracted worldwide attention as one of the candidates to connect the distant sites in higher stability. In general, however, during a transmission through optical fiber, the transmitted frequency is exposed to the Doppler effect, which is attributed to fiber length variation caused from mechanical stress or temperature variation. The longer the transmission distance is, the larger the effect becomes. For stable dissemination via optical fiber link, active compensation to cancel the Doppler shift is required.