High-stability Microwave Frequency Transfer Over Fiber Links

In recent years, with the rapid development time and frequency technology, the stability and accuracy of time and frequency reference(cesium atomic fountain clock) are greatly improved. These advancements contributed to the development of fundamental physics and precision measuring and other areas, as well as high-resolution time and frequency dissemination technology to a higher demand. High-resolution time and frequency transfer based on satellites cannot reach the fractional instability of frequency reference. The optical fiber as a transmission medium has excellent, low loss and low noise characteristics, high-resolution time frequency signal dissemination has become a hot research topic in the field of time-frequency science. In this paper we design ultra-stable microwave frequency transfer system, and set up the experiment system over 50 km lab fiber links, afterwards we assess the performance of our scheme.We develop a real-time noise cancellation system based on the method of phase conjugation stabilization. The system which is a modular structure is composed of microwave reference signal generating, phase compensation and optical fiber transmission module. We conducted the following three experiments The ultra-stable 9.1GHz frequency signal transfer via a 50-km fiber spool 9.2GHz frequency signal transfer via a 10-km fiber spool 9.2GHz frequency signal transfer via a 50-km fiber spool. The last experiment, in 9 days laboratry measurements, the system exhibits frequency transfer stabilities(standard Allan deviation) of 4.2E-13@ls/4.3E-14@lday for free-running and 5.8E- 4@ls/1.9E-17@lday for noise-compensated link. This system match the requirement of 100-km scale frequency transfer of ultra-stable microwave atomic clocks.