Research On High Precision Time And Frequency Distribution Based On Femtosecond Laser Frequency Comb

The technology of time-frequency distribution is particularly important for radar detection,navigation and large-scale scientific facilities.Compared with some tradition time-frequency distribution methods,the time-frequency distribution based on femtosecond laser frequency comb has a unique advantage,which can achieve femtosecond precision in time-synchronization,to reach the harsh requirement about the high-precision collaborative between functional components in these facilities.Based on the background in the previous paragraph,this thesis studies the time-frequency distribution method that chose the femtosecond fiber laser as our local oscillator signal source which is based on nonlinear polarization evolution mode-locking.Also,the balanced optical cross-correlation technique and the fast-slow compensation method for fiber link time delay can achieve time synchronization in fs precision.Specific research work is summarized as follow:1.The importance of time-frequency distribution based on femtosecond laser is mentioned.Also,its advantage in time-frequency transmission and the development of this technology at home and abroad is described.In the meanwhile,this paper analyzes the current methods of time-frequency distribution in large scales.The characteristic about ultra-low time jitter and optical frequency comb in femtosecond laser is the core information of our system.High stability to environment noise in fiber link is also introduced.2.The local oscillator signal source in this experimental system is described in detail.The femtosecond fiber laser based on NPE mode-locking is used as the system local oscillation signal source.It can output the mode-locked pulse with center wavelength of 1550nm,pulse width of 560fs,repetition of 126MHz and output average power of 38mW,which has ultra-low time jitter and optical frequency Comb characteristics.After that,the local oscillator signal source through the optical fiber link transmission into the photodetector can produce RF frequency comb which has the low phase noise benefiting from the ultra-low timing jitter in femtosecond laser.The bandwidth of this high flat RF frequency comb can be observed from 126MHz to26.5GHz after using spectrum analyzer.3.The methods of using the balanced optical cross-correlation?BOC?to detect the system time delay signal and the fast-slow compensation method based on the optical fiber stretcher and the stepping motor are mentioned.Also,the process of comparing the timing jitter in unlocked and locked states of phase locked-loop is discussed.Finally,over 2km fiber link,the standard deviation of the residual timing error is less than 1.1 fs and the time instability is 10^-18 at 1000s over 2 hours observation.