Research On Time And Frequency Transfer Technology In Optical Fiber

Time and frequency（T&F）transfer and synchronization is the key enabling technology in modern electronic information systems such as time and frequency metrology and the next-generation unified networks like 6G.Due to the advantages of low transmission loss,low noise and high reliability,deploying ground-based time and frequency transfer network over optical fiber links has been considered as a crucial part of modern infrastructure.The current T&F transfer technology is now evolving along two directions,i.e.,（1）long distance end-to-end transmission of time and frequency,and（2）multi-end flexible T&F transmission and networking,with the latter of which has a larger technological significance in the next-generation distributed information systems.The innovative work of the thesis are listed as follows:1.Aiming for the demand of remote frequency comparison of frequency sources in multiple laboratories,the frequency back-transferring technique from arbitrary remote site in fiber-optic ring-form link to one central laboratory is proposed.The 1.21-GHz frequency signal back-transferring in the 50-km fiber ring achieves the stability of 1.0 × 10^-12@0.1 s,1.3 × 10^-13@1 s,and 1.1 × 10^-15@104 s,and has a phase jitter suppression ratio larger than 100 compared to free-running situation.The proposed frequency back-transferring technique from arbitrary remote site has the advantage of quick response to link delay change,as well as infinite phase error cancellation range,and can be adopted in the constructing multi-lab remote frequency comparison network.2.To overcome the multi-user limitation of end-to-end fiber-optic T&F transfer caused by the wired（i.e.not wireless）optical fiber channel,the techniques enabling multi-end time and frequency dissemination are studied.a)The technique of one-to-multiple simultaneous time and frequency distribution is proposed,based on the λ-dispersion technique.Particulary,the real-time delay information from central station to an arbitrary time receiving site is sensed and calculated,which differs from the end-to-end time transfer.The sensing-and-calculating paradigm conforms to the technique trend in the next-generation unified networks such as 6G.The frequency signal disseminating to an arbitrary remote site in a 45-km fiber ring achieves the stability of 2.0 × 10^-13@1 s and 1.7 × 10^-16@104 s;the simultaneous time information distribution has a delay jitter of only 40 ps,and achieves the time deviation of 19.79 ps@1s and 0.896 ps@103 s.b)The one-to-multiple T&F dissemination technique is further extended.The arbitraty-to-arbitrary frequency injection and recovery technique is proposed,which supports the construction of a highly flexible and multiple-to-multiple oriented frequency dissemination and comparison network.The injected and recovered frequency signal on arbitrary sites in the 90-km long fiber ring achieves the stability of 3.5 × 10^-13@1 s and 2.1 × 10^-15@104 s.The arbitrary frequency injection point does not require additional laser source,which further lowers the cost and complexity.3.As the number of distributed stations increasing,new synchronization solution with more effort on extensibility is highly expected.The requirements on extensibility of fiber-based sync systems are firstly analyzed.Next,a phase-stabilized side-branch radio-over-fiber link,which fully satisfies the extensibility requirements,is propsed and demonstrated.The extensible side branch link can be constructed at any intermediate point along the main link,without any reconfiguration at the central station,and is inherently extensible to multiple frequency signals.The 2.465-GHz local oscillator（LO）transferred to the end of branch link achieves the stability of 2.6 × 10^-13@1 s and 2.3 × 10^-15@104 s,and the 900-MHz LO simultaneous disseminated achieves the stability of 4.3 × 10^-13@1 s and 2.6 × 10^-15@104 s.Both the LOs have a long-term stability optimization of two orders of magnitude.The stable side-branch RoF link shows the potential of constructing a highly-extensible frequency dissemination network.