All Fiber High-Precision Time And Freauency Transfer By Mode-Locked Laser

High-precision time-frequency transfer technology is widely used in precision satellite navigation,earthquake monitoring,particle accelerators,laser interference measurement,and other fields.With the continuous development of modern science and technology,high-precision timefrequency transfer technology is also constantly innovating and developing.Optical fiber time-frequency transfer technology is one of the cutting-edge research directions in high-precision time-frequency transfer technology.It uses optical principles to achieve high-precision time-frequency transfer,with advantages such as long transmission distance,low noise,and strong anti-interference ability.It is widely used in international time services,satellite communications,and precision measurement fields.Compared with traditional frequency transfer technology,fiber-based frequency transfer technology can improve accuracy by 3-5 orders of magnitude,which is of great significance for the construction and development of satellite navigation systems such as GPS,Galileo,and BeiDou.However,optical fiber frequency transfer technology faces two bottleneck problems:one is the phase jitter detection error caused by the end reflection of the node,and the other is the deterioration of the signal-to-noise ratio of the loopback signal,which reduces the frequency transfer stability.Currently,the main methods to solve the end reflection problem of the node are to use optical fiber fusion splicing or wavelength division multiplexing technology,and to use phase-locked regeneration technology to solve the problem of signal-to-noise ratio deterioration of the loopback signal,but there are problems such as the use of non-optical fiber devices and low system robustness.In this study,based on the optical frequency comb transfer method,a method combining dispersion management,nonlinear optical effects,and wavelength division multiplexing is proposed to perform spectral broadening and filtering of the optical frequency comb of the loopback signal,complete wavelength conversion,and improve the coherence of the optical frequency comb,thereby enhancing the signal-to-noise ratio of the loopback signal and enhancing system robustness.A "all-fiber" highprecision time-frequency transfer system was achieved by using the spectrally broadened and regenerated optical frequency comb signal as the remote signal.This technology solves two bottleneck problems faced by current optical fiber frequency transfer technology:the phase jitter detection error caused by the end reflection of the node and the deterioration of the signal-to-noise ratio of the loopback signal,and eliminates an optical frequency comb,saving system costs.The main research contents of this paper are as follows:1.Nonlinear frequency shift theory was analyzed and modeled,and the optimal length of nonlinear fiber required for different mode field diameters was analyzed through numerical simulation.A 10-meter photonic crystal fiber was selected as the main nonlinear fiber for the project.The mode and power matching issues required by the photonic crystal fiber in the nonlinear frequency shift experiment were determined through testing.The nonlinear frequency shift module developed in this study achieved wavelength conversion,replacing a re-locked optical frequency comb,retaining the coherence of the optical comb,and ensuring the optimal signal-to-noise ratio of the output microwave signal.2.A full-fiber high-precision time-fi-equency transfer system based on nonlinear frequency shift technology was built.By comparing the rubidium clock signal with the test system signal through the all-fiber opticalmicrowave locking module,the frequency transfer instability of the system was evaluated by calculating the Allan deviation.When the length of the transmission fiber is 1 meter,the frequency transfer instability of the 34channel output signal after spectral broadening is about 6.97×10-15 at 1 second and about 1.21×10-16 at 100 seconds.When the length of the transmission fiber is one hundred kilometers,the frequency transfer instability of the 34-channel output signal after spectral broadening is about 9.14×10-15 at 1 second and about 1.98×10-15 at 100 seconds.The research results of this project show that this technology is feasible in the hundredkilometer-level high-precision optical frequency comb transmission process,and this all-fiber high-precision time-frequency transmission system based on optical frequency comb has certain stability.The system does not need to be relocked at the remote end,avoiding the loss of lock caused by temperature effects,and improving the robustness of the system.The "all-fiber" high-precision time-frequency transmission technology based on optical frequency comb researched in this project will become one of the key technologies in navigation,next generation mobile communication network and new generation precision timing network.