Research On High Stable Radio Frequency Transfer Via Optical Fiber Link

In the modern metrology,time and frequency is the most precise and ac-curate quantities can be measured.Radio telescope array,atomic clocks com-parison,and Beidou system in our country all need radio frequency(RF)signals with high stability.Distributing atomic clock reference signals to remote users becomes a hot spot in the research field of time and frequency.Due to elec-tromagnetic interference in the atmosphere,the system transfer stability based on satellite frequency transfer could only be achieved by averaging data for a long time,which is limited to 10-15 for a long-term stability.With improve-ment of the atomic frequency standard stability,frequency transfer based on satellite transmission technology is not qualified.Frequency transfer based on the optical fiber transmission technology breaks through the bottleneck of satel-lite frequency transmission,the stability of frequency transfer increases at least three orders of magnitude.It has inestimable development prospects,espe-cially in mainland optical fiber link with high frequency stability.Noises in the long fiber link will seriously deteriorate frequency signal transmission stability.Theoretical analysis of the noise would contribute to designing the frequency transmission system and improving the frequency stability.Theoretical and experimental research have been carried out based on high stability of RF frequency transmission technology.Effective solutions are put forward according to RF transmission system noise calculation,multi-node RF signal distribution and long distance RF signal transmission,and outstanding innovative research results have been achieved.In this paper,the main research results are as follows:1.For the issue of deterioration of RF signal transmission stability,I ana-lyze the long-distance optical fiber delay asymmetry of RF transmission system,photoelectric device noises,the residual phase noise frequency source and op-tical fiber link intermediate coupling optical amplifier noise,and a quantitative calculation is carried out.The results show that laser relative intensity noise and the dispersion are especially important for short term stability,and the long term stability is limited by temperature.Noise theory research of long distance high stability of RF transmission has important guiding significance for scheme design and optimization.2.For the issue of multiple remote users demands for the same frequency reference signal,the optical fiber ring network based scheme is proposed and designed for multi-node RF signal distribution.The system contains only one laser source,and the signal is not sensitive to the effects of dispersion.The scheme realizes stable RF signal distribution to any node in the optical fiber ring network,and it is also scalable.The experimental verification is carried out in the laboratory 100 km optical fiber link,the signal phase jitter without compen-sation is 1.87 rad,after phase noise compensation,2.4 GHz signal phase jitters of two remote nodes are 0.024 rad and 0.027 rad,and phase jitter inhibitory factor is 70.The study results have application value for radar and telescopic antenna array.3.For the issue of high stability and low cost requirements for RF signal transmission,a point-to-point RF transmission scheme is designed and opti-mized based on passive compensation method.The optimal experiment scheme eliminates the effects of mixer nonlinear and backward scattering noise.The system contains only two sets of lightning and photoelectric conversion device,which reduces the system cost.The verification experiments have been done in Guangzhou and Beijing area.In buried 100 km optical fiber link(Beijing area),the RF transmission stability after the compensation is 6.3×10-14@1s and 5.0×10-17@104 s,which is superior to the stability of the reference ru-bidium atomic clocks nearly two orders of magnitude.This is the first time in the world that the radio frequency transmission system performance is tested in the buried optical fiber link,which plays an important reference value in the practical application of the system.4.For the requirements of very long baseline interferometry for RF signal transfer in a long distance,a point to point RF transmission scheme is designed based on the dual phase-locked loops.The frequency conversion phase-lock receiver accomplishes high-quality phase tracking of the RF signal which is transmitted after long distance optical fiber link.The phase-locked loop built in high stability crystal at remote site not only improves the signal-to-noise ratio of the signal but also effectively improves the short-term stability of the system.The system performance is tested via thousands of kilometers fiber link in the laboratory and buried optical fiber link.RF transmission stability in thousands of kilometers fiber link is 8.2×10-14@1 s and 7.9×10-17@104s.In addition,signal-to-noise ratio of the RF signal which is transmitted in thousands of kilo-meters optical fiber link is theoretical calculated,and the calculation result is consistent with the experimental result.