Study On The Application Of Frequency Division Phase-locked Circuits In Frequency Transfer

One of the important issues in the applications frequency standard,is the highprecision transferring of microwave or optical frequency sources.The traditional time and frequency transferring method using microwave link and satellite will not meet the requirement in the future era of optical clock.Because of low loss and high disturbance resistance,optical fiber links become the main candidate for long-distance highprecision time-frequency transferring.The kernel technique in the high-precision frequency transfer via optical fiber is the compensation of the phase noise introduced by the transfer link.Among the existing noise compensation methods,the active phase compensation scheme based on phase-locked loop is the most widely used method for its advantages of fast compensation,mature technology and high structural integration.Besides the compensation of the noise in fiber links,the frequency division phaselocked technique can also realize frequency conversion and high-precision frequency source design in frequency transfer,which also has great application value.This thesis investigates the application of frequency division phase-locked circuits in the frequency transfer via optical fiber.High-precision signal source and phase noise compensation circuits were developed.These circuits were applied to frequency transfer experiments,and good experimental results were obtained.The main contents of the thesis are divided into the following parts.(1)Developing of a frequency synthesizer based on an external phase-locked loop and direct digital frequency synthesizer(DDS)has been developed.The frequency synthesizer has been used as a low-phase noise frequency source for driving acoustooptic modulators in optical frequency transfer.By using the fractional frequency division function to solve the problem of interference between odd harmonics of the output signal to the reference of the DDS,the synthesizer has the advantages of low phase noise level and high frequency stability,and is amplitude and frequency adjustable in the range of 400 MHz.(2)Developing of a frequency division phase-locked circuit for optical frequency transferring.The circuit has a low noise floor and the number of frequency division ratio is adjustable by using a dip switch,which simplified the optimization of the parameter procedure in the test of optical frequency transfer.By using the circuit,we have realized a 60 km round-trip optical frequency transfer between the Institute of Precision Measurement of Chinese Academy of Sciences and Huazhong University of Science and Technology with the transfer stability of 2.4×10-17/s and 6.5×10-21/65000 s,which meets the requirement on the clock signal transferring for the current highest level optical clock.(3)Developing of a 10 MHz RF reference transfer system based on the optical fiber link.The 1 GHz transferring signal is directly phase-locked to the 10 MHz RF reference signal(hydrogen clock)by means of frequency division,which compensates the noise of the optical fiber link.The 10 MHz reference signal at the remote end is reproduced by frequency dividing the 1 GHz transferring signal.The transferring stability of 4.8×10-13/s and 2.1×10-16/10000 s in 20 km fiber was obtained,which meets the requirement on sharing hydrogen clock signals among different buildings(km distance)in the research park.