Research On Phase Stabilized Transmission Based On Radio-frequency Modulation Over Fiber Link

Ultra-stable frequency standards are widely used in satellite navigation,aeronautical exploration,radar systems,and basic physical quantity research.With the development of accurate clocks and frequency sources,traditional satellite links are unable to meet the requirements of phase-stabilized frequency transmission.Benefiting from the advantages of optical fiber,which include low loss,wide bandwidth,and anti-electromagnetic interference,fiber-based frequency transmission is a new technology for transmitting ultra-stable frequency reference signals.In recent years,it has become the research hotspot around the world.However,according to the transmission characteristics of the optical fiber,the optical signal is affected by external temperature changes and mechanical vibrations,which causes random delay of the optical fiber transmission and is ultimately reflected in the phase drift of frequency signal.In order to detect and compensate the phase fluctuation introduced by the fiber link,the phase-stabilized radio-frequency(RF)system by passive compensation is proposed and experimentally realized in this thesis.The experimental system is tested over a commercial telecom fiber link.Based on the analysis of numbers of factors affecting transmission stability,a single-wavelength stabilized-phase frequency transmission system by remote reconstruction is designed and achieved to improve the transmission stability.The fiber-optic phase-stabilized transmission system based on RF transmission generally includes passive compensation and active compensation.This thesis chooses to design and implement a stable phase transmission system based on passive compensation.The passive scheme is more suitable for short distance transmission because of its reliability in long-term running.In order to verify the feasibility of the compensation scheme,this thesis implements a round-trip phase-detection passive compensation frequency transmission system and conducts experimental tests on 80 km commercial optical fiber link.Through long-term measurement and recording,the transmission of the phase-stabilized system is obtained.The short-term and long-term stabilities are 6.22×10-13/1 s and 7.92×10-17/104 s,respectively,which proves that the dissemination system has obvious compensation effect for the jitter of the fiber link.In view of the influencing factors such as link asymmetry,backward Rayleigh scattering and frequency doubling interference in the transmission process,the single-wavelength remote reconstruction phase-stabilized transmission system is designed for optimization.This scheme not only has the advantage of passive compensation,but also uses only one optical wavelength for bidirectional transmission in the system,which ensures the symmetry of the link.In addition,combined with the design mentality of active compensation,the system uses the phase-locked loop(PLL)structure to add signal reconstruction module at the remote end.The experimental results of the system with and without PLL reconstruction on the same length of 80 km fiber are compared and analyzed,which verifies the effectiveness of the active compensation design.The short-term stability and long-term stability without PLL reconstruction are 8.50 X 10-14/1 s and 7.42 X 10-17/104 s,respectively.On the contrary,short-term stability and long-term stability after adding reconstruction are 2.86 X 10''4/1 s and 6.62 X 10-17/104 s,respectively.The experimental results show that the single-wavelength and multi-frequency scheme can effectively overcome the negative effects in passive compensation transmission.In addition,it is verified that the remote reconstruction scheme can improve the transmission stability of the system and meet the requirements of stable phase transmission for ultra-stable frequency sources.