Study On Passive Compensation Fiber-optic Radio Frequency Transmission System With A Nonsynchronous Source

Highly stable radio frequency standards play an important role in frequency measurement,time synchronization and deep space exploration.However,high-performance atomic clocks tend to be complex and have a large structure,which are not suitable for moving.Therefore,it is necessary to transmit the atomic clock's frequency signal through a link for users in different places.As the frequency stability of radio atomic clocks continues to increase,the traditional satellite link-based transmission technology can not meet the existing application requirements,while the fiber link has the advantages of low transmission loss,large bandwidth,wide distribution,etc.High-precision fiber-optic frequency transfer has become a promising technology.When frequency signal is transmitted over the fiber link,the stability of signal will be deteriorated by the noise on the link.The noise comes from two main sources:One is the noise floor of the fiber link,which is the noise of the optoelectronic device itself contained in the transmission system.The other is the additional phase noise introduced by the fiber link due to temperature changes and mechanical disturbances.In order to obtain a lossless high-stability frequency signal,it is necessary to compensate for noise.The phase noise compensation technology based on the loop method can effectively suppress the phase noise introduced by the link.The existing compensation techniques can be divided into active and passive compensation schemes.Active phase noise compensation technology is realized by the phase noise extraction of the link,real-time phase discrimination,and using algorithm to drive the phase compensator dynamically compensating for link.Passive phase noise compensation technology uses mixers to compensate for link noise without extracting phase noise and control algorithms.Its characteristics are simple structure,fast compensation and infinite compensation range.However,in the existing passive schemes,in which is compensation is finished in one round-trip transmission,the problem of backscattering is common.Aiming at this problem,passive compensation fiber-optic radio frequency transmission scheme of nonsynchronous source is designed in this thesis.It does not need high-precision phase-locking,and only uses two wavelengths to effectively avoid the impact of backscattering.The main work of this thesis includes:(1)The principle of passive compensation fiber-optic radio frequency transmission is elaborated,and the noise existing in the fiber-optic radio frequency transmission link is analyzed.The residual phase noise introduced by the non-strict integer relationship between the detection signal and the transmitted signal,the phase noise introduced by the fiber dispersion and wavelength asymmetry,as well as frequency crosstalk noise are analyzed.(2)The passive compensation fiber-optic radio frequency transmission system with a nonsynchronous source is designed.The basic principle and the influence of nonsynchronous source coherence are analyzed.The software and hardware design and implementation of the system are completed.(3)The experimental system was built,and the test of electric noise floor and back-to-back noise is completed.The frequency transfer experiments were carried out over the 40km fiber link with the nonsynchronous source of Rigol,R&S and Hittite respectively.Further analysis verified the impact of the asynchronous source.In the case where the nonsynchronous source can remain stable within one round trip time,the frequency stability can reach about 3×10-14/s and 2×10-16/104s.