| Stable radio frequency transmission plays an important role in navigation,deep space network,radio astronomy and atomic clock comparison with the development of information society.However,for the traditional radio frequency transmission methods based on wireless,such as Global Position System and Two-Way Satellite TimeFrequency Transmission,the transmission signal is severely interfered by the atmospheric interference of the open air channel.And the transmission accuracy cannot meet the requirements of highperformance applications.Optical fiber has shown its superiority as a transmission medium with low loss and high security.The existing underground optical fiber network has been relatively mature,which brings convenience to the research of fiber-based RF transmission.In the actual environment,temperature changes and mechanical vibrations will cause optical path fluctuations of optical light transmitted in optical fibers,and introduce random jitter of transmission delay.Therefore,in order to obtain a stable signal at the remote end,it is necessary to compensate the random phase changes caused by the fiber link in real time.In addition to the above environmental factors,some special transmission effects in optical fiber,such as Rayleigh scattering,dispersion,laser relative intensity noise,will affect the symmetry of optical fiber link in bidirectional transmission,thus reducing the stability of the transmission system.In the stable radio frequency transmission,it is helpful to further improve the transmission stability of the compensation scheme by studying the noise of the optical fiber stable frequency transmission system.The noise of optical fiber link and the noise of active components are two factors that have great influence on the stability of RF phase stabilized transmission via optical fiber.The link delay of optical fiber,including the influence of temperature on fiber length and the influence of temperature on core refr-active index,and the dispersion caused by laser wavelength jitter,the link noise causes phase jitter through the accumulation of delay fluctuation on optical fiber link,which leads to the deterioration of the system’s Allan variance.The noise of active devices will lead to the decline of signal-to-noise ratio in the signal detection process,which will lead to the deterioration of the stability of the system.In order to reduce the influence of noise in optical fiber stable frequency transmission,it is necessary to design a reasonable stable frequency transmission system for noise research.However,in the past,researchers at home and abroad mostly studied a single system noise,and few systematically classified and analyzed the system noise and carried out simulation research based on actual experimental data.In addition,theoretical noise research and simulation of compensation system are also very rare.In order to solve this problem,this paper first analyzes the main noise of transmission system based on optical fiber and carries out simulation.Then,based on the VPI simulation software,the residual noise caused by the asymmetry of compensation system is simulated and analyzed theoretically.The main work is as follows:1.Aiming at the problem that it is difficult to judge the specific source of residual noise in the RF phase stable transfer compensation system in the experiment,the theoretical analysis of the compensation system link delay is carried out,and the formula of residual noise after compensation is obtained and simulated.The influence of temperature in the compensated 3000km optical fiber link is Allan variance stability at 9E-18@1s,and the simulation results are in good agreement with the theoretical analysis results.The link delay jitter caused by dispersion is related to the degree and mode of dispersion compensation.When the dispersion compensation reaches 99.5%in a single wavelength transmission system,the influence of dispersion is 1E-15@1s.2.The conversion relationship between the SNR and the variance of the non-typical noise type is derived,and the distribution forms of each noise in the system are analyzed.Most system noise types are white phase noise,and Erbium doped fiber amplifier(EDFA)spontaneous emission beat noise is scintillation noise.Simulation analysis and comparison under different noise distribution types are carried out.3.The asymmetry analysis of link in compensation system is presented,including temperature asymmetry and wavelength asymmetry.In round-trip transmission,the difference between the center wavelength of forward and backward optical carrier will lead to deterioration of stability,and the asymmetric effect of temperature on ultra-long-distance transmission cannot be ignored.The round-trip wavelength difference in 3000km optical fiber link is simulated in VPI simulation software,and the influence of wavelength asymmetry on optical fiber stable phase transmission system is obtained.In 3000 km optical fiber link,when the center frequency difference is at 100 MHz～100GHz,the influence of stability is in the order of 1E16@1s～1E-13@1s,with a linearly change.4.In view of the lack of theoretical analysis of noise in the current actual environment,the influence of temperature on system stability is obtained according to the change of actual temperature in the link delay analysis,and the influence of dispersion on system stability is simulated according to the actual frequency drift of laser measured by experiment.The noise in the one-way transmission system of optical fiber RF signal is analyzed,and the simulation results of the influence of temperature,dispersion and active device intensity noise on the system stability are obtained.The thermal noise and particle noise of the detector,the relative intensity noise(RIN)of the laser and the noise of the erbium-doped fiber amplifier(EDFA)are discussed emphatically. |
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