Simulation Research Of Fiber Radio Frequency Trasmission System

With the emergence of highly stable frequency sources,many applications that rely on high-precision time and frequency signals have grown rapidly,such as navigation and positioning,deep space exploration,5G communications,radar arrays,and other important areas of national economy that require highly stable time and frequency signals.The traditional satellite-based frequency transfer technology obviously can no longer meet the requirements of higher standard transmission stability,while the fiber optic due to its inherent anti-electromagnetic interference,low loss and low intrinsic noise characteristics,making the fiber opticbased stable frequency transfer technology has become a current research hot spot.In the real environment,fiber optic links are subject to temperature variations and mechanical vibrations,resulting in random time delay fluctuation in signal transmission.In addition,the noise of some common devices in the fiber optic frequency transfer system will also directly affect the signal-to-noise ratio of the transmitted signal,such as the relative intensity noise(RIN)of the laser,the shot noise and thermal noise of the detector,the spontaneous radiation noise(ASE)of the optical amplifier,etc.The accumulation of these noises will seriously affect the transmission stability of the frequency signal.Therefore,the study of each noise in the system is essential for the design of the frequency scheme and the improvement of frequency stability.Temperature variation is one of the main factors causing phase fluctuation in fiber optic links.Some research groups have studied the deterioration of frequency stability in fiber optic links caused by temperature variations,but most of these studies are based on theory,using a simple sinusoidal model to simulate the actual temperature variations and applying the same variation trend to all fibers.However,the temperature model deviates from the actual temperature variation,and the fibers are subjected to different temperature variations at different placement locations(e.g.,dispersion-compensated fiber(DCF)is placed in the server room,where the temperature variation is larger,and single-mode fiber(SMF)are buried,where the temperature variation is smaller).Therefore,it is necessary to analyze its impact on the system frequency stability according to the actual temperature variation.1.The noise in the fiber optic frequency transfer system is studied,including temperature,dispersion and intensity noise of active devices,where temperature mainly affects the long-term stability of the system,and dispersion and intensity noise mainly affect the short-term stability of the system.The experimental measurement and error analysis of residual dispersion in fiber optic frequency transfer systems were carried out,and simulation studies were conducted for three different dispersion compensation methods,concluding that symmetric compensation in unidirectional transfer EO/OE systems is useful for improving the frequency stability of the system.2.For the temperature variation in fiber optic links,the actual temperature variation data in different links were collected using high precision data acquisition cards,and the temperature variation in various locations was investigated.A passive compensation system was built using a simulation software,and the collected measured temperature was imported into the simulation model to obtain the effect of temperature variation of DCF and bare SMF on the stability of the system.3.In order to verify the correctness of the simulation,the stability of the actual 80 km fiber optic frequency transfer system was compared with that of the simulation,and the stability of the simulation was found to be 4.2×10-17@104 s,while the stability of the experimentally measured system was 7.9×10-17@104 s.The simulation results are consistent with the experimental results,which verifies the correctness of the built simulation model and the authenticity of the simulation results.