Design And Implementation Of Signal Detection And Processing Unit In Optical Fiber Frequency Transmission System

With the rapid development of frequency standards,high-stability frequency transmission technology is widely used in various fields such as space observation,positioning and navigation,mobile communication etc.,which has become a hotspot of research.In recent years,optical fiber communication has continued to develop.Because optical fiber channels have the characteristics of strong anti-interference ability and high stability,frequency transmission technology based on optical fiber has obvious advantages compared with traditional synchronization methods based on satellite links,and has very significant research value.In the optical fiber frequency transmission system,the transmitting end transfers the high-stability time base signal to the remote end through the optical radio frequency method,and the receiving end needs to detect the optical signal transmitted through the link,extract the required radio frequency signal and perform subsequent processing.Since this process involves a variety of radio frequency(RF)circuit devices,the performance of these devices have important impacts on the system.However,commercial RF devices are not suitable for high-precision frequency transmission due to their shortcomings such as large bandwidth,high noise,and inconvenient integration size.Therefore,it has important research significance and value to design the signal detection and processing unit circuits to improve the system performance according to the special requirements of the optical fiber frequency transmission system for the radio frequency devices.This thesis mainly completes the design and implementation of the related circuits of the signal detection and processing unit at the receiving end in the optical fiber RF transmission system,and tests many performances of the physical circuits.The main research work is as follows:1.Research on the basic methods of signal detection and processing unit of optical fiber RF transmission system.This thesis studies the frequency standards and main measurement indicators in the optical fiber RF transmission system,and expounds the time-domain characterization of frequency stability--Allan Deviation and its measurement method,indicating that the circuit design for a specific frequency is very important for obtaining good frequency stability.At the same time,this paper introduces the working principle of photodiode,analyzes the characteristics of different photodiode preamplification modes and their influence on circuit design,and clarifies the basic method of RF circuit design.The above research provides theoretical support for the following circuit design and testing.2.Design and implementation of related circuits of signal detection and processing unit of optical fiber RF transmission system.Focusing on the 2.4GHz frequency band,this thesis analyzes the design requirements of the related circuits of the detection and processing unit,and completes the design of RF photodetection circuit,filter circuit and power splitting circuit through the steps of device selection,circuit structure and schematic design,PCB drawing,and physical welding,etc.In the design process,this paper not only carried out ADS simulation design and circuit parameter optimization for the necessary parts,but also emphasized the problems that need attention.3.The performance testing of related circuits of signal detection and processing unit in the optical fiber RF transmission system.In this thesis,the circuit test plan design is carried out,and the completed circuit is debugged and tested step by step.The results show that the RF photodetection circuit has ideal gain and linearity,and can output frequency signals with pure spectrum.On this basis,this thesis also proposes an improvement plan for the RF photodetection circuit.Through testing in the back-to-back transmission system,the frequency stability of the system are 1.5×10-15/s and 5.6× 10-18/104 s;The 3dB bandwidth of the RF filter circuit centered at 2.4GHz is 66MHz,and the in-band ripple is small,which is basically consistent with the results of simulation;The two output signals of the RF power splitting circuit have a relative phase jitter of only 7 to 8 ps,and a good amplitude balance value.Apart from this,the overall performance of the filter circuit and the RF photodetector in the back-to-back RF transmission system is better.In summary,this thesis carries out the circuit design and implementation of related circuits of signal detection and processing unit in the high-precision frequency transmission system and completed the functional test.The results show that the designed circuit is superior to commercial products in terms of frequency stability,bandwidth,and on-board integration.The research results are of great significance for improving the performance of frequency transmission system.