| Time synchronization systems are widely used in positioning and navigation,deep space exploration,telecommunications and power systems,and the synchronization accuracy of time synchronization systems plays an important role in those applications.However,the accuracy of traditional satellite-based time synchronization systems can no longer meet the requirements of systems that require high-precision time synchronization,such as 5G communications and autonomous driving.Due to the advantages of strong anti-interference ability,wide laying and low cost of optical fiber,high-precision time synchronization based on optical fiber is a current research hotspot.In the optical-fiber time synchronization system,the local site generally modulates the local time synchronization second pulse electrical signal to the optical pulse by means of intensity modulation or phase modulation,and then transmits the optical pulse on the optical fiber link and sends it to the remote site.However,optical fibers are easily affected by factors such as temperature and pressure,resulting in delay jitter.At present,two-way synchronization method and round-trip method are mainly used to compensate for delay jitter.To compensating for time delay jitter,the optical signal needs to be completely received and then converted into the electrical signal,and time synchronization is performed relying on the rising edge of the electrical signal.The rise time of the signal recovered by the photodetector is inversely proportional to the bandwidth.A photodetector with a large bandwidth can reduce the rise time of the recovered signal.Therefore,a large bandwidth photodetector is the basis for high-precision time synchronization,which can improve the time accuracy of the synchronization system.To meet the bandwidth requirements of high-precision optical-fiber time synchronization systems for photodetectors,the research contents of this paper are as follows:1.Starting from the actual requirements of the optical-fiber time synchronization system for the photoelectric detector,the design goals and difficulties are clarified.To meet the design goals,the components of the photoelectric detector are analyzed,and the simulation and the selection of key components are completed.According to the solution of key components,the overall circuit design and physical realization are carried out.In addition,the issues to be aware of in the PCB design process are pointed out.Finally,continuously iterate the design and debugging to improve the performances,such as bandwidth.2.A test scheme is designed,and a test optical circuit is built,and the parameters such as the bandwidth of the two photo detectors are tested,and the test results and analysis are given.Among them,the bandwidth of the balanced homodyne detector reaches 580 MHz,the electrical noise power spectral density is 0.15μV/(?),the gain is 115.8 dB,the shot noise ratio to electrical noise reaches 13 dB,and the common mode rejection ratio is 41.16 dB.The bandwidth of a single PD is about 600 MHz,the electrical noise power spectral density is 0.19μV/(?),and the gain is 116.8 dB.The performance test results of the two photodetectors show that the theoretically recoverable signal rise time of the photodetectors can be reduced to 0.6 ns,which can meet the requirements of the high-precision optical fiber time synchronization system for parameters such as the bandwidth of the photodetectors. |
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