Microwave Photonic Frequency Conversion System Based On A Dual-loop Optoelectronic Oscillator

Frequency conversion is a crucial part of the radio frequency system.However,electronic mixer used in the existing radio frequency system are limited in bandwidth.Besides,the high-frequency local oscillation(LO)signal generated by the microwave source has the problem of high phase noise,which seriously affects the working performance of the radio frequency system.Based on the background of radio frequency system,a microwave photonic frequency conversion system based on a dual-loop optoelectronic oscillator(OEO)is proposed in this thesis.Compared with traditional frequency conversion system whose local oscillator sources is commercial microwave sources,the proposed frequency conversion system improves the phase noise of the conversed signal,which is beneficial to the quality of digital signals transmission.And126 QAM signals is transmitted by the system to verify the digital signal transmission performance of it.The main research works of the thesis are summarized as follows:(1)The problems of the existing radio frequency systems are analyzed.The development status of microwave sources and microwave photonic frequency conversion systems are studied,and a frequency conversion system based on dual-loop optoelectronic oscillators is proposed.In addition,the principle of the optoelectronic oscillators,the microwave photonic frequency conversion system and the dualpolarization dual-drive Mach-Zehnder modulator used in the system are introduced,which lays the foundation for the research of the frequency conversion system based on a dual-loop optoelectronic oscillator.(2)The performance of the microwave photonic frequency conversion system based on a dual-loop optoelectric oscillator is studied.Aiming at the problem of low spurious suppression ratio of the conversed signal,an improved scheme is proposed,and the frequency conversion performance of the two schemes is compared.It is showed that the coversed signal of the improved scheme has higher spurious suppression ratio,but the spurious free dynamic range is smaller.Then the reasons are analyzed theoretically.In addition,based on the improved scheme,the phase noise performance of the conversed signal is compared between the commercial microwave source as the local oscillator and the optoelectric oscillator as the local oscillator.And it is known from the comparison result that the phase noise performance of the conversed signal can be improved when the optoelectric oscillator serves as the local oscillator.(3)The relationship between phase noise and the quality of digital signal is analyzed,and the transmission of the 128 QAM signal on the proposed frequency conversion system with optoelectronic oscillator and commercial microwave source as local oscillation respectively is done.It is showed that the transmitting performance of the frequency conversion system is better when the local oscillation signal is produced by optoelectronic oscillator.At the same time,the effects of the input signal power and rate on the quality of digital signal after transmission are also studied and it is showed that stable transmission of the digital signal can be realized by the proposed frequency conversion system,and the quality of digital signal can be effectively improved by controlling the power of the input signal.