Frequency Down-conversion System Based On Microwave Photonics

With the rapid development of the wireless communication technology,the demand for communication spectrum and speed is increasing,and the spectrum resources of low frequency band can no longer meet the requirements of the wireless communication.The frequency conversion based on the microwave photonics technology has attracted much attention due to its advantages of low loss,high bandwidth,and anti-electromagnetic interference.Therefore,it is of great practical significance to carry out in-depth research on the frequency conversion technology based on microwave photonics.First,the research background,as well as the research status,of the frequency conversion technology based on microwave photonics is introduced.Then,the mathematical modeling and theoretical analysis of the core optoelectronic devices of the frequency conversion system are described in detail.After that,the main performance parameters of the system are listed.Finally,three schemes of frequency conversion based on microwave photonics proposed in this paper are deeply studied.The feasibility of the schemes proposed in this paper are fully verified.The schemes proposed in this paper are as follows:1.A microwave photonic frequency down-conversion scheme based on a dual-driven Mach-Zehnder modulator is proposed,which utilizes an integrated modulator to achieve frequency down-conversion in a wide range.Experiments show that the RF and local oscillator signals with frequencies of 16GHz and 18GHz are successfully down-converted to IF signals with frequency of 2GHz.The spurious suppression ratio of useful signals is greater than 30d B.In the frequency range of 6-18GHz,the system flatness is better than 0.5d B.The spurious-free dynamic range of the system reaches 95.5 d B·Hz^2/3.2.A dual-channel microwave photonic down-conversion system based on double-parallel dual-polarization Mach-Zehnder modulator is proposed.This scheme utilizes the polarization-multiplexing property of the modulator to realize dual-channel microwave photonics frequency conversion function with single modulator.The experiment based on the scheme successfully down-converted two groups of radio frequency signal（one group is 22GHz,and the other group is 16GHz）to the intermediate frequency signals of 1GHz,2GHz respectively.The spurious rejection ratios of the two channels of the useful signals are greater than 27d B and34d B,respectively,and the spurious-free dynamic ranges reach 110.4d B·Hz^2/3and 113.4 d B·Hz^2/3,respectively.3.A dual-channel microwave photonic down-conversion scheme based on carrier-suppressed single-sideband modulation with large dynamic range is proposed.The scheme is verified by the simulation in VPI platform.The simulation results show that the optical carrier suppression ratio reaches 45d B,and the spurious suppression ratio of the useful signal is greater than 37d B.The dynamic range of the two channels reaches 148.4d B·Hz^2/3and 149.8 d B·Hz^2/3,respectively.Compared with the carrier-suppressed double-sideband modulation method,the dynamic range of the system is improved by 6.7d B,indicating that this method can not only realize dual-channel frequency conversion,but also improve the dynamic range of the system.