Study On The Generation Of Millimeter-wave Based On External Modulation Technology In RoF System

With the advancement of the times,various kinds of communication methods have been increasing,and the demand for the quality of wireless communication services has been continuously improved.In order to satisfy people's demand for high-quality of wireless communication and broadband,domestic and foreign scholars have proposed radio over fiber(RoF)technology through extensive research and repeated verification.This novel technology combines millimeter wave communication and optical fiber communication,making the advantages of optical fiber and millimeter-wave communication perfectly utilized in the same system.Based on previous research results,this paper makes further research and analysis on the generation technology of millimeter wave in RoF system,and makes structural optimization of RoF system.The main research contents are as follows:This paper introduces the research background of the technology of light load millimeter wave,and the basic principle,structure,advantages and defects of RoF system,and studied several generation schemes of millimeter-wave in RoF system.Based on the above research foundation,the principle of the millimeter-wave generation in external modulation technology is introduced.The double-sideband(DSB)modulation,single-sideband(SSB)modulation,optical carrier suppression(OCS)modulation and odd-even-sideband modulation based on Mach-Zehnder modulator(MZM)are analyzed.The spectrum structure of these several modulation methods are simulated.The dual parallel Mach-Zehnder modulator(DPMZM)is introduced,and a theoretical analysis of the technology of generating millimeter wave based on DPMZM is carried out,and the parameters for generating different multiplication factors such as quadrupling,sextupling and octupling are given.Based on these parameter conditions,discussing the impact of the extinction ratio and modulation depth of the DPMZM on the millimeter wave generation.The system based on the DPMZM structure is improved,and a twenty-fourth harmonic millimeter wave signal is generated by using four-wave mixing(FWM)effect.The principle of the millimeter wave generated by the tandem modulator structure is analyzed.Based on the improved tandem modulator structure,quadrupling,sextupling and octupling signals are generated.The structure is simulated and verified by simulation results.This structure can be concluded to obtain high frequency microwave signals from the low frequency drive signal.The difference from other research schemes is that the power amplifiers of two RF signals are removed from the structure in this paper,which makes the system structure more compact and simple,and reduces the system cost.A full-duplex RoF system was introduced and a 16-tupling optical millimeter wave was generated based on the new full-duplex RoF system.Compared with the techniques proposed in other research projects,this paper greatly reduces the requirements of the central station for high-frequency RF local oscillators and achieves full-duplex transmission through wavelength multiplexing,which reduces the system cost.The simulation of the full-duplex millimeter-wave RoF system verifies the feasibility and effectiveness of the system.In the downlink,the maximum transmission distance is25 km,and the eye Q factor is 10.27747.Compared with the full-duplex 16-tupling system proposed by other literatures,the Q factor increases by 3.45;in addition,the uplink transmission distance is reached to 140 km,the transmission distance has also increased by 80 km.