| With the increasing demand for communication rate and bandwidth of communication system,the communication system turns its attention to millimeter wave.In order to solve the problem of long-distance transmission,Radio-over-Fiber(Ro F)technology has gradually become a research hotspot.Ro F technology combines the advantages of wireless communication and optical fiber communication.It not only has high bandwidth and low loss,but also has simple system structure and convenient equipment maintenance.Photonic millimeter-wave generation technology is an important technology in Ro F system,and the generation of high quality millimeter-wave signal without using any filters is the focus of research.This article mainly researches and analyzes the performance of filterless high frequency millimeter-wave signal generation and the full-duplex Ro F system.The research work is as follows:(1)The basic pinciples,applications and advantages of the Ro F system are introduced.We study four common millimeter-wave optical generation methods: direct intensity modulation,external modulation,frequency up-conversion and optical heterodyne.Next,the structural principle of the optical devices used in external modulation systems is analyzed,including Mach-Zehnder modulators(MZM),fiber gratings and photodetectors,and so on.Finally,the simulation implements three modulation modes: double-sideband modulation,single-sideband modulation and carrier-supressed double-sideband modulation.(2)Three kinds of multi-frequency millimeter-wave generator without using any filters are proposed.The filterless structure reduces the complexity of the system.First of all,the scheme based on the structure of three mutually parallel MZM modulators is proposed.Two modulators work at the maximum transmission point,and the other modulator is used to suppress the optical carrier.The system can generate 8-tupling frequency millimeter-wave signal.Secondly,based on the previous scheme,the structure of three parallel MZM modulators is cascaded with a single MZM,which can generate 16-tupling frequency millimeter-wave signal.In this scheme,the first-stage MZM works at the maximum transmission point,and the influence of its extinction ratio on the system can be ignored.The second-stage MZM works at the minimum transmission point.The performance of the system can be improved by properly adjusting the phase of the phase shifters and the bias value of the modulators.Thirdly,the scheme based on the polarization multiplexing technology and the cascaded structure of MZM is proposed.By controlling the bias voltage of modulators and the phase difference of the driving signal,and adjusting the angle deviation between the polarization controller and the polarization beam splitting / combining device,the scheme can generate 24-tupling frequency millimeter-wave signal.In this scheme,when the modulation depth,the modulator bias and the phase difference are within a certain offset range,the system can maintain the good performance.The narrow linewidth laser can improve the system performance.Three schemes can generate high quality millimeter-wave signals without using any filters,which reduce the cost of the system.But as the multiplication factor increases,the complexity of the system also increases.(3)A full-duplex Ro F system based on polarization multiplexing technology and modulator parallel structure is proposed.By controlling the modulator to work at the maximum transmission point and setting the angle difference between the analyzer and the polarization combiner,the system can obtain 8-tupling frequency millimeter-wave signal in the downlink.The system reuses the separated optical carrier signal in the uplink.Therefore,the scheme can save laser source and reduce the cost of base station.This solution does not use any optical / electrical filters to achieve reusing wavelength,which has a high frequency multiplication factor. |
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