Research On Technique Of Millimeter-wave Generation With High And Tunable Frequency Multiplication Factor Based On OCS

With the popularity of Internet services,such as the mobile Internet and the Internet of Things,the capacity and speed demands for communication systems are increasing.The next-generation communication network is evolving towards the trends of large bandwidth,low latency,high reliability and massive connectivity.Radio over fiber(RoF)communication system combines the advantages of optical fiber communication and wireless communication effectively.Thus,it is becoming one of the key technologies in the future communication areas.RoF system has the advantages of large capacity,low loss,and high network flexibility.This research is devoted to investigating the generation of millimeter-wave signal in RoF system,by theory and simulation.The main works are as follows:(1)The advantages and disadvantages of several common methods for millimeter-wave signal generation in RoF systems are compared.Among them,the external modulation method can generate the required millimeter-wave signals simply and efficiently,with high reliability and low cost.Three analog modulations,including ODSB(Optical Double-Sideband)modulation,OSSB(Optical Single-Sideband)modulation and OCS(Optical Carrier-Supressed)modulation,are further analyzed.Moreover,the influence of fiber dispersion is studied.(2)The anti-dispersion abilities of four kinds of transmission pulses in conventional OCS-RoF system are studied respectively,including Return-to-Zero(RZ)code,None-Return-to-Zero(NRZ)code,sine wave and triangle wave.It is concluded that the NRZ pulse is the best transmission pulse.To solve the problem of time shift of code edges caused by the fiber chromatic dispersion,an improved scheme which only modulates data on the upper sideband of OCS signal is proposed.The time shift of code edges is avoided effectively.It is also founded that the NRZ pulse is still the most suitable pulse for signal transmission in the improved system.(3)Based on the improved OCS modulation,a scheme of generating millimeter-wave signal with high and tunable frequency multiplication factor(FMF)is proposed and verified.Tunable FMFs can be obtained by using a uniform fiber Bragg grating based on acousto-optic tunable filter(UFBG-AOTF).The NRZ code is used for the signal transmission in the scheme.In the case of the modulation index of 2.5?,six kinds of FMFs can be tuned and the best FMF can reach to 22.Under the condition of the FMF of 22,the fiber distance of 50km and the data rate of 2Gbit/s,the system performance simulation results show that the eye diagram opens widely,and the power penalty is only 0.4dB.Compared with ODSB modulation,the proposed scheme can avoid the problem of power periodic attenuation caused by fiber chromatic dispersion effectively.And,with the same modulation index,the proposed scheme can generate millimeter-wave signals with much higher FMFs than that of OSSB modulation.