Research On High Frequency Optical Millimeter Wave Generation Technology In Radio-over-Fiber System

With the rapid development of mobile communication technology,the requirement of broadband capacity and quality of wireless communication system is increasing.According to Shannon's law of information theory,high frequency optical millimeter wave can provide larger bandwidth capacity.Therefore,people focus on the high-frequency millimeter wave band.However,the high-frequency millimeter wave has suffered a serious transmission loss in the atmosphere,and it can not be transmitted over long distances.Radio over Fiber?ROF?technology effectively solves the above problems and has been considered as one of the ideal schemes for future broadband wireless access.ROF technology is a promising new technology which organically combines wireless communication and optical fiber communication.It has been developed vigorously in the field of communication.Among them,the generation of optical millimeter-wave is a key technology in ROF system.In this paper,we mainly use optical frequency doubling technology and external modulation technology to study the generation of high frequency optical millimeter wave in theory and simulation.The main research results as follows:Firstly,a scheme of generating octuple frequency optical millimeter wave by using two parallel phase modulators?PMs?is theoretically proposed and investigated by simulation.By adjusting the phase shift constants of the upper and lower phase modulators,the second order sideband of the output lightwaves is suppressed.Then the central carrier and fourth order sidebands are left by adding up the couple of the upper and lower lightwaves.After filtering the central carrier,the fourth order sidebands are left.The octuple frequency millimeter wave signal is obtained by beating frequency of the two fourth order sidebands in the photoelectric detector.The simulation results show that the 60GHz optical millimeter wave with 2.5 Gb/s NRZ signal can transmit 100km single mode optical fiber It is proved that the ROF system has good transmission performance.Secondly,a scheme of generating 18-tuple frequency optical millimeter wave by using a LiNbO₃ Mach-Zehnder modulator?LN-MZM?and four-wave mixing?FWM?effect in semiconductor optical amplifier?SOA?is theoretically proposed and simulated.By adjusting the DC bias voltage and modulation depth of LN-MZM and the phase difference between RF signals,the central carrier,first order sidebands and second order sidebands are suppressed.Two third order sidebands are filtered out by filters and then they are injected into the SOA for FWM.The 18-tuple frequency millimeter wave signal is obtained by beating frequency of the two ninth order sidebands in the photoelectric detector.The scheme also studies the influence of the injection current of SOA on the sideband ratio?SR?and the performance of the ROF system.As the system performance is optimal,the SOA current is 0.37A and the SR is 3.41 dB.Thirdly,a scheme of 18-tuple frequency optical millimeter wave generation by utilizing a LN-MZM and FWM effect in high nonlinear fiber?HNLF?is theoretically proposed.Two third order sidebands that obtained after LN-MZM are amplified and then input into HNLF.The two ninth order sidebands are gained after FWM and filtering.The18-tuple frequency millimeter wave signal is obtained by beating frequency in the photoelectric detector.The simulation also studies the effects of the input power and length of HNLF on the performance of the ROF system.When the input power of HNLF is 19.4 dBm and the length of HNLF is 1.8 km,the system has the best performance.