Research On Optical Millimeter-wave Generation And Transmission For Radio-Over-Fiber System

ROF(Radio over Fib er) system combines the advantages of fiber-optic communication and wireless communication, and provides the ideal solution to solve the large-capacity(at Gbit /s level), high bandwidth and m obility and other issues for the users. Generation and transmission of optical millimeter wave are key techniques in the ROF system, so this article re volves around generation way of optical millimeter and link pe rformance analysis of ROF system, and the m ain contents include the following aspects.Firstly, this paper conducts a summary for the current domestic and international existing generation manners of ROF millimeter wave. The common wave generating principles, such as: direct m odulation technique, optical heterodyne technique, phase modulation technique, the use of n onlinear effects to produce millimeter wave, and external modulation technique are introduce d, also we discuss the advantages and disadvantages of these program s, and we propose the advantages of external modulation based on MZM.Secondly, we m ake a detailed theore tical study and corresponding simulation through Optisystem7.0 software about th e several common m illimeter-wave generation manners: double-sideband(DSB), double-sideband suppressed carrier(OCS), single sideband(SSB) and the modulation sidebands method.Thirdly, due to fiber dispersion, the tr aditional external modulation technique exists two typical: “cyclical decline effect” and “symbol narrowing effect”. To have a further study, we make a detailed theoreti cal analysis and simulation for those two typical dispersion effect.By Optisystem7.0 software, we first esta blish the three comm on system models of double sideband(DSB), single sideband(SSB), double-sideband suppressed carrier(OCS), and then we m ake theoretical study and corresponding simulation about the existing chromatic dispersion and system performance of these three system s. By Optisystem simulation, we obtain the sim ulation eye diagram of DSB, SSB and OCS light millimeter wave at different distances through optical fiber transmission, we find that eye qu ality gradually deterio rates, and “eyes” tend to close with increasing transmission distance, such phenom enon indicates that the fiber dispersion lim its the transmission distance of optical millimeter wave signal.Fourthly, for the two shortcom ings of the traditional external m odulation: “The cyclical decline effect” and “symbol narrowing effect”, this paper proposes a novel single sideband modulation scheme. Theoretical analysis and simulation results show that the technique not only ef fectively suppress the fiber dispersion on the transmission performance of ROF s ystem, and also improve the signal transm ission distance. The specific implementation process: First, the program theoretically how to overcome the fiber dispersion caused by th e “symbol narrowing ef fect”; then b y Optisystem simulation, we obtain simulation eye diagrams of optical millimeter-wave through different optical fiber transmission. In the new modulation scheme, when the transmission distance improves at 90 km, eye diagram quality is still very good, and when the transmission distance improves at 100 km, eye diagram quality has declined. Compared to traditional system s, the new single-sideband m odulation scheme proposed can well inhibit “cyc lical decline problem” and “symbol narrowing effect”. In terms of long-distance transm ission quality,this new scheme has very significant improvement.