The Research Of Optical Millimeter-wave Transmission Characteristic Based On External Modulation

According to the shannon’s law, it can provide greater storage capacity and communication bandwidth by improving the wireless signal carrier frequency. To meet the demand for high-speed wireless communication in future, Researchers focus in the high frequency of millimeter wave band. Radio over fiber technology not only effectively solves the problem of resources shortage in low frequency spectrum,it also bring up the wireless communication higher bandwidth and larger capacity. At present, the development of ROF technology is confronted by two major problems. On the one hand, the generation and the modulation of high frequency millimeter wave require high demands of device bandwidth. On the another hand, with the increasing carrier frequency, optical millimeter signal is vulnerable to the serious effect of fiber dispersion, limiting the fiber transmission distance. To solve two problems, this thesis uses the optical frequency multiplication technology and the improved single external modulation to study the transmission performance of ROF system, and use the Optisystem of optical communication software for simulation.Firstly, transmission performance of millimeter wave band(40 GHz,60 GHz, 100 GHz) in ROF system were studied. Using the traditionalexternal modulation, it compared the transmission performance of 40 GHz,60GHz and 100 GHz millimeter-wave with quadruplicated frequency multiplication and octupled frequency multiplication. It analyzes the transmission performance of the system. Loading the 5Gb/s data rate of OOK signal, the transmission distance of millimeter wave which generates by quadruplicated frequency multiplication technology,is the double of octupled frequency multiplication technology. Thus, the performance of quadruplicated frequency multiplication technology is better. Loading the 2.5Gb/s data rate of OOK signal, the transmission performance of two kinds of millimeter wave frequency multiplication technology system is roughly the same. Because octupled frequency technology can take advantage of lower RF signal of millimeter wave and has lower power consumption, so octupled frequency technology can reduce the system cost.Secondly, the article studied an improved external modulation technique. Using the principle of frequency doubling to produce two optical sidebands which frequency space is 40 GHz, 60 GHz and 100 GHz,only one optical sideband is used to carry the data.To arrive at the base station through the optical fiber transmission,the millimeter wave with high purity power spectrum can be obtained, restrained the influence of optical fiber dispersion on system transmission performance. The simulation results show that the system transmission distance of theimproved external modulation technique is twice as long as the traditional external modulation, and it has lower power consumption. Therefore, the improved external modulation technique is well suppressed the influence of fiber dispersion,then it has better system transmission performance.Establish the QPSK-ROF system,using the improved external 60 GHZ millimeter wave modulation technology and loading the QPSK modulation signal,the simulation results show constellation diagram has good convergence after 100 km by optical fiber transmission and the bit error rate is under910-. It indicates that the improved external modulation technology can still maintain good system transmission performance by loading QPSK modulation signal transmission.