Research On Radio Over Fiber System With Optisystem

During the past years, radio-over- fiber technology has developed fast which has got widely attention and research. Due to its low loss and huge capacity, radio-over- fiber technology has been used all over the world. In the center station, baseband signals are loaded on the optical carrier and transmitted to the base station through the optical fiber. The optical signals are conversed into electrical signals via photoelectric converter after reaching the base station. Then transmitting antenna sends them to end users. Radio-over- fiber technology has been one of the most promising solutions that can solve the problem of last kilometer in the future. The article will study radio-over-fiber technology as follows:First, this dissertation introduces the basic principle of the direct modulaton and external modulation simply. External modulation can get a higher rate of transmission. Then the three kinds of external modulation are carried on the analysis and simulation in detail. The input signal is divided into two signals and transmitted into two light branchs of Mach-Zehnder Modulator. To control the input offset voltage and phase can choose one of the three kinds of external modulation. Then this paper studies the minimum error rate of DSB, SSB and OCS in different distances of optical fibers.Then, the dissertation introduces the photoelectric diode coherence properties. The optical heterodyne method is used to produce millimeter wave. Compared with direct modulation/direct demodulation, optical heterodyne method has many advantages through the analysis and simulation. The signal frequency of optical heterodyne method is very high, and can reach 60 GHz which can be got in the receiving end.Optical heterodyne balanced detection technique is introduced. Compared with the direct detection, optical heterodyne balanced detection can offer higher gain, lower noise and higher signal to noise ratio of the link.Wavelength division multiplexing technology can satisfy the current situation of the increase in the number of network users nowadays. The WDM technology combined with radio-over-fiber technology can yield both of the advantages of both. This paper briefly describes the basic principle of 8 port array waveguide grating, the analysis of the input and output through the simulation by using AWG during the WDM technology.Finally, this dissertation introduces WDM base on DPSK gigabit passive optical network. The signal is modulated by differentia phase keying sequence generator. CW laser array produces two optical signals whose frequency is 193.1THz and 193.2THz. Then, the two signals are transmitted through optical fiber. And the de- multiplexer separated the coupling of the two optical carriers. Last, research about SNR and received power in different transmission rates and distances is studied.