Key Technologies Based On Two Parallel Optical Phase-modulated RoF System

Radio over fiber (RoF) has the benefits of optical fiber communication and wirelesscommunication. So it can simplify the base station，and accommodate the development tendencyof communication. It acts as important role infields of the indoor signal coverage, intelligent roadvehicle communication, broadband wireless access networks and military, and so on. With theevolution of the RoF system, RoF is a significant part in forward broadband wirelesscommunications.Since the optical phase modulator is applied to the RoF system，it can be avoided theproblem of bias voltage. Meanwhile, the optical phase modulator has the advantages of lowinsertion loss, and it produces a high-frequency millimeter-wave signal. Therefore, the RoFsystem.based on a dual parallel optical phase modulation is researched in this paper, and the maincontents are listed as follows:(1) The system architecture, the advantages and disadvantages, key techniques and mainapplications of the RoF systems are researched. Research status of the RoF system is summarized.Then, a conclusion of various methods to generate millimeter-wave is made. The main methodsinclude the direct modulation, the external modulation, and the optical heterodyne. They aredescribed and compared.(2) Based on a scheme of radio over fiber system, which can generate frequency-quadrupledmillimeter-wave, a RoF system based on optical phase modulator which can generated six-octavemillimeter-wave, is proposed and demonstrated. A dual parallel optical phase modulator is usedto achieve frequency tripling. With phase deviation adjusting, optical phase modulator generatesinhibition of first-order sidebands of the spectrum. After removing the optical carrier with anoptical subtractor, third-order sidebands are generated. The sidebands beat frequency in thephotoelectric detector. The simulation result shows that the60GHz optical millimeter-wave isgenerated by10GHz RF signal. The eye diagram result proves that the2.5Gbit/s baseband data issuccessfully transmitted at least20km by single-mode fiber.(3) Because OFDM technology can effectively overcome the dispersion, combined with RoFsystem based on a dual parallel optical phase modulation, an OFDM-RoF system is built andsimulated. In the center station, double sideband optical millimeter wave signal is generated by adual parallel optical phase modulator, which separates the upper and lower sidebands with lightinter leaver. The OFDM signal is modulated through a Mach-Zehnder modulator onto one of thetwo optical carriers and transported along optical fiber. The system of modulation anddemodulation of OFDM is builted by Matlab software and OFDM-RoF system is constructed byOptisystem software. The simulation result that the system not only produces a high-frequency millimeter-wave signal, but also can effectively overcome the impact of the dispersion afterchannel compensation. Then the system performance is improved.