Study On Source-Free Basestation RoF System Based On Polarization Multiplexing And Link Transimission

Driven by the requirements of high speed and large capacity of wirelesscommunication, the Radio-over-Fiber (RoF) technology emerged, it is a noveltransmission technology which integrates the advantages of both optical communicationand wireless access technology. The RoF technology will play an important role in thewireless cellular access systems and radio frequency optical transmission systems in thefuture. This thesis mainly studied the low-cost and full-duplex60GHz RoF accesssystem of which the base station is source-free, the broadband radio frequency signaloptical transmission link based on RoF technology is also discussed in detail.First, the research background and significance are presented, the research situationand development trends of RoF technology as well as the key components andtechnology are also summarized. The basic theory and technology principle of RoFtechnology are elaborated in detail, which laid the foundation for further research in thisthesis.Second, a full-duplex60GHz RoF system with novel source-free base stationstructure based on polarization multiplexing is proposed. Compared with traditionalRoF system, optical LO source and intermediate frequency data signal are transmitted intwo orthogonal polarization, respectively. Because the optical LO source is transmittedwith down link signal, mm-wave LO which used for up/down conversions can beobtained by optical methods at base station. At the same time, the optical LO sourceprovide reused optical carrier for uplink base-band data signal. Therefore, there are nooptical or electric sources in each base station which results in significant cost reductionof the system.At last, the optical fiber transmission link based on RoF technology is studied,including the large dynamic range, the high linearity and small harmonic interference.The experimental results show that the direct modulation transmission has the problemof small transmission bandwidth and low frequency. So a scheme base on externalmodulation is designed, it increases the transmission frequency to18GHz with largedynamic range and high linearity. In addition, the influence factors of radio frequency over fiber is studied by experiment, the emphasis is placed on the bias voltage ofmodulator and the input power of signal, both of them can affect the performance of theoptical transmission system.