| RoF (radio over fiber) technique, which uses fiber-optic links to transmit and distribute radio signals, combines the advantages of mobile, point-to-multi-points access technology provided by ultra wideband wireless communication network and high-bandwidth, highly reliable connection provided by optical networks. It will play a very important role in future wideband wireless communications. Based on the considerations, we have investigated the optical generation and distribution of millimeter-wave (mm-wave) signal, simplified base station design based on wavelength reuse technique and full-duplex communication in RoF systems, specifically including:Firstly, a novel RoF system employing a single-electric Mach-Zehnder modulator (MZM) and optical Mach-Zehnder Interferometer (MZI) interleaver to generate optical mm-wave is proposed and experimentally demonstrated. The transmission performance of optical mm-wave over dispersion fiber has been investigated, and the un-match problem of frequency between modulation signal and free spectrum range (FSR) of optical MZI interleaver is also discussed. On the basis of the theory for optical mm-wave generation, the 2.5Gbit/s baseband data carried by 40GHz optical mm-wave is successfully transmitted over 40km standard single mode fiber (SMF). Secondly, a new exact analytical model is presented to analyze the dispersive transmission in mm-wave fiber-optic links using an optical phase modulator and optical filtering. A compact and closed-form expression of all-order generated harmonics at the output of the mm-wave fiber-optic link is derived. The effect of three parameters such as modulation index, dispersion distance and optical carrier suppression ratio is also discussed. It can be induced that, under the condition of small signal modulation and high carrier suppression ratio, the generated second-order harmonic can be overcome the fiber dispersion. According to this analysis, the 40GHz optical mm-wave is experimentaly generated by an optical phase modulator driven by a 20GHz RF signal. The power penalty of the 40-GHz RF signals carrying the 2.5 Gbit/s baseband signal through transmission over a 60-km SMF is only 2 dB.Thirdly, we have theoretically investigated the transmission performance of the baseband signal, which carried by optical millimeter-wave generated from an optical phase modulator, with the double sidebands (DSB) and optical carrier suppression (OCS) schemes. According to our theoretical analysis, fiber chromatic dispersion leads to fading effect and time shifting of the codes; therefore, signals are greatly degraded. The detail change description of baseband data signal carried by DC, first-order harmonic and second-order harmonic is illuminated. Furthermore, we have proposed a novel system configuration to overcome the dispersion affection and thus extend the transmission distance, in which only one sideband is used to modulated baseband data signal. Experimental and simulated results confirm the feasibility of the proposed system.Fourthly, by using wavelength reuse technique, we have proposed and experimental demonstrated two novel full-duplex RoF communication schemes. In these two schemes, the directional 2.5Gbit/s data signals are successfully transmitted over 40km SMF.In the first scheme, only one of the first-order optical sidebands of the OCS optical mm-wave is used to carry downlink data, while the other first-order sideband is reused for uplink optical carrier. In the second scheme, an optical interleaver is used to separate the spectrum of the otpical DSB signals generated by a single-electric MZM. The separated first-order optical sidebands are used to generate optical millimeter-wave with double RF frequency, while the separated optical carrier is reused for uplink connection.Fifthly, based on the direct modulation laser (DML), we have proposed and experimentally demonstrated two RoF systems. In the fisrt sytem, a DML along with an optical external modulator is used to generate OCS mm-wave signal. The ablility to overcome fiber dispersion of OCS singal and low cost configuration of DML are utilized in this system. In the second system, the optical DSB signal is generated by using only one inexpensive broadband DML, to which a mixing RF signal is applied. An optical interleaver is then used to separate the first-order optical sidebands from the optical carrier of optical DSB signal. The separated first-order optical sidebands are beat to generate mm-wave signal that has double the frequency of the RF drive signal, while the separated optical carrier is reused as light source to remodulate uplink signal. By this system, all power of optical mm-wave signals is fully utilized, and the configuration is furtherly simplified.
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