Researches Of Radio-Over-Fiber System Based On Microwave Photonics Technologies Application

Radio-over-Fiber (ROF) system can provide high speed wireless access because it combines advantages of both optical fiber communications and wireless communications. Consequently it receives more and more attentions. In this dissertation, theoretical and experimental researches on the key technologies of Radio-over-Fiber system by using microwave photonic technologies have been made. The works in this dissertation include:1. Optical generation of Millimeter wave and Radio-over-fiber system for hybrid services access based on the Mach-Zhender Modulator (MZM). The nonlinearity of MZM was theoretically analyzed and a method of simultaneously generation both double-frequency microwave and sextuple-frequency millimeter wave base on a MZM and a comb filter was proposed and realized. In the experiment, the microwave signal with a frequency of 11.2GHz and the millimeter wave with a frequency of 34.8GHz were generated. Only a 5.8GHz microwave source and a MZM with a bandwidth of 10GHz were used. The optical and wireless transmissions of 1.25Gbit/s data on 34.8GHz millimeter wave were also demonstrated successfully. Based on this method and the polarization multiplexing technology we proposed a hybrid Radio-over-Fiber system which could provide multiple services including millimeter wave, microwave and fixed wire-line access services.2. Millimeter-wave phase modulation technology and full-duplex ROF system application based on the electrical-optical phase modulator (PM). A scheme of generating millimeter wave with PSK modulation based on the mono-direction operation of PM was proposed and realized. Two sidebands of the optically generated millimeter wave were separated by filter and then injected to PM with opposite directions. A phase difference which was modulated by the driving signal of PM will be generated between the clockwise (CW) and counter-clockwise (CCW) lights. Then after the photoelectric conversion the millimeter wave signal with PSK modulation could be generated. Based on above method, a full-duplex ROF system with a passive base station was proposed and realized by using a half-reflecting Fiber Brag Grating (FBG) and an intensity modulator with low insertion loss. In the experiment, 1.25Gbit/s downlink data on 32GHz millimeter wave with PSK modulation was transmitted in 20km single mode fiber (SMF) and the power penalty is 0.8dB. Uplink 1.25Gbit/s data was ASK modulation was transmitted in 20km SMF and the power penalty is 0.2dB.3. UWB pulse generation technology based on a nonlinear optical loop mirror (NOLM). The principle of optical switch based on NOLM was theoretically analyzed. An approach of generating UWB pulses based on NOLM was proposed and realized. The NOLM based optical switch was used to generate overlapped positive and negative Gaussian pulses at first. Then pulses with different wavelengths were properly delayed and separated by SMF. Finally UWB pulses with different shapes and different polarizations could be generated. The above method has the potential of realizing Pulse Shape Modulation (PSM) and Pulse Polarization Modulation (PPM). In addition, the SMF acting as a chromatic dispersion media in generating the UWB pulses can also be used to distribute UWB signals from the central station (CS) to remote access points (AP). Different distance between CS and remote APs has no effects on the generated UWB pulses by adopting a wavelength tunable laser as the probe in CS. In the experiment, the generated monocycle pulse has a central frequency of 5.2GHz, 10dB bandwidth of 8.7GHz and bandwidth fraction of 167%. The generated dublet pulse has a central frequency of 6.2GHz, 10dB bandwidth of 8.1 GHz and a bandwidth of 130%.