Microwave Photonic Vector Modulation Technology For Radio-over-Fiber Applications

Because of the severe attenuation of millimeter wave signal when transmitted by air, some kind of modulation format, such as ASK, PSK. QAM and so on, must be employed in order to ensure the quality of transmission, realize the frequency utilization so as to increase the capacity and distance of the transmission system. The electrical circuits at radio frequency band are quite expensive and somewhat not reliable. As a result, the microwave photonic vector modulation technology becomes more and more popular. The usage of microwave photonic vector modulation (PVM) technology in Radio-over-Fiber (RoF) system can lead to many advantages, for example, realizing the frequency utilization, overcoming the electrical bottle-neck effect and the limitation of storage, so it is no doubt that this technique would have a great development in future. This thesis is mainly about the research on the microwave photonic vector modulation technology for Radio-over-Fiber applications, and has the following two main parts:(1) The microwave PVM technology for multi-level ASK and QAM signal generation based on Mach-Zehnder modulator (MZM)Firstly, a theoretical model of MZM was proposed, and then came with the theoretical analysis and experiments of several microwave PVM architectures for 4ASK, 16QAM, 16ASK, asymmetry 15QAM and other multi-level QAM/ASK signals generation. In the experiments, by employing several MZMs, lasers and other optical devices, 4ASK and 16QAM signals with 25GHz carrier and 1.8GBaud symbol rate were generated successfully through optical approaches. In the numerical simulation, the analysis of the generation of 16ASK signal with 40GHz carrier employing microwave PVM technology was proposed.(2) The microwave PVM technology for DPASK and Star QAM signal generation based on Electro-optical phase modulator (EOPM)Based on the of EOPM whose modulation characteristic is sensitive to the velocity of the input light, two architectures for DPASK and Star QAM signal generation were proposed. In the experiments, firstly a 12.5GHz clock from the local oscillator was modulated on the 1539.9nm optical carrier via a MZM with 20GHz bandwidth at its double-sideband carrier-suppression (DSB-CS) mode. Then, the upper and lower sidebands are separated by an optical interleaver with 25/50GHz channel spacing and injected into the EOPM with opposite directions. For the reason that EOPM is a velocity-matched device, there was a phase difference which was proportional to the applied 2Gbits/s phase signal between the upper and lower sidebands. After a MZM with 10GHz bandwidth which was employed to modulate the 2Gbits/s amplitude signal, at the receiver side, DPASK signal with 25GHz carrier was finally generated. By simply adding the amplitude information in proper proportion to the phase signal to form the driven signal of EOPM, the star QAM signal can also be generated.