Research Of Multi-shape Microwave Photonic Generator Based On Mach-Zehnder Modulator

Microwave Photonics is an inter-disciplinary field of study which combines microwave engineering and photonic technology together. It is considered as a new technology which is widely applied in both military and civilian areas, such as remote broadband communication, satellite communications, sensor networks, micro/millimeter-wave imaging and radar system. As a key component in the field of microwave photonics, microwave photonic generator technology has broad application prospects in the future broadband mobile communication systems. Under the supports of the National Nature Science Foundation of China, this thesis is devoted to investigate temporal multi-shape microwave of microwave photonic generator by theory and simulation analysis. The main innovative research efforts are summarized as follows:1. The structure, basic operating principle and features of Mach-Zehnder modulator (MZM) have been analyzed. Theoretical analysis of optical carrier suppression modulation principle based on MZM has been verified. An implementation scheme of generating periodic triangular microwave based on MZM combined with fiber dispersion has also been introduced. The influence of fiber dispersion on periodic triangular microwave photonic generator has been theoretical analyzed, and the feasibility of generating periodic triangular microwave combining MZM and fiber dispersion has been verified by simulation.2. The scheme of periodic triangular microwave photonic generator has been proposed. In the proposal, optical carrier suppression modulation and fiber grating dispersion characteristic are employed, making the expression of output optical intensity approximately equals to the Fourier expansion of ideal triangular-shaped pulses. In the optimizing design, using fiber grating instead of normal dispersion fiber (NDF) to introduce dispersion effects, a periodic triangular microwave signal could be preferably generated by selecting appropriate modulation depth, length, chirp coefficient and apodization function of chirped fiber Bragg grating. The simulation analysis results are:a lager length, a smaller modulation depth, more appropriate apodization function chosen is the key to get a better linear stable triangle shape microwave signal. In addition, the modulation depth of fiber grating affects the linearity and stability for the final temporal waveform of the triangular microwave greatly.3. A novel scheme of microwave photonic generator based on optical carrier suppression modulation and phase modulation has been proposed. In the proposal, using the modulation index of MZM and phase modulator to control the amplitude and phase ratio of harmonics in optical intensity separately makes the expression of output microwave approximately equals to the Fourier expansion of ideal triangular, rectangular, and sawtooth pulses. The simulation results show that it is feasible to use the first three harmonics to synthesize microwave with different shapes. However, rectangle and sawtooth with respect to triangular wave need more frequency components to achieve smooth linear temporal characteristics. The prototype utilizing two variables to control the amplitude and phase of the harmonics makes it possible for generating multi-shape microwaves with tunable repetition rates, which improves the usability of the system.