Study Of ROF Technology Based On Microwave Photonic Filter

Microwave photonic filter (MPF) is an important device in the field of Microwave Photonics. Due to its high bandwidth, anti-electromagnetic interference, conversion in electro-optical system without high speed signal, and it can overcome the electronic bottleneck, and so it has caused wide public concern. Therefore, this thesis is concentrated on the study of the structure and technical characteristic of the microwave photonic filter. In this thesis, the design and manufacture essentials of various systems are expounded, and the advantages and disadvantages of different kinds structures are proved by simulation results, and their respective applications are analyzed. The main works in this thesis are listed as follows:1. The formation and features of Microwave Photonics and Radio-Over-Fiber (ROF) systems are briefly introduced. The thesis also shown the research area of Microwave Photonics and the applications of ROF system, and the research reason of MPF is introduced.2. The principle of MPF is studied. The basic structure of MPF is analyzed. The usual devices used to design MPF—Fiber Bragg Grating (FBG) and modulators are researched. The figures of spectrum, dispersion and delay are obtained by simulating the FBG The spectrum relationship with key parameters which are length and chirped is analyzed, and the relationship of grating parameters with grating reflectivity and bandwidth is obtained. On this basis, microwave photonic filters are analyzed which based on FBG and modulators, the value of reflectivity is obtained while the filter on the maximum notch depth.3. The principle that using the positive tap obtain negative tap for designing MPF is introduced, then illustrate the design process. In this thesis, a novel MPF is proposed which based on cascaded modulators. The first modulator is used to change the single wavelength light source to multi-wavelength light source, which used to enhance the filter Q value. The structure is analyzed by simulation, the figure of frequency response is obtained while we just consider two sidebands and four sidebands, and from the figure we know the notch depth can achieve 50dB.4. The noise caused by laser and radio frequency signal(RF) oscillator in the ROF system are analyzed, and carrier to noise ratio is obtained by theoretic calculation. A microwave photonic filter based on FBG is applied in ROF system, which can filtered the noise of laser and RF oscillator in ROF system, the eye diagram show the effect of microwave photonic filter. The thesis also analyzed the improvement of MPF for radar system and optical communication system.