Microwave Photonic Filters And Their Applications In Microwave Signal Generation And Radio-over-Fiber Systems

Nowadays, microwave photonics has attracted great interests from both the research community and commercial sector all over the world. The technology takes the advantages of photonic technologies to provide functions in microwave systems that are very complex or even impossible to carry out directly in the radiofrequency (RF) domain, such as microwave signal transmission and processing etc. It is also succeeding in incorporating a variety of techniques used in microwave engineering to improve the performance of broadband wireless access networks and systems. The main topic of this thesis is microwave photonic filters and their applications in microwave signal generation and radio-over-fiber (RoF) system. Theoretical analyze and experimental results are both carried out.First,a brief overview is given about the basic concepts and historical developments behind microwave photonics, describing its advantages campared to traditional microwave engineering and its main technologies and field of applications. The basic concepts and historical developments behind microwave photonics filters (MPFs) are also introduced.Then, we describe the basic theory of single-source microwave photonic filters (SSMPFs) and multiple-source microwave photonic filters (MSMPFs). A few design examples are presented based on these two kinds of MPFs. Both the theoretical analysis and the experimental results are given. The main works are listed below: an optical variable delay line and an Erbium-doped optical Fiber Amplifer (EDFA) are introduced into the fiber ring structure to form a microwave photonic filter with tunable free spectrum range (FSR) and controllable output power; a microwave photonic notch filter with wide tunability and large FSR is presented based on a fiber Sagnac-loop structure which comprises an off-centre electroabsorption modulator (EAM); a filter with switchable passbands based on a single-wavelength optical source and phase-intensity hybrid modulation scheme is presented; a tunable and reconfigurable microwave photonic filter based on a tunable Mach-Zehnder interformeter (MZI) and a wavelength-controllable Raman fiber laser is also presented in this part. The FSR and the spectral response of the microwave photonic filter are tuned and reconfigured by controlling the optical variable delay line in one arm of the MZI and the powers of the pump LDs; a tunable all-optical microwave notch filter with a negative tap based on the cross gain modulation in the semiconductor optical amplifie is proposed and demonstrated; a microwave photonic filter based on Mach-Zehnder modulator and phase modulator with negative coefficients is also proposed and demonstrated, the FSR and the spectral response of the microwave photonic filter are tuned and reconfigured by controlling the microwave signal and the bias voltage applied on the MZM.After that, we describe some technologies used in optical generation of microwave signals and make comparison beween them. In this part, an optical generation of microwave signals method based on single resonance MPF and a microwave-photonic frequency doubling method based on the phase modulator and fiber Bragg grating have been proposed.Then, the basic theory and the architecture of RoF system are introduced. Two key problems in RoF system are analyzed, which are subcarrier demultiplexing and frequency conversion. A few design examples based on MPFs are proposed to solve these problems. Detailed characteristics of these examples are experimentally studied and the corresponding principles are explained.In the last part, we conclude the thesis and make several suggestions for the future work.