Research On Microwave Photonic Filter Based On Stimulated Brillouin Scattering

Broadband,tunable,and reconfigurable microwave filters are one of key components in radar,communication and measurement systems.Due to limited operating bandwidth,traditional microwave filters cannot meet the demand of flexible tuning and wide-band operation applications.The principle of microwave photonic filter is that the electrical signal is first modulated onto the optical wave.Then the signal is processed in the optical domain.Afterwards,the processed signal is converted back into the electrical domain to obtain the filtered electrical signal.Thereby the shortcomings of the conventional microwave filter can be overcome.In addition,MPF also has the advantages of low loss and immunity to electromagnetic interference,making it as one of the powerful alternatives to solve the traditional bottleneck of microwave filter technology.Stimulated Brillouin scattering is a nonlinear effect that occurs only in the axial direction of the fiber.Because of its excellent characteristics of narrow bandwidth,high gain,and low threshold,SBS is widely used in the implementation of new types of microwave photonic filters.In this thesis,the basic concepts and principles of microwave photonic filter system based on stimulated Brillouin scattering are studied.The bandpass and band stop filters based on stimulated Brillouin scattering are verified by experiments.Two types of the dual-passband microwave photonic filters based on stimulated Brillouin scattering are proposed and demonstrated.The main contents of the thesis are listed as follows:1.The research progress,basic concepts and structure of microwave photonic filter are introduced,especially the microwave photonic filter based on stimulated Brillouin scattering.On the basis of the experimental results of Brillouin frequency shift and Brillouin threshold,the bandpass and band stop filters based on stimulated Brillouin scattering are discussed and experimentally verified.In the experiment,the frequency tuning range of the two filter systems are two times of the Brillouin frequency shift,and the suppression ratio and the notch depth are both greater than 20 dB.2.A fixed frequency-difference dual-passband microwave photonic filter based on stimulated Brillouin scattering is proposed and validated.The experimental results show that the two fixed-frequency bands with 2.434 GHz interval can be continuously tuned in the frequency range of 0-9.644 GHz.The out-of-band rejection ratio is more than 20 dB,and the 3-dB bandwidth is less than 57 MHz.3.A free-tuning dual-band microwave photonic filter based on stimulated Brillouin scattering is proposed and verified.In the experiments,a highly selective and stable dual-passband MPF with flexible and shape-invariant tuning characteristics is realized.For MPF in loss mode or gain mode,the two passbands can be tuned freely in the frequency range of 0-9.644 GHz.The out-of-band rejection ratio of the filter is greater than 25 dB and the 3-dB bandwidth is less than 55 MHz.