Research And Optimization Of Microwave Photonic Filters Based On Fiber Bragg Grating Structure

With the development of microwave technology and informationtechnology, people have higher demand on the communicationcapacity and transmission rate. Microwave communication can belaunched in any direction and easy to be built and reconstructed. Butthe traditional transmission media in the microwave transmission systemwill induce great losses after long distance transmission. The emergenceof wavelength division multiplexing technology and the invention oferbium-doped fiber amplifier make rapid development of opticalcommunication. Optical fiber communication has the advantagessuch as very low loss, ultra-bandwidth and ease to be multiplexed onwavelength, space and polarization et al. All the advantages that listabove have obvious advantage for microwave signal transmission andprocessing. Under this application background, radio over fiber (ROF)technology has been put forward which is the combination of opticalfiber technology and microwave technology. Optical fiber technologyand microwave technology have been integrated together to formmicrowave photonics, an interdisciplinary. Microwave photonic filter(MPF) is one of the most important research subjects of the ROF system.Microwave photonic filter can process microwave signals directly inthe optical domain.It can overcome the electronic bottleneck caused by the limitedsampling frequency. It’s immunity to electromagnetic interference andno need of complex OE/EO conversion device. Currently theinternational researchers have a lot of interest in the design of the newfilter with better performance. This includes a higher Q factor of thefrequency response, negative coefficients, tenability, reconfigurabilityand larger dynamic range et al. FBG has very good performance of thewavelength selection and filter characteristics. Besides, it can construct microwave photonic filter with different functions and the fabricationtechniques for FBGs with various profiles are quite mature and manydevices are commercial available. Q factor is one of the mostimportant parameters of the frequency characteristics of microwavephotonic filter. In this thesis we focus on the studies of improving Qfactor for FBG based structures.In this paper we study, design and optimize the structures of FBGbased microwave photonic filters. The main work and contributions areas follows:1. We study the major components used in the microwavephotonic filter structures, especially the Gauss apodized linear chirpedfiber gratings and Erbium-doped fiber amplifier. We use MATLAB tosimulate and analyze them in detail.2. Proposal of an improved FBG pair based microwave photonicfilter structure and make further improvement in the Q factor. We usethe Optisystem software to simulate the structure. After optimization, thevalue of the highest quality factor can reach342.545. And this improvesthe performance of the filter for frequency selection.3. Adaptive genetic algorithm with disturbance operation is usedin designing FBG array based microwave photonic filter. We make auseful attempt in optimization for the parameters including the numberof FBGs and the reflection coefficients of the fiber Bragg grating array.We employ MATLAB to achieve genetic algorithm and simulateamplitude frequency response and phase frequency response of theMPF. After fixing the number of the FBGs we optimize the tapcoefficients of the FBGs. Disturbance operations are used in thealgorithm and the simulation time is reduced by half comparing withthat using the traditional genetic algorithm without disturbance. Thesimulation time is reduced from23.5088seconds to10.7841seconds.The influences of two crucial parameters, the number of the FBGs and the range of the tap coefficients of the FBGs, are detailed studied in thisthesis. Finally, it is concluded that when the range of the tapcoefficients of the FBGs () becomes smaller, the amplitude frequencyresponse of the MPF will deteriorate. And when we use the disturbancegenetic algorithm to design a FBG array based MPF, the reasonablerange of the number of FBGs should be not larger than7.