Optimization Design And Implementation Of Optoelectronic Oscillator Based On Microwave Photonic Filter

Optoelectronic oscillator(OEO)can generate microwave signals which have a high purity,high frequency stability and wide tunability.It has various applications in wireless communication and radar system.Traditional OEO uses an electronic filter to select frequency,but its frequency tunability is limited.Recently,OEO based on microwave photonic filter(MPF)has been proposed to increase the frequency tunable range.However,the OEO based on MPF has a relatively high phase noise.Meanwhile,the OEO has a serious mode hopping effect because of the long fiber.In this thesis,an OEO module based on MPF(MPF-OEO)is designed and fabricated.On this basis,the performance of the OEO is improved by optimizing the phase noise and eliminating the mode hopping effect.A method of balanced detection is used to reduce the noise of the optical link.Consequently,the phase noise of the generated signals is decreased,thus improving the noise performance of the OEO.A chirped fiber Bragg grating(CFBG)is used to increase the oscillating mode spacing and further eliminate the mode hopping effect of the OEO.This thesis gives detailed theoretical analyses and experimentally verifies the correctness and effectiveness of the two methods.The specific contents of this thesis are concluded as follows:(1)The basic theory of classical OEO and MPF-OEO is introduced first.Then the entire scheme of the MPF-OEO module and the layout of each device are described.Finally,the basic function of OEO is realized.(2)In order to improve the phase noise performance of the MPF-OEO which is previously described,a new structure of MPF-OEO based on balanced detection is proposed.From the theoretical analyses and experimental results,the method of balanced detection is proven to be effective for reducing the phase noise of the microwave signals generated by OEO.The influence of the polarization states and the frequencies of the generated microwave signals on the phase noise of the OEO are also analyzed.In addition,this thesis discusses the influence of the length difference between the two fibers fed to the two inputs of the balanced photodetector(BPD)on the whole OEO system.(3)The method of eliminating the mode hopping effect of the MPF-OEO by using the chirped fiber Bragg grating(CFBG)is proposed.The long fiber in the original structure of MPF-OEO is replaced by a CFBG,which can effectively suppress the mode hopping effect.By means of further cascading an infinite impulse response filter or using the method of balanced detection,the mode hopping effect of OEO can be fully eliminated.The phase noise performance of the microwave signals generated by OEO is also discussed.In addition,the influence of the third order dispersion of CFBG on the whole OEO system is analyzed.