Research On Fourier Domain Mode-Locked Optoelectronic Oscillator

Linearly chirped microwave waveforms(LCMW)with large time bandwidth product are widely used in radar and wireless communication systems.In radar system,pulse compression can be performed by LCMW signal to improve the range resolution of the system.Therefore,how to generate low phase noise LCMW signal has become a research hotspot.A number of studies have investigated the optical method to generate large bandwidth LCMW signals with low phase noise.The Optoelectronic oscillator(OEO)is a photonic method to generate LCMW signals to overcome electronic bottlenecks and bandwidth limitations.It uses a long distance and low loss delay line,usually a long optical fiber,to generate microwave signals with low phase noise,which is not only convenient but also highly effective.However,due to the existence of long optical fiber,each mode needs a certain amount of time to build up from the noise by using the traditional OEO.So,for the traditional frequency adjustable OEO,its frequency scanning speed is relatively low.Therefore,in order to generate microwave signals with fast and adjustable frequency,Fourier domain mode locking(FDML)was used in this thesis.A fast scanning Microwave photonic filter(MPF)was generated by Stimulated Brillouin SBS and Phase-shifted Fiber Bragg Grating(PS-FBG)to generate the LCMW signal.This thesis introduces the current research situation of OEO,describes the current research situation of OEO at home and abroad and Fourier mode-locked OEO,and focuses on a variety of different structures of OEO,as well as how to effectively suppress the vibration of the side mode.Fourier mode-locked OEO with different structures is introduced,and some shortcomings of them are analyzed.Then,according to the characteristics of OEO,the key device in OEO,modulator,is introduced,and its working principle and characteristics are described.At the same time,the basic model of OEO is described,and the oscillating power of OEO and the threshold condition of starting vibration are explained.Combined with the theoretical basis,this thesis proposes the Fourier Domain modelocked OEO based on stimulated Brillouin scattering and the Fourier Domain modelocked OEO based on phase-shifted Bragg grating.The frequency shift of Brillouin scattering and the reflection spectrum of Bragg grating are described theoretically.The Brillouin frequency shift,the position of Bragg reflection spectrum and the 3-d B bandwidth of the reflection spectrum are measured by experiments.The filtering response and single frequency oscillation of LCMW are studied.The center frequency adjustability,bandwidth adjustability,time-bandwidth product and chirp rate of LCMW signal are studied when working in Fourier domain mode-locked state.The bandwidth of LCMW signal generated by SBS scheme is adjusted from 1 GHz to 4 GHz,and the central frequency is up to ten GHz,the time bandwidth product is up to 81200,and the chirp rate is up to 0.392 GHz /?s.The LCMW signal generated by PS-FBG scheme is adjusted from0.5 GHz to 2 GHz,the center frequency can also reach more than ten GHz,the time bandwidth product is up to 41400,and the chirp rate is up to 0.097 GHz/?s.