Research On Active Mode-locking Optoelectronic Oscillator

Optoelectronic oscillator(OEO)is a non-linear,dissipative and closed microwave photon system,composed of long distance optical branches and electrical branches.Optoelectronic oscillator has very low phase noise and does not deteriorate with the increase of frequency,which makes it promising to replace microwave oscillator.The research of single frequency optoelectronic oscillator has made great progress in performance optimization,system integration and system application,etc,but the research of Multifrequency optoelectronic oscillator is relatively lacking,unable to directly generate stable low-phase noise multifrequency microwave signals.This paper studies and proposes an active mode-locking optoelectronic oscillator,which can directly generate low-phase noise microwave frequency comb signal(periodic microwave pulse signal in time domain),and is expected to be applied in pulse radar and multi carrier communication.Based on optoelectronic oscillation principle and active mode-locking technology,a new type of optoelectronic oscillator structure is proposed-Active mode-locking optoelectronic oscillator,and carry out theoretical modeling,system simulation and experimental verification.The main innovations and academic contributions of the paper are as follows:1.For the first time,a new type of optoelectronic oscillator structure is proposed-Active mode-locking optoelectronic oscillator,by adding an active mode locking module to the traditional optoelectronic oscillator loop,the frequency of the active mode locking signal is controlled to be equal to an integral multiple of the fundamental frequency of the optoelectronic oscillator loop,so that the multi longitudinal modes can establish a fixed phase relationship and excite multi-mode oscillation,which overcomes the problem of modes competition in the traditional optoelectronic oscillator,and generates a microwave frequency comb signal with low phase noise(periodic microwave pulse signal in time domain).2.The working principle of active mode-locking optoelectronic oscillator is described,and the evolution process of signal in active mode-locking optoelectronic oscillation cavity is analyzed from the perspective of time and frequency domain.Based on the traditional optoelectronic oscillator model,the theoretical model of active mode-locking optoelectronic oscillator is established,and the small signal gain formula and the complex amplitude representation of oscillation signal are obtained;Based on the theoretical model,the performance of fundamental frequency mode-locking and harmonic mode-locking optoelectronic oscillation is simulated,the spectrum,waveform,phase noise of the mode-locking signal are output,and the simulation results are analyzes.3.Experiments verify the feasibility of active mode-locking optoelectronic oscillator,and test the system performance under fundamental frequency mode-locking and harmonic mode-locking state.According to the needs of different application scenarios,narrowband active mode-locking optoelectronic oscillator and broadband active mode-locking optoelectronic oscillator are constructed to generate high-quality microwave pulses and broadband microwave frequency combs.The key performances of active mode-locking optoelectronic oscillator are deeply studied,such as mode locking frequency range,pulse width,phase noise,signal stability and so on.Then,we analyze the factors affecting these key performances and propose a corresponding improvement method.