Research On Generation Technology Of Low Phase Noise Microwave Signal Based On Sigma Cavity

Coupled optoelectronic oscillators can generate microwave signals with high frequency and low phase noise,which have extremely wide application in many fields,such as communication systems,aerospace and radar.This dissertation mainly focuses on the polarization sensitivity and supermode competition in coupled optoelectronic oscillators,and researches on technology of anti-polarization disturbance and supermode suppression.The main research work of the thesis is as follows:The influence factors of phase noise in coupled optoelectronic oscillators are studied and analyzed.Firstly,the system construction and parameter design of the coupled optoelectronic oscillator are carried out to achieve the generation of 10-GHz microwave signal.Secondly,the influence factors of phase noise are analyzed based on experiments.The polarization disturbance leads to power fluctuation in the fiber ring cavity,and affects the polarization stabilization of the coupled optoelectronic oscillator.The supermode competition leads to the mode jump and supermode spurious.The phase noise can be reduced by increasing the fiber length and decreasing the dispersion level in the cavity.In this dissertation,an anti-polarization disturbance technology based on sigma-shaped cavity and a supermode suppression technology based on self-gain modulation of SOA are proposed,and a coupled optoelectronic oscillator system with stable polarization and high supermode suppression ratio is realized.Firstly,the polarization disturbance in the oscillation loop is eliminated by sigma-shaped fiber ring cavity to realize the polarization-insensitive coupled optoelectronic oscillator.Secondly,the self-gain modulation effect of SOA is used to suppress supermode spurious in the coupled optoelectronic oscillator.Finally,a 10-GHz microwave signal with a high supermode suppression ratio(95.51 dB)and a low phase noise level(-134.05 dBc/Hz@10 kHz)is realized after designing the gain of SOA.