Research On Nonlinear Effect And Generation Of Optical Frequency Comb Based On Microring Resonator

The optical frequency comb has achieved precise measurement of optical frequencies because of the characteristic of equal frequency spacing.Early optical frequency comb is generated by mode-locked lasers.However,the repetition frequency is limited by the length of the cavity,which is difficult to exceed 10 GHz.What’s more,the entire system is huge and expensive,making it inconvenient for industrial use.In recent years,Kerr optical frequency comb is generated based on Kerr nonlinear effects in a microresonator.With the advantages of high repetition rate(GHz-THz),low power consumption(hundreds of m W),high coherence,small volume,and integration,it shows great potential in range measurement,atomic clock,photonic radar,wavelength division multiplexing and other systems.In this dissertation,the theoretical and experimental research on the on-chip optical frequency comb is carried out based on the silicon nitride microring resonator.The main studies and innovations of this dissertation are summarized below:1.Microring resonators with different free spectral ranges(～100 GHz-～300 GHz)are designed and fabricated.The dispersion curves of waveguides with different structures and sizes are simulated by using the finite-difference eigenmode(FDE)solver.Then,the structure,size,and anomalous dispersion design of high-quality factor(Q)microring resonators are realized.Finally,the experimentally measured results show that the Q value of the microring resonators can reach 2.5×10~6,which is conducive to the excitation of the optical frequency comb.2.Based on the fabricated microring resonators and solving the Lugiato-Lefever(LLE)equation,the generation of optical frequency combs is studied,and the optical frequency combs with different spacings are realized by the thermal tuning method.In our experiments,a broadband optical frequency comb with a spectral width greater than 200 nm and a comb spacing of about 150 GHz has been successfully realized.3.A scheme of reconfigurable optical frequency comb based on the optical switchs is proposed.Based on the 3-d B multimode interference coupler,a Mach Zehnder interferometer type thermo optical switching unit is designed and fabricated.The experimental results show that the extinction ratio is more than 30 d B and the insertion loss is 0.57 d B,which provides the basis and possibility for the high integration and reconfiguration of the optical frequency comb.4.Based on the designed silicon nitride microring resonators with different radii,the optical frequency comb generation with different repetition frequencies(100 GHz-300 GHz)is realized by solving the LLE equation.