Theoretical Study On Generation Of Soliton Optical Frequency Comb In Silicon-Based Microcavity

An optical frequency comb is a ruler made of light that consists of a series of discrete,equally spaced,and phase-locked frequency components of a spectrum.The optical frequency comb is initially generated by a mode-locked laser,which produces ultrashort pulses with the period of the resonant cavity.However,the repetition frequency of the optical comb generated by this method was limited by the length of the cavity to more than 10 GHz and it was more difficult to reduce the size of the structure so that it could be integrated and developed.With the development of optical frequency combs and processing technology,optical microcavities have received more attention because of their small size,high repetition frequency,high quality factor and compatibility with CMOS,and have a wide range of applications in microphoton pulse compression,ultra-efficient low-noise frequency comb and resonant supercontinuum spectrum generation,optical data transmission and spectroscopy,etc.However,the current microcavity fabrication process is not mature enough,which limits the application of microcavity optical frequency comb applications.In this paper,the Lugiato-Lefever equation is used to simulate the generation of intracavity optical frequency combs and the variation of their intracavity dynamics.The main research of this paper is as follows:First,the cavity structure of the microcavity is simulated in COMSOL software to find the effective refractive index and obtain the parameters of the Lugiato-Lefever equation.Second,the simulation software is used to solve the Lugiato-Lefever equation to theoretically study the generation and evolution of soliton optical frequency combs in the Si-based micro-ring cavity.The chaotic state optical frequency comb is achieved when the Si3N4 waveguide width is 2400 nm.When the waveguide width is 200 nm,soliton crystal pulses are obtained and the transition from chaotic to soliton optical combs is observed.It is found that the kinetic evolution of the soliton generation process is influenced by the optical power,nonlinear effects and thermal effects,and the soliton pulses are generated at the step unlike the chaotic state.Finally,a SiO₂ micro-ring cavity with the same structure and the same waveguide width and height as the micro-ring radius are constructed,and a four-soliton optical comb is achieved when the waveguide width is 200 nm,and a single-soliton optical comb is expected.Due to the better coherence of the soliton optical frequency comb,it has important application prospects in optical communication and other fields.