Research On Optical Frequency Comb Generator Based On Nonlinear Optical Fiber Ring Cavity

Optical frequency comb(OFC)is represented as an optical pulse with regular and fixed repetition frequency in the time domain.While in the frequency domain,it is represented as a spectrum composed of a series of evenly spaced spectral components.At present,many methods have been used to generate OFC,such as mode-locked laser method,external modulator method,micro-ring resonator method,photoelectric resonator method and optical fiber nonlinear effect method,etc.With the continuous development of optical communication technology,optical frequency comb,as one of the key technologies in the field of optical communication and microwave,has important applications in optical arbitrary waveform generation,precision measurement,dense wavelength division multiplexing,precision laser spectroscopy,super laser and so on.This paper mainly focuses on the research of optical frequency comb generator based on nonlinear fiber ring cavity.The main content includes the following aspects:(1)We have briefly introduced the research background and significance of optical frequency comb,including the application field of optical frequency comb,the research status of optical frequency comb at home and abroad and the research status of switchable frequency interval multi-wavelength fiber lasers.(2)We have elaborated several common nonlinear effects in optical fiber and the performance index of optical frequency comb in detail,which lies the theoretical foundation for the subsequent research work.(3)An optical frequency comb generator with switchable frequency interval is proposed.A polarization preserving fiber coupler with a coupling ratio of 1:99 and a high nonlinear fiber with a length of 1km are mainly used in the scheme.By changing the output direction of the coupler,the optical frequency combs with double Brillouin frequency intervals consisting of even-order Stokes signals and odd-order Stokes signals can be obtained respectively.In addition,by adjusting the polarization state of the polarization controller and the power of the bump signal entering the cavity,the free switching between single-double Brillouin frequency interval optical frequency combs can be realized.(4)A research scheme of optical frequency comb generator based on nonlinear fiber ring cavity is proposed.The proposed scheme is based on Rayleigh scattering,stimulated Brillouin scattering and cascade four-wave mixing effects in Brillouin-Erbium fiber ring cavity.The difference with the above scheme is that a four-port coupler with a coupling ratio of 10:90 is used to replace the polarization maintaining fiber coupler as the output.From the experimental results,the performance of the obtained optical frequency comb has been significantly improved.The optical frequency combs obtained in the experiments have good stability at room temperature,and may find some applications in various fields such as highcapacity optical communications,low-noise tunable microwave and spectroscopic studies.