Research On Optical Frequency Comb Based On Periodically Poled Lithium Niobate Waveguide

Recently, with the rapid development of optical communication technology, the optical frequency comb has attracted great attention of researchers because of its widespread applications in the fields such as dense wavelength division multiplexing, optical orthogonal frequency-division multiplexing, optical arbitrary waveform generation, short optical pulse generation and so on. To date, a lot of methods have been proposed to generate an optical frequency comb as follows. Optical frequency comb composed of mode locked laser,composed of phase, amplitude and polarization modulators, composed of a nonlinear medium such as microresonators, composed of periodically poled lithium niobate(PPLN)waveguide. This article combines stimulated Brillouin scattering and second-order nonlinear effects to generate an optical frequency comb, more details are as follows:The dissertation introduces the theory of optical frequency comb based on mode locked laser, modulators, microresonators and PPLN briefly. After studying the principle of second-order nonlinear effects in PPLN, we have experiment to research the relationship between pump power, signal power, their single-pass or two-pass PPLN and the conversion efficiency of second-harmonic generation cascaded with difference-frequency generation.Because of the need to use multi-wavelength Brillouin erbium fiber laser(MBEFL) for the seed light, we review the basic theory of MBEFL and propose several schemes based on continuous light or Rayleigh scattering light acting as the Brillouin pump. Afterwards, we choose the right way to suppress the self-lasing cavity modes according to the experiment results. Due to the temporal property of optical frequency comb, we have theoretical derivation to indicate the phase of MBEFL is locked, the time-domain waveform of MBEFL is pulse. Above all, we propose the schemes of optical frequency comb based on PPLN and set forth the experimental procedures and results. The optical frequency comb using closed cavity MBEFL have 10 comb spectral lines, the maximum extinction ratio is 15 dB, the optical frequency comb can be tunable in a large range with the change of pump wavelength.The optical frequency comb adopting open cavity MBEFL have 8 spectral lines, its flatness is about 4.8 dB, we study how the change of Brillouin pump power and 980 nm pump power affect the optical frequency comb in the experiment. Finally, we measure the line width ofmulti-wavelength by experiments, and the line width is very narrow, about 6 MHz.