| The optical frequency comb refers to dozens or even millions of comb-like spectrum structures in the frequency domain.With its excellent stability and amplitude strength,optical frequency comb has attracted widespread attention since it appeared,and has many important applications in the fields of astronomy,biomedicine,and communications.The optical frequency comb can be obtained by electro-optic modulators,microcavity structures,highly nonlinear optical fibers,and nonlinear waveguide structures.Among them,using nonlinear waveguides to generate optical frequency comb is more in line with the current trend of miniaturization and integration of devices in the era of information intelligence.This method is based on obtaining high-coherence and multi-octave supercontinuum in the nonlinear waveguides.Therefore,the generation of supercontinuum in nonlinear waveguides should be investigated first.In this paper,two kinds of new waveguide structures based on different nonlinear materials are proposed.By controlling the dispersion,low and flat dispersion profile can be obtained,which is conducive to the generation of high-coherence and multi-octave supercontinuum.The influence factors on the generation of supercontinuum and its coherence are deeply investigated.For the two designed waveguides,reliable methods on the generation of highly coherent and multi-octave mid-infrared supercontinuum are proposed,respectively.Based on the supercontinuum obtained,high-quality optical frequency combs can be generated in the two waveguides,respectively.The main work contents and innovation results of this paper are summarized as follows.1.A T-type Germanium(Ge)waveguide is designed.By optimizing the geometric parameters,low and flat dispersion profile is obtained in the considered wavelength range.Moreover,the nonlinearity coefficient of the designed waveguide is calculated as 30.48 W-1·m-1 at wavelength 3.0 μm.2.The generation of supercontinuum in the designed T-type Ge waveguide is investigated by simulation.The influences of the pump pulse parameters,waveguide length,and noise coefficient on the nonlinear dynamics of the supercontinuum generation are investigated.Simulation results show that with the designed waveguide,the highly coherent and octave-spanning mid-infrared supercontinuum can be generated in the wavelength range from 1.85 to 9.98μm,more than 2.4 octaves.The generation of optical frequency comb is investigated by simulation,and the simulation results show that optical frequency comb with stable amplitude and equal interval is generated based on the highly coherent and octave-spanning mid-infrared supercontinuum generated in the designed T-type Ge waveguide.3.A reverse-strip AlGaAs waveguide is designed.By optimizing the geometric parameters,the dispersion value changes between-8.2 and 14.0 ps/nm/km in the wavelength range from 3.74 to 8.89μm,and the low and flat dispersion profile is achieved,along with the three zero-dispersion wavelengths of 3.74,6.56,and 8.89 μm,respectively.4.The generation of supercontinuum in the proposed reverse-strip AlGaAs waveguide is investigated by simulation.The influences of the pump wavelength,peak power,pulse width,and waveguide length on the generation of supercontinuum are investigated.The effect of the noise coefficient on the coherence characteristic is also investigated.Simulation results show that the highly coherent and multi-octave mid-infrared supercontinuum spanning from 2.2 to 14.5 μm(more than 2.7 octaves)is obtained in the waveguide designed.The generation of optical frequency comb is investigated by simulation,and the simulation results show that the octave-spanning mid-infrared frequency comb with equal interval and stable amplitude is generated with the designed reverse-strip AlGaAs waveguide.In this paper,utilizing the good nonlinear characteristics of the T-type Ge waveguide and reverse-strip AlGaAs waveguide,the generations of optical frequency comb based on supercontinuums are investigated.The research and achievements enrich the research and technology of generating optical frequency comb using the nonlinear waveguide.The generation of optical frequency comb based on supercontinuum plays an important role in promoting the research and development of nonlinear optics,spectroscopy,and metrology. |
