Research on supercontinuum generation in a dispersion-engineered silicon nitride waveguide

Frequency stabilized optical frequency combs has been crucial for applications of high-precision measurements, optical clocks, and parallel communications, et al. The most effective way of frequency stabilization of combs is stabilizing the repetition rate and carrier-envelope offset frequency of a generated comb, which requires octave-spanning spectrum generation. However, the spectrum bandwidth of microcavity comb is greatly limited in the existing microresonator-waveguides due to the interaction of dispersion and phase modulation. In this paper, we mainly study the generation of supercontinuum in Si₃N₄ waveguides of different sizes. Supercontinuum generation refers to the phenomenon that the frequency spectrum of the ultrashort pulse is greatly broadened after the linear and nonlinear effects, which has been the mainly mechanism of spectrum broadening in Si₃N₄ nonlinear medium. In this paper, the dispersion of different size of Si₃N₄ waveguides has been studied. Different structure of waveguides has been built of which the effective index, propagation constant and dispersion parameter has been simulated and calculated through mode analysis. The electric field mode of waveguide cross section is simulated, and light is well confined in the waveguide with height of 0.8 μm and width of 1.6 μm. Based on this structure, we can access the effective index neff, based of which we calculate the group velocity dispersion of waveguide. We can get flatter dispersion curve through dispersion-engineered waveguide and more broaden spectrum through dispersive wave with zero-dispersion.