Fig. 1. (a) A modified Damascene process for the fabrication of Si₃N₄ film; (b)-(c) Atomic force microscope analysis of silicon nitride film grown by LPCVD; (d) Absorption spectrum of the grown Si₃N₄ film

Fig. 2. Defects of microresonators produced from the processing with or without the Damascene microstructures. (a) Tiny crack on microrings and waveguides from stress conducting; (b) Bubbles at the bottom of micoring and waveguide; (c) Broken defects of the waveguide at the coupling area of waveguide/conterpart microring; (d) No defects with Damascene microstructures

Fig. 3. (a) Si₃N₄ microresonator fabricated by the modified Damascene microstructure; (b) Cross-section profile of the critical coupling area between ring microcavity and conterpart waveguide

Fig. 4. Light path for measuring the optical frequency combs by dual-pumping

Fig. 5. Comb spectra. (a) Chaotic state comb; (b) Soliton state comb matched with sech² function fitting