Fig. 1. Characteristics of optical phenomena in silicon nitride microresonators. (a) 100 GHz FSR silicon nitride microresonator^［47］; (b) mode spot of silicon nitride waveguide^［47］; (c) group velocity dispersion in different wavelength ranges; (d) schematic of FWM; (e) soliton spectra^[47] (inset: temporal waveform of soliton)

Fig. 2. Experimental setup for bright soliton generation, forward and backward tuning processes, and spectra of solitons with different numbers^[85]. (a) Experimental setup; (b) forward and backward tuning processes; (c) spectra of soliton (N=1, 2, 3)

Fig. 3. Generation of dark pulses. (a) Transmission power of the microresonator (inset: principle diagram of intensity modulation); (b) 10 GHz dark pulses obtained by simulation and experiment (inset: temporal waveforms of dark pulses)

Fig. 4. Optical parametric amplification and relation between wavelength and gain^[9]. (a) Optical parametric amplification schematic diagram; (b) relation between wavelength and gain

Fig. 5. Principle of supercontinuum generation, and spectra and dispersion in various wavelength bands^[128]. (a) Schematic diagram; (b) spectra and dispersion in different wavelength bands

Fig. 6. Self-injection locking^[105]. (a) Schematic diagram; (b) tuning curve

Fig. 7. FWM in the microring. (a) Microcavity resonance line and generation of photon pairs; (b) experiment scheme and condition of energy conservation

Fig. 8. Applications of nonlinear optics. (a) Astrospectroscopy^[175]; (b) dual-comb spectroscopy^[176]; (c) coherent communication^[177]; (d) atomic clock^[178]; (e) optical computing^[2]; (f) optical ranging^[179]; (g) optical imaging^[180]; (h) microwave synthesis^[105]; (i) quantum light source