Fig. 1. Basic principle and excitation method of optical frequency combs. (a) Time and frequency domain characteristics of optical frequency comb^[1]; (b) optical frequency comb based on mode-locked laser^[1,3]; (c) optical frequency comb based on electro-optical effect^[3]; (d) optical frequency comb based on microcavity Kerr effect^[1,3]

Fig. 2. Integrated Kerr optical frequency combs based on different material platforms and corresponding spectra. (a) SiO₂^[15]; (b) Si₃N₄^[8]; (c) AlN^[18]; (d) SiC^[20]; (e) AlGaAs^[22-23]; (f) GeSbS^[28]; (g) LiNbO₃^[26]; (h) LiTaO₃^[29]

Fig. 3. Development trend of on-chip integrated Kerr optical frequency combs. (a) Large-scale preparation^[39]; (b) image of hybrid integrated turnkey optical frequency comb^[9]; (c) concept of on-chip optical system^[47]

Fig. 4. Integration progress of on-chip integrated Kerr optical frequency combs. (a) Battery-operated integrated frequency comb generator^[42]; (b) electrically pumped integrated soliton microcomb^[43]; (c) microcomb heterogeneously integrated on silicon^[33]; (d) integrated turnkey soliton microcomb^[9]

Fig. 5. Ranging schemes based on on-chip integrated Kerr optical frequency combs. (a) An on-chip ranging device based on dual-comb ToF method^[49]; (b) DPI ranging scheme based on soliton microcomb^[51]; (c) parallel FMCW lidar based on microcomb^[52]; (d) parallel chaotic lidar based on microcomb^[54]; (e) large-scale dynamic imaging based on on-chip dual-comb^[58]

Fig. 6. Gas sensing methods based on integrated Kerr optical frequency combs. (a) Sample absorption spectrum measured directly^{by optical frequency comb[59]; (b) sample absorption spectrum measured by dual-optical frequency comb[60]}

Fig. 7. Spectral analysis and gas sensing based on integrated Kerr optical frequency combs. (a) Measurement of acetylene absorption spectrum by microcavity optical frequency comb high-resolution spectral measurement system^[61]; (b) measurement of H¹³CN absorption spectrum by microcavity soliton dual-optical comb system^[62]; (c) measurement of dichloromethane absorption spectrum by a single pump driven dual-optical comb system^[63]; (d) absorption spectrum of acetone liquid measured by silicon microcavity soliton dual-optical comb system^[64]; (e) measurement of methane absorption spectrum by iDFG^[65]; (f) measurement of methane and ethane absorption spectra by backpropagation soliton microcomb^[66]

Fig. 8. Parallel DAS using on-chip dual Kerr soliton microcombs^[11]