Fig. 1. Principle of an optical frequency comb^[30], where the carrier-envelope phase is Δϕ=2πf₀/f_rep

Fig. 2. Venation of optical-frequency-comb-based profilometry

Fig. 3. Schematic of frequency-comb-referenced scheme of multi-wavelength interferometer^[51]

Fig. 4. Time-of-flight (TOF) ranging based on OMPD^[44], in the PLL (in the red box), the reference optical frequency comb is used to construct a low-noise RF source, and out-of-loop (in the blue box) is used for TOF ranging

Fig. 5. Line-scan spectrum-encoded dual-comb interferometry^[47]

Fig. 6. Coherent scanning interference profilometry based on scanning optical frequency comb repetition frequency^[77]

Fig. 7. Principle of surface topography reconstruction by synthetic-wavelength-linked pulse alignment and carrier interference phase^[82]

Fig. 8. Schematic of single pixel optical frequency comb profile measurement system based on DMD^[90]

Fig. 9. One-shot three-dimensional imaging by spectral interferometry of a chirped optical frequency comb^[42]. (a) Diagram of the experimental setup, in which the optical frequency comb spectrum and autocorrelation curve are shown in the upper left corner; (b) a fiber bundle probe consisting of 190 single-mode fibers is shown on the left, and the spectrum captured by the imaging spectrometer is shown on the right

Fig. 10. Principle of dual-comb digital holography^[98]

Fig. 11. Comparison of representative comb-based topography measurement techniques, the test conditions of different works are not uniform