Fig. 1. Setup for distance measurement based on femtosecond pulse cross-correlation

Fig. 2. Schematic of distance measurement based on femtosecond pulse cross-correlation. (a) Coarse measurement based on rapid time of flight; (b) fine measurement based on cross correlation fringes

Fig. 3. Detection setup and measuring principle of balanced cross correlation. (a) Detection setup; (b) measuring principle

Fig. 4. Setup of pulse-to-pulse alignment based on synthetic wavelength interferometer

Fig. 5. Unbalanced Michelson interferometer with stable long fiber reference arm

Fig. 6. Time-of-flight distance measurement system under two femtosecond combs

Fig. 7. Distance measurement system based on intermode beats

Fig. 8. Distance measurement system based on spectral-resolved interferometer

Fig. 9. Distance calculation method based on spectral-resolved interference. (a) Spectral interference intensity; (b) band-pass filtering after Fourier transfer; (c) wrapped phase; (d) unwrapped phase

Fig. 10. Principle of distance measurement based on chirped pulse spectral interferometer. (a1)-(a3) Pulses in time-domain; (b1)-(b3) fringes in spectral-domain

Fig. 11. Structure and principle of dual-comb heterodyne multi-wavelength interferometer. (a) Structure of measurement setup; (b) dual-comb spectrum; (b) spectrum of heterodyne interference signals