Fig. 1. Schematic diagram of asynchronous optical sampling
(a): Time domain; (b): Frequency domain

Fig. 2. (a) Structure diagram of dual-wavelength laser controlled by filter and attenuator effect; (b) optical spectrum; (c) RF spectrum

Fig. 3. (a) Schematic of the polarization-multiplexed dual-comb fiber laser; (b) abnormal dispersion; (c) normal dispersion : optical spectra and RF spectra of polarization-resolved outputs

Fig. 4. (a) Experimental setup of bidirectional dual-comb fiber laser; (b) fluctuation of the repetition rates; (c) the difference in the repetition rate (Δf_rep). STD: standard deviation, ADV: Allan deviation. Inset: magnified of (c)

Fig. 5. (a) Schematics of pulse-shape-multiplexed dual-comb laser; (b) time domain interferogram; (c) spectrum of dual-comb laser

Fig. 6. Structures of (a) polarization maintaining laser based on SWNT; (b) polarization-maintaining dual-wavelength mode-locked laser based on Sagnac filter; (c) all-PM dual-comb fiber laser with SWNT; (d) bidirectional partly polarization-maintaining fiber laser

Fig. 7. (a) Principle of spectral measurement; (b) two different path measurement methods

Fig. 8. The spectral range of dual-comb measurement and the corresponding dual-comb source technologies

Fig. 9. (a) Configuration of comb-mode-resolved adaptive sampling THz-DCS; (b) comparison of the temporalwaveforms averaged 100 000 times obtained with different sampling clocks. Inset: a zoomed-in plot of the main THz pulse; (c) comb-mode-resolved THz spectrum through air at room pressure. Inset: a zoomed-in plot around 0.567 2 THz

Table 1. Output characteristics of reported dual-comb mode-locked laser based on polarization-maintaining fiber laser