Fig. 1. Experimental setup of the dual-comb source. (a) Dual-pump seeds generator. (b) Dual-comb generator. PM, phase modulator; EDFA, erbium-doped fiber amplifier; OC, optical coupler; CIR, optical circulator; FBG, fiber Bragg grating; PC, polarization controller. Fiber1 and Fiber2 are different fibers selected from the following five fibers: HNLF with anomalous dispersion (HNLF1, YOFC, BFS=9.33  GHz), HNLF with normal dispersion (HNLF2, OFS, BFS=9.65  GHz), dispersion compensation fiber (DCF, YOFC, BFS=9.70  GHz), SMF with non-zero dispersion shift (SMF1, YOFC, BFS=10.62  GHz), and SMF with bend-insensitivity (SMF2, YOFC, BFS=10.82  GHz).

Fig. 2. (a) Optical spectra of the 20-GHz-spaced EO comb, DP1, and DP2. (b) Beating RF spectrum between DP1 and DP2.

Fig. 3. (a) Optical spectra of Comb1 versus the power of DP1. (b) Beating RF signals of the laser at short wavelength in DP1 (marked by a rhombus in the inset) and the corresponding Brillouin laser in Comb1 [marked by a triangle in panel (a)] versus the power of DP1.

Fig. 4. (a) Optical spectra of Comb1 before FBG2 (upper blue curve) and the dual combs after FBGs (lower curves) at pump power of 28 dBm. (b) Beating RF spectrum of the dual-comb source at an RBW of 200 kHz. (c) The left third beating note (arrow marked) with an RBW of 300 Hz.

Fig. 5. Measured autocorrelation traces of Comb1 before FBG2 (blue dashed curve), Comb1 after FBG2 (top solid curve), and Comb2 after FBG3 (bottom solid curve).

Fig. 6. (a) Linewidths of lasing lines in Comb1 (red circle) and Comb2 (blue triangle) versus the order number of comb lines. The delay self-heterodyne beating RF spectra of (b) the comb line with N=−5  in Comb1, (c) the comb line with N=−1  in Comb2, and (d) the CW laser (blue curve) and the short wavelength mode of DP1 (green curve).

Fig. 7. (a) Beating RF spectra between DP1 and DP2 with an RBW of 100 kHz. The beating note interval is 202, 323, 916, and 1486 MHz when Fiber1/Fiber2 in the frequency shifter is SMF1/SMF2, HNLF1/HNLF2, DCF/SMF1, and HNLF1/SMF2, respectively. (b) Optical spectra of the central 10 lasing lines of Comb1 and Comb2 and (c) the corresponding beating RF spectrum of the dual combs with an RBW of 1 MHz.