Fig. 1. Schematic diagram of the fiber-type DFG mid-infrared optical comb

Fig. 2. Output pulse characteristics and locking results of repetition frequency of the oscillator. (a) Pulse spectrum measured by OSA; (b) time domain distribution of the pulse after compression measured by FROG; (c) real time jitter of phase-locked repetition frequency with sampling time of 1 s; (d) Allan deviation calculated according to the data in Fig. 2(c)

Fig. 3. Results of pulse pre-shaping. (a) Pulse spectra after filtering with filter (solid line) and amplification with EDFA-1 (dashed line); (b) pulse time domain distribution of OC 30% port (solid line) and 70% port (dashed line)

Fig. 4. Output pulse characteristics of EDFA-2 and EDFA-3. (a) Time domain distribution of EDFA-2 and EDFA-3 output pulses; (b) spectra of EDFA-2 and EDFA-3 output pulses

Fig. 5. SC generated by negative dispersion HNLF-PM and time domain synchronization characteristics of bicolor fundamental frequency pulses. (a) SC measured by OSA; (b) autocorrelation curves of two-color fundamental frequency pulses measured by autocorrelator with time interval of 35.60, 20.35, 0 ps, respectively

Fig. 6. DFG mid-infrared comb prototype. (a) Optical module chassis; (b) internal structure of the optical chassis; (c) electrical module cabinet

Fig. 7. Test results of DFG mid-infrared comb prototype. (a) Measured tunning spectra and average power; (b) measured difference frequency optical power within 1 h