Fig. 1. Schematic of the fiber-based mid-IR comb source. PD, piezo driver; PID, proportional integral derivative controller; LO, local oscillator; Mix, RF mixer; FC, fiber coupler; EDFA/YDFA, Er- or Yb-doped fiber amplifier; HNLF, highly nonlinear fiber; DCF, dispersion compensating fiber; ODL, fiberized optical delay line; PZT, piezoceramic fiber stretcher; PMF, polarization-maintaining single-mode fiber; COLL, collimator; GC, grating compressor; FL, focusing lens; PPLN, 3-mm-long periodically poled lithium niobite crystal; G, germanium filter; BS, beam splitter; DET, MCT detector; AMP, RF amplifier; LA, logarithmic amplifier. Fibers are indicated in black, and electrical connections are in green.

Fig. 2. Optical spectrum of the compressed 1565 nm pulses. The inset shows the measured autocorrelation trace.

Fig. 3. Optical spectrum of the compressed 1 µm pulses. The inset shows the measured autocorrelation trace.

Fig. 4. Generated optical spectra for different PPLN crystal periods, with average output power indicated in each measurement. Absorption lines of several molecules within the spectral coverage of the source are depicted in the upper panel.

Fig. 5. (a) Heatmaps showing the time evolution of the spectrum for non-stabilized and stabilized cases. (b) Average output power stability as a function of time.

Fig. 6. Absorption spectrum of CH₄ and C₂H₆ measured using the DFG comb and a Fourier transform spectrometer (black) compared to the spectra of the two molecules (blue and red). The residuum of the fit is shown in the lower panel.