Fig. 1. Experimental setup. (a) Passively synchronized Er- and Yb-doped mode-locked fiber lasers; (b) wavelength-tunable signal source preparation; (c) high-power pump source preparation; (d) synchronously pumped nonlinear frequency-difference generation

Fig. 2. Characterization of pump and signal pulses. (a) Spectrum and pulse width of pump source; (b) signal spectra before and after broadening; (c) spectrum and pulse width of filtered signal

Fig. 3. Experimental results on MIR generation. (a) With and (b) without signal light injection, MIR output power and pump conversion efficiency change with the pump power; (c) tunable MIR spectra and the corresponding maximum output power