A Broadband Infrared DFG Optical Comb Using All-PM Nonlinear Pulse Fiber Amplification Technique

A scheme for fiber-type infrared optical comb based on the difference frequency generation (DFG) method is proposed and demonstrated. All-polarization-maintaining nonlinear pulse fiber amplifications are used to generate the nearly transform-limited two-color fundamental pulses, such that precise temporal synchronization for the broadband spectra between the fundamental pulses can be stably achieved. The 3-dB bandwidth of the DFG comb achieved is 2.05 mu m near 9 mu m. The DFG comb can be widely tuned from 7 to 10.5 mu m, where the bandwidth for any tuning position is close to the theoretical limit. Moreover, we show that it is essential to suppress the amount of the fundamental pump pulse chirp and narrow the transform-limited fundamental signal pulse for achieving the broadband and efficient DFG comb.