[en] In this paper we report a fiber-type widely tunable CW mid-IR DFG/QPM laser source based on periodically poled MgO-doped LiNbO₃ (PPMgLN), which uses a ytterbium-dope fiber laser (YDFL) as the pump source and a tunable erbium-dope fiber laser (EDFL) cascaded with an erbium-doped fiber amplifier (EDFA) as the signal source. Our experimental results show that, with the PCs to adjust the pump and signal polarization orientations being parallel to the crystal principle optical axis the conversion efficiency may be optimized. The pump and signal beam spots and their longitudinal evolution behaviors determine the RCE and the crystal longitudinal position tolerance, which are measured to be 0.717 (mW)^-2 and 44 mm for the mid-IR laser source, respectively. The idler output of the mid-IR DFG/QPM laser source may be continuously tuned from 3.1 to 3.6 μm with almost the same RCE