The core part of mid-infrared tunable lasers is dielectric superlattice(periodical-polarized LiNbO3,PPLN) which can effectively transform near-infrared laser to tunable mid-infrared laser. Mid-infrared lasers possess great penetrability and directivity, and its wavelength lies in the active excitation area of various atoms and molecules, thus it has important applications in fields like national defense, environmental protection, bio-medical treatment, scientific research and so on.