Broadband mid-infrared difference frequency generation in uniform grating periodically poled lithium niobate

A novel broadband mid-infrared (mid-IR) difference frequency generation (DFG) scheme in a uniform grating periodically poled lithium niobate (PPLN) on the basis of gradient temperature control technique is proposed. Our theoretical results show that the quasi-phase matching bandwidth (BW) for the idler is <10 nm under a fixed crystal temperature condition for two fundamental lights operating in the 1060 and 1550 nm regions. The BW for the idler is remarkably enhanced with increasing temperature gradient across the crystal. When the pump wavelength is fixed at 1.08 μm, the BW for the idler is increased to 18, 40, and 102 nm at 20, 40, and 60 °C, respectively. However, when the signal wavelength is fixed at 1.58 μm, two idler QPM bands for each crystal temperature are achieved. These bands can be simultaneously broadened (in nanometers) to 21 and 14, 54 and 64, and 158 and 161, at 20, 40, and 60 °C, respectively. The broadened idler QPM bands can also be moved over a wide range by adjusting the temperatures at both endfaces of the crystal while maintaining a certain temperature gradient. This scenario is quite useful for further enhancing the mid-IR wavelength coverage.