Abstract
THz radiation has been extensively explored in recent years due to the great potential in a variety of applications. The THz frequency is typically defined in the range of 100 GHz to 10 THz within the electromagnetic spectrum. The development of THz source is limited by the high of configuration and operation. In this work, we intend to utilize the nonlinear optical approach to generate coherent THz wave. In this thesis, we simulated the evolution of THz wave in nonlinear crystal by using three coupled wave equations for difference frequency generation (DFG). We analyzed the dependence of THz generation on pump and signal intensities and pump-to-signal intensity ratio. In our simulations, different input intensities or pump-to-signal ratio correspond to different conversion efficiencies and optimal interaction distances. In our experiment, we fabricated an annealed proton exchange-periodic poled LiNbO3 (APE-PPLN) waveguide as the nonlinear conversion crystal. Although there is no measurable THz signal, we analyzed the problems of failure, and provided some solutions in the end.