Photonic and electric control in terahertz quantum cascade lasers: Review

As one of the most effective methods to generate terahertz laser,how to improve the performance of terahertz quantum cascade laser has been the focus of the scientific community. In this review,the current performance of terahertz quantum cascade lasers is described from the perspective of photonic and electric control. Starting from the principle of active region design of laser,several new active region designs are introduced,and then a series of new structures are introduced from the perspective of resonator,and their improvement on power and beam quality is shown. Finally, we describe the recent progress in polarization regulation and frequency tuning of terahertz quantum cascade lasers.