On May 23, the Chinese Journal of Lasers announced the Top 10 China Optical Advances 2021. Two projects of NKU were chosen for the basic optical research category, namely Nonlinear Control of PT Symmetry and Non-Hermitian Topological States and The Realization of Nonlinear Huang-Kun-like Equation and Enhanced Nonlinear Effects at Terahertz Frequencies.

Nonlinear Control of PT Symmetry and Non-Hermitian Topological States is a project of the research team led by Prof. Chen Zhigang and Prof. Xu Jingjun from the School of Physics, Nankai University. The team has developed an optical platform with both nonlinear and non-Hermitian topological for the first time in the world. The researchers prepared one-dimensional non-Hermitian topological photonic crystals with nonlinear crystal materials by applying the self-developed continuous laser direct writing method for the first time, realized the nonlinear regulation of parity time symmetry and non-Hermitian topological states, and further explored theoretically the impact of nonlinear effects on non-Hermitian singularities and the antagonistic effects of sensitivity and robustness when topological states approach singularities. The research finds that local optical nonlinearities can affect and change the global symmetry of a system. The outcome has changed the common cognition of nonlinearities in an open topological system and provides feasible experimental platform and new directions for research of nonlinearity in a non-Hermitian topological system. Nankai University is the first unit for the research outcomes. Doctoral student Xia Shiqi and Prof. Song Daohong of the School of Physics, Nankai University, are both the co-first authors, and Prof. Chen Zhigang is the first corresponding author.

The Realization of Nonlinear Huang-Kun-like Equation and Enhanced Nonlinear Effects at Terahertz Frequencies is a project of the research team led by Prof. Wu Qiang and Prof. Xu Jingjun of the School of Physics of Nankai University. The team expanded the Huang-Kun-like equation from linear application to nonlinear application for the first time, developed the nonlinear Huang-Kun-like equation to describe stimulated phonon-polaritons and discovered that the delocalized stimulated phonon-polaritons can significantly enhance the nonlinear effects of terahertz waves. The team proved that the second-order nonlinear polarizability of terahertz waves can be improved by five to six orders of magnitude by phonon polariton with self-designed experiment, which also proved the accuracy of nonlinear Huang-Kun-like equation. The outcome could play a big role in the research and application of phonon polariton, material property control, terahertz wave physics and technology, light-regulated spin qubit and other fields. The research also shows that nonlinear Huang-Kun-like equation, when combining with terahertz phonon polariton and ionic crystals, can provide a new research direction. Nankai University is the first unit for the research outcomes. Doctoral student Lu Yao and Zhang Qi of the School of Physics of NKU are the first authors, and Prof. Wu Qiang is the first corresponding author.

The poll of Top 10 China Optical Advances was initiated by the Chinese Journal of Lasers in 2005 in a bid to introduce the optics-related papers with important academic and application values written by domestic researchers. The award is widely recognized by the academic community and has become one of the most popular annual events among the researchers of optics, due to the academic excellence of the winning entries and the strictly impartial jury.

(Edited and translated by Nankai News Team)