PT Symmetry Induced Rings of Lasing Threshold Modes Embedded with Discrete Bound States in the Continuum
Qianju Song1†, Shiwei Dai1†, Dezhuan Han1*, Z. Q. Zhang2, C. T. Chan2*, and Jian Zi3*
1College of Physics, Chongqing University, Chongqing 401331, China 2Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China 3Department of Physics, Key Laboratory of Micro- and Nano-Photonic Structures (MOE), and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China
Abstract：It is well known that spatial symmetry in a photonic crystal (PhC) slab is capable of creating bound states in the continuum (BICs), which can be characterized by topological charges of polarization vortices. Here, we show that when a PT-symmetric perturbation is introduced into the PhC slab, a new type of BICs ($pt$-BICs) will arise from each ordinary BIC together with the creation of rings of lasing threshold modes with $pt$-BICs embedded in these rings. Different from ordinary BICs, the $Q$-factor divergence rate of a $pt$-BIC is reduced and anisotropic in momentum space. Also, $pt$-BICs can even appear at off-high symmetry lines of the Brillouin zone. The $pt$-BICs also carry topological charges and can be created or annihilated with the total charge conserved. A unified picture on $pt$-BICs and the associated lasing threshold modes is given based on the temporal coupled mode theory. Our findings reveal the new physics arising from the interplay between PT symmetry and BIC in PhC slabs.
. [J]. 中国物理快报, 2021, 38(8): 84203-084203.
Qianju Song, Shiwei Dai, Dezhuan Han, Z. Q. Zhang, C. T. Chan, and Jian Zi. PT Symmetry Induced Rings of Lasing Threshold Modes Embedded with Discrete Bound States in the Continuum. Chin. Phys. Lett., 2021, 38(8): 84203-084203.
2021, Vol. 38 
