Bound states in the continuum of nanohole array with symmetry broken in THz

We investigate the modulation and mechanism of BIC of the 7-shape nanohole array penetrated in a layer of Si3N4 Photonic crystal (PhC). Results show that Q-factor at bound states in the continuum (BIC) can exceed 105. We demonstrated that the resonance width can be adjusted by the nanohole size. In this structure, the variation of resonance width may provide a method to control the amplification of electromagnetic field. The resonance reflectance formants are very sensitive to the refractive index of the surrounding medium. This structure can detect the impurities in the structure, which is of certain significance for making impurity detector. In addition, we also investigated the modulation and mechanism of BIC in double layer of Si3N4 PhC. The formation of Fabry Perot type BIC found in this symmetrical double-layer structure. We simulate the structure by using both finite difference time domain (FDTD) method and coupled mode theory (CMT) method, and the results from both methods are in agreement with each other well. Result are helpful for the design of many potential applications of photonic nanostructures.