Sharp angular and unidirectional filter based on accidental degeneracy between two twisted Weyl semimetal-based defect modes in a one-dimensional photonic crystal.

Abstract

To address the challenges associated with the realization of optical non-reciprocity and enhance the efficiency of GaAs solar cells, among other systems, in this study, we investigated defect-mode interactions in a one-dimensional photonic crystal containing two Weyl semimetal-based defect layers. Moreover, two non-reciprocal defect modes were observed, namely, when defects are identical and nearby. Increasing the defect distance weakened the defect-mode interactions, thus causing the modes to gradually move closer and then degenerate into one mode. It should be noted that by changing the optical thickness of one of the defect layers, the mode was found to degrade to two non-reciprocal dots with different frequencies and angles. This phenomenon can be attributed to an accidental degeneracy of two defect modes with dispersion curves that intersect in the forward and backward directions, respectively. Moreover, by twisting Weyl semimetal layers, the accidental degeneracy occurred only in the backward direction, thus resulting in a sharp angular and unidirectional filter.