Fig. 1: Geometric-symmetry-free and higher-order BICs induced by zero-index media (ZIM) in a waveguide.
From: Geometry symmetry-free and higher-order optical bound states in the continuum
a A two-dimensional (2D) waveguide structure with reflection symmetry for symmetry-protected BICs, where two identical objects (blue circle with solid boundary) are placed symmetrically in space. If one object is shifted (the blue circle with a dashed boundary), the BIC disappears. b After filling ZIM in the waveguide, the system supports a BIC which is independent of the location of objects. c The geometric-symmetry-free BIC is insensitive to the doping objects’ shapes, materials, and distributions. d Higher-order BICs are implemented by embedding multiple objects in ZIM.
