Fig. 1From: Conformal optical black hole for cavityConformal transformation for optical black hole (OBH) cavity. Mapping the homogeneous refractive index distribution in the original straight space (a) to a circular OBH cavity (b) with gradient index. The black and orange straight lines in (a) are transformed into the interior and exterior circle. The core region of OBH cavity is truncated as homogeneous index. The quadrupole cavity (c\(_1\)) and peanut-like cavity (c\(_2\)) are transformed from the circular OBH cavity under different structural parameters, \({{R}_{\text {w}}} = \sqrt{{{u}^{2}}+{{v}^{2}}}\). The black curve is the cavity boundaryBack to article page