Fig. 1: Concept of TPs using orbital meta-atoms and the resulting interference effect in analogy with Malus’s law.
From: Super-resolution acoustic displacement metrology through topological pairs in orbital meta-atoms
a Schematic diagram of two orbital meta-atoms (left) carrying topological charges ±q, which are paired to form the conjugate TPs (right) in mode space, i.e., TP: (+q, −q) and TP* (−q, +q), where the total OAM is zero. b Illustration of the evolution process of incident plane wave passing through two orbital meta-atoms in a cylindrical waveguide, where it is gradually converted to conjugate OAM waves and then transformed back to the plane wave (see the inset). The outgoing plane waves (red and blue colors) are from two distinct routes in mode space enabled by the conjugate TPs. c By twisting one of two meta-atoms with angle of θ, such two kinds of outgoing plane waves can experience geometric phases of \({\varphi }_{{{\rm{g}}}}^{\pm}=\pm q\theta\) via conjugate TPs, enabling the generation of acoustic interference.
