Analogous Optical Activity in Free Space Using a Single Pancharatnam–Berry Phase Element

It is commonly believed that optical activity (OA) is manifested mainly in chiral media, but rare in non-chiral structures. Here, an analog of OA in free space is experimentally demonstrated by using a single liquid-crystal Pancharatnam–Berry phase element (PBPE), for which the mechanism is highly consistent with that of the traditional OA. The specifically designed PBPE supports the direction-dependent polarization rotation of a Bessel beam with controllable “rotatory power.” Such a polarization rotation can be revoked by another PBPE with the same structure. Unlike in a chiral medium, this scheme shows simultaneous realization of equivalent leverotation and dextorotation merely by switching the optical element orientation, promising for applications non-magnetic optical devices such as optical isolators.