Chiral dynamics of exceptional points in weakly absorbing biaxial crystal

Abstract

In this Letter, we report the chiral dynamics of optical exceptional points (EPs), the singular axes in weakly absorbing biaxial crystal, arising due to a fine balance between the birefringence and dichroism. Taking advantage of the coincidence of the singular axes and C-point singularity, the EPs are characterized using conoscopic Stokes polarimetry. We observe that the two optic axes of the biaxial crystal split into two pairs of singular axes upon introducing weak dichroism which, upon application of a transverse electric field, follows a helical trajectory to coalesce and disappear. Our results show a fine control on the chiral behavior of EPs due to an electrogyration effect, which controls the retardance gradient and the fast-axis orientation in the crystal.