Multiple exceptional points in bulk parity-time symmetric optical media

Abstract

We study bulk optical modes in media with a parity-time symmetric permittivity tensor via the k-surface approach. We show that k-surfaces support multiple exceptional points (EPs), and the off-axial EPs can be manipulated by tuning the tensor elements. They merge into diabolic points if they have opposite handednesses, and annihilate each other otherwise. The underlying physical mechanisms and the potential applications are discussed.