  The ideas of topology have found tremendous success in Hermitian physical
systems, but even richer properties exist in the more general non-Hermitian
framework. Here, we theoretically propose and experimentally demonstrate a new
topologically-protected bulk Fermi arc which---unlike the well-known surface
Fermi arcs arising from Weyl points in Hermitian systems---develops from
non-Hermitian radiative losses in photonic crystal slabs. Moreover, we discover
half-integer topological charges in the polarization of far-field radiation
around the Fermi arc. We show that both phenomena are direct consequences of
the non-Hermitian topological properties of exceptional points, where
resonances coincide in their frequencies and linewidths. Our work connects the
fields of topological photonics, non-Hermitian physics and singular optics, and
paves the way for future exploration of non-Hermitian topological systems.
