  We show that Weyl semimetals with broken time-reversal symmetry can host
chiral electromag- netic waves. The magnetization that results in a momentum
space separation of a pair of opposite chirality Weyl nodes is also responsible
for the non-zero gyrotropy parameter in the system. It is then shown that a
chiral electromagnetic wave can propagate in a region of space where the
gyrotropy parameter changes sign. Such waves are analogs of quantum Hall edge
states for photons.
