  We discuss several aspects of chiral optomagnonics in antiferromagnetic
insulators by considering common symmetries between the electromagnetic field
and spin excitations. This approach allows us to look at optical and magnetic
materials from similar perspectives, and discuss useful analogies between them.
We show that spin waves in collinear antiferromagnets and the electromagnetic
field in vacuum are both invariant under the same eight-dimensional algebra of
symmetry transformations. By such analogy, we can extend the concept of optical
chirality to antiferromagnetic insulators, and demonstrate that the spin-wave
dynamics in these materials in the presence of a spin current is similar to
that of the light inside chiral metamaterials. Photo-excitation of magnonic
spin currents is also discussed from the symmetry point of view. It is
demonstrated that a direct magnonic spin photocurrent can be exited by
circularly polarized light, which can be considered as a magnonic analogue of
the photogalvanic effect. We also note that the Zitterbewegung process should
appear and may play a role in photo-excitation processes.
