  Using the Kubo formalism we have calculated the local dynamic conductivity of
a bulk, i.e., three-dimensional (3D), Dirac semimetal (BDS). We obtain that at
frequencies lower than Fermi energy the metallic response in a BDS film
manifests in the existence of surface-plasmon polaritons, but at higher
frequencies the dielectric response is dominated and it occurs that a BDS film
behaves as a dielectric waveguide. At this dielectric regime we predict the
existence inside a BDS film of novel electromagnetic modes, a 3D analog of the
transverse electric waves in graphene. We also find that the dielectric
response manifests as the wide-angle passband in the mid-infrared (IR)
transmission spectrum of light incident on a BDS film, which can be used for
the interferenceless omnidirectional mid-IR filtering. The tuning of the Fermi
level of the system allows us to switch between the metallic and the dielectric
regimes and to change the frequency range of the predicted modes. This makes
BDSs promising materials for photonics and plasmonics.
