  We demonstrate that a strong asymmetric transmission for forward and backward
propagation of tilted circular polarized optical waves is supported by
ultrathin epsilon-near-zero hyperbolic slabs. We find that, remarkably, this
effect is solely triggered by anisotropy without resorting to any breaking of
reciprocity and chiral symmetries or spatial nonlocal effects. In addition, we
show that the asymmetric transmission undergoes a dramatic enhancement if the
slab is hyperbolic in the epsilon-near-zero regime. This happens since, close
to epsilon-near-zero point, the hyperbolic dispersion activates etalon
resonances where extraordinary waves accumulate propagation phase even though
the slab is ultrathin. The proposed strategy holds promise for realizing
ultra-compact and efficient polarization devices at different frequency bands.
