  Nonreciprocal (NOR) transmission with magneto-optical materials plays a
critical role in a broad range of applications, such as optical isolation,
all-optical signal processing, and integrated photonic circuits. The underlying
mechanism is that a static magnetic field can break the time-reversal symmetry
in the presence of magneto-optical materials. However, the typical NOR devices
usually need a large size because the weak magneto-optical activity of
materials. Here, our theoretical investigations show that the NOR transmission
can be obtained in the one-dimensional photonic crystal with a magnetized
epsilon-near-zero (ENZ) defect due to strong field localization in the ENZ
medium. The inherent weak magneto-optical activity is significantly enhanced in
ENZ medium. In our configuration, the wavelength shift of transmission peaks
along two opposite incident directions can be up to 100 times higher than that
in the case that the defect layer is a normal bismuth iron garnet. Such results
will provide a new degree to design novel magneto-optical devices with small
size, and may open novel routes to exploit advanced materials for steering the
electromagnetic waves in nano-scale structures.
