An optical one-way device constructed with an epsilon-near-zero prism inserted in a metal slit

We demonstrate theoretically that an optical one-way transmission device can be constructed by inserting an epsilon-near-zero (ENZ) prism into a metal slit. Similarly to the $p\text{-}n$ junction in the electron diode, the oblique surface of the ENZ prism is a key factor that can block the transmission of the light striking on it and allows the transmission of the light leaving from it. The performance of the device is shown by numerical simulation based on the finite-difference time-domain technique. (letter)