  We propose theoretically an optical diode based on exciton-polaritons in
semiconductor microcavities. A flow of polaritons in the bistable regime is
used to send signals through an asymmetric fixed potential that favours the
tunneling of particles in one direction. Through dynamic modelling of the
coherent polariton field, we demonstrate the characteristics of an ideal diode,
namely that the forward signal is fully transmitted while the transmission in
the reverse direction tends to zero, without any additional external control.
Moreover, the system proves to be robust to the presence of disorder, intrinsic
to microcavities, and can function at gigahertz repetition rates.
