Nonlinear optical diode based on nonreciprocal cross-phase modulation in coupled microcavities

In this work, a novel concept for the design of an all-optical diode is proposed, which is based on the nonlinear interaction between forward and backward propagating waves in multilayered structures. It is known that the Kerr nonlinearity is able to shift resonance frequencies in the transmission spectrum of the crystal, producing hysteresis curves showing bistability or multistability. For spatially asymmetric structures, the switching thresholds are different for signals incident from the opposite directions, and this leads to a pronounced nonreciprocal behaviour. However, this approach has a major drawback: the maximum contrast in the passive scheme turns to be fundamentally limited despite the fact that the device operates at the resonance of perfect transmission.