Credit: B. Peng, S.K. Ozdemir, and L. Yang/ WUSTL
In an optical diode, the light input in one direction is transmitted while the light input in the opposite direction is blocked. The new optical diode, designed by Lan Yang and her collaborators, is made from parity-time (PT) symmetric microresonators in which loss of one of the resonators is balanced by the gain in the other. Breaking the PT-symmetry, by tuning the coupling strength between the resonators, leads to strong field localization and hence enables nonlinearity-based one-way transmission for light.