Optical Diode (image) Washington University in St. Louis Caption 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 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. Credit Lan Yang Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.