Supercritical coupling (IMAGE) National University of Singapore Caption Figure illustrates the principle of “supercritical coupling” and directive upconversion emission through supercritical edge BIC coupling. It shows the layout of the photonic-crystal nanoslab with unit cell geometry and demonstrates collimated upconversion achieved through supercritical coupling tuned at the edge. Credit Nature Usage Restrictions NA License Licensed content 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.