19 October 2012
Vol 338, Issue 6105

About The Cover

Cover image expansion

COVER Optical vortices emitted by an array of silicon ring resonators. The helical phase fronts, indicated by spirals, denote photons with orbital angular momentum. Emission results from the embedded angular gratings that extract the light waves traveling around the ring. The small emitters (diameter: 8 micrometers) can be integrated on a large scale into photonic integrated circuits, enabling new applications in optical communications and sensing, quantum photonics, and lab-on-a-chip. See page 363. Image: Yue Zhang (, based on data from Xinlun Cai, Jiangbo Zhu, and Siyuan Yu