Hollow-Core Optical Fiber (IMAGE) Physikalisch-Technische Bundesanstalt (PTB) Caption This is a microscopic image of a hollow-core optical fiber. Credit (Photo: MPL) Usage Restrictions None 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.