EurekAlert  December 8, 2020 Researchers in the UK re-examined the refractive index and found a general way to calculate the direction-dependent refractive index and the condition for zero index in a given direction. By analogy with linear versus circular polarization, they showed that when the zero-index direction is complex-valued, a material supports waves that can propagate in only one sense, for example, clockwise. They showed that there is an infinite family of both time-reversible and time-irreversible homogeneous electromagnetic media that support unidirectional propagation for a particular polarization. The work extends the concept of the refractive index, shedding new light on […]