First Method for Filtering Light Waves Based on Direction

Light waves can be defined by three characteristics - their color (or wavelength), polarization, and direction. It has long been possible to selectively filter light according to its color or polarization, but selectivity based on the direction of propagation has remained elusive. Now, for the first time, MIT researchers have produced a system that allows light of any color to pass through only if it is coming from one specific angle; the technique reflects all light coming from other directions. This new approach could ultimately lead to advances in solar photovoltaics, detectors for telescopes and microscopes, and privacy filters for display screens.