Nanoscale One-Way-Street for Light

An optical device at nanoscale which allows light to pass in only one direction has been developed at TU Wien (Vienna). It consists of alkali atoms which are coupled to ultrathin glass fibres. If light is able to propagate from left to right, the opposite direction is usually allowed as well. A beam of light can normally be sent back to its point of origin, just by reflecting it on a mirror. Researchers at TU Wien have developed a new device for breaking this rule. Just like in an electrical diode, which allows current to pass only in one direction, this glass fibre-based device transmits light only in one direction. The one-way-rule holds even if the pulse of light that passes through the fibre consists of only a few photons.