Optical transistor developed using Faraday Effect

Through the Faraday Effect, the polarisation of light can be rotated by a small amount by the application of a magnetic field. Two years ago, Professor Andrei Pimenov and his team at the Institute of Solid State Physics of TU Vienna, together with a research group from the University of Würzburg, created a massive Faraday effect as they passed light through mercury telluride platelets and applied a magnetic field. At that time, the effect could only be controlled by an external magnetic coil. However, the team has now managed to turn terahertz radiation by the application of an electrical potential of less than 1V, making the system much simpler and faster. With the latest development, the team says it has shown that the strength of the magnetic field is not the dominant factor, but the number of electrons involved. By regulating the electrical potential, all the optical transistor needs is a permanent magnet and a voltage source suffice – said by the team to be 'comparatively easy to manage'. The rotation of the light beam will determine whether a light signal is sent or blocked. "This is the very principle of a transistor," said Prof Pimenov. "The application of an external voltage determines whether current flows or not and, in our case, the voltage determines whether the light arrives or not." Using this definition, the team believes its developmente is the optical equivalent of an electrical transistor.