Terahertz radiation has high potential for both imaging and communications; any photonic devices that can be developed for better control of terahertz light will be greatly appreciated, and undoubtedly designed into practical systems. Along these lines, researchers at the University of Geneva (UNIGE), working with the Federal Polytechnic School in Zurich (ETHZ) and two Spanish research teams, have developed a technique, based on the use of graphene, that can potentially very quickly control both the intensity and the polarization of terahertz light.
Working within the framework of the European project Graphene Flagship, the scientists have made a graphene-based transistor adapted to terahertz waves. "By combining the electrical field, which enables us to control the number of electrons in graphene and thus allows more or less light to pass through, with the magnetic field, which bends the electronic orbits, we have been able to control not just the intensity of the terahertz waves, but also their polarization," says Jean-Marie Poumirol, a member of the UNIGE research team and the first author of the study. "It is rare that purely electrical effects are used to control magnetic phenomena."
The UNIGE research team's focus is now to move on from the prototype and develop practical applications and new opportunities through the control of terahertz radiation. Their objective is to make terahertz waves industrially competitive in the next few years. There are two main areas of application for this innovation, the first being communications. "Using a film of graphene associated with terahertz waves, we should be potentially able to send fully-secured information at speeds of about 10 to 100 times faster than with Wi-Fi or radio waves, and do it securely over short distances," says Poumirol.
Uses in bioscience, biomedical, and pharma
The second area of application is that of imaging. Being non-ionizing, terahertz waves do not alter DNA (as do x-rays) and therefore are very useful in medicine, biology, and pharma. Additionally, control of the circular polarization of the terahertz waves will allow a distinction between different symmetries (left-handed or right-handed) of biological molecules, which is a very important property in medical applications. Terahertz imaging is also important in homeland security.