Due to physical limits, data transmission based on direct modulation of the light intensity cannot take place much faster than with a bandwidth of 40 to 50 gigahertz without complex modulation concepts. In order to achieve such high bandwidths, high electrical currents are required; the energetic efficiency of data transmission decreases massively with increasing bandwidth. "Unless we change the technology soon, data transmission and the Internet will consume more energy than we currently produce on Earth," predicts Prof. Dr. Martin Hofmann of the University of Bochum. Together with colleagues, Martin Hofmann is therefore researching an alternative technology.
Using lasers measuring just a few micrometers, provided by a team from the University of Ulm, the researchers generate a light wave whose oscillation direction changes periodically in a special way. This is circularly polarized light that is produced by superimposing two light waves polarized linearly perpendicular to each other.
In linearly polarised light, the vector that describes the electric field of a light wave oscillates constantly in one plane. With circularly polarized light, it rotates around the direction of propagation. The trick: If the two linearly polarized light waves differ in their frequency, an oscillating circular polarization is created in which the direction of oscillation reverses again and again - at an adjustable speed. The researchers have now experimentally shown that oscillation can take place at 200 gigahertz. How much faster it can still become is unclear. A theoretical limit has not yet been defined.