Sound system

A group of scientists from a German research institute have developed a new type of light modulator that is driven by surface acoustic waves. It is 300 times smaller and can transport more data than comparable modulators.

Light modulators convert electrical signals into light so they can be transferred into fibre-optic networks. The new devices could one day be used in lasers by the telecommunications industry to improve signal modulation.

The modulator, which has been developed at the

, Berlin, consists of a device called a Mach-Zehnder interferometer (MZI). This divides and recombines light waves, using interference to change the amplitude of the wave.

An interferometer works on the principle that two waves coinciding in the same phase will add to each other, while two waves with opposite phases will cancel each other out, assuming both have the same amplitude.

The modulator divides an incoming light signal into two light beams. The refractive index of the material through which one of the beams passes can be altered and, as a result, the light passing through the material is slowed down. This puts the beam in a different phase to the other and, when the two beams are recombined, the reunited rays interfere with each other. Thus, the transmitted light intensity is altered.