The researchers now believe that these problems have been solved. At the heart of the electro-optomechanical switch that has now been developed is a gold membrane that is only 40 nanometers thin and a few micrometers wide, separated from a silicon substrate by an aluminum oxide disk. The size of the gap between the gold membrane and the substrate can be mechanically controlled by electrical forces. If a voltage is applied, the membrane bends slightly and the gap becomes smaller.
The size of the gap in turn determines whether a light wave simply flies on straight or is deflected around the gold membrane. This is where plasmons come into play: for a certain gap width, only plasmons with a certain wavelength can be excited on the gold membrane. If the light has a different wavelength, it is not coupled to the membrane and propagates in a straight line in the silicon waveguide.
"We have considerably lower losses than in previous electro-optical switches," explains postdoctoral fellow Christian Haffner, who led the project as the first author of the recently published science article. "We have also made the gold membrane very small and thin so that we can switch very quickly and with low voltage." The scientists have already been able to show that their new switch can be turned on and off several million times a second with an electrical voltage of just over one volt.
This eliminates the need for bulky and power-guzzling amplifiers previously used for electro-optical switches. In the future, the researchers want to further improve their switch by making the gap between gold and silicon even smaller. This will significantly reduce both the light losses and the control voltage.
There is plenty of application potential for the new switch. Lidar systems for automated cars, for example, where the intensity and direction of propagation of light beams have to be changed extremely quickly, could benefit from the fast and compact switches. And pattern recognition required to control the vehicles can be made faster with such switches.