Femtosecond Logic Gates With Lightwave Electronics
There won’t be any chips using light based logic gates for sale anytime soon, but thanks to researchers at the University of Rochester in the US and the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) in Germany have shown how it could be possible. Their light field-driven logic gate consisted of tiny graphene-based wires connected to two gold electrodes which they illuminated with a laser pulse that lasted a few tens of femtoseconds.
The laser pulse excites the electrons in the graphene wires, forcing them to propagate in single direction to create an electrical charge and thus being measurable as a 1 or 0. The big difference between their past experiments and this one is that they were able to maintain that propagation even after the laser was off, as opposed to the charge being transient.
Their calculations suggest that their light based logic gates can operate at up to 0.36 Petahertz (360,000 GHz), carrying operations out in 2.8 femtoseconds. You can find more details at PhysicsWorld, including how these light based logic gates depend on virtual and real electronic charge carriers to reach this impressive frequency. There is also a link to their published research in Nature on that page.
With the parameters used in their experiment, the Rochester-FAU team anticipates an upper limit for the bandwidth of their logic gate at the driving optical frequency of 0.36 PHz, or equivalently, 2.8 fs.