Ultra-fast all-optical switching demonstrates key step toward future computing

An international research team including physicists from the University of Southampton has demonstrated the world’s first ultrafast all-optical room temperature transistor, paving the way for on-chip circuitry with ultrafast logic operability.

The all-optical transistor exploits the material properties of an organic semi-conducting polymer by using an engineered micro cavity where an incoming optical signal can be switched on, off or amplified using a second laser beam.

The international research collaboration led by Professor Pavlos Lagoudakis, which involves the IBM Research Labs in Zurich, the University of Southampton and Skoltech, has been featured on the front cover of the peer-reviewed journal Nature Photonics.

Dr Anton Zasedatelev, of the School of Physics and Astronomy, explains: “All-optical devices that allow for information processing could enable much faster switching and logical operations. There are a huge variety of different applications for such kind of devices, spanning from classical digital processing of the optical signals in telecoms to routing of flying qubits in quantum optical circuits. But such all-optical devices are very difficult to build and efforts to make all-optical processing units have been around for about 50 years.”

One challenge posed by optical signalling is that photons do not interact with each other in a vacuum. The team applied principles of strong light-matter interaction to the problem to boost the interaction of photons in an organic optical cavity and explored ways of harnessing the highly nonlinear phenomena of exciton-polariton condensation towards all-optical switching and amplification.

“We developed a novel organic semiconductor structure capable of ‘clever mixing’ light and matter and found a strong nonlinear effect associated with polariton condensation based on the unique properties of organic materials to support intense and high energy molecular vibrations,” Anton explains.

The tri-partite research collaboration led to the first operating room-temperature transistor exhibiting an unprecedented 6500-fold optical signal amplification with a device length of just a few micrometres. The innovation also features ultrafast switching in the sub-picosecond range, offering a similar switching speed to some previous all-optical devices with the added advantage that it doesn’t require cryogenic cooling to operate.

Professor Pavlos Lagoudakis comments: “A polariton all-optical transistor presents an interesting platform for all-optical coprocessors. The recent breakthrough in our labs opens new avenues for research and development. A major milestone ahead of us is the realisation of the Universal Polariton Gate that would enable full logic functionality.”