A step towards optical transistors?

As demand for computing and communication capacity surges, the global communication infrastructure struggles to keep pace, since the light signals transmitted through fibre-optic lines must still be processed electronically, creating a bottleneck in telecommunications networks.

While the idea of developing an optical transistor to get around this problem is alluring to scientists and engineers, it has also remained an elusive vision, despite years of experiments with various approaches. Now, McGill University researchers have taken a significant, early step towards this goal by showing a new way to control light in the semiconductor nanocrystals known as ‘quantum dots’.

In results published online recently in the journal Nano Letters, PhD candidate Jonathan Saari, Prof Patanjali (Pat) Kambhampati and colleagues in McGill’s Department of Chemistry show that all-optical modulation and basic Boolean logic functionality - key steps in the processing and generation of signals - can be achieved by using laser-pulse inputs to manipulate the quantum mechanical state of a semiconductor nanocrystal.

“Our findings show that these nanocrystals can form a completely new platform for optical logic,” said Saari. “We’re still at the nascent stages, but this could mark a significant step toward optical transistors.”

Quantum dots are already used in applications such as photovoltaics, light-emitting diodes and lasers, and biological imaging. The Kambhampati group’s latest findings point towards an important new area of potential impact, based on the ability of these nanocrystals to modulate light in an optical gating scheme. “These results demonstrate the proof of the concept,” said Kambhampati. “Now we are working to extend these results to integrated devices and to generate more complex gates in hopes of making a true optical transistor.”