A "light" transistor

An illustration of a silicon nanoparticle switching between modes, depending on the intensity of a laser pulse. Credit: Nano Letters

Transistors are at the core of the digital revolution that has changed all aspects of our world and our life They are based on silicon doped with specific atoms to work as a conductor or an insulator (a semiconductor) depending on the way it is activated by an electrons flow. The switching time is very fast, in the order of a few nanosecond: this is the time it takes to move from being a conductor to being an insulator, to let electrons flow or to stop them. This on/off switching is the enabler of processing.

The electrons flow generates heat and engineers have been working in the last 40 years to decrease as much as possibile the flow of electrons to decrease the heat generation and at the same time to find new ways to dissipate the heat, as more and more transistors are packed per volume unit.  In spite of all the progress we are coming near to the point where further increase in speed and density becomes impossible.

Now a team of researchers at the University of St. Petersburg, Russia, have published a paper announcing the success of an experiment where a silicon nanoparticle can be switched on/off using photons forming a burst from a laser.

The burst changes the dielectric permittivity of the silicon nanoparticle in picoseconds, that is a thousand times faster than the fastest transistors we have in our chips. This change affects the way a laser beam (carrying the signal) is scattered hence we can take the scattering in one direction as a "1" and in the other direction as a "0". We have an optical switch, a very very fast one and one that uses very little power.

This is probably the first time that we see an optical transistor with characteristics far exceeding the ones of an electron based transistor. It is still a long way from the complexity of today's chip but it is a very important step towards an optical computer.

Author - Roberto Saracco

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