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Optical transistors from silicon a reality

by Alistair Lowe on 1 May 2012, 11:27

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Ultimately, photons instead of electrons is where we want to end up in computing, after all, the speed of light, the fastest known speed in the universe, is understandably quicker than the two third's speed of light that electrons travel at.

Having said this, photons are quite tricky to handle and there's a reason we're not all running around with optically powered processors. For one, photons exist at different wavelengths; this varies the size of their pathways with which to travel, requiring hard to generate, high-frequency photons for smaller circuitry, which, often when passed around and manipulated have a naughty habbit of changing frequency or losing power, becoming useless in an optical circuit, often requiring the intervention of electricity.

Researchers at Purdue University have, however, invented a viable silicon transistor that can be operated entirely on photons, whilst being produced on a standard CMOS fabrication process, with the group even going so far as to build a 10GHz working sample.

Optical Transistor

The technology functions by heating up a micro-ring resonator with a photon source via the gate. When the gate is off and the ring is cold, light travelling down the supply line remains unaffected, the input is the output; however, when the gate is on and the ring is hot, its resonant frequency and effective size increase, causing it to interact and absorb energy from the supply photon, reducing the output signal, resulting in a different logic level.

What's more is that the micro-ring absorbs more energy from the gate than it does the supply line, leaving photons with enough power to operate two further gates, making it possible to form logic circuits.

This technology is a great step forwards in realising optical processors, the next task, is to reduce the power wastage of the lasers providing chips with their photons, as this is what continues to make the technology unviable for market deployment.

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