We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

Emerging Technology from the arXiv

A View from Emerging Technology from the arXiv

10 GHz Optical Transistor Built Out Of Silicon

In a significant step forward for all-optical computing, physicists build a silicon transistor that works with pure light

  • April 30, 2012

Electrons are pretty good at processing information but not so good at carrying it over long distances. Photons, on the other hand, do a grand job of shuttling data round the planet but are not so handy when it comes to processing it.

As a result, transistors are electronic and communication cables are optical. And the world is burdened with a significant amount of power hungry infrastructure for converting electronic information into the optical variety and vice versa.

So it’s no surprise that there is significant interest in developing an optical transistor that could make the electronic variety obsolete. 

There’s a significant problem, however. While various groups have built optical switches, optical transistors must also have a number of other properties so that they can be connected in a way that can process information. 

For example, their output must be capable of acting as the input for another transistor–not easy if the output is a different frequency from the input, for instance. What’s more, the output must be capable of driving the input for at least two other transistors so that logic signals can propagate, a property known as fanout.  This requires significant gain. On top of this, each transistor must preserve the quality of the logic signal so that errors do no propagate. And so on. 

The trouble is that nobody has succeeded in making optical transistors that can do all and can also be made out of silicon. 

Today, Leo Varghese at Purdue University in Indiana and a few pals say they’ve built a device that take a significant step in this direction. 

Their optical transistor consists of a microring resonator next to an optical line. In ordinary circumstances the light supply enters the optical line, passes along it and then outputs. But at a specific resonant frequency, the light interacts with the microring resonator, vastly reducing the output. In this state, the output is essentially off even though the supply is on. 

The trick these guys have perfected is to use another optical line, called the gate, to heat the microring, thereby changing its size, its resonant frequency and its ability to interact with the output. 

That allows the gate to turn the output on and off.   

There’s an additional clever twist. The microring’s interaction with the gate is stronger than with the supply-output line. That’s significant because it means a small gate signal can control a much bigger output signal.

Varghese and co say the ratio of the gate signal to the supply is almost 6 dB. That’s enough to power at least two other transistors, which is exactly the fan out property that optical transistors require. 

These guys have even built a device out of silicon with a bandwidth capable of data rates of up to 10 GHz.

That’s an impressive result, particularly the silicon compatibility. 

Nevertheless, there are significant hurdles ahead before an all-optical computer made with these devices can hope to compete against its electronic cousins. 

The biggest problem is power consumption. Much of the power consumption in electronic transistors comes from the need to charge the lines connecting them to the operating voltage. 

In theory, optical transistors could be even more efficient–their lines don’t need charging at all. But in practice, lasers burn energy as if it were twenty dollar bills. For that reason, it’s not at all clear that optical transistors can match the efficiency of electronic chips.  

And with the computer industry now responsible for almost 2 per cent of global carbon dioxide emissions, almost as much as aviation, power consumption may turn out to be the overarching factor for the future direction of information processing.

Ref: arxiv.org/abs/1204.5515: A Silicon Optical Transistor

AI is here.
Own what happens next at EmTech Digital 2019.

Register now
More from Intelligent Machines

Artificial intelligence and robots are transforming how we work and live.

Want more award-winning journalism? Subscribe to Insider Plus.
  • Insider Plus {! insider.prices.plus !}*

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    Print + Digital Magazine (6 bi-monthly issues)

    Unlimited online access including all articles, multimedia, and more

    The Download newsletter with top tech stories delivered daily to your inbox

    Technology Review PDF magazine archive, including articles, images, and covers dating back to 1899

    10% Discount to MIT Technology Review events and MIT Press

    Ad-free website experience

You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.