Nano-holes punch a path to photonic computing

Silicon nanohole photo detector
A computer-generated image modeling the propagation of photons through a silicon wafer after they enter a tapered nanohole.
Saif Islam, UC Davis Department of Electrical and Computer Engineering

Scientists have developed new silicon-based devices that could speed up data transfer using light – a vital advance to deal with the world’s insatiable appetite for more data.

The work, which involves punching micro- and nano-sized holes in silicon, has led to “ultrafast” devices, Nature Photonics reports.

Global internet traffic grew 200-fold between 2002 and 2015. This phenomenal growth was fuelled by widespread adoption of mobile devices, video content, cloud computing and new users.

That upsurge is pushing the world’s techno-giants, such as Intel, IBM and HP, to invest in faster ways to transfer data using light.

That’s because light can be pulsed at higher frequencies than electric currents, so you can cram in more information per second. You can also send multiple signals down a single optical fibre at the same time, using different colours of light.

Optical fibre cables are now a commonplace for long-distance communications – but integrating light within smaller networks, or even individual computer chips, is the next challenge.

One problem is that silicon, the material most computer processors are made of, is fairly transparent to the most important frequencies of light. This means the crucial step of converting a light-based, or photonic, signal to an electronic signal is very inefficient.

To compensate, device makers have to make the silicon layer very thick so the light detectors catch enough photons to register.

Now a team led by M. Saif Islam at the University of California, Davis, has improved silicon’s light-catching ability more than ten-fold by punching holes in it.

The holes help set up special resonances of light within the silicon – a bit like how a cello is specially shaped to sustain a musical note for longer.

To create the holes, the team used an etching process in which the silicon was blasted with a plasma of reactive ions. With the processes used all being standard for device manufacture, the techniques could be easily integrated in modern chips.

The improved interaction led to a data transmission rate of 20 Gb s–1 or higher per device. That’s an HD movie streaming every second onto a device half the width of a human hair.

The authors highlight how their device could find immediate application in big data centres where optical data cables are vital for shuttling the world’s data.

It’s also part of a bigger picture – the potential switch from electronics to photonics, using light to transmit information not only between computers but also within them.

Last year British scientists made a huge breakthrough with the first reliable and efficient laser grown directly on a silicon chip.

Scientists can now both create light and detect it with high efficiency using silicon, at rates that could far surpass anything electronic processing can do.

It means that some day we might look at plain old electronics and see a technology as quaint as steam engines are to us today.

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