‘Plasmonic’ material could bring ultrafast all-optical communications

‘Plasmonic’ material could bring ultrafast all-optical communications

5:38 PM, 1st August 2015
‘Plasmonic’ material could bring ultrafast all-optical communications
This rendering depicts a new “plasmonic oxide material” that could make possible devices for optical communications that are at least 10 times faster than conventional technologies.

WEST LAFAYETTE, US: Researchers have created a new “plasmonic oxide material” that could make possible devices for optical communications that are at least 10 times faster than conventional technologies.

In optical communications, laser pulses are used to transmit information along fibre-optic cables for telephone service, the Internet and cable television.

Researchers at Purdue University have shown how an optical material made of aluminum-doped zinc oxide (AZO) is able to modulate – or change – how much light is reflected by 40 percent while requiring less power than other “all-optical” semiconductor devices.

“Low power is important because if you want to operate very fast - and we show the potential for up to a terahertz or more - then you need low energy dissipation,” said doctoral student Nathaniel Kinsey.

Being able to modulate the amount of light reflected is necessary for potential industrial applications such as data transmission.

“We can engineer the film to provide either a decrease or an increase in reflection, whatever is needed for the particular application,” said Kinsey, working with a team of researchers led by Alexandra Boltasseva, an associate professor of electrical and computer engineering, and Vladimir Shalaev, scientific director of nanophotonics at Purdue’s Birck Nanotechnology Centre and a distinguished professor of electrical and computer engineering. “You can use either an increase or a decrease in the reflection to encode data. It just depends on what you are trying to do. This change in the reflection also results in a change in the transmission.”

Findings were detailed in a research paper in the journal Optica, published by the Optical Society of America.

The material has been shown to work in the near-infrared range of the spectrum, which is used in optical communications, and it is compatible with the complementary metal–oxide–semiconductor (CMOS) manufacturing process used to construct integrated circuits. Such a technology could bring devices that process high-speed optical communications.

The researchers have proposed creating an “all optical plasmonic modulator using CMOS-compatible materials,” or an optical transistor.

In electronics, silicon-based transistors are critical building blocks that switch power and amplify signals. An optical transistor could perform a similar role for light instead of electricity, bringing far faster systems than now possible.

The Optica paper, featured on the cover of the journal, was authored by Kinsey, graduate students Clayton DeVault and Jongbum Kim; visiting scholar Marcello Ferrera from Heriot-Watt University in Edinburgh, Scotland; Shalaev and Boltasseva.

Exposing the material to a pulsing laser light causes electrons to move from one energy level called the valence band to a higher energy level called the conduction band. As the electrons move to the conduction band they leave behind “holes” in the valance band, and eventually the electrons recombine with these holes.

The switching speed of transistors is limited by how fast it takes conventional semiconductors such as silicon to complete this cycle of light to be absorbed, excite electrons, produce holes and then recombine.

This cycle takes about 350 femtoseconds to complete in the new AZO films, which is roughly 5,000 times faster than crystalline silicon and so fleeting that light travels only about 100 microns, or roughly the thickness of a sheet of paper, in that time.

The increase in speed could translate into devices at least 10 times faster than conventional silicon-based electronics.

© Purdue University News

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