All-Optical Computing Gets Another Arrow in Its Quiver

Nanowire networks produce all-optical logic gates

A set of vertical purple lines, some broken, sit atop a horizontal green line that bisects the image
Image: Aalto University/Science Advances
A false-color micrograph of nanowires made of indium phosphide (purple) forming junctions with a nanowire made of aluminium gallium arsenide (green).

All-optical computing promises to replace sluggish electrons with photons zipping along at light speed in digital logic. But despite years of effort and some progress in related areas such as plasmonics, such computing has remained largely just a promise. 

All-optical computing still needs some tools to make it into a reality. One key component of this toolbox will likely be all-optical logic gates, and researchers at Aalto University in Finland announced they have been able to fabricate such gates from nanowires in way that’s easier than ever before. The scientists believe that this represents a significant step in the development of on-chip, all-optical logic components that will serve as a key element in future photonic computing systems.

In the research, described in the journal Science Advances, the Finland-based scientists managed to get their logic gate to perform AND, OR, NAND, and NOR binary logic functions—basic building blocks from which all other logic and mathematical functions can be built.

“It is nice to fabricate such a nanostructure that can perform arithmetic functions by using only light in the operation,” said Henri Jussila, a senior process engineer at ASM International and postdoctoral researcher at Aalto University as well as coauthor of the research. “That is different compared to all other processors used in our everyday life that utilize electricity.”

The scientists already have plans for future functions of these logic gates. “The next step is either to find a method how to cascade these logic gates if current “CMOS” type [computer architectures are wanted], or to figure out a completely new way to perform the desired logic operations,” added Jussila.

There are, of course, other all-optical logic gates. It has already been shown that silicon photonics can serve as all-optical logic gates using wave guides. Also, there has already been some previous work using nanowires as logic gates.

However, Jussila argues that the nanowire networks they have developed are easier to fabricate and assemble into a large area, as they don’t need highly sensitive and complex fabrication steps, such as electron beam lithography or focused-ion beams.

“The methods used to realize [previous] nanowire structures were extremely complex and that is a clear advantage of this work,” said Jussila. “In addition, our proof-of-principle demonstration occurs at room temperature due to a completely different operating principle of our device compared to those earlier nanowire-based works.”

Jussila and his colleagues believe that the engineering to get these all-optical logic gates viable is fairly straightforward. The nanowire growth can be done in standard chemical vapor deposition. Nonetheless, Jussila concedes that in the future it will be important to improve the material quality of the nanowires.

He added: “The quantum efficiency of the nanowires needs to be higher so that these switches and logic gates lose as few photons as possible when they are operating.”

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