
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. (Purdue University image/Nathaniel Kinsey)
Researchers in the US have demonstrated what is in effect an ‘optical transistor’ which can modulate light, as in optical fibre communications, at terahertz frequencies.
The team at Purdue University claim that the so-called “plasmonic oxide material” could make possible devices for optical communications that are at least 10 times faster than conventional technologies.
The optical material made of aluminum-doped zinc oxide (AZO) which can modulate a light signal by 40%, has been shown to work in the near-infrared range of the spectrum, which is used in optical communications.
Significantly, the fabrication process is compatible with a CMOS manufacturing process, which opens the way to commercial devices.
The researchers have proposed creating an “all optical plasmonic modulator using CMOS-compatible materials,” or an optical transistor.
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.
“So what we would like to do is drastically speed this up,” said doctoral student Nathaniel Kinsey.
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.
“We were surprised that it was this fast,” said Kinsey.
The increase in speed could translate into devices at least 10 times faster than conventional silicon-based electronics.
The AZO films are said to be “Epsilon-near-zero,” meaning the refractive index is near zero, a quality found normally in metals and new “metamaterials,” which contain features, patterns or elements that enable unprecedented control of light by harnessing clouds of electrons called surface plasmons.
The pulsing laser light changes the AZO’s index of refraction, which, in turn, modulates the amount of reflection and could make higher performance possible.
“If you are operating in the range where your refractive index is low then you can have an enhanced effect, so enhanced reflection change and enhanced transmission change,” he said.
The ongoing research is based at Purdue’s Birck Nanotechnology Center and is funded by the Air Force Office of Scientific Research, a Marie Curie Outgoing International Fellowship, the National Science Foundation, and the Office of Naval Research.
Findings were detailed in a research paper appearing in July in the journal Optica, published by the Optical Society of America.
Richard Wilson