A new ultra-fast, ultra-small optical switch has taken us a step closer to the day where photons could replace electrons in technologies ranging from smartphones to smart cars.
The device is capable of turning on and off trillions of times per second vis-à-vis individual switches that measure one five-hundredths the width of a human hair in diameter — a size significantly smaller than the current generation of optical switches.
The team involved in this project includes scientists and engineers from Vanderbilt University, the University of Alabama-Birmingham, and Los Alamos National Laboratory. Their work, published in the March 12 issue of the journal Nano Letters, describes a switch made of an artificial material specially engineered to not have properties found in nature.
Specifically, this “metamaterial” is made up of nanoscale particles of vanadium dioxide — a crystalline solid that can rapidly switch back and forth between an opaque, metallic phase and a transparent, semiconducting phase.
When deposited on a glass substrate, coated with a “nanomesh” of tiny gold nanoparticles, and exposed to brief pulses from an ultrafast laser, hot electrons generated in the gold nanomesh jumped into the vanadium dioxide, causing it to undergo its aforementioned opaque-to-transparent phase change.
And amazingly enough, the material switched its state over and over again, every few trillionths of a second.
“We had previously triggered this transition in vanadium dioxide nanoparticles directly with lasers and we wanted to see if we could do it with electrons as well,” said Richard Haglund, Stevenson Professor of Physics at Vanderbilt, who led the study. “Not only does it work, but the injection of hot electrons from the gold nanoparticles also triggers the transformation with one fifth to one tenth as much energy input required by shining the laser directly on the bare VO2.”
As one can imagine, there is a great deal of excitement surrounding this super-fast, super-efficient technology. That’s because the marriage of optics and electronics is considered the next logical phase in the evolution of information and communications technology, and the group’s discovery is considered a major step forward in its progress.
“Vanadium dioxide switches have a number of characteristics that make them ideal for optoelectronics applications,” said Haglund. Along with being fast, small, and efficient, they’re also compatible with current integrated circuit technology (both silicon-based and high-K dielectric-based), operate in the visible and near-infrared region of the spectrum (ideal for telecommunications applications), and generate an amount of heat low enough that the switches can be packed tightly together to make devices practical in size.
“Vanadium dioxide’s amazing properties have been known for more than half a century. At Vanderbilt, we have been studying VO2 nanoparticles for the last ten years, but the material has been remarkably successfully at resisting theoretical explanations,” said Haglund. “It is only in the last few years that intensive computational studies have illuminated the physics that underlies its semiconductor-to-metal transition.”
Story via vanderbilt.edu
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