By Carol Clark
The National Science Foundation awarded two Emory physicists a $2 million Emergent Frontiers grant, for development of miniaturized optical transistors to take computers and telecommunications into a new era.
“We are working to change some properties of light — such as making it travel in only one direction — by using atomically thin, two-dimensional materials,” says Ajit Srivastava, assistant professor of physics and principal investigator for the grant. “These novel materials are being touted as the next silicon. They could open the door to even smaller and more efficient electronics than are possible today.”
Srivastava’s co-investigators include Hayk Harutyunyan, also an assistant professor of physics at Emory, as well as scientists from Georgia State and Stanford universities.
“The ultimate goal is making it possible to devise all-optical computers and telecommunications,” Harutyunyan says.
A major revolution in telecommunications occurred in the 1950s, driven by the development of silicon semiconductors as miniature transistors to control the flow of electrical current. These transistors led to smaller, faster computers and paved the way for everything from flatscreen TVs to cell phones.
“They changed civilization,” Harutyunyan says. “Every year new computers would come out with faster processors as the transistors got tinier and more efficient. But about a decade ago this progress stopped, because these transistors cannot be made any smaller than about 15 nanometers and still function well.”
Meanwhile, the gradual replacement of copper wiring with fiber optics is speeding up transmissions between computers and other electronic devices and allowing for greater bandwidth. “When you send an email from Atlanta to Europe, the information is encoded into light and relayed by fiber optic cables running under the ocean,” Srivastava explains. “It’s super fast, because light is the fastest thing that you can imagine.”
Unlike in our everyday life, however, where the arrow of time moves in one direction, light photons operate at the quantum scale and can move back and forth. This lack of a fixed direction is called reciprocity. “Reciprocity in optics,” Srivastava says, “can best be described by a familiar observation: ‘If I can see you, you can see me.’”
Fiber optic cables use magnetic fields to break reciprocity and prevent light from reflecting off surfaces and creating “noise” in a signal. The required magnetic devices, known as optical isolators, are typically bulky and heavy because tiny magnets are not strong enough to do the job.
The Emory project aims to develop powerful nonreciprocal optical devices that are not based on magnets and can function at the nanoscale.
Srivastava’s lab is investigating the potential of transition metal dichalcogenides, or TMDs. TMDs are semiconductors within a new family of two-dimensional, extraordinarily thin materials. While the smallest feature of a current computer processor is 14 nanometers thick, a TMD monolayer is smaller than a single nanometer.
Harutyunyan’s lab, meanwhile, is exploring ways to make interactions between light and matter stronger through the use of metallic nano particles. Metals are shiny because of their free electrons that easily interact with light. The oscillations of these free electrons, called plasmons, allow metallic nano-particles to funnel large amounts of light into tiny dimensions.
A long-term goal of the project is to hybridize TMDs and metallic particles into nanomaterials that use laser fields to create the same light-guiding effects of magnetic fields. Such devices have the potential to be faster and cheaper and offer more precise control of the light-directing process. They would also be much smaller than existing optical isolators and transistors.
“Nano-science is an exciting area,” Srivastava says. “You can imagine the possibility of flexible cell phones or even wearable electronic membranes that would take the shape of your body.”
More powerful computers could also ramp up the ability of scientists to analyze massive datasets faster, Harutyunyan notes.
The Emory grant will also fund public outreach projects in Atlanta area schools. “We want people to understand the importance of fundamental science research,” Harutyunyan says. “And we want to inspire young people to think about science careers.
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