Scientists invent smallest known way to guide light

 Directing light from place to the place is the backbone of our modern world. Beneath the oceans and across continents, fiber optic cables carry light that encodes everything from YouTube videos to banking transmissions -- all inside strands about the size of a hair.

University of Chicago Prof. Jiwoong Park, however, wondered what would happen if you made even thinner and flatter strands -- in effect, so thin that they're actually 2D instead of 3D. What would happen to the light?

Through a series of innovative experiments, he and his team found that a sheet of glass crystal just a few atoms thick could trap and carry light. Not only that, but it was surprisingly efficient and could travel relatively long distances -- up to a centimeter, which is very far in the world of light-based computing.

The research, published Aug. 10 in Science, demonstrates what are essentially 2D photonic circuits, and could open paths to new technology.

"We were utterly surprised by how powerful this super-thin crystal is; not only can it hold energy, but deliver it a thousand times further than anyone has seen in similar systems," said lead study author Jiwoong Park, a professor and chair of chemistry and faculty member of the James Franck Institute and Pritzker School of Molecular Engineering. "The trapped light also behaved like it is traveling in a 2D space."

Guiding light

The newly invented system is a way to guide light -- known as a waveguide -- that is essentially two-dimensional. In tests, the researchers found they could use extremely tiny prisms, lenses, and switches to guide the path of the light along a chip -- all the ingredients for circuits and computations.

Though theoretical scientists had predicted that this behavior should exist, actually realizing it in the laboratory was a years-long journey, the scientists said.

"It was a really challenging but satisfying problem, because we were walking into a completely new field. So everything we needed we had to devise ourselves -- from growing the material to measuring how the light was moving," said graduate student Hanyu Hong, the co-first author of the paper.

Myungjae Lee (formerly a postdoctoral researcher at UChicago, now faculty at Seoul National University) was the other first co-author of the paper. Postdoctoral researcher Jaehyung Yu, Fauzia Mujid (PhD'22, now at Ecolab), and graduate students Andrew Ye and Ce Liang were also authors on the paper.

The scientists used the University of Chicago Materials Research Science and Engineering Center, the fabrication facilities of the Pritzker Nanofabrication Facility, and the Cornell Center for Materials Research.