Researcher sheds light on using subwavelength photonic systems

Electrical and optical components continue to get smaller and smaller. As this occurs, it becomes necessary to find new ways to transfer information to, from and between these components. One proposed method of linking these elements and transferring this information is to use optical signals (light). But as components continue to shrink in size, that approach is reaching its limits. 

New research by Daniel M. Wasserman, an assistant professor of electrical and computer engineering (ECE), may help point the way to link ever-shrinking nanoscale components to the macro-scale world around them.

Though Wasserman, a researcher in the Micro and Nanotechnology Lab, has only recently joined the Illinois faculty, he hit the ground running with an article that was published in Physical Review Letters, titled “Funneling Light Through a Subwavelength Aperture with Epsilon-Near-Zero Materials.” This article features work he did while at the University of Massachusetts, Lowell, and will continue while at Illinois.

Wasserman and his team tackled some major issues facing the integration of macro-scale optical components with increasingly subwavelength photonic and electronic subsystems. “There’s something of a limit as to how small you can make a traditional photonic component,” said Wasserman, “and this is the wavelength of the light you are working with. So many people are really interested in making sub-wavelength optical devices like nanolasers, devices that emit light that with a wavelength larger than the device itself.  We are trying to figure out how to efficiently connect or couple these devices with the macro-scale outside world.

In other words, if you decrease the size of your emitter or detector below the wavelength of the light which it emits or detects, how can you get it to work with a traditional photonic waveguide.

In their experiment, Wasserman’s team grew “doped” semiconductors, adding more and more electrons to their material, which turns the semiconductors into metals. As Wasserman explained, semiconductors have a positive permittivity, and metals have negative permittivity. At a certain crossover point, the permittivity would be zero. At this point, it becomes an epsilon-near-zero (ENZ) material.

Usually, materials with many electrons absorb light, eliminating transmission. However, Wasserman’s team discovered that when the highly doped semiconductors are covered with very small apertures the combined structure will actually transmit more light through the subwavelength aperture than an identical device where the ENZ material is replaced by a standard (lossless) semiconductor.

“Light that’s incident on that ENZ slab—even away from the subwavelength aperture—all contributes to excite the oscillation of electrons,” said Wasserman. “And excitation is funneled into the aperture, which can’t happen with your traditional semiconductor. “

The importance of this research, said Wasserman, is that it offers a new path to efficiently coupling subwavelength devices to free-space radiation, which in turn will optimize the integration of increasingly nanoscale optical structures into macro-scale systems.

Many of the authors on the article are students of Wasserman’s from the University of Massachusetts, Lowell. Already for his laboratory at Illinois he is working with three graduate students, and he is expecting more to join in the coming years?. If the work he did as he was leaving Massachusetts is any indication of what he’ll be doing at Illinois, the University can expect an exciting—and enlightening—collection of results.
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Contact: Daniel M. Wasserman, Department of Electrical and Computer Engineering, 217/333-9872.

Writer: Tom Moone, communications coordinator, Department of Electrical and Computer Engineering, 217/244-9893.

If you have any questions about the College of Engineering, or other story ideas, contact Rick Kubetz, Engineering Communications Office, 217/244-7716, editor. University of Illinois at Urbana-Champaign.