"Potential applications in medicine are exciting," says J. Gary Eden, professor of electrical and computer engineering (ECE) at the University of Illinois Urbana-Champaign (UIUC). "We have made optical systems at the microscopic scale that amplify light and produce ultra-narrowband spectral output," he adds, explaining a new optical amplifier (or laser) design that paves the way for power-on-a-chip applications. Actuated by light that penetrates human skin, the amplifiers can transmit signals—produced by cells and biomedical sensors—to electrical and optical networks outside the body.1
The speed of currently available semiconductor electronics is limited to about 10 GHz due to heat generation and interconnect delays. Dielectric-based photonics, though not limited in speed, are limited in size by the laws of diffraction. The researchers, led by Eden and ECE associate professor Logan Liu, discovered a path to the best of both worlds: Plasmonics—metal nanostructures—can serve as a bridge between photonics and electronics, to combine small size and high speed.
"We have demonstrated a novel optoplasmonic system comprising plasmonic nanoantennas and optical microcavities capable of active nanoscale field modulation, frequency switching, and amplification of signals," states Manas Ranjan Gartia, lead author of an article describing the work.1 "This is an important step forward for monolithically building on-chip light sources inside future chips that can use much less energy while providing superior speed performance of the chips."
At the heart of the amplifier is a polystyrene or glass microsphere about 10 µm in diameter. When activated by an intense beam of light, the sphere generates internally a narrowband optical signal that is produced by a process known as Raman scattering. Molecules tethered to the surface of the sphere by a protein amplify the Raman signal, and in concert with a nano-structured surface in contact to the sphere, the amplifier produces visible light having a bandwidth that matches the internally generated signal.
Precise manipulation of light at the micro- and nano-spatial scales is necessary for realizing physical analogs of optical processes in biology, and for pursuing applications in areas such as embedded biomedical sensors.
1. M. R. Gartia et al., Sci. Rep., 4, 6168 (2014); doi:10.1038/srep06168.