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Exploring a Plasmonic Alternative

Plasmonic AlternativeZhaolin Lu and his team at RIT's Novel Material Photonics lab are exploring the integration of optical and electrical signals. "Recently, nanoplasmonics has risen from a relatively obscure science to a prominent field of research, says Lu, assistant professor of microsystems engineering. "Our lab is focused on experimental and theoretical aspects of this rapidly developing field. "The work has application in areas ranging from the semiconductor industry to development of surface plasmon-enhanced solar cells. Lu has received funding from the National Science Foundation, Department of Defense Advanced Research Projects Agency (DARPA), and the American Chemical Society.

Plasmons are nanoscopic waves in the sea of free electrons inside and on the surface of metals. Surfaceplasmon-based circuits, which merge electronic and photonic circuits at the nanoscale, offer the potential to carry optical signals and electric currents through the same thin metal circuitry, effectively combining photonics and electronics on the same chip.

One of the biggest challenges with photonics is that the wavelength of a guided photon is relatively large-on the order of 100 nanometers. That's much larger than what's currently possible with electronic semiconductors, where resolution of 32 or even 26 nanometers is possible. Lu is developing techniques using plasmonics to reduce the wavelength of light to potentially 10 nanometers.

To couple light into a waveguide supporting nanoscale mode size and consequently to squeeze light into an ultra-small spot are critical to imaging quality, optical data storage, manipulation of nanostructures, and optical lithography in the semiconductor industry. The extremely high light intensity resulting from the ultra-small spot can be used to make ultra-small and ultra-fast electric-optic or all-optic modulators.

Lu has successfully squeezed a 1550 nanometer infrared beam into a 21 x 24 nanometer spot with 62 percent efficiency. The project coupled light from a dielectric waveguide into a metal-dielectric-metal plasmonic waveguide, a technique developed by the RIT team. Lu's demonstration was covered in "Beam Shaping:Plasmonics Squeeze IR Light into Nanospot," an article published in Laser Focus World (January 2009).

"Plasmonic waveguides support nanoscale modes with acceptable propagation loss and are believed to be the technique merging photonics and electronics at nanoscale dimensions," Lu reported. "In this sense, nanoscale confinement of light is the initial motivation to develop surface plasmon-based circuits. A key feature of our device is that it is a planar structure and can be fabricated with standard semiconductor techniques."

Lu, who received his Ph.D. from the University of Delaware, came to RIT in 2007. He has published numerous publications, including a book, Dispersioin Engineered Photonic Crystals (2008). In 2008, he received the Texas Instruments/Douglass Harvey Faculty Development Award.