THz Plasmonic Crystal is Tunable

Normally the light passing through the atomic structure of a photonic crystal is of a fixed frequency, but light passing through a crystal containing plasma can be tuned by adjusting the voltage applied to it, say researchers in New Mexico.

Photonic crystals are artificially constructed to allow light transmission of particular wavelengths. A plasmonic crystal has the ability to direct light like a photonic crystal but has a subwavelength size and could lead to smaller photonic crystals and tunable metamaterials.

A team led by Sandia National Laboratory created a plasmonic crystal that can transmit terahertz light at varying frequencies, something potentially useful for high-speed data transmission.

Greg Dyer is co-principal investigator of a Sandia-led team that has created a plasmonic, or plasma-containing, crystal that is tunable by adjusting the voltage applied to it. The technology potentially could increase the bandwidth of high-speed communication networks. Photo by Randy Montoya, courtesy of Sandia National Lab.

The crystal's electronic plasma forms naturally at the interface of semiconductors with different bandgaps. It sloshes between their atomically smooth boundaries that, properly aligned, form a crystal. Patterned metal electrodes allow its properties to be reconfigured, altering its light transmission range. In addition, defects intentionally mixed into the electron fluid allow light to be transmitted where the crystal is normally opaque.

“Our experiment is more than a curiosity precisely because our plasma resonances are widely tunable,” said Greg Dyer, co-primary investigator. "Usually, electromagnetically induced transparencies in more widely known systems like photonic crystals and metamaterials require tuning a laser's frequencies to match a physical system. Here, we tune our system to match the radiation source. It's inverting the problem, in a sense."

A paper on the work, “Induced transparency by coupling of Tamm and defect states in tunable terahertz plasmonic crystals," appeared online Sept. 29 in Nature Photonics (DOI: 10.1038/NPHOTON.2013.252) and is expected in print in November. Other authors include Eric Shaner, Albert D. Grine, Don Bethke and John L. Reno of Sandia; Gregory R. Aizin of the City University of New York; and S. James Allen of the Institute for Terahertz Science and Technology, University of California Santa Barbara.

For more information, visit: www.sandia.gov