Robert Chang of the Northwestern University in Evanston, Illinois, USA, and colleagues hope to give the digital world an infrared boost that will allow much larger amounts of data to be transmitted more quickly. The team has found a way to tune plasmons in semiconducting indium tin oxide nanorod arrays and so modulate light signals in the near-infrared to mid-infrared region. They report details in the journal Nature Photonics [Chang et al., Nature Photonics (2016) DOI: 10.1038/nphoton.2016.14]

The team reports that localized surface plasmon resonances (LSPRs) of metallic nanostructures in the near infrared can be used to confine light at sub-wavelength scales. This phenomenon has been used in sensing, nanolasers, photovoltaic devices and nano-antennas. Controlling plasmon, which are quantum particles that arise from the collective oscillations of free electrons, might also lead the way to ultrafast switching for devices that use enhanced harmonic generation and optical processing. The team points out that systems that use ultraviolet to visible with noble metals, such as gold, have been investigated previously, but infrared despite its promise for telecommunications has remained at the whim of solvent effects and instabilities.

As such, the team has turned to transparent semiconducting oxides which they suggest, with their lower carrier densities than gold and being compatible with semiconductor processing might be useful for developing devices for controlling plasmons and so enabling optical switches, for fiber optic signals that would work at terahertz switching rates. The same developments might be used not only in ultrafast data transfer in telecommunications, but in thermal engineering, infrared sensing, light emission and imaging.

Chang and his colleagues Peijun Guo, Richard Schaller (Argonne National Laboratory) and John Ketterson, have now successfully controlled plasmons using indium-tin-oxide (ITO) nanorod arrays. ITO has a lower electron density and this enables a significant redistribution of electron energies. The team explains that this results in light signal modulation with very large absolute amplitude. They add that by simply changing the geometry of the ITO nanorod arrays, they were able to further tune the spectroscopic range of the signal modulation to suit a particular requirement. The system displays dynamics on a timescale smaller than a picosecond. This is far faster than the earlier work with noble metal systems, all of which opens the door for improved telecommunications and molecular sensing.

"Our results pave the way for robust manipulation of the infrared spectrum using heavily doped, semiconductor-enabled material platforms," the team concludes. "Using a similar principle, we are now working on ultrafast switching extending all the way to the visible spectrum and beyond," Chang told Materials Today.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the bestselling science book "Deceived Wisdom".