Keio University develops a direct light source with polarized broadband radiation

A research group comprised of Professor Hideyuki Maki of the Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, and Professor Junichiro Kono of the Department of Electrical and Computer Engineering, Rice University, has successfully developed an electrically driven light source that directly generates polarized and broad-spectrum light using a nano-device of densely packed and highly aligned carbon nanotube (CNT) films on silicon chips.

The Maki Laboratory at Keio University has previously developed various light sources using graphene and other materials. The laboratory was also working on utilizing the densely packed and highly aligned carbon nanotube (CNT) films developed at Rice University in the hopes that it would lead to a light source with new properties based the film's strong anisotropy not seen in the previous nanocarbon materials.

In this research, the group used a CNT film with 1 billion carbon nanotubes densely packed per square centimeter and placed it on a silicon chip to develop a light source device that can emit light in a wide range from visible to infrared bands. When heated with electric current, it was found that direct polarization was possible despite the broad wavelength of the broadband thermal radiation derived from blackbody radiation. Furthermore, by creating devices with a variety of carbon nanotube orientations, they found that they could obtain polarization according to the orientation of those nanotubes.

The group then developed a theoretical model based on the light emitting and polarization properties they obtained and found that the low dimensionality of the carbon nanotubes comprising the CNT film contributes significantly to the polarization, and that polarization also depends on the temperature of the nanotubes. Finally, by making aggressive use of the electrical and thermal anisotropy of the CNT film, the group also succeeded in controlling the light emitting properties and achieving localized luminescence in the micrometer range.

Professor Maki commented on the developments, saying "This polarized light source achieves direct polarization over a broadband range and can be created directly on a flat substrate or chip. We believe that this light source will enable new applications using polarization, such as use in an integrated optical device that integrates polarized light directly on the substrate, or technologies for utilizing polarization analysis or spin measurement at the micro level."