March 9, 2022
Keio University
Rice University
A research group led by 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 at Rice University has successfully developed an electrically driven thermal light source that directly generates polarized light over a broad wavelength band. This was achieved using a carbon nanotube alignment film, which consists of densely aligned and stacked one-dimensional nanomaterials called carbon nanotubes. This new light source overturns the conventional wisdom that “thermal light sources can only produce unpolarized light” and is expected to have applications in various fields that utilize polarized light.
Technology using polarized light is important in many fields, such as analysis, sensing, and optical devices, and is widely used in everything from basic research to industry. Currently, laser sources are used to directly generate polarized light, but in principle, they can only produce light of a specific single wavelength, resulting in an extremely narrow emission spectrum. On the other hand, thermal light sources, such as incandescent light bulbs, have a very broad emission spectrum and are still widely used today, mainly as light sources in the wide visible to infrared wavelength range. However, conventional thermal light sources can only produce unpolarized light and cannot directly generate polarized light, requiring the incorporation of a polarizer to utilize polarization.
In this study, we developed a light-emitting device using a high-density, close-packed carbon nanotube alignment film as a new thermal light source material, and realized a polarized thermal light source that emits over a broad wavelength band from visible to infrared. This achievement demonstrates the direct generation of “polarized” thermal radiation from a macroscopic material with a diameter of 1 cm or more. Furthermore, by utilizing the electrical and thermal anisotropy of the carbon nanotube alignment film, we also succeeded in controlling emission characteristics such as localized emission. The fact that light from a thermal source is normally “unpolarized” is a well-known physical phenomenon, even introduced in science education, but this result shows that this is a new thermal light source that overturns this conventional wisdom. In addition to being an electrically driven light source, it can be a polarized thermal light source on a micro-fabricated chip, and is expected to open up completely new applications for polarization in various fields such as analysis, sensing, and optical devices.
The results of this research were published in the online edition of *ACS Materials Letters* by the American Chemical Society (ACS) on March 7, 2022.
Please see below for the full press release.