Terahertz (THz) waves have garnered significant interest over the past decades for their capability of passing through media without causing any damage, making them ideal candidates for biomedical applications. The main issue with THz wave control is the tunability of their polarization. The latter is a crucial condition for the optimization of THz applications allowing to enhance signal strength as well as imaging and sensing. Current solutions for polarization control use bulky wave plates and metamaterial rendering them cumbersome for system integration and rely on narrow frequency ranges. Hence, the search for flexible ways of controlling THz wave polarization is central for a wide range of applications.
In their paper issued in Advanced Photonics, a group of researchers from Beihang University in China developed a device based on spintronic sources allowing to modulate the polarization of the THz wave during its generation. The emitters were made from trilayer heterostructures of tungsten, cobalt-iron-boron, and platinum nanofilms. A femtosecond laser irradiates the heterostructures and induces a spin-polarized current which is then transformed via inverse spin Hall effect in ultrafast transverse in-plane charge current radiating THz waves (c.f. figure). The rotation of the emitter allows the fine tuning of the polarization state of the THz waves. Moreover, seven groups of stripe-array emitters were designed each with a specific aspect ratio proportional to the polarization state. It was found that emitter configurations with large aspect ratios combined with a precise rotation angle adjustment led to an efficient switching between left-hand and right-hand polarization.
These results obtained with this level of integration and without the use of external optical components hold tremendous promises for future applications in the domain of wireless communication and biomedical imaging.
More information: Terahertz wave control for enhanced wireless and biomedical technology
Original article: 10.1117/1.AP.7.2.026007