Fabricating efficient terahertz polarisation rotators via two photon lithography

Although advances in THz radiation sources have resulted in a wide variety of applications in communications, security scanning, medical imaging, spectroscopy, etc., an absence of viable sources has stalled the transition of THz technologies from the laboratory into the real world. This has in turn led to a resounding lack of commercially available THz components. Typical computer numerical control (CNC) machining tolerances are on the order of 100 µm, which is much higher than the submicron accuracy that would be ideal for the fabrication of THz components. Here, we present a twisted waveguide designed to rotate the electric field polarisation of free space THz radiation from 1 THz to 2.5 THz by 90° with near perfect efficiency, fabricated using two-photon lithography. We envision such methods being utilised for the quick prototyping of various passive THz components in both the laboratory and commercial settings.