Terahertz (THz) technology has shown great potential for non-invasive imaging, spectroscopy, and high-speed communication with a tied efficiency to the performance of active and passive elements in the system. The development of passive devices has turned towards additive manufacturing (AM) due to its flexibility and rapid prototyping. However, AM's potential in THz technology is constraint by a lack of materials with both high transparency and refractive index in the THz range.

Our research addresses this gap by creating a high refractive index material suitable for AM. We've developed Titania–polymer composites with a refractive index tunable from 1.65 to 1.95 in the THz range, utilizing rutile TiO2's high dielectric constant. This elevation trend was confirmed through THz time-domain spectroscopy, showing the composites' effective frequency response. Further, Fourier Transform Infrared Spectroscopy (FTIR) verified the structural integrity of the base polymer.

To demonstrate the material's practicality, we designed and 3D printed a compact plano-convex lens for THz communication systems. This lens, significantly smaller than existing commercial options, effectively transmitted 16-QAM OFDM signals over a 2-meter free-space link. Our results show this lens maintains a low bit error rate, indicating a significant stride in compact and efficient THz system design. This advancement opens new possibilities in THz technology, enhancing applications in various fields and paving the way for more versatile and effective THz devices.