THz-fiber waveguide composed of a biocompatible Vaseline core and Teflon holey cladding enabling a centimeter bending radius

In this study, we introduce and experimentally validate, to our knowledge, a new type of terahertz (THz) fiber waveguide. The waveguide features a core made from petroleum jelly (commonly known as Vaseline) and a cladding made of holey polytetrafluoroethylene (PTFE), also known as Teflon. Since the core is biocompatible and the cladding is safe for human use, this design has promising applications for biocompatible probes in the THz range. We rigorously analyzed the transmission properties of the waveguide using the finite element method (FEM) and followed up with experimental validation using a THz time-domain spectroscopy (THz-TDS) system. The fiber supports single-mode operation for frequencies below 0.9 THz and demonstrates low-loss transmission of THz waves, even when tightly bent. For instance, with a bending radius as small as 1.61 cm, the fiber exhibited minimal losses of 0.23 dB/cm at 0.2 THz and 0.27 dB/cm at 0.5 THz, surpassing previous technical limitations. Another key advantage is the strong confinement of the THz waves within the petroleum jelly core, which helps maintain low dispersion and ensures stable pulse transmission, even under tight bends. The exceptional stability and flexibility of this biocompatible THz fiber make it highly suitable for sensing and imaging applications in confined, flexible environments, including potential uses within the human body.