Low-loss subwavelength plastic fiber for terahertz waveguiding

We report a simple subwavelength-diameter plastic wire, similar to an optical fiber, for guiding a terahertz wave with a low attenuation constant. With a large wavelength-to-fiber-core ratio, the fractional power delivered inside the lossy core is reduced, thus lowering the effective fiber attenuation constant. In our experiment we adopt a polyethylene fiber with a $200\mu \mathrm{m}$ diameter for guiding terahertz waves in the frequency range near $0.3\mathrm{THz}$ in which the attenuation constant is reduced to of the order of or less than $0.01{\mathrm{cm}}^{-1}$. Direct free-space coupling efficiency as high as 20% can be achieved by use of an off-axis parabolic mirror. Furthermore, all the plastic wires are readily available, with no need for complex or expensive fabrication.