Hollow optical fibers loaded with an inner dielectric film for terahertz broadband spectroscopy

A design method for hollow optical fibers is shown that has a dielectric cover film loaded on the inner metal coating to obtain flexible fiberoptics transmitting a wide wavelength range in THz region with low loss. Spectral losses of fibers that are fabricated by two different methods are measured by using a broadband THz source. The loss of a fiber with an inner diameter of $3\mathrm{mm}$ was $1.3\mathrm{dB}∕\mathrm{m}$ at the wavelength of $200\mu \mathrm{m}$, and the losses were lower than $3\mathrm{dB}$ in the wavelength region from $150\mu \mathrm{m}\text{to}>250\mu \mathrm{m}$. Because these fibers are flexible, robust, and highly efficient in a wide wavelength range, they are useful in remote THz spectroscopy.