  Polymer compounds from titania-doped polyethylene are fabricated and their
linear optical properties characterized by THz-TDS. We show that high
concentration of dopants not only enhances the refractive index of the
composite material, but also can dramatically raise its absorption coefficient.
We demonstrate that the design of Bragg reflectors based on lossy composite
polymers depends on finding a compromise between index contrast and
corresponding losses. A small absorption value is also shown to be favorable,
compared to an ideal lossless reflector, as it enables to smooth the
transmission passbands. Transmission measurements of a fabricated hollowcore
Bragg fiber confirm simulation results.
