  Two highly birefringent polymer terahertz (THz) fibers were proposed in this
paper, which were formed with honeycomb cladding and some elliptical air holes
in the fiber core. The losses and mode birefringence for two different fibers
are investigated by finite-different time-domain method. The results show that
fiber 2 can achieve both high birefringence (larger than 0.022) and low
confinement loss (0.01 dB/m) in a wide THz frequency range. Moreover, compared
with a round solid-core fiber, guiding loss of the THz fiber caused by polymer
material absorption can be reduced effectively as a part of the mode power is
trapped in the air holes.
