  In this work, we present an in-depth experimental and numerical study of the
short-range THz communications links that use subwavelength dielectric fibers
for information transmission and define main challenges and tradeoffs in the
link implementation. Particularly, we use air or foam-cladded
polypropylene-core subwavelength dielectric THz fibers of various diameters
(0.57-1.75 mm) to study link performance as a function of the link length of up
to ~10 m, and data bitrates of up to 6 Gbps at the carrier frequency of 128 GHz
(2.34 mm wavelength). We find that depending on the fiber diameter, the quality
of the transmitted signal is mostly limited either by the modal propagation
loss or by the fiber velocity dispersion (GVD). An error-free transmission over
10 meters is achieved for the bit rate of 4 Gbps using the fiber of smaller
0.57 mm diameter. Furthermore, since the fields of subwavelength fibers are
weakly confined and extend deep into the air cladding, we study the modal field
extent outside of the fiber core, as well as fiber bending loss. Finally, the
power budget of the rod-in-air subwavelength THz fiber-based links is compared
to that of free space communication links and we demonstrate that fiber links
offer an excellent solution for various short-range applications.
