  In this work, a novel infinity 3D printing technique is explored to fabricate
continuous multi-meter-long low-loss near-zero dispersion suspended-core
polypropylene fibers for application in terahertz (THz) communications.
Particular attention is paid to process parameter optimization for 3D printing
with low-loss polypropylene plastic. Three microstructured THz fibers were 3D
printed using the standard and infinity 3D printers, and an in-depth
theoretical and experimental comparison between the fibers were carried out.
Transmission losses (by power) of 4.79 dB/m, 17.34 dB/m and 11.13 dB/m are
experimentally demonstrated for the three fibers operating at 128 GHz. Signal
transmission with BER far below the forward error correction limit (10-3) for
the corresponding three fiber types of lengths of 2 m, 0.75 m and 1.6 m are
observed, and an error-free transmission is realized at the bit rates up to 5.2
Gbps. THz imaging of the fiber near-field is used to visualize modal
distributions and study optimal fiber excitation conditions. The ability of
shielding the fundamental mode from the environment, mechanical robustness and
ease of handling of thus developed effectively single-mode high optical
performance fibers make them excellent candidates for upcoming fiber-assisted
THz communications. Additionally, novel fused deposition modeling (FDM)-based
infinity printing technique allows continuous fabrication of unlimited in
length fibers of complex transverse geometries using advanced thermoplastic
composites, which, in our opinion, is poised to become a key fabrication
technique for advanced terahertz fiber manufacturing.
