Continuous fabrication of polarization maintaining fibers via an annealing improved infinity additive manufacturing technique for THz communications

We report the design and fabrication of a polarization-maintaining fiber for appli-cations in fiber-assisted THz communications. The fiber features a subwavelength square core suspended in the middle of a hexagonal over-cladding tube by four bridges. The fiber is designed to have low transmission losses, high birefringence, high flexibility, and near-zero dispersion at the carrier frequency of 128 GHz. An infinity 3D printing technique is used to continuously fabricate a 5 m-long polypropylene fiber of -6.8 mm diameter. The fiber transmission losses are furthermore reduced by as high as -4.4 dB/m via post-fabrication annealing. Cutback measurements using 3 m-long annealed fibers show -6.5-11 dB/m and -6.9-13.5 dB/m losses (by power) over a 110-150 GHz window for the two orthogonally polarized modes. Signal transmission with bit error rates of -10-11-10-5 is achieved at 128 GHz for 1-6 Gbps data rates using a 1.6 m-long fiber link. The average polarization crosstalk values of -14.5 dB and -12.7 dB are demonstrated for the two orthogonal polarizations in fiber lengths of 1.6-2 m, which confirms the polarization-maintaining property of the fiber at -1-2 meter lengths. Finally, THz imaging of the fiber near-field is performed and shows strong modal confinement of the two orthogonal modes in the suspended-core region well inside of the hexagonal over-cladding. We believe that this work shows a strong potential of the infinity 3D printing technique augmented with post-fabrication annealing to continuously produce high-performance fibers of complex geometries for demanding THz communications applications.