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Terahertz (THz) fiber that provides high-speed connections is an essential component in THz communication systems. The emerging space-division-multiplexing technology is expected to increase the transmission capacity of THz communications. A promising candidate to achieve that is integrating multiple channels in a compact THz multi-core fiber system. Here, we propose and experimentally demonstrate a THz subwavelength rectangular dielectric dual-core fiber structure, where two identical cores can be densely integrated, thanks to the polarization-maintaining feature of the rectangular fiber. Different configurations, including the placements, core-spacings, and polarization states of two fiber cores, are comprehensively investigated to improve channel isolation. Numerical simulations show that the fractional power in core of fiber mode has a dominant effect on inter-core coupling performance. Moreover, we design the core size (1 mm x 0.5 mm) slightly less than the WR5.1 waveguide (1.295 mm x 0.6475 mm) so that the fiber can be conveniently connected with the WR5.1 flange port with mode excitation efficiencies up to 62.8%. A cost-efficient dielectric 3D printing technique is employed for rapid fabrications of dual-core fibers and corresponding polymer flange structures that offer solid integration between the fiber samples and the WR5.1 port. Experimental measurements demonstrate that a 4-mm core-spacing (less than three times the operation wavelengths over 0.17-0.21 THz) supports robust dual-channel propagation with channel isolation values more than 15 dB, which are consistent with theoretical and numerical results. This work provides a densely integrated dual-core fiber system with low fabrication cost and practical connection to the WR5.1 flange, holding exciting potential for high-capacity THz space-division-multiplexing communication systems., Comment: 10 pages, 9 figures, 3 tables

The recent development of the terahertz waveguide makes it an excellent platform for integrating many intriguing functionalities, which offers tremendous potential to build compact and robust terahertz systems. In the context of next-generation high-speed communication links at the terahertz band, engineering the dispersion and birefringence of terahertz waves is essential. Here, we experimentally demonstrate subwavelength birefringent waveguide gratings based on the low-loss cyclic olefin copolymer exploiting micro-machining fabrication techniques. Asymmetric cross-section and periodic-structural modulation along propagation direction are introduced to achieve birefringent THz grating for filtering and dispersion compensation. Because of strong index modulation in the subwavelength fiber, a high negative group velocity dispersion of -188 (-88) ps/mm/THz is achieved at 0.15 THz for x-polarization (y-polarization), i.e., 7.5 times increase compared to the state-of-the-art reported to date. Such high negative dispersion is realized in a 43 mm grating length, which is less than half of the length reported until now (e.g., 100 mm). Further, the subwavelength fiber grating filters two orthogonal polarization states and exhibits transmission dips with 8.5-dB and 7.5-dB extinction ratios for x and y polarization, respectively. Our experiment demonstrates the feasibility of using polymer-based terahertz gratings as a dispersion compensator in terahertz communications and steering polarized terahertz radiations for polarization-sensitive THz systems.

Compact and robust waveguide chips are crucial for new integrated terahertz applications, such as high-speed interconnections between processors and broadband short-range wireless communications. Progress on topological photonic crystals shows potential to improve integrated terahertz systems that suffer from high losses around sharp bends. Robust terahertz topological transport through sharp bends on a silicon chip has been recently reported over a relatively narrow bandwidth. Here, we report the experimental demonstration of topological terahertz planar air-channel metallic waveguides which can be integrated into an on-chip interconnect. Our platform can be fabricated by a simple, cost-effective technique combining 3D-printing and gold-sputtering. The relative size of the measured topological bandgap is ~12.5%, which entails significant improvement over all-silicon terahertz topological waveguides (~7.8%). We further demonstrate robust THz propagation around defects and delay lines. Our work provides a promising path towards compact integrated terahertz devices as a next frontier for terahertz wireless communications., Comment: 18 pages, 4 figures

A novel terahertz hybrid waveguide chip consisting of silicon photonic crystals sandwiched in parallel gold plates is developed. Both simulation and experimental results demonstrate that the hybrid waveguide offers a wide single-mode transmission window with low group velocity dispersion and low loss. This compact, substrate-free terahertz chip would play a significant role in broadband, dense-integrated, multi-functional terahertz systems.

We demonstrate that porous fibers have low effective material loss over an extended frequency range, 4.5 times larger bandwidth than that can be achieved in sub-wavelength solid core fibers. We also show that these new fibers can be designed to have near zero dispersion for 0.5-1 THz resulting to overall less terahertz signal degradation. In addition, it is demonstrated that the use of asymmetrical sub-wavelength air-holes within the core leads to high birefringence ~0.026. This opens up the potential for realization of novel polarization preserving fibers in the terahertz regime., Comment: The following article has been submitted to Applied Physics Letters. If it is published,it will be found online at http://apl.aip.org