Dispersion-limited versus power-limited terahertz communication links using solid core subwavelength dielectric fibers

Terahertz (THz) band (0.1-10 THz) is the next frontier for ultra-high-speed communication systems. Currently, most of communications research in this spectral range is focused on wireless systems, while waveguide/fiber-based links have been less explored. Although free space communications have several advantages such as convenience in mobility for the end user, as well as easier multi-device interconnectivity in simple environments, fiber-based communications provide superior performance in certain short-range communication applications such as multi-device connectivity in complex geometrical environments (ex., intra-vehicle connectivity) and secure communications with low probability of eavesdropping, as well as secure signal delivery to hard-to-reach or highly protected environments. 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 the main challenges and trade-offs in the link implementation. Particularly, we use air or foamcladded 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 similar to 10 m, and data bit rates 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 m 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. (C) 2020 Chinese Laser Press