Flexible single-mode hollow-core terahertz fiber with metamaterial cladding

Abstract

A key requirement for achieving high-density integration of terahertz (THz) systems is a strongly confining single-mode and low-loss waveguide. Several waveguide solutions based on technologies from both electronics and photonics have been proposed; among these, hollow-core waveguides are one of the best options for guiding THz radiation due to their very low material absorption of air. However, to minimize reflection losses, hollow-core waveguides typically have a core diameter larger than the operating wavelength, and as a consequence are multimode. Here, we report on a single-mode, single-polarization hollow-core THz fiber with a metamaterial cladding, consisting of subwavelength-diameter metal wires embedded in a dielectric host. The idea of using metal–dielectric hybrid cladding relies on the extreme anisotropy of wire metamaterials, which reflects transverse magnetic (TM) waves and transmits transverse electric waves, leading to a waveguide structure that only confines TM modes—thus halving the number of modes from the outset. Numerical simulations and experimental measurements confirm a wide single-mode single-polarization window ranging from 0.31 to 0.44 THz, with a wavelength-sized core (0.88 mm diameter). Our work overcomes a stumbling block for achieving compact and flexible single-mode THz waveguides, which may be important for future THz systems with high-density integration.