Flexible terahertz photonic light-cage modules for in-core sensing and high temperature applications

Abstract

Terahertz technology is a growing and multi-disciplinary research field, particularly in applications relating to sensing and telecommunications. A number of terahertz waveguides have emerged over the past few years, which are set to complement the capabilities of existing and bulky free space setups. In most terahertz waveguide designs however, the guiding region is physically separated from the surroundings, making any interaction between the guided light and the environment inefficient. Here we present photonic terahertz light cages (THzLCs) operating at terahertz frequencies, consisting of free-standing dielectric strands, which guide light within a central hollow core with immediate access to the environment. We experimentally show the versatility and design flexibility of this concept, by 3D-printing several cm-length-scale modules on the basis of a single design, using four different polymer-and ceramic-materials, which are either rigid, flexible, or resistant to high temperatures.We characterize both propagation-and bend-losses for straight-and curved-waveguides, which are of order ∼1 dB/cm in the former, and ∼2-8 dB/cm in the latter for bend radii below 10 cm, and largely independent of the chosen material. Our transmission experiments are complemented by near-field measurements at the waveguide output, which reveal the antiresonant guidance for straight THzLCs, and a deformed fundamental mode in the bent waveguides, in agreement with numerical conformal mapping simulation models. We show that these THzLCs can be used either as: (i) flexible, reconfigurable, and bendable modular assemblies; (ii) in-core sensors of resonant structures contained directly inside the hollow core; (iii) high-temperature waveguide sensors, with potential applications in industrial monitoring and sensing. The 3D-printed light cages presented are a novel and useful addition to the growing library of terahertz waveguides, marrying the waveguide-like advantages of reconfigurable, diffractionless propagation, with the free-space-like immediacy of direct exposure to the surrounding environment.