Microstructured optical fibers for terahertz waveguiding regime by using an analytical field model

•Analytical field model developed earlier is used for triangular lattice based index-guiding MOFs at terahertz (THz) regime.•Scalar variational approach is used for studying the fundamental propagation properties of MOFs at terahertz frequency realm.•Evolution of the fundamental mode is investigated in transition from near-to-far-field domain at the terahertz frequency.•Coupling losses between identical solid-core triangular lattice MOFs, and between the terahertz source (e.g., laser diode) and the MOFs, is evaluated at THz domain.•Fraction of the power coupled to core of an MOF at terahertz domain is investigated for the compact evanescent field devices.

Microstructured optical fibres (MOFs) are seen as novel optical waveguide for the potential applications in the terahertz (THz) band as they provide a flexible route towards THz waveguiding. Using the analytical field model (Sharma et al., 2014) developed for index-guiding MOFs with hexagonal lattice of circular air-holes in the photonic crystal cladding; we aim to study the propagation characteristics such as effective index, near and the far-field radiation patterns and its evolution from near-to-far-field domain, spot size, effective mode area, and the numerical aperture at the THz regime. Further, we present an analytical field expression for the next higher-order mode of the MOF for studying the modal properties at terahertz frequencies. Also, we investigate the mode cut-off conditions for identifying the single-mode operation range at THz frequencies. Emphasis is put on studying the coupling characteristics of MOF geometries for efficient mode coupling. Comparisons with available experimental and numerical simulation results, e.g., those based on the full-vector finite element method (FEM) and the finite-difference frequency-domain (FDFD) method have been included.