Topas-based octa-circular cladding and rectangular porous core photonic crystal fibre for terahertz waveguide

This article presents a novel design for guiding terahertz (THz) waves, which utilises a photonic crystal fibre with a porous core (PC-PCF). This approach is substantiated by a Topas-based octagonal-shaped core with rectangular air slots. By utilising Finite Element Method and Perfectly Matched Layer boundary condition, the guiding properties of a structure consisting of octagonal air holes integrated with circular air slots in the cladding region have been investigated. The proposed structure exhibits a birefringence value of 0.05 and a low effective material loss of 0.013 cm⁻¹. Moreover, it exhibits flattened dispersion measuring $0.6\pm 0.16ps/THz/cm$ at a wide-ranging frequency of 0.4 to 1.6 THz. In addition to that, the proposed structure offers 60% high core power fraction, 10⁻¹⁸ cm⁻¹ confinement loss at 65% porosity of 290 μm core diameter and 1.6 THz frequency. Other significant waveguide properties: effective refractive index, effective area, spot size, and beam divergence of the proposed fibre are numerically analysed and discussed rigorously along with the fabrication viability of the fibre with existing techniques.