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The terahertz regime lies between microwave and infrared ranges, taking up a substantial portion of the electromagnetic spectrum. Due to its unique features, terahertz radiation has received significant attention from researchers. This paper reviews the current status of Porous Core Photonic Crystal Fibers (PC-PCF) for terahertz propagation. While the review partly focuses on general introduction as well as the methods of generating and detecting terahertz radiation, an overview of the applicability of terahertz radiation in medical and telecommunication industries is provided. The paper also reviews the fundamental guiding principles and properties of PC-PCFs. The discussed optical features of PC-PCFs include effective material loss, confinement loss, bending loss, core power fraction, dispersion variation, and birefringence. A research timeline which systematically analyses proposed PC-PCFs from 2014 to 2020 is also presented. Finally, the paper discusses the most common fabrication methods of PC-PCFs.

A highly birefringent photonic crystal fibre, with horizontal arrangement of three elliptical air holes in the core and hexagonal arrangement of circular air holes in the cladding, has been proposed for transmission of terahertz waves. Guiding properties of the fibre have been rigorously investigated using finite element method with perfectly matched layer boundary conditions. It has been demonstrated that high birefringence of 0.08 can be achieved with low effective material loss of 0.03 cm−1 at 1.3 THz. Moreover, it has been shown that about 42 % of useful power flows through the elliptical core air holes. Near-zero flattened dispersion of 1.18 ± 0.01 ps/THz/cm is obtained for the x-polarisation mode of the fibre. Other important optical properties such as confinement, bending and total losses have also been investigated; further strengthening potential applicability of the proposed fibre for next-generation terahertz research.