Hybrid-cladding hexagonal-core photonic crystal fiber: A platform for ultra-sensitive terahertz detection of industrial liquid

In this work, a hexagonal-core photonic crystal fiber (PCF) with hybrid rectangular and triangular cladding air holes for extremely sensitive chemical detection in the terahertz regime is proposed and numerically investigated. The finite element technique (FEM) in COMSOL Multiphysics is used to model the design, guaranteeing precise optical parameter evaluation. At 2.4 THz, the suggested sensor achieves record-high relative sensitivities of 99.98%, 99.88%, and 99.65% for water, ethanol, and benzene, respectively, with ultra-low confinement loss (1.4 × 10 −12 dB/m) and effective material loss (0.0012 cm −1 ). A numerical aperture of 0.259, an effective area of 6.9 × 10 −2 m 2 , and a spot size of 2.37 × 10 −2 μm are further performance characteristics. The novelty lies in the hybrid cladding geometry, where triangular and rectangular air-holes jointly strengthen field confinement, yielding near-unity relative sensitivity (99.34% for benzene). Existing PCF-based THz sensors do not combine multi-shape asymmetry for low-loss propagation.