Optimized Hollow-Core Photonic Crystal Fiber Based Gas Sensor

Abstract

This paper proposes the design of a rigorously optimized hollow-core photonic crystal fiber (HC-PCF) gas sensor for sensitive detection of methane (CH4) at the 1.67µm near infrared absorption line. A complete vector finite element method (FEM) within COMSOL Multiphysics and a Python-based numerical method employing an Anti-Resonant Reflecting Optical Waveguide (ARROW) model were used with perfectly matched layer (PML) boundary conditions to assess the modal attributes, confinement loss, and gas sensing features of the proposed fiber. The central hollow-core diameter, cladding air-hole diameter, and hole pitch are essential geometric parameters, which have been optimized to enhance the interaction of the guided fundamental mode’s evanescent field with the target analyte gas in the hollow core. The optimization demonstrates that this HC-PCF exhibits a relative sensitivity of about 97% with a confinement loss of 0.007dB/m at 1.67µm. In addition to conventional sensitivity and loss characterization, the paper provides three analyses that have, to the best of authors’ knowledge, not been previously reported for this class of sensor: (i) curvature loss characterization for bend radius of 5–20 mm; (ii) temperature dependent sensitivity analysis over −20 ◦C to 80◦C; and (iii) fabrication tolerance assessment quantifying effect on sensing performance of ±5 % deviations from manufacture of core diameter, pitch and hole diameter. Moreover, the effective refractive index, numerical aperture, V-parameter, and power fraction were retrieved to ensure that stable single-mode guidance occurs in the sensing region. The high sensitivity plus low propagation losses, good tolerance to the ambient environment, and ease of fabrication of this design make it a serious contender for methane detection for environmental monitoring and industrial safety applications.