Gas sensing with Hollow-Core Photonic Crystal Fibres: A comparative study of mode analysis and gas flow performance

The design flexibility of Hollow-Core Photonic Crystal Fibres (HC-PCFs) is a significant feature that allows the fibres to achieve excellent optical properties. Changes in the design parameters of HC-PCFs used for gas sensing can affect their optical and gas flow properties. The aim of this paper is to investigate the performance of three HC-PCFs with different geometries (HC-800-02, HC-1550-02, HC-2000-01) in terms of their optical mode and gas flow performance. The numerical model for the optical mode analysis is presented. The optical performance of three HC-PCFs is examined at different wavelengths in terms of their effective refractive index, mode field diameter, confinement loss and relative sensitivity. The numerical model for gas flow simulations based on Navier-Stokes and gas diffusion equations is also presented. This model is used to examine the gas velocity, relative average concentration, volumetric flow rate and gas filling time for three different HC-PCFs and three different gases. A series of gas sensing experiments based on pulsed continuous-wave modulated photothermal spectroscopy is conducted to validate the gas flow numerical model. A comparison between the three HC-PCFs indicates that the HC-PCF with the smallest size is associated with the lowest confinement loss but the highest gas filling time.