Thanks to the guidance of an optical wave in air, hollow-core fibers may serve as sampling cells in an optical spectroscopic system. This paper reviews applications of hollow-core optical fibers to laser-based gas sensing. Three types of hollow-core fibers are discussed: Hollow capillary waveguides, photonic band-gap fibers, and negative curvature fibers. Their advantages and drawbacks when used for laser-based trace gas detection are analyzed. Various examples of experimental sensing systems demonstrated in the literature over the past 20 years are discussed.
Keywords: Kagome hollow-core fiber; anti-resonant hollow-core fiber; gas sensing; hollow-core fiber (HCF); laser spectroscopy; negative curvature hollow-core fiber (NC HCF); photonic band-gap hollow-core fiber (PBG HCF).