Transmittance of Tapered Photonic Crystal Fibers With Absorbing Coatings

Abstract The interaction effect of the fundamental mode of a photonic crystal fiber (PCF) with a thin-film absorbing coating deposited on a surface of a fiber cladding on the optical transmission of the PCF is studied. It is shown that the transmission has a quasi-periodic spectrum that is determined either by a resonance coupling between the leaky fundamental PCF mode and leaky modes of the coating, or between the leaky fundamental PCF mode and cladding modes localized between PCF air channels and the coating. Examples are presented of using this effect for fiber-optic sensors of refractive index, pressure, and for sensing an adsorption layer of ammonia molecules deposited on a coating surface contacting with air.