Sensing Properties of Indium Oxide Coated Optical Fiber Devices Based on Lossy Mode Resonances

Abstract

In this work, lossy mode resonance (LMR)-based optical fiber refractometers fabricated by using a transparent coating (indium oxide) as the LMR supporting layer are studied. The utilization of the high refractive index indium oxide coatings enables the fabrication of highly sensitive optical fiber refractometers, the resonance of which can be tuned by adjusting the fabrication parameters, such as the coating thickness. The detection technique is based on the wavelength shift of the resonances produced by both TE and TM polarization modes. Here, the influence of the coating thickness on the sensitivity of the device to external refractive index variations is observed. Maximum sensitivities of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$2.03{\rm e}^{-4}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$2.35{\rm e}^{-4}$</tex></formula> refractive index units (RIU) per nanometer for TE and TM polarizations have been obtained, respectively. The sensitivity of the devices to diverse volatile organic compounds (VOCs), such as ethanol, methanol, isopropyl alcohol, acetone, and ammonia has been studied and the cross-sensitivity to temperature and moisture as well.