LMR-based optical fiber refractometers based on transparent conducting and semiconducting oxide coatings: a comparative study

In this work, it is described the fabrication and characterization of optical fiber refractometers based on lossy-mode resonances (LMR) originated by deposition of different thin-film coatings around the optical fiber core. Two devices with different coating materials are compared: one coated with conducting tin doped indium oxide (ITO) coatings and the other one coated with semiconducting indium oxide. The response of these devices is characterized and compared as a function of the external refractive index. The sensitivity obtained for indium oxide based refractometers resulted 39% higher than that of ITO based ones when the resonance is located in the same spectral region. This behaviour is attributed to the spectral characteristics of indium oxide, which allow an earlier generation of the resonance thanks to its higher refractive index as well as permitting the accomplishment of LMR conditions in a wider spectral range. Moreover, these devices are an adequate platform for the development of a wide variety of sensors by the addition of the suitable layer onto the transparent oxide coating.