Comprehensive investigation on chalcogenide thin film coated multimode optical fiber: Visible evanescent-wave absorption refractometer

In this work, a different insight into the absorption characteristics of the chalcogenide thin film over the visible-wavelength range is studied in detailed. A comparative study of the lossy mode resonance (LMR) dips stem from the evanescent-wave absorption is theoretically and experimentally investigated towards refractive index measurement in aqueous environment. The absorbing layer of thermally evaporated arsenic trisulfide chalcogenide (As2S3) thin film coated onto the low OH etched optical fiber (ChOF) is prepared. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy, were used to characterize the chemical species, the crystal structure, and the morphology of the degradation layer confirming the As2S3, thin-film deposition on the curved optical fiber surface. The LMR dips condition hinging on the adoption of the chalcogenide layer was comprehensively explored by referring to the absorption spectra as a function of the wavelength and its thicknesses. Taking the advantage of the chalcogenide absorptive features within the visible spectral range, the results verified that coating even a thin subwavelength thickness of As2S3 chalcogenide on a bare has the ability to provide liquid refractometer with a versatile absorbing features. Our results point to a new path for the development of LMR-based chemical sensors, environmental sensors, or to be combined to the integrated micro-photonics device biosensors.