Optical fiber interferometer for temperature-independent refractive index measuring over a broad range

• Published in: Optics and laser technology 2021-07, Vol.139, p.106977, Article 106977
• Main Authors: Flores-Bravo, J.A., Illarramendi, M.A., Zubia, Joseba, Villatoro, Joel
• Format: Article
• Language: English
• Subjects: Chemical sensors; Fabry-Perot interferometers; Fast Fourier transformations; Fourier transforms; Gels; Mathematical analysis; Optical fiber sensors; Optical fibers; Polymer cavities; Refractive index sensors; Refractivity; Refractometers; Signal processing; Stability; Thermo-optic coefficient
• ISSN: 0030-3992; 1879-2545
• DOI: 10.1016/j.optlastec.2021.106977

•An optical fiber refractive index sensor for broad measuring range is reported.•The fabrication method and the data processing minimize the effect of temperature.•The interferometer coated with sensitive materials allows the development of sensors. The present work relates to manufacturing of a simple interferometric optical fiber refractometer that features broad refractive index measuring range without ambiguity. The device consists of a cylindrical polymer cavity whose shape and dimensions are easily controllable. This in turn allows to control the performance of the refractometer. The signal processing is simple; it consists of calculating the amplitude and phase of the fast Fourier transform of the normalized interference spectra. In this manner, the refractive index value of the sample is obtained independently of the temperature. The refractometer can be used to measure the refractive index of liquids or viscous samples and can operate in a broad wavelength range. As an application, we demonstrate the measuring of the refractive index of gels at different temperatures from which the thermo-optic coefficient can be calculated.