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

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.