Ge-Sb-Se-Te -coated tilted fiber Bragg gratings sensor for the refractive index measurement of transformer oils.

• The GSST-TFBG has an extended SRI range, and the resonance amplitudes remain strong and detectable beyond the cut-off point. • The s-mode resonances are practically insensitive whereas the p-mode remains sensitive to the changes of SRI. • Refractive index measurement for transformer oil using GSST-coated TFBG. In this work, a tilted fiber Bragg gratings coated with a 130 nm thick Ge-Sb-Se-Te (GSST) layer, a high refractive index soft glass had been fabricated and demonstrated for the refractometric test of transformer oil. The findings indicated that the introduction of the high refractive index coating had enhanced the polarization property and extended the refractive index detection range of the tilted fiber Bragg gratings beyond the cut-off point of the cladding modes. In the experiment with transformer oils, the Ge-Sb-Se-Te -coated tilted fiber Bragg gratings has shown a good linear sensitivity of 9.952 dB/RIU for the refractive index range of 1.472–1.484 RIU. [ABSTRACT FROM AUTHOR]