We present a refractometer with main- and vernier-scale to measure the refractive index (RI) of liquids with high precision by using the fine spectrum structure of a tilted fiber Bragg grating (TFBG). The absolute RI values are determined by the accurate wavelength of cut-off mode resonances. The main- and vernier-scale are calibrated by measuring large groups of fine spectra at different cut-off mode resonances in a small RI range, and the use of vernier-scale certainly reduces the RI measurement uncertainty resulted from the discrete cladding mode resonances. The performance of the TFBG-based vernier refractometer is experimentally verified by exploring the temperature dependence of RI of anhydrous ethanol in a near infrared region, showing an enhanced accuracy to the order of 10−4, high repeatability and temperature self-calibration capability.
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Funding: Marie Skłodowska-Curie Individual Fellowships in the European Union’s Horizon 2020 Research and Innovation Programme (660648); National Natural Science Foundation of China (61505165); Natural Science Basic Research Plan in Shaanxi Province of China (2016JQ6032).
- Fiber optics components
- Fiber Bragg gratings;
- Fiber optics sensors