Self-temperature-compensative refractometer based on singlemode-multimode-singlemode fiber structure

It is important to precisely measure the refractive index (RI) of liquids with the variation of temperature in many chemical and biological applications. In this paper, an all-fiber refractometer with the capability of self-compensation for the temperature-induced cross-sensitivity is reported. The refractometer is based on the singlemode-multimode-singlemode fiber structure, in which a piece of no-core fiber is used to serve as the multimode section. Because the dips in the transmission spectrum have different sensitivities to the surrounding RI but the same sensitivity to temperature, the influence of temperature on the RI measurement can be compensated by measuring the difference of the wavelength shifts of two dips. A refractometer was fabricated and experimentally studied by measuring the RI of distilled water with the change of temperature. The results show that with the proposed method, the measurement error can be notably reduced.