Liquid sealing is an effective method to convert a fiber-optic refractometer into\na simple and highly sensitive temperature sensor. A refractometer based on the thin-core\nfiber modal interferometer is sealed in a capillary tube filled with Cargille oil. Due to the\nthermo-optic effect of the sealing liquid, the high refractive-index sensitivity refractometer is\nsubsequently sensitive to the ambient temperature. It is found that the liquid-sealed sensor\nproduces a highest sensitivity of 2.30 nm/�°C, which is over 250 times higher than its\nintrinsic sensitivity before sealing and significantly higher than that of a grating-based fiber\nsensors. The sensing mechanisms, including the incidental temperature-induced strain effect,\nare analyzed in detail both theoretically and experimentally. The liquid sealing technique is\neasy and low cost, and makes the sensor robust and insensitive to the surrounding refractive\nindex. It can be applied to other fiber-optic refractometers for temperature sensing.
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