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The purpose of this paper is to demonstrate a simple fiber sensor for simultaneous measurement of liquid refractive-index (RI) and temperature.

The sensor structure is formed by a long period fiber grating cascaded with a section of thin-core fiber. The long period fiber grating is fabricated on single mode fiber, followed by a section of 20-mm length thin-core fiber which is a modal interferometer.

Cladding mode interference between long period fiber grating and thin-core fiber modal interferometer is weak in the experimental investigation. Both of these two cladding mode type fiber devices are sensitive to surrounding RI and temperature. So the RI and temperature can be measured simultaneously by monitoring the spectral characteristics of the compound sensor. The sensitivity is calibrated and sensor matrix is provided in the experiment.

This proposed fiber sensor is simple, tough, cost-effective and suitable for discriminate the liquid RI and temperature with high sensitivity.