Ultrahigh Sensitivity Temperature Sensor Based on Harmonic Vernier Effect

A high-sensitivity and miniature open cavity Fabry–Perot interferometer (OCFPI) encapsulated with the polydimethylsiloxane (PDMS) film based on the high-order harmonic Vernier effect is designed and experimentally investigated. To the best of our knowledge, PDMS is applied for the first time to fill the OCFPI to obtain high-temperature sensitivity. The resonant dip (peak) wavelength of the designed temperature sensor monotonically moves toward the shortwave direction as the temperature increases from 40 °C to $60~^{\circ }\text{C}$ due to the effects of expansion and thermo-optic property of PDMS. The proposed OCFPI encapsulated with PDMS film provides the following excellent performance advantages: 1) compared with traditional all-fiber air-cavity OCFPIs with the temperature sensitivity of approximately 10 pm/°C, the proposed OCFPI sensor has a much higher temperature sensitivity of −3.4 nm/°C at the temperature range of $40~^{\circ }\text{C}$ – $60~^{\circ }\text{C}$ with a magnification factor ( ${M}$ -factor) of approximately 11 when the order of harmonic Vernier effect ${i} =4$ ; 2) the proposed OCFPI exhibits good reversibility during the heating and cooling processes, and the measured ${M}$ -factor matches well with the theoretically calculated ${M}$ -factor; 3) the proposed OCFPI shows excellent stability with maximum wavelength deviation of 0.567 nm (internal envelope based on a fourth-order harmonic Vernier effect) and 0.042 nm (upper envelope) within 450 min; and 4) the proposed OCFPI is inexpensive, robust, easy to fabricate, and compact, which can be used in harsh environments. Therefore, it provides excellent potential in dynamic temperature measurement.