High-Performance Fiber-Optic Temperature Sensor Enhanced by Vernier Effect With Switchable Sensitivities

Current high-sensitivity fiber-optic temperature sensors are often limited to narrow measurement ranges, thus restricting their applicability to specific scenarios. However, it is not uncommon to find that a wide range of temperature measurements is required. Aiming for different application scenarios, sensors with different sensitivities and corresponding different dynamic ranges are needed. However, it is difficult to achieve simultaneously in one fiber-optic sensor. Here, a novel fiber-optic temperature sensor based on the Vernier effect with switchable sensitivities and dynamic ranges was theoretically proposed and experimentally demonstrated. This sensor consists of two single-mode fibers (SMFs) with thermal-sensitive polydimethylsiloxane (PDMS) caps on their end faces inserted into quartz capillaries, with an air cavity between the two PDMS caps. In the proposed sensor, high-performance temperature demodulation is achieved. By controlling the amplification coefficient of the Vernier effect, both temperature sensitivities of 9.57 nm/°C within the range of $35~^{\circ }$ C– $42~^{\circ }$ C and 1.80 nm/°C within the range of $- 10~^{\circ }$ C to $45~^{\circ }$ C are achieved. The sensitivity can be simply switched by choosing different signal directions. Experimental validation confirms the performance of this sensor, demonstrating its advantages such as switchable sensitivity, good stability excellent repeatability, and potential for real applications requiring different sensitivities.