High Sensitivity Humidity Fiber-Optic Sensor Based on All-Agar Fabry-Perot Interferometer

A high sensitivity humidity fiber sensor based on all-agar Fabry-Perot (FP) interferometer is proposed and experimentally demonstrated. The sensor is fabricated by filming a thin layer of moisture-sensitive agar to single mode fiber with end dipping method. Due to the all-agar FP cavity structure, both the size and the RI changes of agar film in the swelling effect are fully utilized to induce the frequency shift, the sensor exhibits a high sensitivity of 4.20 nm/%RH, with relative humidity (RH) ranging from 25%RH to 95%RH at 25 °C. Moreover, owing to the short FP cavity, $7.10~\mu \text{m}$ , the proposed sensor provides a short response time less than 340 ms with the humidity level changed from 64.0%RH to 74.2%RH. The proposed sensor also exhibits other superior performances in terms of good stability, low cost, and easy fabrication. Such good characteristics make the proposed sensor a good candidate for practical applications.