Abstract:Optical fiber temperature sensors gave attracted significant interest owing to their compact structure and resistance to electromagnetic interference. Nevertheless, it is imperative to enhance the detection sensitivity to adequately fulfill the existing requirements. This study proposes and demonstrates a sensitivity-enhanced optical fiber temperature sensor using the cascaded Lyot filter and Mach-Zehnder interferometer (MZI), based on the Vernier effect. The MZI has two consecutive bubble-type upper tapers and is employed as a reference interferometer, owing to the exceptional stability of its totally polarization-maintaining fiber (PMF) construction. A Lyot filter is created by fusion splicing a segment of PMF at a 45° angle between two linear polarizers, functioning as a sensing interferometer. The sensitivity of the cascaded sensor is improved through the Vernier effect, which is produced when the length of the sensing PMF in the Lyot filter is modified to closely match the free spectral range (FSR) of the MZI. Experimental results reveal the sensitivity of the Lyot filter is -1.4nm/℃, while the cascaded sensor achieves an increased sensitivity of -28.3nm/℃, with a sensitivity amplification factor of 20.2. The proposed PMF sensor structure leverages the controllable polarization characteristics to enhance system performance, effectively addressing the issue of detection errors that arise from the fluctuating polarization state of the optical signal being transmitted throughout the sensitivity test. This proposed optical fiber temperature sensor, with a robust polarization stability, simple fabrication, and high sensitivity, is suitable for high-precision industrial applications.
