Experimental design of fiber-optic temperature sensor technology teaching based on Vernier effect enhancement

By deeply integrating scientific research achievements with the teaching of foundational optical design courses and following the closed-loop experimental process of “principle derivation–structure preparation–performance testing data demonstration,” this study closely adheres to the core principles of “theoretical implementation, practical orientation, and ability advancement.” A comprehensive experiment based on the enhanced Vernier effect for all fiber temperature sensing was designed to achieve high-sensitivity temperature detection. The experiment enables students to master the working principle and structural design of enhanced Vernier-effect fiber optic sensors, understand the preparation methods of Mach-Zehnder interferometer (MZI) and fiber Sagnac interferometer (FSI), cultivate scientific research thinking and innovative practical abilities, and provide a feasible approach to teaching foundational optical design courses.

With enhancement of the Vernier effect as the core principle, a sensing structure is constructed by combining a Sagnac loop composed of polarization-maintaining fiber (PMF) and an FSI composed of couplers with an MZI composed of dual side hole fiber (DSHF) and no core fiber (NCF), both of which exhibit opposite temperature responses. Both interferometers participate in temperature detection as sensing arms. The fiber optic Vernier effect is based on the optical Vernier effect and simulates the “main ruler” and “auxiliary ruler” of a Vernier caliper by constructing two interference structures with similar (free spectral range) FSR. The FSRare controlled by the length of the interference cavity or the refractive index of the medium inside the cavity. Changes in external temperature cause changes in the refractive index of the fiber optic sensing unit, leading to a shift in the Vernier effect spectrum and enabling quantitative temperature analysis. The FSR of the Vernier envelope and the amplification factor were derived theoretically to measure the sensor performance.

The enhanced Vernier effect is generated by an FSI composed of a Sagnac loop formed by PMF and a coupler with an MZI composed of DSHF and NCF, which exhibit opposite temperature responses, allowing both interferometers to participate in temperature detection as sensing arms. Subsequent temperature detection experiments have shown that the temperature sensitivity of the sensor can reach up to 15.43 nm·℃^–1 over the temperature range of 20–44 ℃. This value is 9.35 and 11.42 times higher than the sensitivities of the individual FSI and MZI structures, respectively. In addition, the sensor demonstrates excellent reversibility, repeatability, stability, and response speed. Moreover, its performance was unaffected by variations in humidity or environmental gases, demonstrating superior performance to similar sensors across multiple evaluation metrics.

The experiment is based on the essence of teaching and closely follows the forefront of scientific research, with distinct cutting-edge, comprehensive, and practical characteristics. It effectively integrates scientific research results into course teaching, enabling students to deeply understand the working principle of the fiber optic Vernier effect, sensor structural design, and temperature detection mechanism. It also helps them master basic scientific research methods such as fiber optic fusion splicing, spectral analysis, and data fitting. At the same time, it cultivates students’ scientific research thinking, innovative practical abilities, and interdisciplinary knowledge integration abilities, effectively bridging the gap between traditional course experiments and scientific research applications.