High Sensitivity Strain and Temperature Sensing With Cascaded Sagnac Interferometer Based on Harmonic Vernier Effect

To further improve sensor sensitivity, a strain and temperature sensor based on the harmonic Vernier effect with cascaded Sagnac interferometers (SIs) is proposed. Through a combination of simulation and experimentation, it is shown that the basic Vernier effect can be realized when the lengths of the polarization-maintaining fiber (PMF) in two SIs are slightly different. Furthermore, the first-order harmonic Vernier effect can be achieved when the lengths of two PMFs are approximately integer multiples. This sensor, leveraging the harmonic Vernier effect, demonstrates higher sensitivity. Compared to a single SI, the strain sensitivity based on the basic Vernier effect is improved to 61.93 pm/με with a magnification factor of 7.6, and the temperature sensitivity is improved to 14.29 nm/℃ with a magnification factor of 9.4. For the first-order harmonic Vernier effect, the strain sensitivity increases to 146.35 pm/με with a magnification factor of 18, and the temperature sensitivity increases to 24.92 nm/℃ with a magnification factor of 16.5. Additionally, the sensor based on the harmonic Vernier effect exhibits good stability in strain and temperature measurement. Unlike the basic Vernier effect, the harmonic Vernier effect does not require strict control of the reference and sensing interferometer lengths, further increasing sensitivity. Due to its simple structure and low cost, the proposed sensor shows significant potential for applications in high-precision measurement engineering and medical treatment.