Hybrid Interferometer Sensor Based on the Enhanced Vernier Effect for the Simultaneous Measurement of Strain and Temperature

A hybrid interferometer sensor based on the enhanced Vernier effect was proposed for the simultaneous measurement of strain and temperature. The sensor was composed of a Fabry-Perot interferometer (FPI) made of hollow core fiber (HCF) and a Michelson interferometer (MI) made of few-mode fiber. Unlike the traditional Vernier effect, the reference arm of enhanced Vernier effect does not need to be isolated but participates in sensing along with the sensing arm, and its response to strain is opposite that of the sensing arm, thereby improving the sensitivity of the traditional Vernier effect. Given that the two interferometers participate in sensing, a coefficient matrix was used for the simultaneous measurement of strain and temperature, which overcame the cross-sensitivity problem of temperature. First, we theoretically analyzed the relationship between the mode excited in a few-mode fiber and the offset and the relationship between the coupling efficiency and the offset of different modes when a few-mode fiber was coupled with a single-mode fiber (SMF). Then, we conducted experimental verification and measured the strain and temperature responses of the sensor. The sensor had a strain sensitivity of −13.7 pm/<inline-formula> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula>, which was 4.28 and 1.36 times the sensitivity of the traditional Vernier effect using MI or FPI as the sensing arm, and the temperature sensitivity was −97.7 pm/°C. The proposed sensing device exhibits the benefits of straightforward fabrication, an extensive measurement range, and low-temperature interference, holding promising prospects for strain assessment.