Ultrasensitive Temperature and Strain Sensor Based on a Hybrid Fiber Interferometer With the Vernier Effect

We propose and experimentally demonstrate an ultrasensitive temperature and strain sensor based on a hybrid fiber interferometer (HFI) with the Vernier effect. The HFI consists of a fiber coupler, a section of hollow-core photonic crystal fiber (HCPCF), and a certain length of high birefringence polarization-maintaining fiber (Hi-Bi PMF) to form a composite structure with a Fabry-Perot interferometer (FPI) built into the fiber Sagnac interferometer (FSI). The HCPCF-based FPI is insensitive to temperature and strain and is an ideal reference interferometer. By adjusting the length of the HCPCF and Hi-Bi PMF, the Vernier effect can be created, which significantly increases the sensitivity of the sensor. The experimental results show that the proposed sensor has high temperature and strain sensitivities up to 50.671 nm/°C and −81.69 pm/
$\mu \varepsilon $
, respectively, with a high resolution of
$\pm 0.0018~^{\circ }$
C and
$\pm 0.86~\mu \varepsilon $
. The proposed sensor is low cost, compact, and easily fabricated, making it ideal for applications that require high-precision temperature and strain measurement.