Compact Fiber Optic Sensor for Temperature and Transverse Load Measurement Based on the Parallel Vernier Effect

An optical fiber sensor based on the parallel Vernier effect for temperature and transverse load measurement is reported in this paper. The sensor is composed of a novel compact fiber Michelson interferometer (MI) and a closed-cavity Fabry–Perot interferometer (FPI) connected in parallel. The fiber MI consists of a bent single-mode fiber (SMF) structure and a short length of hollow core silicon tube (HCST). A section of HCST is fused between two segments of SMF to form the fiber FPI. Two sensors in parallel can easily measure different physical parameters independently, thus realizing multi-parameter sensing. The fiber MI and FPI are used for temperature and transverse load measurement, respectively. Fiber optic MI and FPI are Vernier effect mutual reference interferometers. When MI is used for temperature sensing, FPI is the reference interferometer. When FPI is used for transverse load sensing, MI is the reference interferometer. It can improve the sensitivity of temperature and transverse load. Two samples were made and the sensing experiment was carried out. Through the sensing experiment, we get the maximum temperature sensitivity of 85.1 pm/°C in the temperature range of 30–80 °C and a transverse load sensitivity of −3.15 nm/N in the temperature range of 0–1.96 N. In addition, the sensor has the advantages of tiny size, low cost, and easy manufacture, which is suitable for temperature and transverse load sensing applications.