Highly sensitive temperature and pressure fiber optic sensor based on harmonic Vernier effect

Abstract

We have developed a highly sensitive fiber optic sensor that can measure temperature and pressure. The sensor comprises two Fabry–Perot interferometers (FPIs), FPI₁ and FPI₂, connected in parallel. FPI₁ is composed of single mode fiber (SMF)—capillary—SMF spliced together, with a ventilation hole on the capillary. FPI₂ is composed of SMF—capillary—SMF, and the capillary is filled with polyimide (PI). It is found that FPI₁ is almost insensitive to temperature, but sensitive to air pressure. FPI₂ is sensitive to temperature, but not sensitive to pressure. When the free spectra range (FSR) of FPI₁ and FPI₂ approaches twice the relationship, they are connected in parallel to form a first-order harmonic vernier effect (HVE). When the HVE sensor is used for air pressure sensing, FPI₁ is the sensing cavity and FPI₂ is the reference cavity. When the HVE sensor is used for temperature sensing, FPI₂ is the sensing cavity and FPI₁ is the reference cavity. The experimental results showed that the sensitivities of the pressure and temperature of the HVE sensor are 76.71 nm/MPa and 113.29 nm/ °C, respectively. This is currently the highest temperature sensitivity reported in literature. The accuracy of the obtained intersection point in HVE sensor is higher and than that of that of traditional Vernier effect. In addition, the FSR relationship required to form HVE is easier to achieve. By utilizing the temperature and air pressure sensitivities of FPI₁ or FPI₂, as well as that of the HVE sensor, a sensitivity measurement matrix can be formed to achieve simultaneous measurement of temperature and air pressure.