Sensitivity-enhanced temperature sensor based on encapsulated S-taper fiber Modal interferometer.

• Optical fiber temperature sensor based on encapsulated S-taper fiber. • Different taper configurations and filling liquids are investigated. • Maximum sensitivity of −15.66 nm/°C in the range of 28–32 °C was experimentally achieved. • The multimode interference behavior in various external environments was calculated. • The "critical cladding mode" model explained the underline principle for wavelength shift and high sensitivity. We demonstrated a simple technique for a highly sensitive temperature sensor based on an "S"-shape fiber taper Mach-Zehnder interferometer (MZI) with no need of special fibers or micromachining technique using high power lasers. To enhance the sensitivity, an S-shape single mode fiber (SMF) taper was encapsulated in a capillary filled with high thermos-optic coefficient liquid. We experimentally investigated the tuning parameters for the sensor, such as the taper shape, the material of the capillary, and the role of the filling liquid. Our results show a maximum sensitivity of −15.66 nm/°C in a measurement range of 28–32 °C, and −11.88 nm/°C from 25.1 °C to 35 °C for isopropanol sealed in Teflon capillary. The multi-interference model simulation shows that a critical cladding mode is responsible for the high sensitivity. Simple configuration, ease of fabrication, robustness and low cost make it suitable for high sensitivity temperature sensing applications. [ABSTRACT FROM AUTHOR]