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• A highly-sensitive pressure sensor with sensitivity of 80.8 pm/kPa. • Low temperature cross sensitivity of 2.2 kPa/°C. • Experimental results in good agreement with the "Two-beam" interference model. • Simple fabrication technique without fiber machining, and possible for mass production. We propose and demonstrate a simple highly-sensitive gas pressure sensor based on harmonic Vernier effect. By fusion splicing two hollow silica capillaries, a cascaded Fabry-Perot (FP) cavity is formed. Without special photonics crystal fibers or laser machining involved, the fabrication process is greatly simplified. The interplay between the two interferometers consisting the FP cavity leads to optical Vernier effect. By properly adjusting the length of the silica capillaries harmonic of optical Vernier effect is observed and can be served as a sensitive probe for diagnosing gas pressure. Our results showed a sensitivity of 80.8 pm/kPa from 1 to 101 kPa with good linearity of 99.7%, and a low temperature cross sensitivity of 2.22 kPa/°C, a factor of three lower than that of the microstructure fiber-based gas pressure sensors. Combining both ease of fabrication and high sensitivity, this sensor can be a good candidate for mass production in fields of gas sensing and environmental safety monitoring. [ABSTRACT FROM AUTHOR]

• 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]