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An optical fiber sensor based on a fiber surface waveguide and Bragg grating is proposed for a simultaneous refractive index (RI) and temperature sensing. The device consists of two fiber Bragg gratings fabricated by a femtosecond laser, one of which is situated in the fiber core for temperature sensing; the other is located in the fiber surface waveguide for both temperature and RI measurements. The RI and temperature sensitivities achieved are 10.3 nm/RIU and 9.94 pm/°C, respectively. The device is featured with a compact structure, high robustness, and convenient operation.

We propose and demonstrate parallel structured optical fiber in-line Fabry–Perot interferometers for high temperature sensing. The device consists of three Fabry–Perot cavities in parallel connection, which allows three independent fringe patterns superimposed at its output, and, as a result, a number of dominant fringe peaks/dips appear, thus enabling unambiguous measurement in a large range. The device is featured with compact size, robust structure, and excellent high temperature sustainability, which makes it promising in extreme environment monitoring.

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