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In this article, a reflective-type optical fiber probe, which can measure salinity and temperature simultaneously, is proposed. The proposed probe integrates Mach–Zehnder interferometer and Fabry–Perot interferometer in the same channel skillfully and effectively, which makes it possible to integrate more information into the sensor. The reflected spectrum is improved greatly by adopting special sputtering technology. The spectrums of Mach–Zehnder and Fabry–Perot are separated by applying the frequency division multiplex technique. The simulation and experimental results prove that the proposed probe has a highly sensitive response to temperature and salinity. The experiment result verifies that the salinity sensitivity is up to 2.7 nm/‰ and the temperature sensitivity is better than 0.4 nm/°C. The reflective probe makes the sensor easy to use and paves the way for practical application. [ABSTRACT FROM AUTHOR]

In this study, a fiber-optic sensor based on Fabry-Perot interferometer (FPI) and Mach-Zehnder interferometer (MZI) cascaded structure is proposed and demonstrated for seawater salinity and temperature simultaneous measurements. A section of hollow-core fiber (HCF) with a U-shaped defect is spliced between single-mode fibers to form FPI. The U-shaped defect inscribed by the femtosecond laser facilitates liquid flow-through and enables the salinity measurement. The MZI composes of laser-induced optical waveguides written in the cladding of the coating-retained single-mode fiber. There is an interaction between the evanescent field of the in-fiber waveguides and the coating due to the written waveguide is close to the cladding-coating interface. Part of the incident light is reflected by HCF to form the FPI spectrum, while the transmitted light in the core is coupled to the written waveguides and guided along the cladding region, which finally returned to the core to obtain the MZI spectrum. Theoretical analysis and experimental verification are carried out, and the results show that the proposed sensor offers a salinity sensitivity of 0.244 nm/‰ and a temperature sensitivity of − 2.767 nm/℃. Such a cascaded interferometer has advantages of high sensitivity and compact size, which is expected to be widely used in seawater parameter measurements due to the flexible structure and precise control. • An F-P and M-Z interferometer cascaded fiber-optic sensor is proposed for salinity and temperature measurements. • F-P interferometer is formed by splicing a section of hollow-core fiber with a femtosecond laser-inscribed U-shaped defect. • M-Z interferometer composes of laser-induced optical waveguides written in the cladding of the fiber. • The sensor realizes simultaneous salinity and temperature measurements with sensitivities of 0.244 nm/‰ and − 2.767 nm/℃. [ABSTRACT FROM AUTHOR]