An all-fiber temperature sensor is proposed for operational characterization, which is based on a Dual-Mode Fiber Bragg Grating (DM-FBG). This DM-FBG embedded in a Multilayer-Core Dual-Mode Fiber (MC-DMF) could sense the surrounding temperature depending on the transmission dips. The MC-DMF, with only two modes available for propagation, would make it easier to fabricate an FBG with two transmission dips. These two transmission dips have varying sensing precision. The propagation features and the working principle are described at length. With the temperature range of 30–70°C, the sensitivity of the DM-FBG, ~9.32 pm/°C and ~9.41 pm/°C are experimentally achieved, respectively. DM-FBGs could be scattered along a single fiber easily, and then a quasi-distributed sensing network would be built by these multi-node ones. Thus, this sensor has great potential for the internet of things.
An in-fibre temperature sensor based on a novel dual-mode fibre is proposed and experimentally characterized. The sensor head uses an in-fibre Mach-Zehnder(MZ) structure to sense the surrounding temperature, which depends on the interference spectrums. The concentric multilayer-core fibre (CMCF), in which only two modes could be propagated, would be easier to fabricate an in-fibre MZI with clean spectrum than many fibres, such as multimode fibres, thin-core fibres, PCFs and et al. And low-loss high-strength splice between CMCF and conventional single-mode fibre can be implemented with a commercial fusion splicer. Both the propagation characteristics and operation principle of such a sensor are demonstrated in detail. A sensitivity of ~50.13 pm/°C within temperature range of 30–70 ℃ are experimentally achieved, respectively.
A novel temperature-insensitive sensor probe is proposed and experimentally characterized. The sensor probe uses an etching cladding Few Mode Fiber Bragg Grating (FM-FBG) to sense the surrounding refractive indexes (SRI), which depends on the reflection peaks. To compensate for the temperature effect in SRI sensing, various guides modes in FM-FBG that have the different sensing behaviors are used for implementation. Both the propagation characteristics and operation principle of such a sensor are demonstrated in detail. A sensitivity of ~2 nm per refractive index unit (RIU) are obtained within the SRI range of 1.333–1.373. This sensor is temperature independent due to the temperature-insensitive nature of wavelength differential Δλ between the two reflection peaks of the etching cladding FM-FBG.
An all-fiber microstructure Mach–Zehnder/Michelson interferometer (MZI/MI) fabricated from dual-mode elliptical multilayer-core fibers (EMCFs) is proposed and experimentally characterized. The index profile of the EMCF is particularly designed to support a distinct dual-mode operation, LP01 and LP11even modes, with approximately equal excitation coefficients. Thus, the detected interference patterns, rather clean due to the few-mode property, shift as the environmental parameters due to strong interaction between high-order modes and measurands through evanescent waves. The MZI/MI has potential for improving the surrounding refractive indexes (SRI), axial micro-strain and liquid-level measurement resolutions. Both the propagation characteristics and operation principle of such a sensor are demonstrated in detail. A sensitivity of ~213 nm per refractive index unit (RIU) within the SRI range of 1.333–1.373, ~4.98 pm/μɛ within the axial strain range of 0-800 μɛ and ~32 pm/mm within the liquid-level range of 0-35mm are obtained through simulation, respectively.
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