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, LP<sub>01</sub> and LP<sub>11</sub><sup>even</sup> 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.