Strain, bending, refractive index independent temperature sensor based on a graded index multimode fiber embedded long period fiber grating

A novel embedded ultra-long period fiber grating (EULPFG) based on a graded index multimode fiber (GI-MMF) is proposed for temperature measurement. Due to the small RI difference of the modes near the GI-MMF self-imaging point, the resonant peak of transmission spectrum is wavelength-insensitive to refractive index (RI), strain and bending. However, the sensor is sensitive to temperature. The experimental results show that the temperature sensitivity of the EULPFG is 90.77 pm/degrees C. The sensitivities of other physical parameters are suppressed, and the suppressed sensitivities are at least one order of magnitude less than those of similar sensors. The EULPFG with anti-interference from other parameters is expected to be used in ocean monitoring systems to measure the temperature of the seawater. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement