Optimization and experiment of a miniature multimode fiber induced-LPG refractometer

We design and fabricate a novel highly integrated all-fiber single mode-multimode-single mode long period grating (SMS-LPG) refractometer. The experiment and simulation results confirm that the powerful local refractive index modulation capability of the multimode fiber (MMF) simultaneously reduces the length of the LPG and achieves excellent refractive index sensitivity. The spectral characteristics and sensing responses of different duty cycles are investigated. The optimized SMS-LPG sample achieved a refractive index sensitivity of 427.01 nm/RIU. The miniature SMS-LPG refractometer is a new sensor for measuring the external refractive index.