Highly reflective long period fiber grating sensor and its application in refractive index sensing

In this work a highly reflective long period fiber grating (RLPG) sensor is proposed. The sensor was fabricated by depositing the silver atom on both surfaces of the flat end-face and the tail profile of long period fiber grating (LPG), which makes the LPG work in high reflection mode without interferometric fringe and enhances the coupling at the resonant wavelength of original LPG. The RI-response characteristic of the RLPG was investigated. The reflection spectrum remains the resonant dip without interference infringe and the resonant wavelength has obvious blue shift with the increase of external RI. By utilizing the above characteristic, we propose an application for long distance RI measurement combining a standard optical time domain reflectometer (OTDR). Preliminary results of using the sensor to measure the refractive index of glycerol/water solutions in a distance of 100 km were successfully demonstrated.