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A long-period grating (LPG) sensor working in reflection mode is presented for refractive-index sensing applications. The sensor consists of an LPG, a bubble-like core mode scatterer, and a fibre end-face mirror. The light coupled by the LPG is reflected by the fibre end-face mirror and recoupled back to the core, whereas the light passing through the grating is eliminated by the core mode scatterer. The reflective LPG sensor was experimentally fabricated and demonstrated by measuring glycerol/water solutions.