A　polarization-independent　optical　sensor　is　created　by　fabricating　a　concentric　gold　ring　grating　with　a　period　of　900　nm　on　the　end　facet　of　an　optical　fiber.　The　sensing　function　of　this　miniaturized　device　is　realized　by　sending　white　light　as　a　probe　to　the　gold　rings　and　collecting　the　response　signal　in　the　back-reflection　through　the　optical　fiber.　A　pronounced　peak　due　to　the　Rayleigh　anomaly　of　the　gold　ring　grating　is　observed　in　the　reflection　spectrum,　the　center　wavelength　of　which　is　sensitive　to　the　change　in　the　environmental　refractive　index　of　the　fiber　end　facet.　Theoretical　analysis　not　only　shows　excellent　agreement　with　the　experimental　results,　but　also　gives　insights　into　the　mechanisms　of　this　kind　of　sensor.　Using　the　center　position　of　the　Rayleigh　peak　as　the　response　signal,　a　high　sensitivity　d?/dn　of　900　nm　per　unity　refractive　index　is　realized　for　this　sensor　and　a　resolution　of　?n/n　similar　to　1%　is　demonstrated　in　preliminary　experiments.　The　sensitivity　is　solely　determined　by　the　period　of　the　grating.