In an optical fiber, the distance between the center of the two concentric circles that specify the cladding diameter and the center of the two concentric circles that specify the core diameter. Note: The concentricity error is used in conjunction with tolerance fields to specify or characterize optical fiber core and cladding geometry. Synonyms core eccentricity, core-to-cladding concentricity, core-to-cladding eccentricity, core-to-cladding offset.