A bearing providing a first ring, a second ring and at least one row of rolling elements radially located between raceways disposed on the first and second ring, a single optical sensing fiber mounted in a groove provided on a surface of the first ring radially opposite to the raceway of the first ring, the fiber having at least a sensing part. The groove including a first branch extending from a first frontal surface of the first ring and being at least partially incurved along at least one radius of curvature to extend towards a circumferential groove parallel to the first frontal surface; a second branch extending from a second frontal radial surface of the first ring, axially opposite to the first frontal surface, connected to the first branch, the second branch being at least partially incurved along at least one radius of curvature.