An optical sensor includes an optical device including a microresonator, laid out to guide a light beam along a closed loop optical path, and an injection and/or extraction waveguide, optically coupled to the microresonator; a photodetector, arranged at the output of the injection and/or extraction waveguide; and an analysis device, receiving a signal supplied by the photodetector, and deducing therefrom information relative to a displacement. The microresonator is constituted of a plurality of elementary waveguides spaced apart from each other, and arranged one after the other according to a loop shaped layout. The optical sensor offers increased sensitivity to the measurement of nanometric displacements.