An optical device including a waveguide microresonator, laid out to guide a light beam along a closed loop optical path; and at least one injection and/or extraction waveguide, optically coupled to the microresonator for injection and/or extraction of the light beam. The microresonator is composed of a plurality of elementary waveguides with a spacing between them, and located one after the other to form a loop-shaped layout. Among other things, the invention increases the sensitivity of the microresonator to the surrounding medium.