A method of fabricating a modulator of propagation losses and of index of propagation of an optical signal, including: following bonding of a substrate onto an encapsulated semiconductor layer including a first electrode of the modulator and prior to forming a second electrode of the modulator, the method includes: removing a base substrate onto which the encapsulated semiconductor layer is deposited to expose a face of a buried layer of dielectric material, situated under the buried semiconductor layer, without modifying thickness of the buried layer by more than 5 nm; and forming the second electrode is implemented directly on this exposed face of the buried layer such that, once the second electrode has been formed, it is the buried layer which directly forms a dielectric layer interposed between proximal ends of the electrodes of the modulator.