Modulator (100; 550; 560; 580; 590) of the propagation losses and of the index of propagation of an optical signal, this modulator comprising: - a substrate extending mainly in a plane referred to as "plane of the substrate", - a semiconductor layer encapsulated in a dielectric material, this encapsulated semiconductor layer comprising a lower face directly facing towards the substrate and an upper face facing away from the substrate, this encapsulated semiconductor layer also comprising at least one first electrode of the modulator formed in the semiconductor material, this first electrode extending, in a transverse direction parallel to the plane of the substrate, from a proximal end to a distal end via an intermediate part and the dielectric material continuing, in this transverse direction, until it directly touches the proximal end of the first electrode, the proximal and distal ends and the intermediate part being flush with the upper face of the encapsulated semiconductor layer, - a second electrode (130; 582) made of semiconductor material having a doping of opposite sign to that of the first electrode, this second electrode extending from a proximal end to a distal end via an intermediate part, the proximal end being situated facing the proximal end of the first electrode and the distal end being situated on the opposite side to the distal end of the first electrode with respect to a plane perpendicular to the transverse direction and going through the proximal ends, - a dielectric layer interposed between the proximal ends (12, 32) of the first and second electrodes, the superposition of the proximal ends (12, 32) and of the dielectric layer forming a waveguide able to guide the optical signal to be modulated, - contacts (21, 22) in direct mechanical and electrical contact with, respectively, the distal ends (11, 31) of the first and second electrodes in order to electrically connect these electrodes to different electric potentials so as to modify the density of the charge carriers in the waveguide, characterized in that the proximal end (12; 564; 32) of an electrode, selected from the group formed by the first and by the second electrodes (120; 552; 562; 582), is thicker than the intermediate part (13; 584) of this electrode (120; 552; 562; 582), the thickness of the intermediate part of the selected electrode being, for this purpose, less than 0.8e, where e is the maximum thickness of the proximal end of the selected electrode. - a substrate extending mainly in a plane referred to as "plane of the substrate", - a semiconductor layer encapsulated in a dielectric material, this encapsulated semiconductor layer comprising a lower face directly facing towards the substrate and an upper face facing away from the substrate, this encapsulated semiconductor layer also comprising at least one first electrode of the modulator formed in the semiconductor material, this first electrode extending, in a transverse direction parallel to the plane of the substrate, from a proximal end to a distal end via an intermediate part and the dielectric material continuing, in this transverse direction, until it directly touches the proximal end of the first electrode, the proximal and distal ends and the intermediate part being flush with the upper face of the encapsulated semiconductor layer, - a second electrode (130; 582) made of semiconductor material having a doping of opposite sign to that of the first electrode, this second electrode extending from a proximal end to a distal end via an intermediate part, the proximal end being situated facing the proximal end of the first electrode and the distal end being situated on the opposite side to the distal end of the first electrode with respect to a plane perpendicular to the transverse direction and going through the proximal ends, - a dielectric layer interposed between the proximal ends (12, 32) of the first and second electrodes, the superposition of the proximal ends (12, 32) and of the dielectric layer forming a waveguide able to guide the optical signal to be modulated, - contacts (21, 22) in direct mechanical and electrical contact with, respectively, the distal ends (11, 31) of the first and second electrodes in order to electrically connect these electrodes to different electric potentials so as to modify the density of the charge carriers in the waveguide, characterized in that the proximal end (12; 564; 32) of an electrode, selected from the group formed by the first and by the second electrodes (120; 552; 562; 582), is thicker than the intermediate part (13; 584) of this electrode (120; 552; 562; 582), the thickness of the intermediate part of the selected electrode being, for this purpose, less than 0.8e, where e is the maximum thickness of the proximal end of the selected electrode.