The invention relates to an electro-optical Mach-Zehnder modulator (1) comprising an input divider, first and second main waveguides (10p, 20p), and an output combiner (3). It also includes a first coplanar RF line (30) associated with the first main
waveguide (10p). Finally, it includes a first additional
waveguide (10a), not coupled to the input divider (2) and the output combiner (3), and having a positioning relative to a central track (33), dimensions, and
doping profile symmetrical to those of the first main
waveguide (10p), with respect to a plane of symmetry (Ps) orthogonal to the main plane (XY), parallel to the first main (10p) and additional (10a) waveguides, and passing through a center of the central track (33). Figure for the abstract: Fig. 2A