The present disclosure relates to a method comprising the following steps: a) forming a waveguide from a first material, the waveguide being configured to guide an optical signal; b) forming a layer made of a second material that is electrically conductive and transparent to a wavelength of the optical signal, steps a) and b) being implemented such that the layer made of the second material is in contact with at least one of the faces of the waveguide, or is separated from the at least one of the faces by a distance of less than half, preferably less than a quarter, of the wavelength of the optical signal. The application further relates to a phase modulator, in particular obtained by such a method.