An electro-optical modulator, comprising: - a semiconductor substrate; - at least first and second electrodes distanced from each other along an X-direction; - an optical waveguide embedded within and/or arranged on said semiconductor substrate, an upper face of said optical waveguide being located at, below or above a location between said first and second electrodes, along said X-direction, wherein said optical waveguide longitudinally extends along at least a direction transversal to said X-direction; - a bottom graphene sheet (Gb) arranged and extending along said X-direction over at least a portion of the upper face of the semiconductor substrate, with a first end electrically connected to said first electrode and without the bottom graphene sheet (Gb) reaching the second electrode; - a sheet of a first dielectric material extending over said bottom graphene sheet (Gb); - a top graphene sheet (Gu) arranged and extending along said X-direction over at least a portion of said sheet of a first dielectric material, with a first end electrically connected to said second electrode and without the top graphene sheet (Gu) reaching the first electrode; and characterized in that - a second dielectric material, which is a two-dimensional material with at least dielectric properties different to the dielectric properties of said first dielectric material, covering: - upper and bottom faces of said top graphene sheet (Gu), and/or - an upper face or both upper and bottom faces of said bottom graphene sheet (Gb); wherein at least one of said top (Gu) and bottom (Gb) graphene sheets extends along said X-direction: - above part of the width of the optical waveguide, wherein said part ranges from 50% to 100% of the width of the optical waveguide; or - completely above the whole width of the optical waveguide, and beyond through a respective further projecting portion with a length, along the X direction, of up to 25% of the optical waveguide width. - a semiconductor substrate; - at least first and second electrodes distanced from each other along an X-direction; - an optical waveguide embedded within and/or arranged on said semiconductor substrate, an upper face of said optical waveguide being located at, below or above a location between said first and second electrodes, along said X-direction, wherein said optical waveguide longitudinally extends along at least a direction transversal to said X-direction; - a bottom graphene sheet (Gb) arranged and extending along said X-direction over at least a portion of the upper face of the semiconductor substrate, with a first end electrically connected to said first electrode and without the bottom graphene sheet (Gb) reaching the second electrode; - a sheet of a first dielectric material extending over said bottom graphene sheet (Gb); - a top graphene sheet (Gu) arranged and extending along said X-direction over at least a portion of said sheet of a first dielectric material, with a first end electrically connected to said second electrode and without the top graphene sheet (Gu) reaching the first electrode; and characterized in that - a second dielectric material, which is a two-dimensional material with at least dielectric properties different to the dielectric properties of said first dielectric material, covering: - upper and bottom faces of said top graphene sheet (Gu), and/or - an upper face or both upper and bottom faces of said bottom graphene sheet (Gb); wherein at least one of said top (Gu) and bottom (Gb) graphene sheets extends along said X-direction: - above part of the width of the optical waveguide, wherein said part ranges from 50% to 100% of the width of the optical waveguide; or - completely above the whole width of the optical waveguide, and beyond through a respective further projecting portion with a length, along the X direction, of up to 25% of the optical waveguide width. - upper and bottom faces of said top graphene sheet (Gu), and/or - an upper face or both upper and bottom faces of said bottom graphene sheet (Gb); - above part of the width of the optical waveguide, wherein said part ranges from 50% to 100% of the width of the optical waveguide; or - completely above the whole width of the optical waveguide, and beyond through a respective further projecting portion with a length, along the X direction, of up to 25% of the optical waveguide width.