An electro-optic phase modulator, intended to modulate the optical phase of a lightwave incident on said modulator, including: - an optically transparent electro-optic substrate, comprising an entrance face, an exit face, two lateral faces (115, 116), a lower face and an upper face, said lower and upper faces extending between the entrance face and the exit face, said upper face being planar and opposite to said lower face, - an optical waveguide that extends, in a plane parallel to said upper face, between a guide entrance end located on said entrance face of the substrate and a guide exit end located on said exit face of the substrate, said incident lightwave being partially coupled in said optical waveguide into a guided lightwave propagating in an optically guided manner along the optical path of said optical waveguide between said guide entrance end and exit end, and - at least two electrodes (131, 132, 133) that are arranged at least partially along said waveguide, parallel to and on either side of the latter, and that define between each other an inter-electrode gap, said electrodes (131, 132, 133) allowing to introduce, when a modulation voltage (V m) is applied between them, a modulation phase-shift, function of said modulation voltage (V m), on said guided lightwave propagating in said optical waveguide, said optical waveguide having at least one first curved guide portion between said entrance end and said at least two electrodes (131, 132), so that the extension of a direction tangent to said waveguide on said entrance face deviate from said inter-electrode gap, the gap H introduced by the first curved guide portion corresponding to the distance between said tangent direction and an inner edge of a first electrode located between said optical waveguide and said tangent direction, this distance being measured in a front plane (P a) perpendicular to said tangent comprising a front edge of said first electrode, said incident lightwave being partially coupled in said substrate into a lightwave that propagates in a non-optically guided manner in said substrate and that has, in said front plane (P a), a spatial extension w, characterized in that said gap H is higher than a predetermined threshold value H min, said predetermined threshold value H min being higher than or equal to half of said spatial extension w of the non-optically guided lightwave. - an optically transparent electro-optic substrate, comprising an entrance face, an exit face, two lateral faces (115, 116), a lower face and an upper face, said lower and upper faces extending between the entrance face and the exit face, said upper face being planar and opposite to said lower face, - an optical waveguide that extends, in a plane parallel to said upper face, between a guide entrance end located on said entrance face of the substrate and a guide exit end located on said exit face of the substrate, said incident lightwave being partially coupled in said optical waveguide into a guided lightwave propagating in an optically guided manner along the optical path of said optical waveguide between said guide entrance end and exit end, and - at least two electrodes (131, 132, 133) that are arranged at least partially along said waveguide, parallel to and on either side of the latter, and that define between each other an inter-electrode gap, said electrodes (131, 132, 133) allowing to introduce, when a modulation voltage (V m) is applied between them, a modulation phase-shift, function of said modulation voltage (V m), on said guided lightwave propagating in said optical waveguide,