A diffractive optical element comprising: - a substrate having a first surface (Sm) and a second surface (Se) opposite the first surface, transparent to light in at least one spectral range and has, in said spectral range, a refractive index higher than that of water; - at least one metasurface made of a dielectric material and placed on said first surface (Sm) of the substrate, the metasurface being formed through the repetition of a pattern (E 1) that is periodic in two directions, x and y, that are perpendicular to each other and parallel to a surface of the substrate, said pattern comprising a sub-pattern (E 2) comprising a first strip segment that is rectilinear along y, the metasurface comprising a first strip of dashes in the direction y, said strip of dashes being formed from said sub-pattern, said periodic pattern further comprising a second strip segment that is rectilinear in the direction y, so that the metasurface comprises a second strip that is continuous in a direction y, said metasurface being suitable for diffracting light radiation (L in) of wavelength λ comprised in said spectral range, and incident with an angle of incidence, to form diffracted radiation (L diff), said diffracted radiation being formed in such a way that it propagates through the substrate, and strikes said second surface (Se) of the substrate at a diffracted angle θ d larger than or equal to a limit angle θ c of total internal reflection between said substrate and water, said metasurface being configured to have, at said angle of incidence, a transmittance lower than 5% for the order of diffraction 0 and a transmittance higher than 50% for diffracted radiation (L diff) corresponding to an order of diffraction -1 or +1. - a substrate having a first surface (Sm) and a second surface (Se) opposite the first surface, transparent to light in at least one spectral range and has, in said spectral range, a refractive index higher than that of water; - at least one metasurface made of a dielectric material and placed on said first surface (Sm) of the substrate, the metasurface being formed through the repetition of a pattern (E 1) that is periodic in two directions, x and y, that are perpendicular to each other and parallel to a surface of the substrate, said pattern comprising a sub-pattern (E 2) comprising a first strip segment that is rectilinear along y, the metasurface comprising a first strip of dashes in the direction y, said strip of dashes being formed from said sub-pattern, said periodic pattern further comprising a second strip segment that is rectilinear in the direction y, so that the metasurface comprises a second strip that is continuous in a direction y, said metasurface being suitable for diffracting light radiation (L in) of wavelength λ comprised in said spectral range, and incident with an angle of incidence, to form diffracted radiation (L diff), said diffracted radiation being formed in such a way that it propagates through the substrate, and strikes said second surface (Se) of the substrate at a diffracted angle θ d larger than or equal to a limit angle θ c of total internal reflection between said substrate and water, said metasurface being configured to have, at said angle of incidence, a transmittance lower than 5% for the order of diffraction 0 and a transmittance higher than 50% for diffracted radiation (L diff) corresponding to an order of diffraction -1 or +1.