An integrated optical circuit comprising an optically transparent substrate, said substrate comprising: - an input face, an output face, two lateral faces, a lower face and an upper face, said lower face and upper face extending between the input face and the output face, the upper face being planar and opposite to the lower face; - at least one optical waveguide located in a plane parallel to the upper face, - at least one first waveguide end located on the input face of the substrate and at least one second waveguide end located on the output face of the substrate; and - at least one optical attenuation zone (18, 18a, 18b, 18c, 18d) able to attenuate an optical beam transmitted via the substrate in a non-guided manner by said optical waveguide, - said at least one waveguide and said at least one attenuation zone (18, 18a, 18b, 18c, 18d) have respective dimensions such that said at least one attenuation zone (18, 18a, 18b, 18c, 18d) does not cut said waveguide; - said at least one waveguide has a non-rectilinear optical path between said at least one first waveguide end and said at least one second waveguide end; characterized in that: - being defined a straight line segment (9, 9b, 9c) between said at least one first waveguide end and said at least one second waveguide end, said at least one attenuation zone (18, 18a, 18b, 18c, 18d) extends inside the substrate from the lower face to the upper face of the substrate, said at least one attenuation zone being positioned on said straight line segment (9, 9b, 9c) so as to attenuate a non-guided optical beam transmitted via the substrate between said first waveguide end and said second waveguide end, and in that - said at least one attenuation zone has such dimensions that a straight line (15a, 15b) passing through said first waveguide end (7, 7a, 7b) and tangent to said at least one attenuation zone (18, 18a, 18b, 18c, 18d) has a point of intersection with the output face located at a minimum distance x from said second waveguide end (8, 8a, 8b), such that the distance x is higher than or equal to: Dλ 2 where D is the distance between said attenuation zone and said point of intersection, and λ is the wavelength in the material of said non-guided optical beam. - an input face, an output face, two lateral faces, a lower face and an upper face, said lower face and upper face extending between the input face and the output face, the upper face being planar and opposite to the lower face; - at least one optical waveguide located in a plane parallel to the upper face, - at least one first waveguide end located on the input face of the substrate and at least one second waveguide end located on the output face of the substrate; and - at least one optical attenuation zone (18, 18a, 18b, 18c, 18d) able to attenuate an optical beam transmitted via the substrate in a non-guided manner by said optical waveguide, - said at least one waveguide and said at least one attenuation zone (18, 18a, 18b, 18c, 18d) have respective dimensions such that said at least one attenuation zone (18, 18a, 18b, 18c, 18d) does not cut said waveguide; - said at least one waveguide has a non-rectilinear optical path between said at least one first waveguide end and said at least one second waveguide end; characterized in that: - being defined a straight line segment (9, 9b, 9c) between said at least one first waveguide end and said at least one second waveguide end, said at least one attenuation zone (18, 18a, 18b, 18c, 18d) extends inside the substrate from the lower face to the upper face of the substrate, said at least one attenuation zone being positioned on said straight line segment (9, 9b, 9c) so as to attenuate a non-guided optical beam transmitted via the substrate between said first waveguide end and said second waveguide end, and in that - said at least one attenuation zone has such dimensions that a straight line (15a, 15b) passing through said first waveguide end (7, 7a, 7b) and tangent to said at least one attenuation zone (18, 18a, 18b, 18c, 18d) has a point of intersection with the output face located at a minimum distance x from said second waveguide end (8, 8a, 8b), such that the distance x is higher than or equal to: Dλ 2 where D is the distance between said attenuation zone and said point of intersection, and λ is the wavelength in the material of said non-guided optical beam.