A plasmonic-effect security optical component (10 A, 10 B), comprising: - two layers (2, 4) made of transparent dielectric, - a metal layer arranged between said transparent dielectric layers so as to form two dielectric-metal interfaces (31, 32), wherein said said metal layer is structured to form: ∘ in a first coupling zone, a first periodic two-dimensional coupling grating (C 1) able to couple surface plasmon modes supported by said dielectric-metal interfaces to an incident light wave, the first coupling grating having an asymmetric profile without central symmetry in each of its directions, and, ∘ in a second coupling zone, a second periodic two-dimensional coupling grating (C 2) able to couple surface plasmon modes supported by said dielectric-metal interfaces to an incident light wave, the second coupling grating having an asymmetric profile, without central symmetry, in each of its directions, which profile is different from that of the first coupling grating when it is seen from the same side of the component as the first coupling grating, characterized in that the second coupling grating is the negative of the first coupling grating and the pitch of each coupling grating in each of its directions is comprised between 100 nm and 600 nm and the height of each coupling grating is comprised between 10% and 50% of the pitch thereof. - two layers (2, 4) made of transparent dielectric, - a metal layer arranged between said transparent dielectric layers so as to form two dielectric-metal interfaces (31, 32), wherein said said metal layer is structured to form: ∘ in a first coupling zone, a first periodic two-dimensional coupling grating (C 1) able to couple surface plasmon modes supported by said dielectric-metal interfaces to an incident light wave, the first coupling grating having an asymmetric profile without central symmetry in each of its directions, and, ∘ in a second coupling zone, a second periodic two-dimensional coupling grating (C 2) able to couple surface plasmon modes supported by said dielectric-metal interfaces to an incident light wave, the second coupling grating having an asymmetric profile, without central symmetry, in each of its directions, which profile is different from that of the first coupling grating when it is seen from the same side of the component as the first coupling grating, characterized in that the second coupling grating is the negative of the first coupling grating and the pitch of each coupling grating in each of its directions is comprised between 100 nm and 600 nm and the height of each coupling grating is comprised between 10% and 50% of the pitch thereof. ∘ in a first coupling zone, a first periodic two-dimensional coupling grating (C 1) able to couple surface plasmon modes supported by said dielectric-metal interfaces to an incident light wave, the first coupling grating having an asymmetric profile without central symmetry in each of its directions, and, ∘ in a second coupling zone, a second periodic two-dimensional coupling grating (C 2) able to couple surface plasmon modes supported by said dielectric-metal interfaces to an incident light wave, the second coupling grating having an asymmetric profile, without central symmetry, in each of its directions, which profile is different from that of the first coupling grating when it is seen from the same side of the component as the first coupling grating,