f the chromophores by crosslinking after their polarization by an electric field, wherein each chromophore is included in a unit of the polymer which corresponds to the following formula (I): ##STR19## in which: T is part of the polymer chain,A is an --NO2, --CN or --C(CN)???C(CN)2 group, R1 is a hydrogen atom or a methyl or ethyl group, R2 is a CH2, C2 H4, or C3 H6 or C4 H8 group, and: either X=Y