Low T-g copolymers of [11(N-carbazolyl)undecylmethacrylate] and [2,5-dimethylphenyl-[(4-nitrophenyl)azo] -phenoxyalkylmethacrylate] have been synthesized and the polarized light-induced birefringence of thick films (70 mu m) has been investigated at a constant deducted temperature relative to T-g(T - T-g = 10 degrees C). The optical properties of these copolymers have been studied in relation to the ate-dye content and the length of the alkyl spacer between the ate-dye and the methacrylic backbone. They have been compared with the dispersion of (4-methoxy-2,5-dimethylphenyl)-(4-nitrophenyl)diazene (DMNPAA) within a poly[11(N-carbazolyl)undecyl-methacrylate] and a poly[N-vinylcarbazole] (PVK) matrix. The experimental. curves have been fitted by biexponentials, so emphasizing the effects of the copolymer structure on the kinetics of the writing process. The photoinduced orientation is more than three orders of magnitude higher in a grafted material compared to the dispersion version. The azo-dye concentration also has an important role in both the amplitude and the dynamics of the photo-orientation.