In this paper, the photorefractive properties of a low-glass-transition-temperature polymeric composite based on poly(N-vinylcarbazole) doped with an azo dye system with various lengths of alkoxy chain as an electro-optical (EO) chromophore and 2,4,7-trinitro-9-fluorenone as photosensitizer were studied by using two-beam coupling and four-wave-mixing experiments. The results showed that the alkoxy chain attached to azo dye can perform plasticization. An optimal length of alkoxy chain was selected.