Amorphous bulk composites were prepared by doping azo-dye disperse red 1 (DR1) in poly(methyl methacrylate) (PMMA) matrices. Photoinduced anisotropy of such kind of bulk polymer material was investigated experimentally by measuring the dichroism when irradiating with linearly polarized green light with different polarization direction. With the interaction of bi-photonic beams at 514 and 632.8 nm, transient gratings in the bulk composites could be established, which was a kind of population gratings of trans and cis DR1 isomers and was attributed to the weak absorption of cis isomers at 632.8 nm and the positive dichroism of trans isomers at 514 nm. Furthermore, the all-optical switching behavior of the transient holographic gratings was observed repeatedly by turning on and off the writing beams and a response time of ten milliseconds order could be obtained.