Investigation for the operation mechanism in writing and reading processes are necessary in order to realize practical 3D devices with azo-carbazole dyes which are promising candidates for real-time 3D displays. We made dynamical studies of four-wave mixing and two-beam coupling for dyes 3-[(4-nitrophenyl)azo]-9H-calbazole-9-ethanol (NACzEtOH) and Disperse Red (DR1) doped in a polymer and investigated their dependence on dye concentration. Results indicated the important roles of birefringence on the holographic response and stable but erasable characteristics of the gratings in the azo-carbazole. [DOI: 10.1380/ejssnt.2015.69]